text:
|Publication number
|Publication type
|Application number
|Publication date
|Feb 2, 2010
|Filing date
|Sep 29, 2008
|Priority date
|Mar 23, 2001
|Fee status
|Also published as
|Publication number
|Dennis N. Petrakis
|Original Assignee
|Petrakis Dennis N
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (101), Referenced by (12), Classifications (11), Legal Events (2)
|External Links: USPTO, USPTO Assignment, Espacenet
This application is a division of Ser. No. 10/549,705, filed Jun. 23, 2006 now U.S. Pat. No. 7,445,616, which is a continuation-in-part of application Ser. No. 09/815,643, entitled "Temperature Activated Systems", filed on Mar. 23, 2001, and issued on Jan. 27, 2004 as U.S. Pat. No. 6,682,521. This application also claims priority to PCT/US2004/008338, filed Mar. 17, 2004, which claims priority to U.S. Provisional Patent Application Ser. Nos. 60/454,624, entitled "Arming of Thermally Activated Systems", filed on Mar. 17, 2003; 60/479,481, entitled "Pro-Active Systems", filed on Jun. 19, 2003; 60/489,428, entitled "Mobile Systems", filed on Jul. 23, 2003; and 60/408,809, entitled "Conversion Systems", filed on Oct. 2, 2003, all of which are incorporated herein by reference in their entirety.
The invention relates to shape memory material activated devices, and more particularly, the invention relates to shape memory material activated systems, such as, temperature sensors, drug delivery systems, self-powered devices, energy conversion systems, and the like, which employ a shape memory material activator for self-powering and to create a path through a shell.
Temperature warning devices are used as safety devices for products such as pharmaceuticals, foods, and beverages that are subject to loss of potency or strength, chemical alteration or degradation, spoilage, poisoning, and taste or flavor alteration if they are exposed to high temperature or thawed from a frozen condition. Typically, all products have a restricted temperature range outside of which the product begins to change. Many different types of warning devices exist which warn the consumer if the product has reached or exceed its safe temperature limits. Examples of temperature warning devices are described in U.S. Pat. Nos. 5,735,607; 5,531,180; 5,460,117; 5,335,994; and 4,664,056.
Drug delivery devices, such as transdermal patches or implantable drug delivery systems, are available for delivery of drugs to a patient. These drug delivery devices may be manually activated prior to use, such as by the removal of a peelable liner on a transdermal patch. However, it would be desirable to provide on demand activation of a drug delivery device by use of a shape memory material activator.
It would also be desirable to provide a simple and reliable shape memory activated device for use in a variety of applications. Some of these applications may require release of a substance by a mobile, self powered device, mass delivery of a substance over large areas, and ability to maintain the device at any temperature prior to its usage.
The present invention relates to the creation of a path through a shell wall with the aid of a shape memory material. The path through the shell wall may release a substance contained in the shell or allow a substance to enter the shell. The path may be created while the shell is stationary or self-propelling. The substance may pass through the path instantaneously or over a temperature interval at a specific location or along a course. The shape memory material may stay dormant, unable to create a path at any temperature, until arming takes place. The devices according to the present invention may be used as substance delivery devices, temperature sensors or warning devices, drug delivery devices, actuators, energy conversion systems and the like. The path creation is accomplished by the shape memory material by several means such as fracturing, exploding, imploding, puncturing, peeling, tearing, shearing, rupturing, splitting, separating, abrading, squeezing, debonding etc. the shell. The method depends on the type of shell and on how the shape memory material is utilized.
One aspect of the present invention relates to a temperature warning device, drug delivery device, or other device having a shell containing a first substance and an enclosure containing a second substance. Mixing of the substances is achieved by activation of a shape memory material activator. The shape memory material has been deformed in the martensitic state and its As to Af temperature range includes the predetermined temperature which is considered to be the maximum safe temperature of the product. For the temperature warning device, the enclosure is made of either a transparent or opaque material with a transparent window. Once the predetermined temperature has been attained, the shape memory material recovers its shape and in the process applies a stress (tensile, compressive, shear, torsion, or a combination) that results in the creation of a path for the two substances to come in contact. The color of the enclosure fluid changes to indicate this effect and to provide the temperature warning through the transparent window.
In accordance with one aspect of the present invention, a temperature sensor includes a shell containing a substance capable of providing an indication upon release from the shell, and a shape memory material activator for creating a path through the shell to release the substance from the shell in response to exposure to a temperature which is above a maximum or below a minimum safe temperature. The indication may stimulate one or more senses.
In accordance with an additional aspect of the present invention, a shape memory material activated device for opening a shell containing a substance, the device includes a shell containing a substance, and a shape memory material activator configured to create a path through the shell once the shape memory material attains a predetermined temperature or while it changes temperature within a predefined temperature range. The path creation may be repeatable with temperature cycling of the shape memory material. Multiple paths may be created in a plurality of shells, simultaneously or sequentially with changing temperature of the shape memory material. A plurality of device may be grouped together to form a system to collectively produce a combined effect.
In accordance with a further aspect of the invention, a drug delivery system includes a shell containing a drug, and a shape memory material activator for creating a path to deliver the drug from the shell to a patient when a predetermined temperature of the shape memory material activator is achieved.
In accordance with yet a further aspect of the invention, a self-propelled substance delivery device includes a shape memory material and a shell to deliver the substance along its path. Besides delivering a substance while traveling, the self propelled device is capable of traveling to a specific location to create a path and deliver the substance. In addition, the self-propelled device may be utilized as an actuator to perform tasks other than delivering a substance.
In accordance with yet another further aspect of the invention, an energy conversion system comprises a plurality of shape memory material activators utilized to convert thermal energy to mechanical energy in the form of linear or rotary motion. The mechanical energy may be used to create a path through one or more shells or to actuate other devices.
In accordance with a further more aspect of the invention, a shape memory material activated device comprises a shape memory material activator configured to be armed through transformation form a dormant state, incapable of responding to any temperature, to an active state of readiness, capable of responding to a predetermined temperature. Once armed, it may be utilized to create a path through a shell or to actuate other devices once the shape memory material attains a predetermined temperature.
The invention will now be described in greater detail with reference to the preferred embodiments illustrated in the accompanying drawings, in which like elements bear like reference numerals, and wherein:
This document describes a series of inventions for devices whose principal operation is to create a path through a shell in order to release or admit one or more substances. The path is created with the direct or indirect aid of a shape memory material. The shape memory material acts as a sensor to detect the release temperature and activate or actuate the device to release the substance. The released substance may be utilized alone or may be mixed with a surrounding substance or substances to produce a new substance or group of substances with different properties for further utilization. Mixing can also take place inside the shell between the contained and the admitted substances. Each substance, contained or admitted in the shell or surrounding the shell, can be at any single or combined state of matter; solid, liquid, or gas, whether classifiable or differentiated as one or not. This includes live organisms such as microbes, plant seeds and the like. Further, the substances contained in the shell may be part of a system whose purpose is to control the release or admission of the substance. An example would be a matrix inside the shell that contains the substance to be released or that is ready to absorb the admitted substance. The shell may contain additional means to manage the release rate. Such examples would be a gas bladder that keeps the contents under pressure and accelerates their release upon creation of the path, or a permeable barrier that controls the release or admission rates of the substances. The surrounding substance can be at any static or dynamic state such as still, agitated or flowing. Examples would be a fluid reservoir inside which the shell is contained, an agitated chemical solution or flowing blood in a mammalian body.
The released substance may or may not be the same or at the same state as the substance contained in the shell. Examples of this would be substances that upon release sublime, melt or volatize. In the first case, the contained substance may be in the solid state but the released substance is in the gas state. In the second case, the contained substance may be in the solid state but the released substance may be in the liquid state. In the third case, the contained substance may be in the liquid state but the released substance may be in the gaseous state. The release rate can be instantaneous at a predetermined temperature, continuous (constant or variable), controlled or integrated over time, or over time and temperature. These systems are mechanical in nature. However, they are capable of becoming electromechanical as will be shown later. Conversion to electromechanical operation enhances the performance of the systems and adds further capabilities.
The ability to release and mix substances at a predetermined temperature or temperature range imparts unique capabilities to these devices. Some of these capabilities are: (1) production a new color upon mixing of two substances; (2) direct or indirect absorption of a substance, externally or internally, by a mammalian body; (3) automatic initiation of a chemical reactions; (4) remote controlled mixing rate or concentration adjustment of a chemical solution; (5) germination of seeds and spores; (6) odor generation; (7) grouping of devices to form massive multi-component delivery systems. Utilization of these capabilities can result in a multitude of new or enhanced applications such as: (1) temperature warning devices and specifically, temperature indicators and time-temperature integrator indicators; (2) on demand drug delivery systems; (3) color changing toys; (4) control of chemical reactions; (5) agricultural and forestry products; (6) fragrance devices; (7) food flavoring and taste enhancers. In addition, multiple devices can be employed as variable scale release systems for specific substances such as drugs, odors, disinfectants, sterilizers, fumigants, battlefield and riot control chemicals and the like. These devices have far more capabilities and potential applications than the ones mentioned herein. Four main applications, temperature indicators, on demand drug delivery systems, odor generation systems, and variable scale release systems will be used as the main examples during the description of the invention. In a number of the examples cited in this document, reference is made to two substances; one contained inside the shell and one outside. The purpose of these examples is to demonstrate the main features and function of the devices. As mentioned above, the devices are capable of containing and releasing or admitting more than one substance. However, the embodiments illustrated for one type of system are capable of use for any of the other types of systems described herein.
This document describes additional concepts to improve the operation and utilization of these devices. Several concepts are presented to control and improve the temperature release of the individual devices. To achieve this, multiple means are employed to control: (1) the beginning of the path creation process and (2) the force required to create the path. In addition, several concepts are presented that offer a selection of release temperatures for individual devices. In these concepts, the device remains inactive, in a dormant state, unable to create a path through the shell when exposed to any temperature environment. By following a simple single action arming process, the device can be placed in an active state of readiness, after which time it would create a path through the shell once the shape memory material activator attains a predetermined temperature. The ability to arm the device provides a choice of placing it in an active state by either the supplier prior to shipping or the user prior to the beginning of its service life.
The inventions described herein utilize shape memory material to act as temperature sensors and to either activate or actuate the device when the predetermined temperature has been attained. Most materials with reasonable shape recoveries and development of adequate stresses during the shape recovery process can be utilized for these devices. Presently, nickel-titanium and copper based alloys adequately meet these criteria and therefore are considered good candidates for these designs. For the sake of consistency, the nickel-titanium class of shape memory alloys known as Nitinol is assumed to be used throughout this document. In addition, throughout the description reference is made to a typical shape memory material Displacement vs Temperature graph shown in
The inventions described in this document are not restricted to any particular size or fabrication method. They can be scaled up or down without losing their functionality. They can be fabricated by any method or technique without any restriction or limitation to the type of technology utilized.
Temperature warning devices are generally used as safety devices for products such as pharmaceuticals, foods, and beverages that are subject to loss of potency or strength, chemical alteration or degradation, spoilage, poisoning, and taste or flavor alteration if they are exposed to high temperature. Typically, all products have a restricted temperature range outside of which the product begins to change. The temperature warning devices described below warn the consumer if the product has reached or exceed its safe temperature limits. Although the description is primarily concentrated on the high end of the temperature range, these devices can also be used to provide low temperature protection or warnings. The warning provided may be by visual means of a color change, olfactory means of odor generation, gustation means of taste alteration, haptic means of physical touching modification, and auditory means of acoustic signal creation. The acoustic signal is most useful for implant applications as will be seen later. Besides the devices that indicate exposure to a temperature, this invention also includes designs utilizing the same principle of operation for time-temperature integrator indicators.
The substance release devices, when enabled with frictional means, can become self-powered and travel with temperature cycling. They can travel on surfaces, certain media, and on guided tracks. In the process of traveling they can release a substance along their path or at specific locations. In addition, they can release the substance to an object upon contact with its surface. Besides releasing a substance, they are capable of performing additional tasks such as transporting a load or converting thermal energy into mechanical energy. Types of loads that they can transport include detection, diagnostic and robotic equipment for medical applications. Energy conversion increases the capabilities of the substance release devices by extending the operational temperature release range and providing additional methods to create a path through the shell walls to release the substances.
In the concepts described herein, the path created by the shape memory material activator may be temporary or permanent and the substance may be released once or repeatedly with temperature cycling. Further, the substance can be released over time, once a predetermined temperature has been attained, or while the temperature is changing. Any shape memory material of any configuration that can produce work with temperature change is capable of being used as an activator to create a path though a shell wall for substance release.
To standardize the nomenclature and avoid confusion due to multiple applications of these devices, at times the shell contents, whether they are dye, drug, solute, solvent, or any other substance, will be referred to as the "source". Also, the same contents will be referred to as the substance within the shell to distinguish them from the substance which will be the contents of the enclosure surrounding the shell.
For this to take place, a material of the shell 12 must be brittle enough to fracture with minimal plastic deformation. Fracturing allows the first substance from the interior of the shell 12 to be released and, optionally, be mixed/dissolved or otherwise combined with the second substance within the reservoir 16. The color change (if present) is preferably visible through a window of the reservoir and becomes a warning indication that the predetermined temperature has been exceeded. Alternatively, the visible indication may signal another event such as the release of a drug.
The term "shell" as used herein is intended to mean any container or enclosure which is capable of being fractured, opened, severed, stretched, abraded, or otherwise modified to allow a substance to enter or exit the shell. In certain cases where a substance is in the solid form and it its insoluble to its surroundings, there may be no separate shell. In these cases, release of the substance takes place by abrasion or fracturing of the substance to particles of a size releasable to the surrounding environment. The same definition applies to cases where the substance may consist of agglomerated smaller shells.
A temperature at which the device 10 is activated and the mixing of the two substances begins lies between the "Austenitic start" (As) and the "Austenitic finish" (Af) temperatures of the shape memory material,
The shell in all the embodiments described herein contains the substance or drug to be released. Once the predetermined temperature is reached, a path is created through the shell that allows the two substances to come into contact. The two substances can be at single or multiple states of matter; solid, liquid, or gas. Additionally, the substances can be live organisms, plant seeds and the like. However, in most of the examples cited herein the enclosure substance is preferably in the liquid state and the shell substance is in either the solid or liquid state. Typically, the shell substance is a dye capable of changing the enclosure's color once the two come in contact.
