Chapter 16 - Skin Mechanics

Abstract

The skin is the largest organ of the human body. With its layered structure, it is mechanically a very complicated tissue. From the outer surface down, the main layers are the stratum corneum (10–15μm), the viable epidermis (100–150μm), dermis (subdivided into the papillary and reticular dermis, ≈2mm), and hypodermis. Although the stratum corneum is part of the epidermis, it is often considered to be a separate layer because of its specific barrier properties. It consists of nonviable cells and is very firm, but pliable and wrinkled. The epidermis is mainly composed of cells migrating to the skin surface. When the cells are closer to the stratum corneum, they become more keratinized. The viable epidermis has an undulated geometry. This undulation becomes less with age. The dermis is largely composed of a very dense network of collagen and elastin fibers, dominating the mechanical behavior of the total skin. The deepest skin layer, the hypodermis or subcutaneous adipose tissue, is composed of loose fatty connective tissue. The dermis contains microstructures such as blood vessels, lymph vessels, nerve endings, sweat glands, hair follicles, and different cell types. The influence of the different layers on the mechanical properties has often been ignored, because authors are mainly interested in the bulk mechanical behavior, dominated by the main components of the skin layer.