Skin biothermomechanics for medical treatments.

Electromagnetic heating, such as microwave, radiofrequency, and laser etc., is widely used in medical treatments. Recent advances in these technologies resulted in remarkable developments of thermal treatments for a multitude of diseases and injuries involving skin tissue. The comprehension of heat transfer and related thermomechanics in skin tissue during these treatments is thus of great importance, and can contribute to the further developments of these medical applications. Biothermomechanics of skin is highly interdisciplinary, involving bioheat transfer, burn damage, biomechanics, and physiology. The aim of this study is to develop a computational approach to examine the heat transfer process, heat-induced mechanical response, as well as the associated pain level, so that the differences among the clinically applied heating modalities can be quantified. In this paper, numerical simulation with the finite difference method (FDM) was used to analyze the temperature, burn damage, and thermal stress distributions in the skin tissue subjected to various thermal treatments. The results showed that the thermomechanical behavior of skin tissue is very complex: blood perfusion has little effect on thermal damage, but a large influence on skin temperature distribution, which, in turn, influences significantly the resulting thermal stress field; for laser heating, the peak temperature is higher for lasers with shorter wavelengths, but the peak is closer to the skin surface; the thermal stress due to laser and microwave heating is mainly limited to the top epidermis layer due to the exponential decrease of heat generation along skin depth; the thin (and commonly overlooked) stratum corneum layer dominates the thermomechanical response of skin tissue.