The path creation through the shell is achieved by activation of the shape memory material activator which creates a path by fracturing, exploding, imploding, puncturing, peeling, tearing, rupturing, splitting, or otherwise opening the shell. The shape memory material has been deformed in the martensitic state and its As to Af temperature range includes the predetermined temperature, which is considered to be the maximum safe temperature of the product. The enclosure is either transparent, or an opaque material with a transparent window. Once the predetermined temperature has been reached, the shape memory material recovers its shape and in the process applies a stress (tensile, compressive, shear, torsion, or a combination) that results in the creation of a path for the two substances to come in contact. The color of the enclosure fluid changes to indicate this effect and to provide the temperature warning through the transparent enclosure or window. The path creation is accomplished by the shape memory material by several means such as: fracturing, exploding, imploding, puncturing, peeling, tearing, shearing, rupturing, splitting, separating, debonding delaminating, squeezing, extruding etc. the shell. The method depends on the type of shell and on how the shape memory material is utilized.
For the temperature warning device of
The actual shape of the deformed shape memory material in the martensitic state does not have to necessarily be in the form of a spring 14, as shown in
The shape memory material can be of any shape as long as during recovery it is able to (a) produce sufficient displacement to come in contact with the inside surface of the shell, and (b) produce sufficient force to create a path through the shell walls. Determining factors for the shape of the shape memory material are (a) the amount of displacement required and (b) the properties and sizes of both the shape memory material and the shell material.
If the substances contained within the shell 12, 32 and the reservoir 16, 36, prior to mixing or after mixing, react with the shape memory material to the point that either the function of the device or its effectiveness are affected, the shape memory material must be insulated from the substances. This is achieved by containing the shape memory material in a non-reactant material. Alternatively, this may be achieved by placing the shape memory material outside of the shell and/or reservoir as in the embodiments of
The shape of the shell 12, 32 depends primarily on the amount of substance it has to contain and the shape and size of the shape memory material. The shell can consist of one or multiple parts. Parts can be held together by several methods including, but not limited to; (a) mechanical pressure such as applied by mechanical fasteners, (b) mechanical interlocking such as interference fitting and thermal fitting, (c) chemical and thermo-chemical such as adhesive bonding, heat sealing and thermal shrinking, (d) any type of welding or weld bonding such as solid state, fusion, ultrasonic, brazing or soldering. Material selection for the shell depends on both intrinsic and extrinsic factors. Intrinsic factors are material properties that must be such as to allow the shape memory material to create a path through the shell walls. Extrinsic factors are; the type of heating to be used to activate the device, i.e. ambient, resistive, etc. and the time required for the device to be activated once the surroundings have reached the predetermined temperature. Again, the material (or materials if more than one is used) must not react with the substances contained in the shell and the enclosure prior to mixing or after mixing to the degree that the effectiveness of the device is compromised.
There are cases where it would be desirable to have the shell degrade over time. If no path has been created through the shell to release its contents, release would be achieved by the degradation process itself. This may arise from the inability, in certain cases, to retrieve the shell once placed in an environment where the temperature does not change appreciably to activate the shape memory material, create the path, and release the substance. The shell can be made of any material that would degrade in the environment that it is placed in. Degradation implies any process such as decay, deterioration, decomposition, disintegration, corrosion of the shell that would result in the release of its contents over time. It involves any combination of environment factors and shell material. Examples of such combinations are, but not limited to: (a) Shells made of wood products such as paper placed in a moist environment. (b) Shells made of organic material that degrade in the presence ultra violent radiation. (c) Shells made of material that have a tendency to corrode in specific environments by initiating and propagating a corrosion process. (d) Shells made of biodegradable material and placed in an environment that would induce biodegradation. Another way to degrade the shell would be a reaction with its own contents. Even though in most cases this is not a desirable effect, there are cases where this might be desirable provided that the degradation is a long term effect that does not interfere with the operation and effectiveness of the device during its intended life span. Degradation, at either a rapid or a slow rate, assures the release of the substance, thereby avoiding any problems of having a device placed in a service environment and remaining inactive.
Instead of using a shape memory material to both activate the device and create a path through the shell walls, the shape memory material can be used for the activation process and a regular spring of non-shape memory material or a superelastic material may be used to create the path while the shape memory material is used as a release mechanism.
Materials considered useful for the non-shape memory spring element 44 include those having spring properties, such as carbon or alloy steel, stainless steels, and beryllium-copper alloys. The spring element 44 is restrained by the release mechanism 48 in a position containing stored mechanical. Examples of restrained positions include (a) compressed coil springs, bent wires or strips (as shown in
The spring element 44 of
As illustrated in the embodiments of
In an alternative embodiment, a shape memory material tube may be flattened in the martensitic state to have an oval or other non-circular cross section. The shape memory material tube, upon transformation to the austenitic state, recovers a round cross section and breaks the end seals.
A good example of this concept is the case where the contents of the shell 142 are in solid, loosely packed powder form. This system offers the advantage of reduced cost by having one common enclosure 146 and shell 142 for use at all temperatures and having the shape memory material activator 144, with different As temperatures, installed at the end of the assembly process or prior to the application. Also, it avoids the storage and transportation costs associated with maintaining the devices at a temperature lower that the activation temperature prior to application.
According to one alternative embodiment of the inventions described herein, the invention may employ devices similar to the devices described herein except that the shape memory material activator activates at a minimum temperature. In this embodiment, the shape memory material activator has been trained to achieve a two way shape memory effect. The purpose of this reverse system is to detect minimum temperatures and release a substance from a shell when such a minimum temperature has been exceeded. To do so, a shape memory material is selected whose martensitic transformation range Ms to Mf includes the minimum release temperature. Initially, the shape memory material is trained to achieve a two way shape memory effect with the austenitic (recovered) shape being the installation shape and the martensitic (original) shape being the one undertaken once the material is exposed to the predetermined temperature. At this temperature, the shape memory material creates a path through the shell walls and releases the substance from the shell. For single release type devices, the shape memory material is required to exhibit the two way shape memory effect only once, when the service temperature drops below the predetermined temperature. In essence, the shape memory material in the reverse design operates in the reverse temperature cycle. Actuation takes place during cooling from austenite to martensite, whereas in high temperature activation case actuation takes place during heating, from martensite to austenite. The same features used in all of the other designs described herein can also used with the reverse system. The two way shape memory effect, besides being utilized in shell containing devices, can also be incorporated in embodiments presented elsewhere in this specification to be actuated upon cooling below the Ms temperature.
According to another embodiment of path creation during cooling, the shape memory material activator that is trained in a two way shape memory effect is utilized to restrain a non-shape memory material spring. The non-shape memory material spring is deformed elastically and contains stored mechanical energy. During cooling below Ms the shape memory material begins to undergo reverse shape recovery and releases the restrained spring that in turn unleashes the mechanical energy to create a path by an impact force.
A path can also be created when the temperature of the shape memory material element decreases below a predetermined minimum value within the Ms and Mf range without the sole utilization of the two way shape memory effect described above. This is achieved with the incorporation of a bias spring. A bias spring is a non-shape memory material spring that is capable of storing mechanical energy when deformed elastically by the shape memory material undergoing shape recovery. Initially, the shape memory material spring is deformed in the martensitic state, and then the two springs are assembled together such that the bias spring remains in its free state. Once assembled, they are exposed to a temperature above Af and are maintained at or above this temperature. During the shape recovery process from As to above Af, the shape memory material deforms the bias spring elastically. This becomes the installation state, and activation of the device does not begin until the temperature of the shape memory material begins to decrease below Ms. As the temperature decreases below Ms, the resistance offered by the shape memory material spring begins to decrease and it is overtaken by the force exerted by the bias spring. As the temperature continues to decrease, the bias spring is forcing the shape memory material spring back to its martensitic state while producing a displacement. Once the production of the displacement is restricted by the wall of the shell, a force is generated and, when it reaches a sufficient magnitude, creates a path through the shell wall to release the substance. This force can also be used in alternative designs with enhanced capabilities such as to create a path though a shell wall during cooling (Ms to Mf) and close it during heating (As to Af) or vice versa, and repeat this operation with temperature cycling. Further, this type of force can be used to create a path through the wall of all the shells described herein, including the peeling of the wall of a shell.
For background information,
Besides creating a path directly through the wall of a shell, coupling of leaf springs can also be used to create the path indirectly by releasing an elastically deformed non-shape memory material spring containing stored mechanical energy to create a path through the shell wall. This is the same concept as the one illustrated in
In the first method, unfolding takes place sequentially as the shape memory material spring undergoes shape recovery such that each individual fold opens up after the previous fold has opened up. This is illustrated in
Depending on the particular application, one shell type might be preferred over the other. For example, in some temperature warning systems the accordion type may be preferred in order to provide a more linear indication of time exposure with changing temperature. On the other hand, the sequential method may be preferred in order to provide a substantially increased release with temperature that would accelerate the coloring of the surrounding substance. While in both shell types, the path creation process is the same and both produce the same effect at constant temperature, they differ with respect to the release or admittance rate with changing temperature. The accelerated stepwise release rate of the sequential type qualifies this device as a time-temperature integrator indicator. As an example, at a temperature closer to As an "x" amount of a substance may be released at a given time whereas at a temperature closer to Af and for the same time span a "2x" amount of the same substance may be released.
The unfolding shell provides increased design flexibility. In both shell types, the shape memory material spring can be located either inside or outside the shell. In addition, the shape memory material spring can be of configurations other than a coil spring, such as a leaf or torsion spring. Further, only part of the shell wall can be folded, and folds may not be symmetrical or of equal length. The concept of creating a path through the shell wall by utilizing the mechanical energy stored in an elastically deformed spring that is restrained by a shape memory material element may also be employed with the unfolding shell.
The coiled shape memory material spring can also be used in compression and placed either inside or outside the shell. Instead of opening the folds with increased temperature they are closed. This concept has the advantage that the substance is released out by pressure as the temperature changes and a path is created by converting the shell walls to permeable ones. Alternatively, release can take place through unidirectional flow valves that allow only outward flow and open up only when the contents of the shell are pressurized by the shape memory material spring. This concept is based on the existence of a differential pressure between the substance contained in the shell and the shell's surroundings, and as such it finds applications in environments of increased pressures.
Release of a substance from an accordion type shell can take place though a predetermined path in a weakened area such that the force exerted by the shape memory material spring creates the path in this specific location. The substance may be squeezed out through a clear path, a valve, a filter or membrane and the like. For viscous substances, a clear opening may suffice. In addition, the substance may be released though several paths in locations away from the shell by connecting multiple passages such as tubes to the shell to carry the substance to different locations. The concept of creating a path by pressurizing or squeezing shell substance is not limited to the accordion type shell. Any shell formed from a cylinder and a piston, such as a syringe, with the piston activated by a shape memory material spring is capable of creating similar paths and releasing the substance in an extrusion fashion. In addition, shells may be made of flexible or malleable material that can change their shapes upon application of a force by the shape memory material spring, contain the substance and release it through a predetermined path. Some of the main advantages of this type of shape memory material activated device include the release of the substance through multiple paths, control of path size though permeable walls such as filters and membranes, and the release of substance only while the temperature of the shape memory material is changing. When the temperature stops changing, even though the shape memory material spring has not attained Af yet, pressurization of the shell contents stops and no further substance release takes place.
The shape memory material spring, when trained in a two way shape memory effect, can be used to create a path upon cooling to a predetermined temperature. Also, the shape memory material spring can be coupled with a bias spring to make the device operational from either the martensitic or austenitic state.
The pressurant concept can be used with a shell to admit a substance by having the bellows contract in response to a temperature change, thereby creating a negative pressure inside the shell. The path in this case is created by a pressure differential between the outside and the inside of the shell such that the shell wall becomes permeable under the existing pressure gradient, drawing the surrounding substance into the shell. Additionally, this device can be activated during the fall of temperature from Ms to Mf if the shape memory material spring is trained in a two way shape memory effect or it is coupled with a bias spring. Irrespective of whether the device is activated during the temperature rise or the fall of the shape memory material, the operating principle remains the same; a change in the temperature of the shape memory material results in a pressure change inside the shell. It is this change in pressure that creates the path through the shell wall to release or admit a substance. The amount of substance released or admitted is controlled by the volume change of the pressurant housing and the minimum pressure differential required to transfer the substance into or out of the shell.
Instead of simply releasing or admitting a substance, this device can be used to release a substance when the temperature of the shape memory material activator changes in one direction, and to admit the surrounding substance when the temperature changes in the opposite direction. This is a two way substance transport system that is repeatable with temperature cycling. With multiple cycling, a solid dye contained inside the shell colors the incoming substance that in turn colors the outside substance when forced out with a reverse temperature change. By repeating this operation with temperature cycling, the outside substance continues to change to a darker color, providing an integrated indication of the time and temperature for multiple exposures above a maximum or below a minimum predetermined temperature.
Additionally, the device may be placed between two adjacent chambers such that it admits a substance from one chamber with temperature change of the shape memory material activator in one direction and releases the substance to the second chamber with temperature change of the shape memory material activator in the opposite direction. While the substance remains inside the shell it can combine with a shell substance to change its physical and or chemical characteristics. Such combinations can produce coloring effects, mixing of drug and the like. Alternatively, the device can be used to transport a given quantity of substance from one chamber to another or to the surrounding environment with temperature cycling. An application of this concept would be the drug delivery to a patient from a reservoir. In this application, the first chamber from which the substance is admitted in the shell constitutes the reservoir and, the second chamber to which the substance is released constitutes the patient's body. The preferred construction of a substance transport device, operating by admission and release of a substance, is to have the part of the shell wall, that is in contact with the substance to be admitted, capable of becoming permeable in the inward direction only and the part that is in contact with the released substance capable of becoming permeable in the outward direction. Besides reversing the permeability direction of the two parts of the shell wall, the molecular size of the substance contained inside the shell may change when combined with the admitted substance. In this case, depending on the molecular size change, a different degree of permeability between the two parts of the shell wall may be sufficient to eliminate the need of reversed permeability. Alternatively, one-way valves can be employed at the walls of the shell for the path creation to take place. The valve in contact with the substance to be admitted allows only inward flow, while the one that is in contact with the released substance allows only outward flow. If valves are use, a permeable or semi-permeable membrane or filter can be incorporated in their opening to control type and the rate of the substance that passes through them.
