Human skin, nature epidermis

Lanolin has stood the test of time as an emulsifier and skin emollient. Its complex nature has been a rich resource of derivatives formed from fractionation and chemical reactions. Although the composition of lanolin is different from the lipids found on the surface of human skin, lanolin has been demonstrated to be equivalent in its ability to restore barrier function. In addition to the beneficial effects attributable to its physical properties, lanolin may also have a pharmacological effect on the epidermis. 

Human skin has a multifunctional role, primary among which is its role as a barrier against both the egress of endogenous substances such as water and the ingress of xenobiotic material (chemicals and drugs). This barrier function of the skin is reflected by its multilayered structure (Fig. 5.1). The top or uppermost layer of the skin known as the stratum comeum (SC) represents the end product of the differentiation process initially started in the basal layer of the epidermis with the formation of keratinocytes by mitotic division. The SC, therefore, is composed of dead cells (comeocytes) interdispersed within a lipid rich matrix. It is the brick and mortar architecture and lipophilic nature of the SC, which primarily accounts for the barrier properties of the skin [1,2]. The SC is also known to exhibit selective permeability and allows only relatively lipophilic compounds to diffuse into the lower layers. As a result of the dead nature of the SC, solute transport across this layer is primarily by passive diffusion [3] in accordance with Pick s Law [4] and no active transport processes have been identified. 

Healthy, normal human skin is kept moist by natural body oils contained in sebum, a secretion of the skin s sebaceous glands. The oily sebum helps the epidermis, or outer layer of the skin, retain the 10-30% of water it normally contains. However, some people suffer from skin that is nam-rally dry, or dry because of aging or contact with materials like paint thinner that dissolve and remove the sebum. Such individuals may find some relief by using OTC products called moisturizers. 

Yannas s invention mimics the structure and function of the upper two layers of natural skin. It consists of an upper layer about 0.023 mm thick made of an elastic silicone material that, like the human epidermis, acts as a harrier to the loss of moisture from the body. Silicones are siloxane polymers to which are bonded various organic radicals (groups of atoms that contain carbon). The chemical structures of siloxane and a typical silicone polymer are shown on page 50. 

I have already shown several syntheses of sphingolipids as microbial metabolites or marine natural products. Sphingolipids are building blocks of the plasma membrane of eukaryotic cells. Their function is to anchor lipid-bound carbohydrates to cell surfaces, and to construct the epidermal water permeability barrier. The chemistry of sphingolipids is therefore closely related to dermatology or the science of skin. This section first treats sphingolipid in human epidermis. 

There are two basic roles for carbohydrates in the field of skin replacement. These relate to the bilaminar nature of the skin with the dermal matrix and the cellular epidermis. The matrix is a biomechanical construct and can be made. As already described, there are collagenous and noncollagenous components in the human dermis. There is and has been a considerable amount of research to explore the roles of collagen and GAG polymers in matrix production. Indeed, this is a feature of research and reviews spanning the last two decades. The most successful commercial product is Integra, which was approved for clinical use in 1996 both in the United States and Europe. 

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