Mechanical modeling of a wrinkled fingertip immersed in water.

Fingertips often wrinkle after extended exposure to water. The underlying mechanics issues, in particular the critical parameters governing the wrinkled morphology, are studied by using both finite element simulation and analytical modeling. The wrinkling behaviors, characterized by the wrinkle-to-wrinkle distance (wavelength), wrinkle depth (amplitude) and critical wrinkling stress/strain, are investigated as the geometry and material parameters of the fingertip are varied. A simple reduced model is employed to understand the effect of finger curvature and skin thickness, whereas a more refined full anatomical model provides the basis for analyzing the effect of a multilayered skin structure. The simulation results demonstrate that the stiffness of the stratum corneum and the dermal layer in the skin has a large effect on the wrinkling behavior, which agrees well with the analytical predictions. From the uncovered mechanical principles, potential ways for effectively slowing down and suppressing skin wrinkles are proposed; among them, increasing the modulus of the dermal layer in the skin appears to be the most effective.