Shape memory material springs can also be deformed from a bent shape to a straight shape in the martensitic state. In other words, the shapes shown in
When the temperature of the shape memory material springs 232 and 242 is raised, the segments subjected to the least amount of deformation will begin the shape recovery process first. Each semicircular segment of the shape memory material spring 232 will begin the shape recovery at a different temperature. In this manner, shape recovery will progress sequentially from segment to segment as the temperature continues to rise. On the other hand, shape recovery in the shape memory material spring 242 will begin simultaneously in several locations of the different segments that have been subjected to the same amount of deformation. While the temperature is raised, varying lengths of each segment will be undergoing shape recovery simultaneously. In the first shape memory material spring 232, the beginning of the shape recovery process would appear to be orderly while in the second one 242 it would appear to be random. However, in both cases the beginning of this process is predetermined by the localized degree of deformation. In the first case, the beginning of shape recovery is sequential and segmented, while in the second one, it is simultaneous and continuous.
In fabricating the extended release devices, the substance can be adhered to the shape memory material and the shell can be built around the substance. Some of the methods used to apply the substance are; a powder slurry that is subsequently dried, a gas that is condensed and frozen or a liquid that is frozen. Once the substance is applied, the shell can be build around the substance by methods such as spraying or dipping and drying or curing. It is obvious that no heat should be used that would result in either partial or full shape recovery of the shape memory material activator. Path creation can take place by any of the methods described herein that result in microscopic or macroscopic size openings in the shell wall through which the substance is released.
Instead of a having a single shell with a multi-deformed shape memory material, several shells each containing a different substance can be build around a single multi-deformed shape memory material. With this concept, the path in each shell will be created at a different temperature with the net effect of producing different colors at different temperatures or releasing different types of drugs and quantities. The individual shells may or may not share a common wall. The use of a single multi-deformed shape memory material to produce extended release can replace several individual shells each having their shape memory material deformed by different degrees or each containing a different substance. In addition, a gradually deformed shape memory material with several shells will guarantee continuous release over a large temperature range.
This same concept can be used with a shape memory material trained in two way shape memory effect to create the path upon cooling to below Ms. In this case, assembly of the device must take place in the austenitic state after completion of the shape recovery in order to avoid release during heating from As to Af. Typically, reverse recovery is limited to nominal shape recovery strains and is not applicable to extended release beyond these limits. The same concept of releasing the substance during cooling can also be used with a bias spring coupled to the shape memory material spring.
Extended release is not limited to a single straight wire deformed by bending, other product forms such as sheet, strip, rod, bar or tube, deformed by other methods such as stretching, compressing, twisting can be used. In addition, the shape memory material may surround the substance to be released, as may be the case of a perforated tube. In this case, as an example, the shape memory material tube is deformed in the martensitic state, diametrically to various degrees of severity along its length, is filled with a substance, and has its perforations and its two ends sealed. Different length segments can be filled with different substances and be separated with dividing materials to form individual shells and to isolate one substance from the next. During heating, the localized strains developed in the shape memory material create paths through the sealed perforations to release the substance. The path initiation process progresses until the most deformed regions undergo shape recovery.
In a second example, a wire that is stretched to various degrees, incrementally or continuously to produce increased amounts of deformation along its length, can be used as a single shape memory material activator to peel the wall and create a path in several shells sequentially with rising temperature. In utilizing the extended release concept, it should be understood that transformation temperatures are affected by the stress applied to the shape memory material while undergoing shape recovery. For example, in the case of the peelable shells, once the part of the shape memory material wire with the lowest As temperature begins to undergo shape recovery, a constrained force is developed during the process of peeling and the whole wire is put in tension. As different parts of the wire undergo shape recovery with increasing temperature, the magnitude of the tension varies and influences the transformation temperatures of the balance of the wire. In addition, depending on its magnitude, it may further deform the portions of the wire that have not yet recovered their shapes. Besides stretching a shape memory material wire or rod by varying amounts, different length segments may be stretched by varying amounts while others may be shrunk by varying amounts such that during shape recovery the overall length undergoes multiple expansions and contractions in a predetermined manner. Different modes of deformation can be used to produce shape recoveries to meet specific application requirements.
Extended release offers the advantage of providing an analog type path creation and release with increasing temperature. Assuming "other things being equal", the path creation rate and substance release would depend on the heating rate of the shape memory material as well as the deformation rate change along the length of the shape memory material. Useful applications of this concept include, but are not limited to, dyes and drugs. A dye released can be of a continuously changing color such that the color at any given time is indicative of the temperature of the shape memory material. This type of device offers the advantage of continuous temperature indication with increasing temperature for an extended temperature range, while as a drug release device it offers a controlled release of different drugs, group of drugs or the same drug with varying concentration for an extended temperature range. Further, another advantage that this type of device offers is that release can be controlled in an on-off fashion by the application and removal of heat without the incorporation of switches or valves. Path creation ceases once the temperature of the shape memory material is longer increasing and resumes again with further increase in temperature. This procedure can be repeated several times each time increasing the temperature to a higher level. Extended release of drugs can be used in many applications such as implants and transdermal delivery systems.
The shape memory material used as an activator in these devices can be heated by various methods such as ambient heat, directly or indirectly applied heat and resistive heat. The input of electric energy in the form of resistive heat used to heat these devices can be controlled to allow specific segments of the multi-deformed shape memory material activator to undergo shape recovery and create paths. By resuming the heating to increasingly higher temperatures, more segments undergo shape recovery that results in more path creations and release of more substances.
Variable Volume Shell
The shrinking shell concept is demonstrated in
The growing shell concept is shown in
The concept of the shrinking and growing shell can be used to release or admit a substance during cooling from the Ms temperature instead of heating from the As temperature. This is accomplished simply by reversing the direction of shape recovery in each case. The guide rods, inserted in the holes of the fins, allow the shell to travel axially in one direction and restrict it from traveling in the reverse direction. The conical shape of the teeth allow the fins to slide easily through, from apex to the base, but prevent them from sliding backward. Sliding may entail enlargement of fin holes by stretching while going through the teeth. Instead of using guide rods placed on the outside, a hollow shell with a hollow pressurant housing can be used along with the incorporation of a single center guide rod configured with a plurality of teeth.
In all cases, the bias spring may be eliminated as a separate part if the pressurant housing also serves as the bias spring. This is especially true when the pressurant housing is formed as a bellows that can expand and contract elastically, and in the process, store and release mechanical energy. The mechanical energy is stored during the shape recovery process when the shape memory material spring deforms the pressurant housing elastically, and it is released during cooling when it is utilized to deform the shape memory material spring back to the martensitic shape. Alternatively, in cases where it is not desirable to have the pressurant housing perform as a bias spring, it may be filled with a compressible fluid that would act as a bias spring. Further, the pressurant housing and the bias spring may be combined into one part, made of material such as an elastomer, capable of undergoing volume changes with the application and removal of the shape recovery force. The elastomer may have any shape that will accommodate the shape of the shape memory material spring. For example, a shape memory material tube may be filled with an elastomeric material to act as a couple. The tube may be deformed in the martensitic state, axially or radially, and filled with the elastomeric material. During shape recovery, the shape memory material tube forces the elastomer to change shape, changes the pressure in the shell, creates a path to release or admit the substance. During cooling, along the Ms-Mf path, the elastomer acts as a bias spring and deforms the shape memory material back to its starting shape. The term "pressurant" as used herein implies a part or assembly capable of changing its volume with the application of a force such as the one generated by a shape memory material element and in the process change the pressure of its surroundings when placed in a closed volume container such as inside a shell.
The variable volume shell concept can be accomplished by alternative means besides the ones described herein.
The variable volume concept is not restricted to bellows. Any type of container made of a single or multiple parts, whose volume can vary, preferably in one direction, can be utilized as a shell or a pressurant housing.
The pressure generator, comprised of the pressurant housing with the shape memory material and the bias spring, can be placed either inside or outside of the shell.
Alternatively, the whole device maybe be enclosed in a pressurized and hermetically sealed enclosure with only the area encompassing the path creation exposed to the outside. Here the enclosure's pressure determines the amount of substance to be released. The enclosure pressure decreases as more substance is being released and in turn, release per cycle is decreasing. In essence, a variable (decreasing) release is produced with cycling.
The shape memory material spring does not have to be a coil spring. It may be any shape including a simple straight element that is capable of performing repeated work with temperature cycling either by itself or in conjunction with a bias spring. In addition, the shape memory material may comprise part of the whole pressurant housing or be the pressurant housing. Typically, Nitinol alloys recover up to 8% of their strain during the transformation process from martensite to austenite. The amount of substance released with each cycle depends on the volumetric expansion of the pressurant housing. With a linear expansion of a few percent of the total length of the pressurant housing, the contributing volume change factor becomes its diameter. The amount of substance release with each temperature cycle can be optimized through the selection of the shape memory material spring's geometry and size along with the pressurant housing's diameter.
Alternatively, restraining the pressurant housing by a predetermined amount as it expands and contracts controls the amount of substance released or admitted. FIG. 47 illustrates the concept of the restrained pressurant housing. In addition to the shape memory material spring and the bias spring, the pressurant housing 350 houses two interlocking stops, a male stop 352 and a female stop 354. The two stops move relative to each other in opposite directions with the expansion and contraction of the pressurant housing. However, their movement is limited to a maximum distance "d" that determines the amount of substance to be released. Alternatively, other restraining methods may be use and the distance "d" may be fixed or adjusted by the user prior to placing the device in service.
As with other devices presented herein, the substance can be released to the surroundings or to an enclosure for further enhancements of the device. Such enhancements include mixing with the substance of the enclosure to produce effects such as color changes that are indicative of the temperature exposure history. Color changes can be detected through a transparent window in the enclosure. Besides color change, temperature exposure history may be indicated with a pointer showing the shell's length change.
One of the main advantages of the volume changing shell concept is the fact that the substance is being released or admitted only while the shape memory material is subjected to a temperature change within a predefined temperature range. During this temperature change, it forces the pressurant housing to change volume resulting in the path creation through the shell's wall. In the case where the path is created during shape recovery, once the Af temperature is reached the pressurant housing stops changing volume and path creation ceases. The same applies when the path is created during the cooling part of the temperature cycle. Once the Mf temperature is reached, the pressurant housing stops changing volume and path creation ceases. Flow of the substance in or out of the shell is not restricted to valve paths. The substance may flow through paths created by conversion of shell's wall or sections of the wall to permeable or semi-permeable paths. These wall parts may be rendered permeable only during the path creation process when a pressure differential exists between the contents of the shell and its surroundings. Any substance that is detectable by the senses or not can be released though any path created through the shell's wall by a shape memory material activator. Further, a permeable or semi-permeable barrier, such as a filter or membrane, may be incorporated in the opening of the valves. Opening of the valves makes the substance accessible but the accessibility rate is controlled by the barrier.
Medical applications include drug delivery devices such as transdermals and implants. In all cases, the substance is released only while the shape memory material is undergoing shape recovery or reverse shape recovery. This is advantageous as the amount of substance release is independent of the width of the hysteresis. In the case of body temperature activated release, i.e. fever, the amount of release increases as the fever increases, thereby providing the body with more antipyretic drug. In the case of implanted drug delivery systems, the Af temperature is the limiting release temperature. Release stops at this temperature, irrespective of the heating energy provided to the shape memory material either externally or internally. The width of hysteresis has no influence on the amount released, as no further release takes place once the Af temperature is reached. For implant devices, this concept offers the advantage that with each temperature cycle, there is a predefined amount of substance released. This amount is independent of energy input, above a minimum level, and independent of the time the shape memory material stays at a given temperature. Also, because the shell contains a finite amount of substance, the drug can not be abused. Once depleted, the shell can not be refilled as the shell guide rods prevent its reverse movement.
Variable shell type temperature indicators provide a cumulative temperature record of exposure of the shape memory material to a predefined temperature range. Exposure may be through the whole temperature range or part of it. The exposure record is indicated by a color change of a substance viewed through the transparent window. The intensity of color changes with increased temperature exposures. The total amount released provides an integrated record of the shape memory material temperature exposure. This device integrates the release with respect to temperature over a predefined range. Besides the change in color intensity with temperature cycling, a new color can also be produced. The new color is produced by utilizing a viscous substance in the shell that is structured in layers of different colors. Once the first layer has been released with temperature cycling, the next layer begins to be released with repeated temperature cycling thereby producing a new color. This process continues to produce a new color each time a complete layers of a specific color has been released. The utilization of multiple colors extends the life of the device by allowing interpretation of temperature exposure by color differentiation in addition to color intensity. In addition to filling the shell with a multi-color substance in layers, the substance may have a color gradient. In all devices, drug delivery, indicators and others, the substance quantity released is independent of the heating or cooling rates of the shape memory material.
Renewable Shell
This shell is capable of continuously renewing its substance. With each temperature cycle, it releases the substance to its surroundings or to an enclosure during the first half of the cycle and admits the same or a different substance from the reservoir during the second half of the cycle. To assure continuation of the process of releasing and admitting the substance the supply reservoir, depending on the application, may be refilled by means such as a supply tube, a syringe or a pump.
In both devices 370 and 390, by reversing the direction of the one-way valves the substance can be admitted into the shell and released into a supply reservoir, thereby reversing the direction of the mass transfer. In addition, the release or admission of the substance can take place during either the heating or the cooling part of the temperature cycle. Simply, in one case the shape memory material expands during heating while in the other it contracts.
Similarly to the variable volume concept, the renewable shell concept presents the advantage of path creation and substance release only when the shape memory material undergoes shape change, either by a shape recovery force or by a biased force. The amount of released substance is controlled by the volume change of the pressurant housing. In addition, the refill substance admitted in the shell may be of changing physical or chemical characteristics, that, when combined with the shell's substance, produces a new color, a modified drug or higher strength drug or some other new feature with each release.
Both concepts of variable volume and renewable shell may be used for similar applications. In addition to releasing a substance, either device may be utilized to change the volume and or the pressure of another reservoir. This is a desired benefit in cases where there is a need to change the volume of a reservoir of a given geometry in a predetermined direction or orientation.
Time Dependent Temperature Activated Systems
In the embodiment of
According to the embodiment of
If the seal 510 is made of material that swells with exposure to fluids, the swelling (increase in volume and thereby linear dimensional increase, distance d in
If the source is in the solid state and in the form of a cone, sphere, or other shape, it must be dissolved uniformly such that it can be sealed at the end of each cycle. In the case of a time compensating drug delivery system, the solid state drug source can contain a gradient of the active ingredient such that the released drug increases in potency with increased exposure time. In the case of a time integrator indicator the dye can consist of several layers of different colors (with one color being exposed at any given time) so that different colors are produced with increased exposure time. Color change will be indicative of the time exposure above or below the predetermined temperature.
