Growth on demand: Reviewing the mechanobiology of stretched skin

Abstract

Skin is a highly dynamic, autoregulated, living system that responds to mechanical stretch through a net gain in skin surface area. Tissue expansion uses the concept of controlled overstretch to grow extra skin for defect repair in situ. While the short-term mechanics of stretched skin have been studied intensely by testing explanted tissue samples ex vivo, we know very little about the long-term biomechanics and mechanobiology of living skin in vivo. redHere we explore the long-term effects of mechanical stretch on the characteristics of living skin using a mathematical model for skin growth. We review the molecular mechanisms by which skin responds to mechanical loading and model their effects collectively in a single scalar-valued internal variable, the surface area growth. redThis allows us to adopt a continuum model for growing skin based on the multiplicative decomposition of the deformation gradient into a reversible elastic and an irreversible growth part.redTo demonstrate the inherent modularity of this approach, we implement growth as a user-defined constitutive subroutine into the general purpose implicit finite element program Abaqus/Standard. To illustrate the features of the model, we simulate the controlled area growth of skin in response to tissue expansion with multiple filling points in time. Our results demonstrate that the field theories of continuum mechanics can reliably predict the manipulation of thin biological membranes through mechanical overstretch. Our model could serve as a valuable tool to rationalize clinical process parameters such as expander geometry, expander size, filling volume, filling pressure, and inflation timing to minimize tissue necrosis and maximize patient comfort in plastic and reconstructive surgery. While initially developed for growing skin, our model can easily be generalized to arbitrary biological structures to explore the physiology and pathology of stretch-induced growth of other living systems such as hearts, arteries, bladders, intestines, ureters, muscles, and nerves.

Mathematical and computational modelling of skin biophysics: a review

“…An attractive feature of computational models is the ability to quantify physical parameters required to obtain a specific outcome. For example, Prof. Kuhl's group at Stanford University has pioneered the development of mechanobiological adaptation models for skin to optimize the outcome of reconstructive surgery procedures in children [61][62][63][64][65][66][67] Streamline plots representing the maximum (coloured) and minimum (white) principal strain vectors in a finite deformation 2D plane-strain image-based finite-element model of the skin subjected to 20% in-plane compression (adapted from [20]). Grey arrows indicate the direction and location of the applied load.…”

“…internal variable) strain-like internal variables E k in the reference configuration, the free energy of a viscoelastic material can be defined as follows [87]: 67) where, in analogy with equation (4.52), the free energy (and stress) can be split into equilibrium and non-equilibrium contributions associated, respectively, with elastic and viscous deformation mechanisms:…”

A mechanistic insight into the mechanical role of the stratum corneum during stretching and compression of the skin

“…A wide array of experimental and clinical measurement techniques are used to characterise particular aspects of skin biology and biophysics (Alexiades-Armenakas, 2007;Batisse et al, 2002;Bellemere et al, 2009;Delalleau et al, 2006;Diridollou et al, 2000;Gunner et al, 1979;Hendriks et al, 2006;Jor et al, 2013;Limbert and Simms, 2013;Tonge et al, 2013a;Tonge et al, 2013b;Wan Abas, 1994). Nevertheless, complementary approaches based on mathematical and computational modelling techniques offer promising avenues to further our understanding of the skin (Areias et al, 2003;Bischoff et al, 2000;Boissieux et al, 2000;Buganza Tepole and Kuhl, 2014;Cavicchi et al, 2009;Duan et al, 2000;Evans, 2009;Flynn and McCormack, 2008a, b;Flynn andMcCormack, 2009, 2010;Hendriks et al, 2006;Hendriks et al, 2003;Kuwazuru et al, 2008;Larrabee and Galt, 1986a, b;Larrabee and Sutton, 1986;Lévêque and Audoly, 2013;Tepole et al, 2014a;Tepole et al, 2014b;Tepole et al, 2011;Zöllner et al, 2013).…”

Virtual testing of advanced composites, cellular materials and biomaterials: A review

“…Skin is a pseudo-solid composite microstructural material comprising two layers: the dermis and the epidermis [147] -both of which are inhomogeneous in terms of structure and composition [148]. According to Zöllner and co-workers, skin is a highly dynamic auto-regulated, living system that responds to stretch through a net gain in skin surface area [147].…”

“…According to Zöllner and co-workers, skin is a highly dynamic auto-regulated, living system that responds to stretch through a net gain in skin surface area [147]. The important mechanical properties of skin include: extensibility (stretching capacity), resistance to friction and response to lateral compressive loading [148].…”