Simple shearing of soft biological tissues

Abstract

Shearing is induced in soft tissues in numerous physiological settings. The limited experimental data available suggest that a severe strain-stiffening effect occurs in the shear stress when soft biological tissues are subjected to simple shear in certain directions. This occurs at relatively small amounts of shear (when compared with the simple shear of rubbers). This effect is modelled within the framework of nonlinear elasticity by consideration of a class of incompressible anisotropic materials. Owing to the large stresses generated for relatively small amounts of shear, particular care must be exercised in order to maintain a homogeneous deformation state in the bulk of the specimen. The results obtained are relevant to the development of accurate shear test protocols for the determination of constitutive properties of soft tissues. It is also demonstrated that there is a fundamental ambiguity in determining the normal stresses in simple shear when soft tissues are modelled as incompressible hyperelastic materials owing to the arbitrary nature of the hydrostatic pressure term. Two physically well-motivated approaches to determining the pressure are presented here, and the resulting hydrostatic stresses are compared and contrasted. The possible generation of cavitational damage owing to critical hydrostatic stress levels is briefly discussed.

A novel method for visualising and quantifying through-plane skin layer deformations

“…An electric dermatome (D42, Humeca, Enschede, The Netherlands) was used to prepare full-thickness skin slices (thickness: 1.2-1.6 mm) from which square samples (8 Â 8 mm) were punched. The skin samples had an aspect ratio (thickness/width) of 1:6-1:5, which is close to the ratio of 1:4 recommended to reduce/minimise effects of strain concentrations at boundaries (Abraham et al, 2011;Horgan and Murphy, 2011). Pilot tests showed that the surface of the through thickness plane of the as-received skin did not present a unique, nonrepetitive high contrast pattern that is required for image correlation (Lecompte et al, 2006).…”

“…Even though shearing is induced in soft tissues in numerous applications and situations in everyday life, the study of shear deformation has received little attention in the biomechanics literature (Hollenstein et al, 2011;Horgan and Murphy, 2011), and little literature has concerned the cyclic deformation of skin tissue (Kang and Wu, 2011;Lim et al, 2011). Thus, until now only limited in vivo and in vitro data is available for dynamic shear moduli of (human) skin (Agache et al, 1980;Escoffier et al, 1989;Geerligs et al, 2011a;Holt et al, 2008); shear moduli ranging from 0.2 to 120 kPa have been reported.…”

A homeostatic-driven turnover remodelling constitutive model for healing in soft tissues

“…In some cases, the adequacy of the quasi-incompressibility hypothesis in soft tissues subjected to physiological loading has also been debated [93,94]. The possibility of cavitational damage arising in soft tissues has also been put forth [95]. Nonetheless, the HTR model accounts for remodelling from the granulation tissue obtained in the proliferative phase of the healing process to the scar tissue resulting at the end of the remodelling phase ( figure 1).…”

Determination and Finite Element Validation of the WYPIWYG Strain Energy of Superficial Fascia from Experimental Data

“…We note that square or cube-shaped specimens are used to test different biological tissues, see for example [23,24,25]. However, the stress state within these specimens are far from homogeneous [27], a fact that should be taken into consideration when fitting material parameters from experimental data obtained this way (recall that we obtained α = F ideal /F exp = 1.75). To this end, as we have herein shown, a finite element analysis of the experiment using the constitutive model being calibrated allows to perform this correction in an iterative manner.…”

“…However as it is well-known [27], the actual experimental setting is not an ideal simple shear one mainly because of the length-to-width ratio of the specimen. Then, the stresses are not homogeneous within the specimen and the problem is a general boundary value problem which is to be solved using finite elements; the approach also followed in [19].…”