Instead of using a shape memory material trained in two way shape memory effect, the cycling can also be accomplished with the incorporation of a bias spring 520 along with the shape memory material spring 508, as shown in the embodiment of
The time integrator indicator devices of
The same concept can be used without the swelling effect. In this case the seal must provide the cushioning and sealing, and must exhibit minimal creep in the expected operational temperature range. Again, a bias spring can be used to minimize the amnesia of the shape memory material activator and assure sufficient contact pressure to displace the fluid from the sealer/drug source interface.
In both cases, swell and no swell of the seal 510, the source 506 can be made the stationary member and the sealer 505 the moving one. In addition, as shown in
The concept used for the time dependent shell described above with respect to
The first change requires selection of the source material, membrane (if one is used) and, enclosure fluid such as to control the release or mixing rates with respect to temperature. In other words, release is both material and temperature dependent. With this system, at a constant temperature above As and with increasing time the drug release rate remains constant as time goes by. However, the release rate increases as the temperature increases. If a solid state drug source is used which is built of different strength layers, the release rate will be increasing incrementally, as each layer is dissolved, with either time itself at constant temperature or time and temperature. The strength levels and the rate of change must be calibrated for specific applications, as each application requires different temperatures and times. This concept has only a lower temperature limit. The temperature application range is bounded only at the low end which is the As temperature. Above this temperature the path through the shell wall remains open and release or dissolution of the source is continuous. Upper bound is only limited by material capabilities.
The second change requires modification of the geometry of the source such that there is a progressively larger gap, tip to base, between the sealer and the source, as shown in
With this design change, the drug release rate of the time and temperature compensating drug delivery system remains constant with time at a constant temperature but it increases as the temperature increases. The increase can be designed to be either linear or non-linear. The increase in release rate translates into an increase in drug strength. In the case of time and temperature integrator indicator, the mixing rate of the dye remains constant with time at constant temperature and increases the color depth of the enclosure's fluid at a constant rate. The mixing rate of the dye increases with temperature, linearly or non-linearly, and in return it accelerates the increase in color depth accordingly. Additionally, the dye source, if used in the solid state, can be made up of several layers of different colors. Each layer as it is mixed with the enclosure's fluid will produce a new color that will reflect, in a more discerning way, the time and temperature history.
As shown in the embodiments of
As shown in
In all the embodiments discussed herein, the closing member or the shell can be made the moving part and the other part the stationary one simply by exchanging places of the shape memory material and bias springs with the compensating spring.
In all the embodiments described herein, more than one shell, containing the same or different substances, such as drugs of various degrees of potency in the case of a drug delivery system, can be used with a single enclosure. They can all be activated at the same or different temperatures. For shape memory materials to be activated at different temperatures, the chemical composition or the processing of the material including the amount of deformation from the austenitic shape must be different. Multiple shells will allow for several reactions/mixings between the two substances to take place. As an example, in a drug delivery system with multiple shells, shell #1 contains a drug that is to be released at a predetermined temperature while shell #2 contains the same drug of higher potency to be released at a higher predetermined temperature. As a second example, if each shell contains a different color dye, the fluid of the enclosure will obtain a different color at each predetermined temperature. Each color will correspond to a different temperature that will be indicative of a different level of warning.
Additionally, the reverse shape recovery concept described earlier can be utilized to create the path during cooling of the shape memory material instead of heating. In this case, the substance will be released once the temperature falls below Ms producing the same effects as in the case when release takes place when the temperature rises above As. Finally, it should be understood that if the shape memory material activator is not trained in a two way shape memory effect or no bias spring is utilized, the path creation process will not be reversible and once the shape recovery takes place, the shell will stay open permanently. In this case, the same effects will be produced but would not be repeated with temperature cycling. However, if other features such as pressurization of the shell contents and variable source concentration are maintained, the device is able to produce integrated release with respect to time once the path is created.
Peelable Shell Systems
The devices illustrated in
For purposes of background, there are two types of transdermal drug delivery systems, also known as patches. One that contains the drug in a reservoir and releases it through a rate controlling membrane, and a second one which contains the drug in a polymeric matrix which is applied directly to the skin. In both cases the skin begins to absorb the drug as soon as the protective liner is removed and the patch is adhered to the skin. The device presented herein takes the patch concept one step further and advances it to be qualified as an on demand transdermal drug delivery system. This is accomplished with the addition of a peelable barrier between the drug and an intermediate layer of the transdermal drug delivery system or the drug and the skin. This layer is automatically removed (peeled away) only, after the patch has been applied to the skin and only when and if there is demand for the drug.
Automatic removal of the barrier is achieved with the incorporation of a shape memory material activator in the device. Demand is determined by several ways. In the case of fever, the shape memory material can act either as both a sensor to detect the rise in temperature and as an actuator to remove the barrier layer at a predetermined temperature or simply as an actuator with the sensor being replaced with a separate temperature detection device. In the second case, activation of the shape memory material will require an external energy source to heat it and enable it to undergo the shape recovery process. In other cases such as cardiovascular and hormonal drugs, the shape memory material device is only used as an actuator with the sensing provided by added detectors. When detectors are used, microprocessors can also be incorporated to provide additional features to further enhance the self controlled characteristics of the device.
An added feature of this system is the fact that actuation can also be achieved manually. This is accomplished with the application of heat source such as a hot towel to the device. For this to work, the temperature of the applied heat source must be high enough for the shape memory material activator to undergo shape recovery. On the other hand, this temperature should not be so high as to alter the nature or potency of the drug nor should it change its ability to be absorbed by the skin.
In addition to the peelable layer, in the case of the drug reservoir type transdermal device, the shell can be placed inside the reservoir. Release of the drug into the reservoir takes place at the predetermined temperature. The reservoir may contain another drug or carrier with which it gets mixed prior to the absorption process.
In all cases, multiple shells can be used with each device to enable incremental adjustment of the drug dosage with respect to fever or other parameters.
The peelable shell drug delivery system consists of substantially the same components as the temperature warning device described above except, the substance delivered from the shell is a drug. The device incorporates a drug containing shell inside a drug reservoir. The shell encapsulates the drug to be released into the reservoir that will deliver it to the patient as a transdermal or implanted system. The reservoir can be either empty to receive the drug contained in the shell or filled with another drug to be mixed with the one released by the shell. The second option provides the advantage of extending a drug's shelf life if mixing is to take place at the time of application instead of the time of manufacturing.
Again, activation of the device 600 takes place when a shape memory material activator 612 peels the protective liner 606 which creates a path through the shell 602 for the drug to be released to the reservoir. The shape memory material can be placed either in the inside or the outside of the shell and must be compatible with the drug or be coated with a coating that is compatible with the drug. For transdermal systems verification of the release can be provided through a transparent window in the reservoir that will exhibit a color change.
As shown in the embodiments of
As shown in the embodiments of
In the embodiments of
The peelable shells can be arranged in different sizes and patterns to accommodate different requirements of temperature spans, types of sources, sequence of releases etc. In addition, the configuration of the peelable protective liners can be varied to accommodate different requirements. Some of the different patterns include shells of different widths, shells arranged in both series and parallel fashion, and shells with circular shaped or blister type drug containing cavities in series and/or parallel.
For transdermal systems the device should be designed such as to prevent any deformation of the shape memory material element during handling and application of the patch in order not to affect its performance. It is recognized that the patch is not applied to rigid flat surfaces and each application is unique in terms of geometry. In order to avoid deformation of the shape memory material during the application process, the shape memory material can be housed separately from the patch in a rigid housing and be connected to the barrier layer with a flexible conduit.
Besides the use of the coiled shape memory material spring as shown in
It should be understood that even though in all peelable concepts described herein, the path creation took place by pulling the tab of the peelable layer while the shell remained stationary; the same can be achieved by holding the tab stationary and moving the shell by coupling it with the shape memory material. The shape memory material can either push or pull the shell, depending on the orientation of the opening, to crate the path and release the substance.
When the drug delivery device is a device of the type where the drug is provided in a matrix the auto-peelable barrier is placed at the bottom of the matrix. An extra liner, between the peelable barrier and the matrix would help minimize the startling effects of the sudden barrier movement during shape recovery. This layer should be transparent to the drug or contain large holes such that the most of the matrix is in contact with the skin. The matrix may be segmented and each segment having its own barrier. The barriers are removed in a "curtain" fashion with each curtain attached separately to the shape memory material activator. By varying the curtain length, each cell can be exposed to the skin at different temperature. Curtains close to the fixed end of the spring tend to produce smaller movements which necessitates smaller cells. However, by adjusting the curtain length of the individual cells, all cells can have the same size.
Another concept involves two barriers, one stationary and one mobile. Both barriers have alternating strips with cut outs of the same size. Initially, the two barriers are placed out of phase such that the drug matrix is sealed. Upon shape recovery one of the barriers begins to move exposing small areas of the matrix to the skin. At the end of the shape recovery process the strips and cutouts of the two barriers are in phase and maximum exposure is achieved.
In the peelable shell concept, the shape memory material spring is not limited to an outside location only. It can also be placed inside the shell as well. In this case, peeling takes place inside the shell. When ambient heat is used for activation of a peelable shell device this concept presents the advantages that both the shell substance and the shape memory material spring are at the same temperature at all times. This advantage exists for all the types of release devices that, contain the shape memory material inside the shell.
An added benefit to peelable shell concept is that besides being a shell capable of releasing a substance, it can also become a temperature indicator without the aid of the released substance. This is achieved by marking or bonding a calibrated temperature strip indicator on the underside of the peelable layer. As this layer is peeled away during shape recovery, the underside is exposed and the temperature strip becomes visible. The highest exposure temperature, if shape recovery is used to create the path, is indicated right at the folding line formed by the peeled portion and the unpeeled portion. This concept can be extended to a peelable temperature indicator without the shell. This is achieved by peeling a layer that is bonded to a substrate that contains a temperature strip indicator. Once the shape recovery begins and the peeling starts, the temperature indicator is exposed continuously with increasing temperature. The latest exposed part is the one corresponding to either the highest or lowest temperature depending whether peeling takes place with rising or falling temperature.
A concept similar to the peelable shell is the sliding cover shell. In this concept, the path to release the substance contained inside the shell is created by the moving of a cover away from a window by a sliding action. The cover may be adhered to the shell and form part of the shell wall. Adhesion can be accomplished by several methods such as bonding, welding, pressure differential, contact stresses, or Van Der Wall forces. Heavy covers may be held in place by gravity without the aid of any adhesion. The cover in turn is connected to the shape memory material spring. Upon shape recovery, the shape memory material spring pulls, pushes or otherwise moves the cover away from the window to release or admit the substance.
Release Rate Control
In all shells described herein, irrespective of how the path is created, a porous barrier such as permeable or semi-permeable membrane may be incorporated between the inside surface of the shell and the substance contained inside the shell. One purpose of this material is to control the transfer rate of the substance as it exits or enters the shell once the path through the shell wall has been created. Another purpose is to control the part of the substance to be released or admitted. An example of this is the release of the volatile part of a substance, in which case the membrane provides the path for the volatile compounds to be released but acts as a barrier to keep the remaining substance inside the shell. A third purpose includes release of a specific substance, among multiple substances contained in the shell, that has the properties to allow it to travel through the membrane. The release rate is mostly controlled by the permeability characteristics of the material and the prevailing pressure differential between the inside contents and the surrounding environment. Pressure differential is achieved with the incorporation of pressurant means to create and maintain a pressure difference for the substances to be released or admitted. Pressurant means may include any of the volume changing devices described herein and the like. In addition, the incorporation of absorptive means inside the shell, such as polymeric matrices, would provide further control by preventing instantaneous release or absorption and stabilizing the existence of any differential pressure. The permeable material can be in the form of a membrane, a coating, film, layer, mesh, screen, strainer, filter etc. Choice of material and design depend on substance to be released or admitted and the desired transfer rate of the substance.
The permeable material can encapsulate the entire substance when the location of the path is indetermined or it can be placed strategically in the location where it is known that the path will be created (predetermined path). Strategic locations are places like the peelable layer of a shell, where the permeable material will provide rate control once the peelable layer is removed. The permeable material may have to be flexible to accommodate any volume changes during the path creation release processes. Further, this jacketing material may not be permeable on its entire surface. By being part permeable and part impermeable, it provides one more degree of freedom to control the transfer or release rate by adjusting the ratio of permeable to impermeable area. This concept of jacketing the substance with a permeable or semi-permeable barrier such as a membrane can be extended to all concepts of release devices presented herein irrespective of how the path is created.
Additionally, the path size or rate of exposed area covering the substance can vary with temperature, This can be accomplished with a peelable shell having a pull-away tab that that becomes progressively wider. As the path creation process begins, a small opening is created to release the substance through a permeable layer. As the path creation process continues with increased temperature, the opening, in addition to becoming longer, also becomes progressively wider, allowing for a variable release rate. As the release rate depends on the exposed area, by varying the geometry of the peelable layer, a relationship between temperature and release rate can be established. With this concept, the release rate will stay constant with time but will vary with temperature.
One more degree of freedom of controlling the release rate can be provided by progressively varying the amount of porosity or degree of permeability of the jacketing layer along the path length. The variation can be continuous or incremental. With this concept, the permeability, and therefore the release rate, can increase or decrease with changes in temperature.
Based on the above, there are several ways to control the release rate of the substance and to produce either a constant or a variable rate: (a) wrap the substance with a permeable layer of either constant or variable permeability (b) wrap the substance with a barrier layer that is permeable only in selective areas (c) design the rate of the path opening area to be linear or non-linear with respect to temperature (d) incorporate pressurant means inside or outside the shell.
An alternative placement of the rate control material is outside of the shell to encapsulate the whole device such that all components, including the shell and the shape memory material, are inside. This concept provides the choice of jacketing the same devices with different rate control material to achieve different release rates. In this case, the jacketing material effectively becomes a reservoir that controls the release rate of the substance to the surroundings.
