Mechanical approach to aging and wrinkling of human facial skin based on the multistage buckling theory

Abstract

A wrinkle formation mechanism with cutaneous aging is addressed through a mechanical calculation of linear buckling. Skin is divided into five mechanically distinct layers in this study. In general, the outer layer is stiffer than the inner layer, so buckling occurs in the outer layer against the uniform compression caused by muscle contraction. This buckling damages the skin and affects the formation of permanent wrinkles. We propose a multistage buckling theory for evaluation of the wrinkle property, namely, the specific wrinkle size and critical strain in three stages. The specific wrinkle size is derived as the wavelength of the minimum-buckling mode for infinite-length skin. A sensitivity analysis is carried out to investigate the effect of age-related changes of the mechanical parameters on the wrinkle property. We employ some aging hypotheses and prepare two sets of mechanical parameters, one for young and one for aged skin. The numerical results show that the buckling mode switch from Stage I to Stage II is the main reason why pronounced wrinkles suddenly appear in aged skin.

Influence of Array Interspacing on the Force Required for Successful Microneedle Skin Penetration: Theoretical and Practical Approaches

“…Since the aim here is to develop a quantitative basis to relate MN interspacing and insertion mechanism of MNs, each layer will be assumed to be homogeneous, isotropic and elastic (Kuwazuru et al, 2008). Prior to insertion, the skin is modelled as an infinitely long beam on an elastic foundation with two concentrated loads.…”

“…As the main barrier is the stratum corneum, with the underlying layers having a much lower stress limit (Kuwazuru et al, 2008;Cua et al 1990), we take E and v to be the young modulus and Poisson ratio of the stratum corneum, respectively. The indentation depth is assumed to be 100% of the thickness of the stratum corneum, this is considering the fact that some compression also occur during cutting (Okamura et al, 2004).…”

“…The skin between the needles must therefore buckle to allow for this insertion to occur; hence cutting and buckling occur simultaneously. The resistance offered by the lower layer of the skin as the SC buckles is represented by the foundation modulus (Kuwazuru et al, 2008).…”

“…The concept of buckling in the skin has previously been considered by Kuwazuru et al (2008). The group applied a multistage buckling model to analyse the mechanism of wrinkle formation as a result of buckling of different layers of the skin, relative to age related changes in skin structure.…”

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).…”