From surface microrelief to big wrinkles in skin: A mechanical in-silico model

Abstract

A major concern associated with skin, the largest organ of our body, is how to prevent it from wrinkling and aging. Understanding the mechanics of skin wrinkling can provide useful insight into skin aging prevention. However, despite decades of endeavors the underlying mechanism of skin wrinkling and aging remains poorly understood. This paper explores the effect of geometrical and mechanical properties of skin on its wrinkling via an integrated theoretical and computational analysis. The skin is modeled with a soft structure having different layers with various thicknesses and material properties. Innovatively, the pattern of skin microrelief is generated and mapped on the model to investigate its effect on the formation of primary lines, secondary lines, and big wrinkles of skin. Analytical interpretation provides preliminary insight into the critical compressive strain for the model skin to start wrinkling, while advanced computational models with surface microrelief offer clues for the skin’s post-wrinkling complex morphology. In particular, tissue geometry, material properties, and microrelief pattern are explored as the determinant parameters to control the location, size, and patterns of skin wrinkles. Our findings allude that the characteristics of compression-induced wrinkles are primarily determined by the geometrical and material property of skin layers rather than the genuine skin microrelief. However, microrelief plays a pivotal role in regulating and determining the locations of primary and secondary wrinkle lines. The edges of the microrelief units are favorable paths for evolving primary and secondary lines. Post-wrinkling analysis reveals that in addition to the periodic sinusoidal pattern, several secondary complex patterns such as non-symmetric periodic, period-doubling and self-contacting folds are observed in the compressed model of skin. Results of the study also show that wrinkle patterns highly depend on the thickness and material property of Stratum Corneum (SC), the outermost layer of skin.