Release Mechanisms
The following description relates to shape memory material activated release mechanisms, such as described above with respect to
In addition to the embodiments described above, a release mechanism can also be used in the impact shell devices shown in
As shown in
As shown in
Several types of release mechanisms can be employed with this concept. The type depends on temperature-release precision required, space availability, design flexibility, compatibility, ease of path creation etc. Different types of release mechanisms are discussed with respect to
A series of concepts for release mechanisms to be used in conjunction with any of the embodiments described herein are described with reference to
To allow for the case where the temperature rises above As and drops to below As before it reaches Af and release is not achieved, a bias spring 920 attached to posts 922 is incorporated in the embodiment of
Without the two way shape memory effect, an additional bias spring 924 integral with or connected to the shape memory material spring 906 should be used. The first bias spring rotates the body back to its original position and the second aids the return of the shape memory material to its original shape.
When mechanisms as the ones described above (that release stored mechanical energy to activate the device) are used to release a drug, an auditory signal is emitted, the strength of which depends on factors such as material of construction and medium the signal has to travel. This property becomes significant for implants where a manual adjustment of a drug dosage can be detected with device such as a stethoscope. This provides assurance of the drug release and eliminates the uncertainty or the requirement for radiography. Other means for producing auditory signals include pressure difference between shell contents and surroundings, shells with brittle walls and shape recovery with a narrow temperature range that results in an accelerated path creation process.
Thermally Activated Transporter
The device illustrated in
When the thermally powered device is left unrestrained, it becomes a self-propelled vehicle that can travel on guided single or multiple tracks, or unguided in different media and on surfaces. The device is capable of traveling on any track, medium or surface, including flat surfaces, that will allow forward movement but will provide traction to prevent reverse movement. The device moves by first thrusting one end forward during the first half of the temperature cycle while the second end provides traction, then, thrusting the second end forward during the second half of the temperature cycle while the first end provides traction. With this sequential movement of the two ends the device expands and contracts with temperature cycling. The order of expansion and contraction with respect to temperature change is determined by the direction of the shape recovery of the shape memory material activator.
The bias spring 1,004 can be eliminated if the variable length body 1,006 is also used as spring or if the shape memory material spring 1,002 is trained in a two way shape memory effect. Further, the variable length body itself can become the shape memory material spring 1,002 trained in a two way shape memory. In addition, the variable length body 1,006 can be eliminated if the work enables are attached directly to the shape memory material spring 1,002 or the bias spring 1,004. In certain applications, the shape memory material spring or the bias spring may perform the function of the work enablers and as such, the need for the variable length body is eliminated. Further, multiple shape memory material springs with the same hysteresis curves, coupled with bias springs, may be incorporated. Multiple springs with reduced cross sections allow for faster heating and cooling. In addition, they allow for the thermally powered device to travel on a curvilinear path. If two sets of shape memory material springs of unequal length coupled with compatible lengths bias springs are placed inside a variable length body in diametrically opposite locations, the longer shape memory material spring would produce a larger expansion, comparing to the shorter one, and force the thermally powered device to travel on a curved path. Depending on the configuration of the shape memory material and the travel environment, there are times that work enablers are not required. A case for this would be a thermally powered device comprised of shape memory material activator that is configured aerodynamically to minimize the forward resistance and maximize the backward resistance. A similar case exists when the device is traveling in a medium of decreasing density where there is less resistance to forward movement and a higher resistance to backward movement. Depending on the prevailing conditions and the design of the device, a slight backward movement may be tolerated but the net effect is a forward movement with each full temperature cycle.
With the sequential advancement of one end followed by the other end, the thermally powered device 1,000, in one temperature cycle, travels a distance equal to the displacement produced by the shape memory material spring 1,002 in one half of the cycle. This way, the device is capable of traveling continuously with temperature cycling of the shape memory material spring. As a traveling vehicle, it is capable of performing multiple tasks. A few of these tasks are; carry a load from one location to another (in essence becoming a thermally activated transporter), release a substance along the travel path or at selected locations, push or pull on object, expand a tube or an opening, place on object at a specific location and, trigger an action as to activate a device by turning on a switch. The travel distance can be measured in whole temperature cycles or degrees of temperature per unit distance.
The thermally powered device is capable of traveling on any two or three dimensional, open or closed loop, guided or unguided path. To avoid kinking of the shape memory material 1,132 and the bias 1,134 springs, they can be housed in telescoping tubes formed in circular segments as illustrated in
Any type of work enablers such as fins, indentations, depressions, wheels, gear teeth, or spikes will advance the thermally powered device if matched it with the right track. The track provides the guiding path and can be comprised of a tube, two parallel surfaces, single or multiple rails, or a flat surface and the like. Also, fastener threads, male or female, can be used as a track for the thermally powered device to travel on. The ability to travel inside threaded holes provides opportunity for several applications such as plugging holes and securing fasteners in place.
Applications of the shape memory material activated transport devices vary from toys to medical and industrial products to scientific instruments. One application is the release of a substance within a predetermined temperature range, while the temperature is either rising or falling, such that each release takes place at a different location along the traveled course. The release is independent of time as there is no release if the temperature stays constant.
In addition to integrating shells on the fins of the tracks, the fins of the thermally powered device can be made progressively longer, from front to back, such that the shells are increasingly squeezed as the thermally powered device goes by. With this concept, all fins contribute to the release of the substance both during the heating and the cooling of the shape memory material activator. Other fin modifications may include progressive adjustment of the fin angles and incorporation of variable stiffness fins. Further, the paths created through the wall of the shells may be through valves or permeable walls and the shells may be connected to supply reservoirs. Connecting the shells to supply reservoirs enhances the capabilities of the circular transport by enabling it to release one or more substances continuously as the thermally powered device travels around a loop. In another concept, the track fins can act as valves to create multiple paths and release a substance. In this case, the deflection of the fins caused by the advancement of the thermally powered device can create paths to release single or multiple substances by opening up valves connected to supply reservoirs.
Besides releasing a substance, the thermally powered device can perform other functions such as pushing or pulling an object to a predefined distance. This can be performed with the thermally powered device remaining on the tracks, extending a part out or using an extension arm. Applications for this concept include location identification and positioning of medical devices. One example is the placement of thermoseeds (magnetic rods) for the treatment of certain cancers. Anchoring the tracks in a mammalian body and utilizing the thermally powered device as a transporter for drug or medical delivery devices allows for a multitude of applications in the medical field. The thermally powered device can be used as means for the transfer or delivery of various objects, substances and the like. As an example, it may transport a shell containing a substance to a specific location to be released at a predetermined temperature or upon delivery.
Means such as the element 1,356 and the extension arm 1,354 can be used to connect several thermally powered devices in series. With this arrangement, the shape memory material spring in each device can have a different hysteresis curve such that at least one device is changing length with a change in temperature within a given range. If the front end of this particular device is advancing forward; all devices ahead of it will be pushed forward without having to change their lengths. If on the other hand, the back end of this particular device is advancing forward, all devices behind it will be pulled forward without having to change their lengths. Thermally powered devices can be connected to each other with various methods such as pin or ball joints to accommodate travel on curved tracks and variable opening passages. In the case of the thermally powered devices, the sequence of activation depends on the arrangement of the hysteresis curves relative to the change in ambient heating. When the shape memory material springs are heated individually by external means such electric heating, a specific powering sequence can be achieved. Advantages of connecting several thermally powered devices in series include increase in the operating temperature range of the overall system and increased flexibility that allows travel along curved paths.
The thermally powered device can be used without tracks to travel in certain mediums that will sustain it and prevent it from sliding backwards. Such mediums include certain types of living mammalian matter, viscous substances and particulate media. As an example, when a thermally powered device travels in particulate media, the work enablers displace the particles of the media ahead of them as they advance forward. These particles flow to the space left behind by the work enablers to occupy it. Once this space is occupied, they provide traction for further advancement. The same principle applies to viscous substances. In a living mammalian matter or other elastic substance, with each advancement of the thermally powered device the substance needs time to relax and flow back to re-occupy the space left behind by the work enables before traction is available for further advancement.
An independent shape memory material activated transport device once deployed can be retrieved using a set of tracks. By placing the tracks in front of the device as it travels, it will be forced to enter the track. By withdrawing the track, the device is retrieved. In this case, the track act as a catcher.
Fins for the thermally powered devices do not have to be fixed. They can be hinged to provide limited movement such as to minimize the drag resistance and increase the thrust. In addition, they can be made of multiple parts to allow for greater flexibility and travel on variable width or diameter tracks. Also, they can be reversible to allow for travel in both directions.
Thermally powered devices, whether traveling on an open, closed or loop track, are capable of becoming temperature indicators and warning systems by releasing a substance. They can achieve the same function through their relative position on the tracks without having to release any substance. This position can be determined through direct visual observation of the device adjacent to a graduated scale. Preferably, the temperature record would be observed easier with a pointer attached to the thermally powered device pointing its exact position on the graduated scale.
The shape memory material activated transport devices can also be used to expand a closed conduit laterally such as a tubular passage or to increase the gap defined by the spacing of two surfaces. In addition, they can release a substance such as a drug or sealant to provide a curative agent or to seal the wall. Further, they can expand and place a retainer such as a stent or other support member to hold the conduit in the expanded position, to provide structural support or to form a sealed joint. Furthermore, they can transport diagnostic and detection equipment such as optical or acoustic devices for the inspection of pipes or the examination of cavities in mammalian bodies such as the colon. Samples of these devices are shown in
The variable length body of any thermally powered device can become collapsible such that it expands while it travels with one temperature cycle and collapses while it travels with the second half. This allows for the selective or continuous expansion of passages.
The same principle used to expand a tube diametrically can also be used to shrink a tube diametrically. For this to take place, the thermally powered device must have the work enablers on the outside and travel inside a track. In addition, it must have sufficient core clearance along its length for the tube, that is to be shrunk, to run through it. The tube is shrunk in a reverse manner to the one shown in
The variable length body made of an elastically deformable material can be utilized as a bias spring, thereby eliminating one element from the device. In addition, the variable length body can be made of a number of longitudinal leaf springs that collectively act as a bias spring. Further, a linkage can be incorporated to produce the lateral expansion.
The lateral expansion device can also release a substance during the tube expansion process. All substance release concepts presented herein can be used for this purpose. An additional concept of a lateral expansion device is shown in
Besides expanding a tubular conduit and releasing a substance, any collapsible tubular expansion device can be used to expand an object such as a tube segment, ring, stent or a specific device and place it in its expanded form on the inner wall of a conduit such as a tube or a blood vessel. The purpose for the placement of such objects includes; to provide structural support, maintain the specific shape, seal a surface, monitor a the performance of a system and the like. This is achieved by producing an interference, snug, fit between the object to be expanded and the variable length body prior to inserting them in the tubular conduit or simply bonding the two together with low tack adhesive. The collapsible tubular expansion device along with its load, the object, are inserted inside the tubular conduit and at the proper location the temperature of the shape memory material spring is raised and it undergoes shape recovery. The shape recovery causes the variable length body to expand laterally and forces one of its ends to advance. Expansion of the variable length body forces the object to expand against the wall of the conduit and stay in place after the collapse of the variable length body. In addition to round objects, other non-round objects or partially round such as patches can also be placed provided they have the ability to stay in place by mechanical, adhesion or other means. Further, the expanded objects may be combined with a shell to perform the additional function of releasing a substance.
The shape memory material activator of the thermally powered device can be heated and cooled by changes in ambient temperature. In addition, it can be actively heated by direct contact, forced heating or resistance heating by an electric source, either induced or direct. In the case of the electric source, the shape memory material becomes part of the electric circuit and its relatively high electrical resistance produces the required heat to raise its temperature through the transformation range. The thermally powered device can travel and expand laterally in the same fashion as described herein without the utilization of a shape memory material. This requires the powering of the device with alternative means such as fluid pressure mechanical or electrical energy. The fluid pressure can be either hydraulic or pneumatic. By running supply lines to the device, the device expands and contacts following the pressurization-depressurization cycle, as in the case of the thermal cycle, and in the process advances forward similarly to the device that is configured with a shape memory material activator. Typically, for most applications, fluid pressurization, pneumatic or hydraulic, requires the sealing of the thermally powered device or a pressure chamber within the device to avoid leaks. Utilization of fluid pressure does not alleviate the need for a bias spring. The bias spring is required to aid the contraction process and to advance the aft end of the device. In addition to fluid pressure, the device can be operated by a cable release system that applies a force at one end of the device to expand it or contract it and, upon removal of the force, the process is reversed by the bias spring. Again, the device is able to travel with the repeated application and withdrawal of the force. One advantage of the cable release system is that it can be attached either to the internal or external surface of the device, at either the forward or aft end. Attachment to either end allows for the applied force to be either tensile or compressive and to either expand or contract the device. When there is no need to expand the device laterally, application of fluid pressure is restricted to devices whose variable length body can expand only axially with internal pressure. Examples of this are bellows and rigid telescoping tubes. The thermally powered device is also capable of traveling by the utilization of electrical energy to operate devices like motors or electromagnets. With these devices, the bias spring is needed only if the variable length body is actuated in one direction only.
The variable length body in all tubular expansion devices can be made eccentric such as to expand tubes laterally to non-circular cross sections. This is achieved by placing the variable length body's axis at a distance from the track's axis or by making the variable length body non-symmetrical. The two axes may or may not be parallel to each other.
Rotating devices, circular or eccentric, when equipped with abrasive means on their outside surfaces can be used to grind a shell's substance and release it by abrasion. Further, they can grind the inside wall of a conduit to abrade away any deposits such as corrosion products in a pipe or plaque in an blood vessel. In certain cases, depending on the nature of the deposits and the flexibility of the tube, the simple lateral expansion of the thermally powered device can be sufficient to break loose the deposits. By incorporating an adhesive layer on the outside surface of the thermally powered device, loose deposits will adhere to it and be carried away upon withdrawal of the device.
Thermally Driven Track
This concept forms the basis for a multitude of applications. Using the same concept as illustrated in
Multiple thermally powered devices can be utilized on the same track to produce additional travel or higher overall recovery forces.
By placing several thermally powered devices of different lengths and hysteresis curves anchored at different points along their lengths on the same track, various profiles of track travel with respect to temperature can be achieved. Such profiles include, but are not limited to: (a) Continuous travel if the Af temperature of one device is the same as the As temperature of another device. (b) Discontinuous travel when the As temperatures of one device is higher that the Af temperature of another device. (c) Continuous or discontinuous travel during heating and cooling of the shape memory material activators by anchoring the devices at different points along their lengths. In each case, the travel rate with respect to temperature can be varied by selecting shape memory material of different hysteresis slopes. In addition to employing thermally powered devices that expand with the rise in temperature, similar effects can be achieved with thermally powered devices that contract during the rise in temperature.
