Analysis of viscoelasticity of human skin for prevention of pressure ulcers

Change in viscoelasticity of human skin with aging is evaluated by measurement of deformation under suction and of resonance frequency change under probe indentation. The elastic modulus of human skin measured by suction increases with aging, but that measured by resonance frequency change decreases; the difference is considered to be caused by the difference in measured depth region of the human skin. In order to clarify the depth region which can be measured by each technique, strain distribution is calculated by the finite element method (FEM). The results show that the epidermis is mainly deformed by the skin suction method, whereas the dermis and subcutaneous tissue are mainly deformed by measurement of resonance frequency change. For confirmation of FEM results, skin models made of silicone rubber are prepared and measured by the two methods. Viscoelasticity in the depth region from the surface to several hundred micrometers of the material is obtained by the skin suction method, while that in the region from several millimeters to several centimeters is obtained by the resonance frequency change. Based on these results, it is observed that the elastic modulus of epidermis tends to increase with aging while that of dermis and subcutaneous tissue tends to decrease, thus causing pressure ulcers.