Human skin in vivo: Overview of mechanical experiments and imaging techniques

Knowledge about the mechanical behaviour of the human skin can help to quantify the effectiveness of cosmetic products and to evaluate skin diseases and pressure sores. Besides that, information about mechanical properties can be used in numerical skin models. Philips is particularly interested in the mechanical behaviour of the skin for shaving research, to predict skin doming. This review will give a short overview on the mechanical testing performed on the skin. Some imaging techniques are mentioned and the mechanical experiments that have been done already will be discussed. Finally a proposal for a research project is presented. The goal of the current project is to determine the mechanical properties of the human epidermis in vivo. From the literature it appears that the epidermis alone is seldom studied. Conclusions: The human skin is a living and complex tissue composed of several heterogeneous and anisotropic layers. A large variety of mechanical experiments have been performed on the skin. Unfortunately, the data obtained are often used descriptively and are mainly based on the observation of indices. There is also a lack of standardization among researchers, mainly due to the large number of factors that play an important role, like heat, relative humidity, age, etc. Little effort has been made to describe the observed material behaviour of the skin with appropriate constitutive models. In most in vivo performed experiments, the measured behaviour of the skin is ascribed to the dermis or a combination of dermis and epidermis [10]. However, as intimate connections exist between the various 2003/00132 iv ã Koninklijke Philips Electronics N.V. 2003 layers, it is also hard to isolate for instance the contribution of the dermis to the mechanical behaviour from that of the epidermis and the subcutaneous tissues. In all experiments, except Diridollou et al. [9,10], Hendriks et al. [19] and van den Berg [20], only deformation of the skin surface was measured. The goal of the current project is to determine the mechanical properties of the human epidermis in vivo. From the literature it appears that the epidermis alone is seldom studied. To achieve this, we want to develop a numerical-experimental method, which is capable to measure and characterize the mechanical behaviour of the epidermis in vivo.