In addition to the design flexibility offered by choice of transformation temperatures and anchoring points, selection of tracks with opposing, non converging, fins offers one more degree of freedom.
The thermally driven track does not necessarily have to be straight. It can be of any configuration that will advance with the application of shape recovery force.
The angular degree of rotation in each half cycle is half of the angular expansion of the circular thermally powered device. As was the case with the straight track, by anchoring the circular thermally powered device at different points along its body, the relative amounts of track rotation between heating and cooling can be adjusted. All thermally driven track systems presented herein can operate, as a minimum, with a single traveling track provided there is sufficient support to eliminate distortion of the thermally powered device and to keep it on track. As an example, the circular thermally powered device 2,200 can operate without the inner track fins 2,216 provided the inner track provides guiding support to the circular thermally powered device 2,200. Of course, with a monorail system as the one shown in
Production of rotary motion is not limited to concentric tracks only. Other embodiments utilizing such means as gears, shafts, belts, or chains can be utilized.
The thermally powered device's body does not have to be flexible in the form of a bellows, neither does it have to be made of one single part. It can be made of tubular telescoping parts requiring a minimum of only one set of fins at the aft end if the thermally powered device is anchored at the other end, or two sets (one at each end) if it is anchored elsewhere along the length of the body. Also, the thermally powered device's body can be an elastomer that performs as a bias spring and can encapsulate the shape memory material spring and become an integral part with it. In this case, the fins can be extensions that are molded or sculptured on the body. Further, the thermally powered device can have no body if the fins are attached to the shape memory material spring directly. The fin spacing on both the track and the body determine the precision of motion transferred from the thermally powered device to the tracks. Typically, the finer the spacing, the better the meshing between the two sets. Again, the shape memory material spring as well as the bias springs can have any configuration. They do not have to be coil springs. As long as the shape memory material can be deformed at one temperature and recover its shape at another temperature by producing a displacement when left unrestrained and a force when it is restrained, it will perform adequately in the devices presented herein. Also, for all the devices presented herein, functionality is independent of shape and size of shape memory material and bias springs. Further, functionality is independent of fabrication and assembly methods utilized to build the devices. The bias spring must have the ability to be deformed elastically by the shape memory material spring during the shape recovery process and produce, as a minimum, a force sufficient to aid the shape memory material spring in its reverse shape recovery process and return it to its deformed cold shape. For metallic shape memory materials such as the nickel-titanium based alloys, the martensitic condition is the cold shape.
The energy generated by thermally powered devices can be utilized to create a path in a shell to release a substance. A linear or rotary thermally driven track device can be used for this purpose. Linear or rotary motion can be used to create a path in shell wall to release a substance by fracturing, exploding, imploding, puncturing, peeling, tearing, shearing, grinding, rupturing, splitting, twisting, stretching, squeezing, separating, debonding, grinding and the like, a shell. The path creation can take place with rising and/or falling of the shape memory activator's temperature. In addition, by adding several thermally powered devices to the same track system, a reversible type path can be created repeatedly over different temperature segments. The energy generated by thermally powered devices can be used for other purposes besides path creation. At times, it becomes beneficial if it is transferred to other devices by mechanical means.
Instead of a free rotating wheel, two or more circular thermally driven track devices can be coupled together with a belt to produce devices with enhanced characteristics. Such a device 2,350 is shown in
In the case where the fins of two coupled thermally driven track devices are oriented in opposite directions, the thermally powered devices will also rotate in opposite directions. Unless both shape memory material springs have similar or overlapping hysteresis curves, the thermally powered devices will not counter rotate simultaneously. By rotating at different temperatures, a back and forth rotation is generated. By selecting the shape recovery characteristics of each shape memory material spring, the temperature span between rotations and will be set. If there is simultaneous counter rotation, there will be no net rotation due to restrained motion, resulting in tensile stress in one span of the belt (or connecting member) and compressive stress on the other. Different combinations of fin orientation, anchoring points and shape memory material properties can be used to produce repeated motion with rising or falling temperatures within predefined temperature ranges. The resulting motion can be (a) unidirectional, where a set or tracks or a belt move in one direction, (b) bidirectional, where two tracks of the same track set move in opposite directions, or (c) oscillating, where a set of tracks or a belt go back a forth between two or more positions without making an overall net advancement. In all cases, when the motion is restrained, a force develops that can be converted into torque with rotary systems. These concepts can be used in applications such as; to create a path to release a substance, to accumulate torque, to apply a controlled force at given location, or generally to actuate or to power other devices.
When the shape memory material activators are actively heated, incorporation of multiple devices into one system enhances the system's output considerably. If heating is sequenced to allow one activator to cool to the martensitic state while another is heated to austenitic state such that at any time there is at least one activator powering the system, continuous rotation will be produced.
The concepts of thermally powered devices and thermally driven track devices can be used to create paths through shells to release substances. In addition, they enhance the path creation process in terms of release types, temperatures, repeated cycles, delayed cycles and the like.
Multiple thermally powered devices can be integrated on a single thermally driven track to produce motion at different temperature ranges.
The embodiment illustrated in
The thermally powered device constitutes an energy conversion machine. It utilizes thermal energy and converts it into mechanical energy. It is capable upon heating or cooling to produce motion and apply a force to perform work. When left unconstrained, it travels on a guided or unguided track. The thermally driven track device expands the capabilities of the thermally powered device in terms of providing the means for power transfer. When a circular thermally driven track device is utilized, the expansion and contraction of the thermally powered devices is converted into rotary motion that can easily be manipulated and transferred via mechanical power transfer mechanisms comprising gears, belts, chains, shafts and the like. The concept of the thermally driven track device is a modular one in that it allows for the integration of multiple devices, interconnected with mechanical power transfer means, to produce a system of increased work output. The modularity of the system is not restricted by the scale of the individual devices. This modularity provides a multitude of opportunities for expansion in both two and three dimensions. For example
By integrating several modules comprised of thermally powered devices, tracks and connecting means, the energy conversion system can be expanded from a linear one to a planar one to a three dimensional system. Each module constitutes a subsystem that funnels the power generated to a single mechanical member such as rotating gear or shaft. There is no limit to the number of modules that can be combined to funnel their power output to a common mechanical member. This modularization provides the flexibility of increasing the capacity of the energy conversion system by the simple addition of more modules. By selecting the shape memory material springs to have different hysteresis curves, a continuous output motion can be produced with the rise and fall of the temperature. In addition, by selecting the shape memory material spring type and size along with the number of modules, different levels of energy output are achieved.
If the shape memory material springs are heated by ambient heat, energy conversion will take place during ambient temperature change. Depending on the hysteresis curves of the individual shape memory material springs, energy conversion may be extended continuously or intermittently from the lowest As temperature to the highest Af of the hysteresis curves. Also, depending on the anchoring arrangements of the individual thermally powered devices, additional rotation can be produced during cooling from the highest Ms to the lowest Mf temperature. Any output during reverse shape recovery is attributed to either the bias springs or to the two way shape memory effect.
For a higher rate of energy conversion, heating of the shape memory material can be achieved by electric power. The electric resistance of the certain shape memory materials such as Nitinol is sufficiently high to allow them to be used as electric resistors. In this case, individual shape memory material springs are connected to a power source and heated resistively. Heating of the shape memory material springs can be simultaneous for maximum torque production with accompanied discontinuous motion, or sequential such as to allow one group of shape memory material springs to cool while another group is being heated up resulting in reduced torque but a continuous rotation. Increased energy output requires a rapid cooling rate in order to allow for fast cycling. A large system consisting of multiple modules of thermally driven track devices can be used to counter the effects of slow cooling. In this case, at any given time, different modules or group of modules will be at different stages of heating-cooling cycle such that there is motion produced continuously.
The shape memory material spring activators can be cooled with a moving fluid, gas or liquid, to accelerate the cooling rate. If the Mf temperature is above ambient, forced ambient air can be used as a cooling medium. In cases where forced cooling is not possible or it is not considered optimum, the individual shape memory material spring activators can be cooled with a cooling fluid contained in individual reservoirs. Such a self cooling device 2,800 is illustrated in
Prior to heating of the shape memory material spring 2,804, the variable length body is in the contracted position occupying a minimum volume while the two reservoirs 2,808 are in their expanded position occupying a maximum volume. The two valves 2,810 are open toward the reservoirs as shown in
When several modules of thermally powered devices are used, individual modules may be forced heated and cooled as groups by a circulating fluid system. By selecting the thermally powered devices in each module to have the same transformation temperatures, fluid used by one module for cooling can be used in another module for heating if the Mf temperature of the first module is the same or higher than the Af temperature of the second module. In this system, the heat of transformation released by the shape memory material activators of one module during cooling is absorbed by the shape memory material springs of second one during the shape recovery process. This way, the temperature increase of the fluid attributed to austenite to martensite transformation in one module is reduced by the same relative amount in the second module by the heat absorbed during the martensite to austenite transformation. This type of closed recirculatory system tends to minimize the energy required to operate the system.
Certain materials suffer fatigue failures when subjected to cyclic loads. In many materials, including metallic shape memory ones, fatigue life is extended by frequent annealing treatments. To eliminate fatigue failures in thermally activated devices, the shape memory material springs can be partially or fully annealed in situ prior to developing permanent damage. Annealing removes the dislocations accumulated during cycling and in general rehabilitates the material. When the shape memory material springs are heated resistively for the operation of the device, the electric circuitry exists and can be used to anneal the spring resistively, in situ. The shape memory material springs already have their shape and since there is no need to re-set them, no restraining tooling is required for annealing. The annealing temperature to extend fatigue life should be kept at a level low enough not to alter the shape memory properties or the shape memory material spring. Typically, this level is below the temperature of the last heat treatment prior to placing the spring in service. When bias springs are used, it is preferable to decouple them from the shape memory material spring to eliminate the application of external stresses.
There are numerous applications for the energy conversion system. They range from the specific ones such as the creation of a path to open a shell or a group of shells to release a substance, to the general use of mechanical energy similar to the one produced by heat engines. Applications also include medical devices such as implants, or drug delivery systems. One of the main advantages of the energy conversion system is the ability to be scaled up and down by either adding modules of thermally powered devices together or by changing the size of the individual thermally powered devices. Both options allow for an extended range of sizes from large scale energy conversion industrial type applications to MEMS (micro electro-mechanical systems) and nano-scale applications. These options are available as the function of these devices is independent of their fabrication method.
A problem encountered by the industry of temperature activated devices is the requirement to keep them inactive, in a dormant state, during manufacturing, storage and transportation. The state of dormancy is maintained by keeping the devices at low temperatures until the beginning of their service life, mostly by refrigeration, in order to avoid premature activation by ambient heating. If the devices are designed to be activated at a temperature lower than the ambient, they must be kept heated at a temperature higher than ambient. A concept of a single action arming process, described herein, solves this problem by allowing the devices to remain dormant until usage time. In the dormant state, the devices are unable to create a path through the shell when exposed to various temperature environments. Upon arming, they are placed in an active state after which time they are ready to create a path through the shell once the shape memory material activator attains a predetermined temperature. This concept allows either the supplier or the user of the devices to arm them at anytime after their fabrication is completed. Arming, as defined herein, is the process of placing the device in an active state of readiness that enables the shape memory material activator to create a path through the shell once it attains a predetermined temperature. Prior to arming, the shape memory material activator can attain any temperature, and change phases accordingly, without being able to create a path to release the substance contained in the shell. Enabling is achieved by deforming the shape memory material activator in situ while in the martensitic state. Arming is performed with a single action involving one simple operation such as pushing, pulling, rotating, or bending. A second arming method involves the deformation of the shape memory material activator as well, but in addition it allows its coupling with the shell. In either case, the ability to arm the individual devices at any time before they are placed in service allows for their transportation and storage at any temperature. In the unarmed configuration there is no need to keep the devices below or above a specific temperature (refrigerated or heated) in order to avoid premature release. Besides the freedom of maintaining the devices at ambient temperature, this concept allows the user to set the release temperature, for a given shape memory material, by controlling the amount of deformation during arming that in turn controls the As temperature. Of course, it is understood that a minimum amount of deformation is required to create a sufficiently large recovery force to create the path through the shell wall. In addition to arming substance release devices, the arming concept can also be used to place other devices in an active or inactive state.
Work enablers, such as fins that resemble featherboards, can be replaced with other means to restrict movement in one direction. Such means are similar to the ones used in the shape memory material activated transport devices that allow one way movement of thermally powered devices on tracks. They include ratchet gears with detents, ball detents, surface characteristics such as preferentially oriented features, one way rotating wheels and the like. These means rely primarily on mechanical locking, frictional and adhesion effects between the contact surfaces of two frames. One of the advantages of utilizing ratchet gears is that that the number of sound "clicks" produced during setting can be indicative of the temperature setting.
The same basic means, in a rearranged configuration, can be used to arm the device by pulling the two ends apart instead of pushing them together. This alternative concept is shown in
Arming can also be achieved by rotating the frames relative to each other.
The work enablers, that provide gripping and locking action, do not have to be placed on the frame sides.
There are cases, such as the ones where the frame parts are held together by friction, that do require the separation or the fracturing of the frame. In these cases, the shape memory material spring must stay deformed to the degree that shape recovery forces would be able to overcome the frictional forces and begin to move the two frames apart. For low pull forces, alternative gripping means such as fastening tape of loops and hooks can be used. In addition, other gripping means such as magnets can be used to replace the gripping element and the engaging tab. The rotating arming device can also be used with the peelable shell. In this case, the gripping element and the locking tab may be replaced with threaded parts (fastener and nut respectively) such that simultaneous engagement is achieved between the frame members and between these two parts during rotary arming. As with all the devices presented above, alternative one-way movement means and temperature indicators can be employed with peelable shells.
Mechanical arming can be achieved manually using finger pressure, hand tools such as pliers or automatically by a machine such as a press. The first two methods offer the advantage that the user can arm the devices in the field without the need of automated machines. The third method offers the advantage that devices can be armed individually or in groups and it is mostly conducive to mass arming. In all methods, arming takes place with a single action such as push, pull or rotation.
The basic concept of arming, can also be used as a force release device.
