Osmo-inelastic response of the intervertebral disc annulus fibrosus tissue

Abstract

<jats:p> The aim of this article is to provide some insights on the osmo-inelastic response under stretching of annulus fibrosus of the intervertebral disc. Circumferentially oriented specimens of square cross section, extracted from different regions of bovine cervical discs (ventral-lateral and dorsal-lateral), are tested under different strain-rates and saline concentrations within normal range of strains. An accurate optical strain measuring technique, based upon digital image correlation, is used in order to determine the full-field displacements in the lamellae and fibers planes of the layered soft tissue. Annulus stress–stretch relationships are measured along with full-field transversal strains in the two planes. The mechanical response is found hysteretic, rate-dependent and osmolarity-dependent with a Poisson’s ratio higher than 0.5 in the fibers plane and negative (auxeticity) in the lamellae plane. While the stiffness presents a regional-dependency due to variations in collagen fibers content/orientation, the strain-rate sensitivity of the response is found independent on the region. A significant osmotic effect is found on both the auxetic response in the lamellae plane and the stiffness rate-sensitivity. These local experimental observations will result in more accurate chemo-mechanical modeling of the disc annulus and a clearer multi-scale understanding of the disc intervertebral function. </jats:p>

Bioinspired Construction of Annulus Fibrosus Implants with a Negative Poisson’s Ratio for Intervertebral Disc Repair and Restraining Disc Herniation

“…Under the tensile test, it is measured that the diagonal fibers open to a maximum angle at 50% strain, corresponding to the maximum NPR effect, and the Poisson’s ratios for − v scaffolds at 50% tensile strains are −0.205. It is inspiring that the anisotropic Poisson’s ratio is also found in the human AF, featuring PPR in the fiber plane and NPR in the lamellae plane. , …”

“…It is inspiring that the anisotropic Poisson's ratio is also found in the human AF, featuring PPR in the fiber plane and NPR in the lamellae plane. 2,30 3.2. Synthesis and Characterization of PCL-PPy Scaffolds.…”

“…1 Under axial compression, the AF with high stiffness restrains the NP from herniating. 2 However, once the outer AF ring ruptures from aging, injury, or even disease, the gel-like NP center will leak into the spinal column to cause nerve compression, finally leading to chronic pain. 3 Surgically, discectomy is often performed to reduce the pressure on nerves by partial excision of the herniated NP, hence effectively alleviating painful symptoms.…”

“…The IVD anatomy consists of two main structures, the nucleus pulposus (NP) and the annulus fibrosus (AF) . Under axial compression, the AF with high stiffness restrains the NP from herniating . However, once the outer AF ring ruptures from aging, injury, or even disease, the gel-like NP center will leak into the spinal column to cause nerve compression, finally leading to chronic pain .…”