Regional and fiber orientation dependent shear properties and anisotropy of bovine meniscus

Abstract

Imaging of meniscal tissue reveals an extracellular matrix comprised of collagen fibrils arranged in circumferential bundles and radially aligned tie fibers, implicating structural material anisotropy. Biochemical analyses demonstrate regional disparities of proteoglycan content throughout the meniscal body, a constituent known to affect the shearing response of fibrocartilagenous tissue. Despite this phenomenological evidence and previous mechanical testing implicating otherwise, the meniscus if often modeled as a homogenous, transversely isotropic material with little regard for regional specificity and material properties. The aim of this investigation was to determine if shear stress response homogeneity and directionality exists in and between bovine menisci with respect to anatomical location (medial and lateral), region (anterior, central, and posterior) and fiber orientation (parallel and perpendicular). Meniscus explants were subjected to lap shear strain at 0.002 sec−1 with the circumferential collagen fibers oriented parallel or perpendicular to the loading axis. Comparisons were made using a piecewise linear elastic analysis. The toe region shear modulus was calculated from the first observed linear region, between 3%-13% strain and the extended shear modulus was established after 80% of the maximum shear strain. The posterior region was significantly different than the central for the extended shear modulus, correlating with known proteoglycan distribution. Observed shearing anisotropy led to the use of an anisoptropic hyperelastic model based on a two-fiber family composite, previously used for arterial walls. The chosen model provided an excellent fit to the sample population for each region. These data can be utilized in the advancement of finite element modeling as well as biomimetic tissue engineered constructs.

Micromechanical anisotropy and heterogeneity of the meniscus extracellular matrix

“…6a,b). Consistent with previous reports on human [2] and bovine [41] menisci, collagen fibrils on the meniscal surface were oriented randomly within the transverse plane. In the interior, the fibrils were aligned along the fiber axis within each structural unit: circumferentially for circumferential fibers, and radially for superficial layer and radial tie fibers.…”

Regional and depth variability of porcine meniscal mechanical properties through biaxial testing

“…Baro et al (2012) found that the contact modulus was significantly higher in the anterior region and lowest at the posterior region, supporting the result of the current study with highest properties in the anterior region. Shear modulus has also been reported in bovine meniscus at three anatomical locations (Abraham et al, 2011). Although not significantly different, the anterior region had a higher shear modulus than the central region.…”

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).…”