Advances in the Materials Science of Skin: A Composite Structure with Multiple Functions
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Materials Science of Skin: A Composite Structure with Multiple Functions
K. Subramanyan, M. Misra, S. Mukherjee, and K.P. Ananthapadmanabhan Abstract This article gives the foundation for understanding the structure and function of human skin and its layers. Skin is our first line of defense against the penetration of external chemicals and bacteria into the body and of water loss from the body. Skin’s visual and tactile properties are very much linked to appearance and beauty. Skin treatments as simple as washing with soap affect the mechanics of skin properties, making it dry and brittle versus smooth and elastic. Likewise, natural aging, hormonal changes, and sun exposure affect the properties of skin. Mild cleansing, moisturizer treatments, and regular use of sunscreens can, however, help skin maintain and even improve its quality, appearance, and functional properties.
Introduction Skin is the largest human organ, complex and essential for survival. The outermost surface of the skin, called the stratum corneum, forms a unique structure that serves multiple functions. From a materials science perspective, the stratum corneum is a dynamic and smart barrier that prevents exogenous materials from penetrating into the body and vital components from leaving the body.1,2 The stratum corneum is also our first defense against pathogenic organisms entering the body. The stratum corneum regulates the loss of water from the body and helps to maintain steady-state equilibrium with the environment.1,2 The tactile and optical properties of the stratum corneum are important for skin to have sufficient elasticity to prevent cracking during stretching or exposure to low temperatures, while
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maintaining a soft and smooth appearance. The stratum corneum also functions as a biologically active sensor that has been designed to renew its surface layers in an ordered manner, exposing new surface layers that make skin look young and beautiful. Healthy stratum corneum has the ability to renew itself completely approximately every 14 days.3 While stratum corneum can maintain its properties within certain limits, it can be weakened or damaged when exposed to stresses beyond these limits, and this can negatively affect its barrier properties, elasticity, water-holding capacity, and optical properties. When such damage occurs, the stratum corneum resorts to biological signaling mechanisms to activate the body’s repair processes. The ability of the body to respond to such signals
is a complex function of age, genetics, nutrition, and environment. In this article, the material properties of the stratum corneum, the mechanisms that regulate those properties during exposure to internal and external stresses, and the methods by which cosmetic products may aid in restoring those properties are discussed. The structure and properties of skin, specifically, the stratum corneum, are reviewed from a materials science perspective, starting from a molecular-to-mesoscale assembly of hierarchical structures. The ability of skin to respond to day
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