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Mathematical Modeling of Drug Release in a Phase-Transient Temperature-Responsive Drug Delivery System in Spherical Coordinates

Abstract A sphere-shaped drug delivery system responsive to temperature, as a unique external stimulus, was introduced and its performance mathematically studied at the pseudo-steady state. The system is composed of three individual sections, including the drug core, phase-transient intermediate shell, and protective polymeric shell. An ON-OFF release of drug could be achieved by increasing or decreasing the environmental temperature around the melting point of the intermediate shell and the smartness of system is due to the solid-liquid phase transition of this shell. The ON-OFF response of the system was mathematically modeled by solving the governing heat and mass transfer equations at the pseudo-steady state. The results showed the lag time of the system in the ON state, the cumulative released drug in the ON state and the fractional undesired release of drug in the OFF state are strongly under the influences of different kinds of factors, including the geometrical characteristics of the system (e.g., the radius of the drug core and the thicknesses of the intermediate and polymeric shells), the physical properties of the system (e.g., the thermal conductivities and diffusion coefficients of the intermediate and polymeric shells), and the environmental and operation conditions.