How stiff is skin?

Abstract

The measurement of the mechanical properties of skin (such as stiffness, extensibility and strength) is a key step in characterisation of both dermal ageing and disease mechanisms and in the assessment of tissue‐engineered skin replacements. However, the biomechanical terminology and plethora of mathematical analysis approaches can be daunting to those outside the field. As a consequence, mechanical studies are often inaccessible to a significant proportion of the intended audience. Furthermore, devices for the measurement of skin function in vivo generate relative values rather than formal mechanical measures, therefore limiting the ability to compare studies. In this viewpoint essay, we discuss key biomechanical concepts and the influence of technical and biological factors (including the nature of the testing apparatus, length scale, donor age and anatomical site) on measured mechanical properties such as stiffness. Having discussed the current state‐of‐the‐art in macro‐mechanical and micromechanical measuring techniques and in mathematical and computational modelling methods, we then make suggestions as to how these approaches, in combination with 3D X‐ray imaging and mechanics methods, may be adopted into a single strategy to characterise the mechanical behaviour of skin.

Biotribology of the ageing skin—Why we should care

“…When considered at a macroscopic level, the mechanical properties of the skin are anisotropic and inhomogeneous. These properties arise from the complex hierarchical structure of skin and its materially nonlinear constituents [17,37] as well as from the existence of residual tension lines in the skin (i.e. the so-called "Langer lines"), all over the body as first recognised by the ustrian anatomist Karl Langer in his seminal study [38].…”

Single‐Mode, 700%‐Stretchable, Elastic Optical Fibers Made of Thermoplastic Elastomers

“…This stiffness of TPE fibers is very close to the stiffness of soft tissues such as the human skin (0.1–0.9 MPa). [ 36,37 ] Therefore, the mechanical property would be well suited for use in wearable or implantable photonic devices. For comparison, Young's modulus of conventional silica fibers is 73 GPa, even higher than those of hard bones (≈20 GPa).…”

Culturing Keratinocytes on Biomimetic Substrates Facilitates Improved Epidermal Assembly In Vitro

“…Despite the evident importance of external mechanics on cell behaviour [ 28 ], conventional in vitro cell culture relies heavily on extremely stiff substrates, such as plastic and glass, which do not reflect the mechanics of the physiological microenvironment. Young’s modulus, or elastic modulus, describes the relationship between stress (force divided by area) and strain (change in shape as a result of stress) of a material, with stiffer materials being associated with a high elastic modulus [ 29 ]. Whilst the literature does not provide an exact value for the stiffness of the epidermis, human skin exhibits a Young’s Modulus range of low to mid kilopascals (kPa) (0.1–10 kPa) [ 30 ].…”