Constitutive modeling of stress softening and permanent set in a porcine skin tissue: Impact of the storage preservation

Abstract

Prior to testing, soft tissues are usually maintained in different media and additives (solution, air, cryopreservant…) under various environment conditions (temperature, storage duration….). In many cases, results from mechanical tests performed on these stored tissues are supposed to be as closed as possible to the fresh ones. In the present work, cyclic tensile tests were performed with increasing values of strain on porcine skin tissues (excised following the Langer's lines) to enhance tissues mechanical nonlinearity such as softening behavior and permanent set. Optical methods were used to follow the in-plane strains evolution. These latest values were used as data to simulate the structural behavior of these heterogeneous materials. The numerical simulation is based on the constitutive pseudo-elastic model accounting for the softening behavior as well as the permanent set. As a result, reliable material parameters were extracted from the experiments/model comparison for each storage solution. The result of this study reveals that preservation conditions must be carefully chosen: at low strain the tissues store in fridge in a saline solution during a short time, or in freezer (-80°C) in water with cryopreservant and the fresh one lead to a similar mechanical response. For larger strain, the freezing (-80°C) in water with cryopreservant is the only procedure for which the tissue recovers its initial behavior.

Mechanical response of human female breast skin under uniaxial stretching

“…The data obtained from the breast skin specimens are consistent with the behavior of skin that has been reported earlier in the literature (Abas and Barbenel, 1982; Dunn et al 1985, Clark et al, 1996; Edsberg et al 1999; Bischoff et al, 2000; Annaidh et al, 2012; Caro-Betelle et al 2016 and others). This data has significant patient-specific variability and contains data on the influence of specimen storage on the mechanical response.…”

“…The microstructure and biomechanical properties of skin (and other soft biological tissues) have been studied by numerous investigators, and there exists a common understanding of both (see for example, Gibson et al, 1965; Fung, 1967; Harkness, 1971; Wilkes et al, 1973; Sanders and Goldstein, 1995; Annaidh, 2012: Menon 2012; Tonge et al 2013a,b; Caro-Bretelle et al, 2015, 2016; Bancelin et al, 2015). A succinct summary of skin composition is provided by Sanders and Goldstein (1995): skin is composed of collagen (27 to 39% by volume, 75 to 80% of fat-free dry weight), elastin (0.2 to 0.6% by volume, 4% of fat-free dry weight), glycosaminoglycans (0.03 to 0.35% by volume), and water (60 to 72% by volume).…”

“…The significant difference in the stress level at a given stretch between the first loading response and the preconditioned response (sometimes called strain-softening) is attributed to viscoelasticity (Lanir and Fung, 1974) or to damage that is analogous to Mullins’s effect in rubber (Emery et al, 1997; Munoz et al, 2008; Johnson and Beatty, 1993, Caro-Bretelle et al 2015, 2016). Lanir and Fung (1974) observed full recovery of strain-softening in rabbit skin after several hours, if all the strains experienced were always positive (note that this is violated in simple uniaxial tension where the transverse strain is negative).…”

“…There are very few studies of the effects of freezing on skin. Foultz (1992) tested rat skin specimens and concluded that “freezing did not affect the resistance of the skin to tensile deformation.” Caro-Betellene et al (2015, 2016) examined different preservation methods and concluded that cryopreservation is the only way to maintain the mechanical behavior of fresh samples. More recently, Ranamukhaarachchi et al (2016) compared fresh and frozen porcine and human skin specimens, under conditions of microindentation and microneedle insertion.…”

Characterization of human female breast and abdominal skin elasticity using a bulge test.

“…Specifically with respect to skin, Foultz (Foutz et al, 1992) tested rat skin specimens and concluded that "freezing did not affect the resistance of the skin to tensile deformation". More recently, Caro-Betellene et al (Caro-Bretelle et al, 2016 examined different preservation methods and concluded that cryopreservation following a specific protocol is the only way to maintain the mechanical behavior of fresh samples of porcine skin. Ranamukhaarachchi et al (2016) compared fresh and frozen porcine and human skin specimens, under conditions of microindentation and microneedle insertion and found significant influence of freezing.…”