An alternative temperature dependent force release device 3,350, with enhanced capabilities, is shown in
Arming examples so far have demonstrated the ability to arm a device by a single action that consists of the application of a tensile or compressive force or torque resulting in relative linear or rotary motion between parts of the device.
Single action arming is not limited to the methods of compression, tension and rotation. Other methods easily adaptable by the user of the device can be employed. In all cases, the objective is to deform the shape memory material during the arming process while it is in the martensitic state. One of these methods is to reposition the shell in the device at the time when the service life is to begin and at the same time deform the shape memory material spring in the martensitic state by a single action. The ability to reposition the shell at any time has several advantages: (1) Eliminates the need to transport and store the device at a safe temperature either by refrigeration or heating. (2) Permits the interchange of devices and shells. (3) Makes the device reusable. The third item is achieved by re-deforming the shape memory material at the martensitic state during the re-arming process. Re-arming is adaptable by many of the concepts described herein.
An arming concept utilizing a deformable shell with the shape memory material inside the shell is shown in
An alternative arming concept that utilizes a device 3,500 with a foldable shell 3,504 and a shape memory material spring 3,502 located inside the shell is shown in
The thermally powered device can be armed by a single action to become active with temperature cycling of the shape memory material spring in similar manner as the rest of the devices as shown in
The thermally driven track device can also be armed by a single action to become active with temperature cycling. In this case, the beginning end of the track 3,584 of the thermally driven track device 3,580, shown in
A shape memory material based substance release device with a bias spring has the ability to produce a displacement during temperature rise from As to Af and recover it with its from Ms to Mf. Depending on the type of shell, this displacement and the associated constrained force can be used to create a path (a) with the temperature of the shape memory material spring either increasing or decreasing or (b) with the temperature increasing and close it with the temperature decreasing or vice versa.
An alternative arming concept for a device that releases a substance with the fall of the temperature of the shape memory material spring is illustrated in
The single action arming concept is not limited to manual or mechanical arming. It can be extended to other single action methods such as hydraulic, pneumatic, electric, and magnetic.
The gripping process can produce an auditory signal (similar to a snapping action) that would be indicative of the completion of the arming process and can be utilized as a verification of the engagement. The number of sounds ("clicks" or "snaps") can be indicative of the degree of shape memory material spring deformation and the release temperature setting. This type of gripping verification applies to all mechanisms utilizing such engagement grips. Other advantages of this arming process include: (1) Faster activation in response to a changing outside temperature as the fluid surrounding the shape memory material spring acts as a heat transfer medium. (2) The tubes connecting the device with the reservoir can be of any length such that arming can take place remotely.
The hydraulically arming device can also be used to arm shells that create and close a path with temperature cycling when a bias spring is coupled with the shape memory material spring. Once the device is armed, the fluid flows in and out of the reservoir with temperature cycling as the piston oscillates back and forth. Optionally, the fluid can be drained out after the second half temperature cycle instead of returning to the reservoir. Hydraulic arming is not limited to peelable shells. Other types of shells whose path can be created with the application of an external force can be incorporated in this device.
The hydraulic arming concept of
Instead of hydraulic arming, the same device can be armed pneumatically. A gas, like air, can be used for this process. The gas can be supplied under pressure by a reservoir or it can be pumped atmospheric air. Advantages of gas arming are that the reservoir used for hydraulic arming can become a gas reservoir or it can be replaced with a manually operated air pump. In either case, the gas does not have to be collected back during shape recovery.
In addition to the methods mentioned above, a magnetic force can also be utilized to arm the device 3,800 by a single action as illustrated in
Optionally, all devices can be armed by electrical energy sources. Such sources include batteries and electric power. Electric arming has the advantage that it eliminates the need for manual arming, especially in cases where either a substantial force is required or manual accessibility does not exist. For arming to take place, the electric energy must be converted to other forms of energy such as mechanical or magnetic to produce a force along with motion to deform the shape memory material spring. With the addition of microprocessors, fine motion control can be achieved that can result in increased arming precision. Single action arming with electrical energy involves a simple operation such as pushing a button. The push of a button may activate an electromagnet, such as a solenoid, to apply a force and arm one or more devices.
In addition to single action arming method, a multi-action method can be adopted to arm the devices. This method typically involves two or more sequentially and separate operations such as the bending of the shape memory material spring and its installation of it in the device. Such a concept is illustrated in
Devices incorporating the arming concept can become reusable. For devices whose path creation is permanent, a new shell must be inserted after each release. Reuse of the device provides the advantage of having to replace only the shell or its contents and avoids the expense of using a new device each time.
Besides the spring presented herein, other springs configurations can be used to arm the device and create a path through the shell wall. "ASME Y14.13M (ANSI Y14.13M-1981) Mechanical Spring Representation" presents springs that can be used for this purpose. Any shape memory material of any configuration that can produce work during temperature change is capable of being used as an activator to create a path though a shell wall.
The release accuracy of the devices can be improved by fine-tuning the arming process. This might be necessary due to of the large influence of chemical composition and processing parameters on the shape recovery characteristics of the shape memory materials, especially the nickel-titanium based alloys. Major influencing processing parameters include cold work and heat treating. Shape recovery characteristics include transformation temperatures and shape recovery forces. Fine-tuning involves certain adjustments that result in a consistent path creation temperature with the minimum required force within the same lot or different lots of materials. It also allows for a "dial-in" path creation temperature for an individual device. Fine-tuning is accomplished by the methods described herein but it is not limited to these methods.
The first fine tuning method is the arming process itself. It controls the shape memory material spring deformation, which in turn controls the relative position of the As to Af curve, and, in general, the hysteresis curve with respect to temperature. The greater the induced deformation, the greater the shift of the curve to higher temperatures, resulting in increased release temperatures. Typically, once deformation exceeds a certain level, the width of the hysteresis begins to expand, usually by shifting the As to Af portion of the curve to higher temperatures. With this method, inconsistencies in the shape memory material behavior can be minimized among the different devices. Further, the shape recovery forces, required to create the path, increase with deformation but tend to level off above a certain level that is of the order of 1.5% strain and begin to slowly decrease above 8%. This way, deformation above a minimum level produces consistent path creation forces while shifting the release temperature to higher levels. However, the variation of the shape recovery force is not important as long as the minimum force required to create the path and release the substance is generated.
The second fine tuning method is the control of the temperature above As at which the shape recovery force begins to develop. Ignoring compliance factors that tend to be device specific, this temperature is controlled by the gap or the slack allowed between the deformed shape memory material spring and the shell. This can be the gap between the shape memory material spring and the shell in the case that path creation takes place by expansion of the shape memory material spring, or the extra tab length allowed on a peelable shell.
An alternative fine tuning method consists of a combination of the first and second method. This involves the adjustment of both the amount deformation induced in the shape memory material and the length of the deformed section. It is applicable to devices, similar to the ones illustrated in
Release of Substances
All devices presented herein are capable of releasing substances that can stimulate the senses; vision, smell, taste, touch and hearing or be undetected by the senses. Applications for release of visible substances was described earlier under temperature indicators. Applications for release of substances that stimulate the rest of the senses are described in this section. Typically, any released substance may be detected by more than one sense and release of a single substance may effectively serve multiple purposes.
Any of the devices described herein are capable of releasing a substance to produce an odor. This odorous substance can be of any type, from objectionable to fragrant. When used in temperature warning devices, the odor may be objectionable to indicate that a safe temperature limit has been exceeded. The device may release the odorous substance directly onto the product that it is protecting. The product may be a type of food such as ground meat that has been exposed to an unsafe temperature. Release of the substance effectively transfers the source of the odor to the product and renders it unusable. Alternatively, the substance can be released into a reservoir. Release of the substance can also take place when a sensor, such as a biological one, detects increased or undesirable microbe activity and commands the release of the odorous substance. In this case, activation requires an external heat source such as a battery to provide the necessary heat to activate the shape memory material. When the odorous substance is released on a product, olfaction based devices not only act as warning devices, they also act as decision makers and inspection devices determining product acceptability and assuring that a rejected product can not be used. When released into a reservoir, the wall of the reservoir must be sufficiently permeable to allow the volatile odor compounds to permeate through and be released to the surroundings. The release rate can be controlled through the permeability and physicochemical properties of the reservoir wall in relation to the properties of the substance. In releasing the substance into the reservoir, the osmotic principle can be used to restrict the flow direction across a surrounding membrane and avoid dilution of the substance inside the shell. Optionally, the substance may be combined with another substance in the reservoir to produce a new odor. If the release rate of the substance into the reservoir is continuous, the type and strength of released odor will change with time due to continuous change in the mix ratio of the two substances.
The release rate of the odor can be controlled either by the permeability of the reservoir walls or the substance can be contained in a permeable or semi-permeable membrane within the shell, such that when the path is created through the shell wall, the substance, and in essence the odor, is released through the membrane. Further, the substance can be pressurized in the shell to provide additional means for release rate control. Use of time dependent and time-temperature dependent release devices to release odor-producing substances enhances the capabilities of the olfactory devices. The release can be integrated once a predetermined temperature is exceeded such that the odor changes in strength and type with either time alone or time and temperature. The features of vision and olfaction based temperature warning devices can be combined to produce one device that would provide a dual indication, a color change and odor. This is achieved by the release of an odorous substance that is also a dye. The reservoir to which such a substance is released must have a transparent window for the color detection and part of its wall must be sufficiently permeable to allow the odorant's volatile compounds to be released to the environment. Control of the permeability and the release area of the wall provide more degrees of freedom to control the release rate of the odor.
Temperature activated olfaction based devices can be used as fire alarms to provide a warning once a predetermined temperature is exceeded. In this concept, the shape memory material creates a path through the shell wall to release a substance containing strong and objectionable odorant components. The substance can be released directly into environment were the odor will be emitted to the atmosphere at a rate controlled by the properties of the substance and the volatility of the odorous compound itself.
For fire alarms, a characteristic odor can be selected such that upon detection it will be associated with the danger of a fire. When multiple shells are incorporated in one device, the path in the shells can be created sequentially with increased temperature. As more substances are being released, the type and strength of the odor can change to indicate the increased danger. These devices can be installed in buildings as wall units, in areas where there is a potential for a fire such as electrical cabinets, on the outside surface of stove hoods etc., and in the heating and air-conditioning ducts of buildings where the released odor can be distributed throughout the building by the re-circulated air. Temperature activated odorous safety devices have several advantages over conventional fire alarms. They are maintenance free as they can operate without external energy sources such a batteries. They can be placed in areas such as the kitchen because they are unaffected by humidity, steam and volatile products generated by cooking. Since they detect temperature, they can be activated and provide a warning by releasing an odor before there are any combustion products in the air. In addition to being able to replace or complement existing alarm systems, they offer warning to visually and auditory challenged people for whom present fire alarm systems may not be beneficial.
Olfaction based devices can also be used as fragrance delivery devices. In this capacity, the released odor produces a pleasant scent. The substance can be released directly to the environment, to a reservoir for mixing with another substance prior to release to the environment, to a mammalian body through a transdermal (patch) device or to an absorbent material that would further control its release to the environment. In all cases, all the devices described herein are capable of delivering the fragrance. However, when the substance is released to an enclosure such as the reservoir mentioned above, means must be provided to allow the fragrant volatile compounds to be released from the enclosure to the surroundings. Such means include permeable or semi-permeable barriers such as membranes or walls. The transdermal drug delivery devices, can be used to deliver a fragrance to a mammalian body when the body temperature exceeds a predetermined level. These devices can be designed to deliver the fragrance to both the environment and to a mammalian body simultaneously. This is achieved by converting part of the top layer of the transdermal device into a permeable or semi-permeable wall. In this case, upon activation of the shape memory material the fragrance is released into a reservoir prior to delivery. If desired, more than one release device can be incorporated in one patch that would either extend the temperature release range, upwards or downwards, or complement the fragrance of the others. Alternatively, the transdermal devices can be used to release the fragrance to the environment only but use the body's heat for activation. Transdermal fragrance delivery devices have distinct advantages over manually applied fragrances such as perfumes. They can provide on-demand perfume delivery once the body temperature exceeds a predetermined level. The need for such situations arises during physical activity such as exercise and emotional changes. In addition, they can be placed strategically in the body to counter any localized sources of odor. Further, they are capable of changing the strength and type of fragrance with time or with time and temperature.
Instead of being body temperature activated, transdermal fragrance delivery devices can also be configured to be activated with changes in ambient temperature. Simply, the shape memory material is thermally isolated from the body, by being worn an a piece of clothing, such that it responds the ambient temperature fluctuations. Since ambient temperature fluctuates more than body temperature these devices are capable of producing fragrances of various types and strengths at higher frequencies as a person moves from place to place.
All the devices with their features described herein can be used as delivery systems to introduce, enhance and in general alter the taste or flavor of foods and drinks exposed above or below a predetermined temperature. These devices can be activated during cooking to release spice flavors to the food once a predetermined temperature is reached without actually releasing the spice seeds and leaves themselves. Utilizing the same principle, instead of spices the shell may contain tea leaves or coffee. The device is immersed in water while it is being heated and when the predetermined temperature is reached, the shape memory material creates the path to allow the hot water to enter the shell and extract the tea and coffee flavor. Using the reversible shell, the path is closed once the temperature drops below a predetermined level thereby stopping the extraction process to avoid extracting unpleasant flavors. For repeated usage, the devices can be modified to allow the opening and closing of the shell to insert new substances.
In addition to being used as gustation delivery systems, these devices can also be used as taste alarms to alert one that the a food product has exceeded a predetermined safe temperature. Taste can be altered by directly releasing a substance that may be safe for consumption but renders the food uneatable due to its objectionable flavor, texture or other attributes intolerable by the sense of taste. In addition, the substance in these alarms can be combined with odor generating substances and or dyes to provide a double or triple alarm. Food and drink alarms that stimulate the sight and especially the smell and taste senses are useful for the general population and provide a great benefit to children whose instinct of safety is not well develop, to elderly and mentally challenged people that can not rely on visual means or slightly altered taste to determine food safety.
Any shape memory material activated device based on the concepts presented herein is capable of releasing substances that can be perceived by the sense of touch. Such devices, among other things, can be used as warning devices for food and pharmaceutical products. Once a predetermined temperature has been reached, the shape memory material creates a path though the shell wall to release a tactile substance that serves as an indication that the product has been exposed to an unsafe temperature. Release substances can be of any type that can be felt by touch and act as warning indicators. Preferred candidate types of substances include the ones that will drastically alter the touch feeling of the product container. Candidates include substances such as adhesives that will produce a sticky feeling, greases that will produce a slippery feeling. The released substance, in addition to being tactile, may contain ingredients to provide visual, olfaction and gustation indications.
