(570e) Wireless Induction Heating of Stratum Corneum for Transdermal Drug Delivery

Transdermal drug delivery using conventional patch technology provides good patient compliance and controlled drug release, but the strong barrier properties of skin prevent delivering effective doses of most drugs. We present a wireless system for generating micron-scale pores in the skin by thermal microablation to dramatically increase skin permeability, while maintaining the patient-friendliness of conventional patches. Micron-scale pores can be created using short, intense, and highly localized heating to painlessly micro-ablate the skin's outer surface (stratum corneum), which provides the primary barrier to drug transport. Our approach overcomes this limitation of previous transdermal drug delivery methods by using wireless inductive heating of micromachined structures integrated within transdermal patches to affect micro-ablation. Figure 1 shows a schematic diagram of the inductive heating system, including an AC power source, excitation (induction) coil, and micro-heating elements. The inductive heating is based on eddy current and hysteresis loss induced in the heating elements by the excitation coil magnetic field. A (20x20) array of hollow posts has been fabricated as micro-heating element prototype. The optical microscopic picture of hollow metallic posts is shown in Figure 2. Nickel was chosen because it has a high relative magnetic permeability, which is favorable for inductive heating. The micro-heating elements were also applied to an in-vitro skin ablation experiment. Figure 3 shows scanning electron microscopic view of human cadaver skin after the micro-heating elements were activated and removed. To understand the mechanism of thermal ablation, skin was investigated by mechanical analysis, skin permeability measurement, thermal analysis, optical microscope and confocal microscope. The skin Figure 4 shows the change in skin permeability and failure force of stratum corneum in terms of ablation temperature. Skin permeability to calcein increases and failure force decreases by increasing ablation temperature and skin permeability is irreversibly proportional to the mechanical strength of stratum corneum. Also the stratum corneum was visualized to investigate the disruption of stratum corneum by optical and confocal microscopy. The disruption of stratum corneum was becoming more as the ablation temperature increases. We can conclude that induction heating can be utilized to generate heat to induce localized ablation in human skin.