Beyond its physiological importance as the largest and one of the more complex organs of the human body, the skin plays a crucial role in how we interact with our external environment as well as with each other. At the primal level, and through mostly subconscious cues, the skin tells a story about our age, health, past traumas, emotions, ethnicity, and our social and physical environments.

The skin is a highly dynamic and adaptive hierarchical biological structure which hosts complex physical and biological processes. Although we might not consciously appreciate these highly desirable characteristics we all experience them daily and over the course of a life time.

Think about it—how valuable would be a coat that can:

• Protect you against mechanical, thermal, biological, radiological and chemical insults.
• Is waterproof and crease-proof.
• Warns you about external dangers through a complex neural sensory network.
• Regulates your temperature.
• Synthesises essential biochemical compounds like vitamin D.
• Self-repairs and can last over 80 years with reasonable care?

The skin can be viewed as our interface to the world, and, as such, is involved in a wide range of contact interactions that operate at different spatial scales and typically feature coupled physics phenomena¹. These surface interactions are an essential part of the physical world and also of how humans perceive their environment for cognitive awareness, social interaction and self-preservation.

Besides medicine, surgery and medical devices², understanding the physiology and biophysics of the skin in health, disease, ageing and trauma is fundamental for many industrial applications ranging from consumer goods (e.g. shaving, personal care, incontinence products) and cosmetics (e.g. tribology of skin lotion and their subsequent effects on skin mechanics and wrinkles) through the design of advanced fabrics, sport equipment and electronic tactile surfaces to electronic “wearables” as well as the development of automotive airbags that minimise friction-induced burn injuries during their deployment.

There is an intimate relationship between structure and function of the skin³ and, as a corollary, a strong non-linear interplay between its material and structural properties^{4, 5} which constantly evolve with age and alterations of environmental conditions. The formidable complexity of such a multiphasic, multiscale and multiphysics structure can be systematically investigated using the advanced modelling capabilities offered by the SIMULIA brand products (e.g. Abaqus) in combination with dedicated experimental and imaging techniques (Figure 1 – Figure 2).

Simulating the mechanics and physics of skin in general is one of the most demanding applications of computational physics: material, geometrical and contact non-linearities, strongly anisotropic properties, near incompressibility, damage, surface instabilities, coupled physics and multiple length and time scales. This calls for advanced element and contact formulations as well as robust non-linear solvers and stabilisation algorithms, all available in Abaqus.

For example, anatomically-based micromechanical models developed in Abaqus enabled us to gain a quantitative and mechanistic understanding of how changes in relative humidity affect the interplay between skin microstructure and variations of the mechanical properties of the stratum corneum which is the upper-most layer of the skin⁴. It was also demonstrated that the skin surface micro-topography made of ridges and valleys provides an effcient mechanism to modulate macroscopic strains.

Over the last decade, the significant increase in the number of scientific papers dedicated to experimental and computational modelling aspects of the skin is a testimony of the emergence of a new field of research, computational skin biophysics. The celebrated features of computer simulations, repeatability, the power and flexibility of “what if” scenarios in conducting hypothesis-driven research, low cost, speed and reduction of the need for animal experiments offer exciting prospects for the future of skin research.

Ultimately, this could lead to new treatments, diagnosis tools, to better products that would be more comfortable to use or, perhaps more exhilaratingly, to make us look younger. In the mean time, let’s develop advanced realistic simulations!

Want to Learn More?

Visit the University of Southampton’s Computational Mechanobiology Group.

References

1. A. McBride, S. Bargmann, D. Pond and G. Limbert, Journal of Thermal Biology, 2016, DOI: http://dx.doi.org/10.1016/j.jtherbio.2016.06.017.

2. A. M. Zöllner, M. A. Holland, K. S. Honda, A. K. Gosain and E. Kuhl, J Mech Behav Biomed Mater, 2013, 28, 495-509.

3. Y. C. Fung, Biomechanics: mechanical properties of living tissues, Springer-Verlag, New York, 1981.

4. M. F. Leyva-Mendivil, A. Page, N. W. Bressloff and G. Limbert, J Mech Behav Biomed Mater, 2015, 49, 197-219.

5. G. Limbert, in Computational Biophysics of the Skin, ed. B. Querleux, Pan Stanford Publishing Pte. Ltd, Singapore, 2014, ch. 4, pp. 95-131.

This article was originally published in the September 2016 issue of SIMULIA Community News magazine.