In all substance release device concepts presented herein, auditory means can be incorporated to generate an acoustic signal upon release of the substance. This feature complements the stimulation of the senses used to detect the release of the substance such as vision, smell, taste and touch. This feature is incorporated by utilizing stored mechanical energy to release the substance. With this concept, the shape memory material releases an elastically deformed spring whose stored mechanical energy is used to create the path by applying an impact force to the shell. During the path creation process, upon impact with the shell wall, a "snap" type auditory signal is produced that can be utilized as verification process. Besides the concepts in which stored mechanical energy is utilized to create the path, other devices are capable of producing an acoustic signal upon release of the substance. They include devices with brittle shells and/or shape memory materials whose shape recovery curves have a steep slope such that shape recovery takes place within a narrow temperature range. Narrow temperature ranges effectively result in the rapid generation of shape recovery forces that can produce auditory signals especially when they fracture brittle shells. Another way to produce a auditory signal upon release of a substance is to seal the contents of the shell in vacuum or to pressurize them. During the path creation process a "popping" sound will be generated, as the pressure equilibrium is achieved, indicating the initiation of the release process.
Release of sense stimulating type substances once a predetermined temperature is attained can be extended to toys that encompasses many of the perceptible substances. A doll can be made to cry or perspire once a predetermined temperature is reached. This is achieved by incorporating shape memory material activated devices to release substances that simulate sweat, tears or other bodily substances. Each substance can have its own color, smell, taste and touch feeling to resemble reality. The path creation can take place though valves resembling the tear glands in case of crying simulation or the though permeable walls in case of sweat.
Any number of substance release devices presented herein can be grouped together to perform as a system and to produce a combined effect. Devices performing collectively as a system have the capacity to produce results different and of a larger scale that no single device by itself can produce. The systems behave differently than their individual components. The release temperatures of the individual devices can be selected such that the system as a whole will produce any release profile with respect to either time, or time and temperature. The system may be designed to begin releasing at temperature "A" and finish releasing at temperature "B". However, the release rate can be kept constant within the "A"-"B" range or it can be variable. In addition, the system may be designed to release substances at more than one temperature range such that a group of devices may be activated within a temperature range of "A"-"B" and another group within a range of "C"-"D". One temperature range may encompass the other, the two ranges may overlap or they may be distanced such that there is no release between them. There is no limit to the number of devices that can participate in a group or groups to form the system. This is truly a flexible and variable scale release system. It can consist of any number of release devices, of any type, with each shell containing the same or a different substance. The substances released by an individual device upon activation and path creation may change state, such as liquid to solid, with either direct release to the surroundings or release to a reservoir first. Further, the physical distances between devices can be variable and depend only on the purpose of the system.
Variable scale release systems can be used in either indoor or odor gatherings such as theaters, concerts, sport events etc. Shape memory material activated release devices containing fragrant producing substances can be placed in inconspicuous places in the gathering area. Activation of the shape memory material materials and creation of the paths can take place with a rise or fall of the temperature. Where there is climatic control such as air-conditioning or heating, release can be programmed to coincide with special timings by increasing or decreasing the temperature. In outdoor gatherings, release will depend on changes in the outside temperature. Different fragrances or combination of fragrances can be produced in different sections of the gathering area simply by selecting the shell substances that would produce the desired fragrances. Also, different devices can be activated at different temperatures to produce different fragrances and to enhance the effectiveness of the special events. The distribution density of the devices can be adjusted to produce the optimum fragrance strength for a given space and population. By combining the release devices with microprocessors and a battery for activation, the release time can be preprogrammed.
The same concept used for the fragrance mass delivery systems can also be used to deliver pharmaceutical products such as vaccines, immunizations and in general prophylactic type drugs to large numbers of people. The people may be city dwellers, villagers or military personnel in the battlefield. Large scale drug delivery systems can be used in emergency cases such as imminent chemical or biochemical terrorist attracts where the affected population must be immunized as soon as possible or an antidote or curative drug must be delivered as soon as possible after such an attract. Besides chemical and biochemical terrorist or war disasters, the same systems can be used to deliver prophylactic drugs to large populations in other types of calamities such as infectious epidemic diseases having the potential for rapid propagation. The devices can be used to deliver drugs to large populations spread over large areas where there is no time to distribute and administer the drugs by conventional means or no distribution system exists at all.
These systems can release drugs that are in the gas, liquid or solid state but volatize and become airborne upon release. The drugs are delivered to humans primarily by the inhalation process. The shell may contain means to volatize or atomize the substance upon release to further aid the delivery process. The mass delivery drug systems offer the advantages of being able to produce slow releases over long times such that the danger of overdosing are minimized. They can be distributed at one ambient temperature and be activated at a different temperature for optimum delivery and to allow maximum exposure to affected population. The devices can be distributed by; airplane, launch rockets or other remote launch systems. The devices can be stored and transported at any temperature and for any length of time as long as the shell contents remain unaffected. They can be armed prior to distribution time i.e. upon dropping from an airplane. If there is rapid depressurization of the devices at this time, such as when they are dropped from a airplane, it can be used advantageously to arm them pneumatically upon exposure to a lower pressure environment. They can be selected to have different activation temperatures and be able to release the substance instantaneously, continuously, with changing temperature or with repeated temperature cycling.
Variable scale release systems can be used as non-lethal weapon delivery systems. The purpose of these delivery systems is to minimize or eliminate lethality, act as deterrent systems and, in general, to replace land mines. They offer a substantial improvement over land mines whose results are probabilistic in nature and are associated with long lasting effects far beyond the end of war conflicts. Their intent is to be used for such operations as warfare, riot control, containment and to deny ground. These systems are similar to the drug mass delivery systems and they are distributed by similar means. The main difference is that the shell may contain any substance that upon release may discomfort or incapacitate the recipients.
Capabilities and advantages of these delivery devices both individually and as a system include: (1) They are not restricted to a particular substance. Shells can contain any substance without affecting the device design. (2) They can be stored indefinitely at any temperature without the risk of accidental activation. Since they are maintained unarmed, there are no stressed parts to undergo stress relaxation or creep and, if shape memory material such as Nitinol is used as the activator, the material remains corrosion free. (3) The shells can be made of material that would degrade with time to release their contents. This provides and added feature to assure that there are no long term effects with these type of non-lethal delivery systems. (4) Use of multi-release device can extend the release for multiple day-night temperature cycles.
There are multiple applications for systems of substance release devices. They include release of substances to remotely sterilize, fumigate, or decontaminate an area or structure. Another application is insect repellant systems in which case the path is created below a certain temperature (typically in the evening) to release the repellant. A nearly insect free area can be created by placing several devices with path reversal in strategic locations. Path reversal is required only if the devices are expected to function daily at a given temperature.
Drug Delivery
The following is an explanation of some of the applications of the embodiments described herein for use in drug delivery systems. On demand drug delivery system applications are subdivided into four general categories as follows:
(1) A first application is a transdermal system that is activated by rising body temperature. In this application the patch is applied when fever is anticipated due to upcoming flu symptoms, a disease or a drug side effect etc. However, there is no need for the drug until the fever rises to a critical temperature. With this device, although the patch may be worn, the drug is not released until the critical temperature is reached. The advantage of this application is the elimination of orally administered drugs, elimination of temperature measurement, and the fact that the drug is used only if and when it is needed. More, background, information on transdermal systems is presented below.
(2) A second application involves transdermal systems used to deliver drugs but not activated by rising body temperature. In this case, the device must be activated with an external energy source when the need for the drug arises. For automatic activation the energy source has to be stored electrical energy (batteries) while for manual activation heat applied directly to the device, such as by a hot compress, will suffice. One example of this case is insulin delivered drugs.
(3) A third application involves implantable drug delivery systems. Again, for an automatic operation, a self-contained energy source is required. For manual operation an external heat source is required. In this case heat is conducted through the body to raise the temperature of the shape memory material and activate the device.
(4) A fourth application involves mixing of predetermined quantities of two or more drugs. This is a useful application when there is a need to mix two or more drugs without having to measure them. This need may arise from field work where it is not convenient to measure or when the shelf life of a drug is extended when mixing takes place at the time of application.
Activation Energy Sources
Various energy sources can be used to heat the shape memory material in order to undergo shape recovery. The choice of energy source depends on the particular application. For most applications, ambient thermal energy is the ideal candidate. This includes mostly temperature warning and alarm systems as well a temperature indicators. For all ambient heating applications the heating source can be substituted with others ones such as electric heating. For drug delivery applications the choices depend on the particular application. Transdermal drug delivery systems can utilize the body temperature for activation or an external source such as batteries. In the second case, a temperature sensor, other than the shape memory material, is required to detect the rise in body temperature and activate the device. When a separate temperature sensor is used, the shape memory material acts as the actuator to create the path and release the drug. For remote heating applications such as in the case of implant drug delivery devices, the primary choices are; body heat, direct application of heat, electric heating, and magnetic induction heating. Body heat can be due to fever caused by ailments or it can be due to induced fever with the objective to activate the shape memory material based implant. Direct application of heat using sources such as hot pads requires the transfer of heat through the body to reach the shape memory material. Electric heating requires stored energy sources such as batteries. Electric heating is achieved by utilizing the shape memory material as a resistor and heating it by passing electric current through it. Magnetic heating of the shape memory material is achieved by conduction from a ferromagnetic material that is heated by magnetic heat induction. All energy sources used for substance release devices can also be used for thermally powered devices, whether they are releasing a substance or not. Thermally powered devices can also be powered hydraulically, pneumatically or mechanically without the incorporation of a shape memory material activator.
For greater flexibility, a more accurate temperature activation system, and better time response, the shape memory material, coupled with a separate temperature sensor and the appropriate controls to activate the device, can be used as the means to generate the force to fracture the shell. Types of temperature sensors that can be used are: thermocouples, resistive temperature devices (RTDs and thermistors), IC temperature sensors etc. Irrespective of the sensor type, an energy source such as a battery or other energy source will be required to provide heat to the shape memory material in order to undergo the phase transformation and create a path through the shell. With this system, means must be provided to connect the shape memory material to the power source and electrically insulate it to avoid short circuits and energy leaks. One advantage of this system is the ability to have the temperature sensor and the enclosure placed in to two different locations, as long as they are connected together. The controls (microprocessor, solenoid, switch etc.) can be placed either inside the enclosure or outside. Because, in this case, the shape memory material is no longer the temperature sensor, its As temperature has to be higher than the activation temperature of the system in order to avoid premature activation. With an electrically activated system, activation does not have to be due to local temperature. Different parameters can be used for activation. This enhances the system considerably when it is used as a drug delivery system. Sensors can be used to detect parameters such as biological activity and concentrations of different substances and to command the activation of substance release device once a predetermined parameter has been exceeded.
In many applications where the drug delivery device is implanted deep in the body such that direct heating is not applicable, magnetic induction heating offers an alternative in terms of minimizing the size of the device. In this concept, a ferromagnetic material is placed in physical contact with the shape memory material. While the ferromagnetic material is being heated by external magnetic induction, it transfers thermal energy to the shape memory material and heats it up. Once the ferromagnetic material reaches the Curie temperature, it becomes paramagnetic (nonmagnetic) and it stays at this temperature as long as the external magnetic field is applied. The concept of heating by magnetic induction is similar to the one used to treat tissue at elevated temperatures by hyperthermia or thermal therapy with the purpose of destroying cancerous tissue selectively or to necrose all cells. The Curie temperature imposes a self-limit as to how hot the material will get before it becomes paramagnetic and loses its magnetism. Magnetic induction heated materials are based on alloys such as; Co—Pd, Ni—Cu, Ni—Pd, Ni—Co, Ni—Si and magnetic stainless steels. The heating of the magnetic material and consequently of the shape memory material is controlled by the selection of magnetic material with the appropriate Curie temperature.
Physical contact between the magnetic material and the shape memory material can be achieved by methods such as physical interference, filling the space around the shape memory material with the magnetic material in a powder form, and coating the shape memory material with the magnetic material. Issues with biocompatibility of the magnetic material do not exist as long as it is placed inside the device and does not come in contact with the device's surroundings.
To add a time delay at temperature the shape memory material and/or the enclosure can be insulated. The level of insulation will depend on the time delay desired. This feature will delay the triggering of the device until thermal equilibrium between the shape memory material and ambient is reached. The delayed trigger will be more representative of the product temperature in the case where the device is used for temperature warning. Insulation can be in the form of a jacket similar to the insulation used for electrical wires. Space can be left between the jacket and the shape memory material to be filled with thermally insulating material to further delay the shape recovery process. In no case should the insulation impede the performance of the device.
While the invention has been described in detail with reference to the preferred embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention.
In the description of the preferred embodiments, for optimum performance, the shape memory material activator is deformed at a temperature in which the material is in the martensitic state. However, certain types of shape memory materials, such as the nickel-titanium based alloys, can be deformed at a higher temperature provided that the temperature at which martensite can be stress-induced is not exceeded. This is known as Md temperature. Generally, strain induced martensitic deformation results in permanent strains after shape recovery and it is not applicable to devices that require temperature cycling of the shape memory material.
While the invention has been described in detail with reference to the preferred embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention.
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|Title not available
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|Citing Patent
|Filing date
|Publication date
|Mar 23, 2009
|Mar 27, 2012
|General Electric Company
|Apparatus for turbine engine cooling air management
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|Sanofi-Aventis Deutschland Gmbh
|Actuator for dispensing fluid from a cartridge
|May 24, 2012
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|Alstom Technology Ltd
|Turbomachine clearance control configuration using a shape memory alloy or a bimetal
|Mar 23, 2009
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|General Electric Company
|Apparatus for turbine engine cooling air management
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|General Electric Company
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|Feb 3, 2012
|Jul 18, 2013
|Fraunhofer-Gesellschaft zur F�rderung der angewandten Forschung e.V.
|Actuator i.e. solid body actuator, for use in medical application to generate control path for dosage of medicament, has shape memory alloy elements arranged between and connected to segments and oppositely bent from each other
|U.S. Classification
|604/890.1, 60/527, 604/95.05
|International Classification
|Cooperative Classification
|European Classification
|Feb 10, 2013
|Fee payment
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|Sep 18, 2017
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