Mechanical restoration and failure analyses of a hydrogel and scaffold composite strategy for annulus fibrosus repair

Abstract

Unrepaired defects in the annulus fibrosus of intervertebral discs are associated with degeneration and persistent back pain. A clinical need exists for a disc repair strategy that can seal annular defects, be easily delivered during surgical procedures, and restore biomechanics with low risk of herniation. Multiple annulus repair strategies were developed using poly(trimethylene carbonate) scaffolds optimized for cell delivery, polyurethane membranes designed to prevent herniation, and fibrin-genipin adhesive tuned to annulus fibrosus shear properties. This three-part study evaluated repair strategies for biomechanical restoration, herniation risk and failure mode in torsion, bending and compression at physiological and hyper-physiological loads using a bovine injury model. Fibrin-genipin hydrogel restored some torsional stiffness, bending ROM and disc height loss, with negligible herniation risk and failure was observed histologically at the fibrin-genipin mid-substance following rigorous loading. Scaffold-based repairs partially restored biomechanics, but had high herniation risk even when stabilized with sutured membranes and failure was observed histologically at the interface between scaffold and fibrin-genipin adhesive. Fibrin-genipin was the simplest annulus fibrosus repair solution evaluated that involved an easily deliverable adhesive that filled irregularly-shaped annular defects and partially restored disc biomechanics with low herniation risk, suggesting further evaluation for disc repair may be warranted.

Angle-ply biomaterial scaffold for annulus fibrosus repair replicates native tissue mechanical properties, restores spinal kinematics, and supports cell viability

“…More recently, the fibrin-based hydrogel was combined with a synthetic NP scaffold and a polyurethane membrane sutured to the outer AF to repair FSUs. Biomechanical evaluations of the repaired FSUs commonly demonstrated NP scaffold herniation/extrusion from the IVDs when physiological loading was applied [35]. In this investigation, we have demonstrated an in-depth mechanical characterization of a collagen-based, multi-laminate angle-ply AF repair patch (AFRP) biomaterial that illustrated its ability to mimic the static and dynamic biomechanical characteristics of the native human AF.…”

Effects of Level, Loading Rate, Injury and Repair on Biomechanical Response of Ovine Cervical Intervertebral Discs

“…FibGen repair reduced the change in torque range and axial ROM induced by puncture injury in this study. Previous biomechanical studies showed that FibGen reduced disc height loss from injury in a bovine organ culture model, restored compressive stiffness, (49) and restored multiple rotational flexibility measurements (50). The restoration of multiple aspects of biomechanical response to intact levels supports future in vivo evaluation of FibGen using live animal testing with the ovine model presented here.…”

Lamellar and fibre bundle mechanics of the annulus fibrosus in bovine intervertebral disc

“…This, in turn, has raised the need for experimental micromechanical data on annulus ultrastructure. Such data are also required to inform the development of techniques of disc repair that aim at integrating a scaffold structure into the tissue [8,9]; indeed, cell survival and restoration of tissue strength depend on the mechanical compatibility between the engineered scaffold and the living tissue at the microscopic scale. A better knowledge of the latter could potentially help improve the design of these scaffolds.…”