The Development of Physical Skin Model for Biomechanical Applications

Abstract

解 説 1．Introduction Consumer, consciously or not, tend to touch and feel the surface of the goods and then make a judgment about whether they like this feel or not. This subjective judgment has been recognized as a key factor to win or lose customers for industries where personal taste on touch-feel perception will be a main purchase criterion 1). A thorough understanding of the mechanical interaction between product and skin, like the friction and deformation behavior of skin, is essential in the development of human-product interfaces, and this is important in establishing safety margins. Tests on animals, humans, cadavers, and explants have been traditionally used to study materials-skin interactions. But unfortunately, measurement of the mechanical and frictional behavior of human skin in vivo has several disadvantages: experiments on human and animal skin raise ethical issues, and these samples are hard to obtain, expensive and give rise to highly variable results. The measurements often suffer from poor reproducibility due to person-to-person variability and involuntary human motions during testing. And the possibility of skin damage limits the severity of the conditions that can be applied. For the reasons above, many mechanical and tribological studies on products involving human skin contact attempt to use physical skin models. Physical skin models have the advantage of obtaining long-term stability, lower costs, easy storage and manipulation, and their physical properties are easier to control, thus are desirable in providing objective and reproducible results within a reasonable time-frame 2). Moreover, physical skin models can be used for the design and experimental testing of functional surface features on medical, healthcare and consumer products that have a physical interaction with the skin, such as certain healthcare devices and tools, cosmetic skin care products and devices, shavers, buttons and touch-screens, etc. Physical human skin models, which were usually developed for the needs of testing, calibration, quality check of devices, or teachinghave been proposed and described in numerous studies concerning testing and development of materials and methods. This review article gives an overview of the development of physical skin model for biomechanical applications, in which the progresses made in the synthesis and the following tests of skin-materials interaction were summarised and discussed. Abstract : The skin, which is known as a complex multi-layered tissue, is vital for protecting the body from potentially harmful external environment and exhibits complex mechanical behaviour. As reported, skin is a non-linear, anisotropic and viscoelastic materials, with its mechanical properties varied in each skin layer and influenced mainly by skin hydration status, environment humidity and test conditions. Therefore, it is difficult to study the mechanical and tribological interactions between human skin and materials for the development of human contacting products. And in order to better understand the mechanical interactions between human skin and various products for optimizing surfaces and materials in contact with human skin, it is significant to use instrumental mechanical and tribological measurements, which could provide objective and more reproducible results without inter-and intra-subject variations. Past decades we have witnessed many endeavors exerted for developing physical skin model to objectively study the interactions between human skin and materials, instead of using in vivo or ex vivo human skin or animal skin. This review article gives an overview of the development of physical skin model for biomechanical applications, in which the progresses made in the synthesis and the following tests of skin-materials interaction were summarised and discussed.