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Thermo-optical skin conditioning: a new method for thermally modifying skin conditions

Background and Objective: Pulsed CO2 laser resurfacing improves photo-damage and acne scarring by removing abnormal tissue with subsequent regeneration and remodeling of collagen through heat induced collagen contraction. On the other extreme, Normal Mode Er:YAG lasers operate yielding ablative tissue removal with a thermal damage zone that can be limited to fewer then ten microns. This study introduces and evaluates the effectiveness of a new method of Thermo-optical Skin Conditioning (TSC). This method allows the user to induce tissue effects that span the entire range from the purely thermal tissue modification (CO2-like) to the highly mechanical effects induced by dermabrasion and Er:YAG lasers. TSC utilizes an optical energy in conjunction with a highly absorbing substance (HAS) deposited on a thin, thermally conductive intermediate material module (IMM) allowing the user to achieve optical to thermal energy conversion. The thermal energy is allowed specific interaction time determined by the scanning spatial pattern and scanning rate. The total amount of power density deposited in the tissue is a function of laser power, scan rate, spot size, and the synchronized action of the energy removal system (ERS) incorporated and synchronously activated at the end of the interaction period. Materials and Methods: A substance capable of efficiently absorbing laser light was applied to one side of an intermediate medium material to be placed in contact with the target skin. The intermediate medium material was then formed into a tape that was capable of advancing along a flat surface. An 810nm diode laser was used as an energy source. Galvanometer scanners and a lens were used to cover an area of approximately 50 mm2. Different power settings and scan rates determined the maximum power density and fluence at the target area. Following the experiments, the skin was then fixed in 10% Formalin and used for histological section preparations and optical light microscopy evaluation. The samples were then evaluated for histological changes and to measure ablation and thermal damage depth. In addition, measurements of thermal tissue response during and after the interaction were performed using both thermocouples and an infrared thermal camera. Results: Epidermis ablation ranged from as little as 10 ?m per pass, to as much as 50 ?m per pass. The depth of thermal damage decreased with scan frequency and with decreased laser power. Temperature increase ranged from 150C to as much as 900C. ERS temperature control allowed restoration of ambient temperature within less then 250 ms. TSC is shown to be a very effective method for inducing a range of tissue modification effects ranging from highly thermal to mechanical /non-thermal effects.