Mechanical characterization and design of biomaterials for nucleus pulposus replacement and regeneration

Abstract

Biomaterials for nucleus pulposus (NP) replacement and regeneration have great potential to restore normal biomechanics in degenerated intervertebral discs following nucleotomy. Mechanical characterizations are essential for assessing the efficacy of biomaterial implants for clinical applications. While traditional compression tests are crucial to quantify various modulus values, relaxation behaviors and fatigue resistance, rheological measurements should also be conducted to investigate the viscoelastic properties, injectability, and overall stability upon deformation. To recapitulate the physiological in vivo environment, the use of spinal models is necessary to evaluate the risk of implant extrusion and the restoration of biomechanics under different loading conditions. When designing devices for NP replacement, injectable materials are ideal to fully fill the nucleus cavity and prevent implant migration. In addition to achieving biocompatibility and desirable mechanical characteristics, biomaterial implants should be optimized to avoid implant extrusion or re‐herniation post‐operatively. This review discusses the most commonly used testing protocols for assessing mechanical properties of biomaterial implants and serves as reference material for enabling researchers to characterize NP implants through a unified approach whereby newly developed biomaterials may be compared and contrasted to existing devices.

Comparison of four in vitro test methods to assess nucleus pulposus replacement device expulsion risk

“…Other recommended extensions to the study include assessing NRDs with significantly different stiffnesses or chemical compositions (e.g., elastomeric devices similar to PDN‐Hydraflex, 31 Aquarelle, 11 NeuDisc, 80 DASCOR, 13 or NuCore 21 ) as these factors were similar here; in the longer term, related studies investigating the response of ex vivo cultured specimens containing cellular components could be of additional value. 81 , 82 As AF closure sutures were implemented, deviating from clinical practice, investigating different closure techniques would also be worthwhile. This step was needed to prevent expulsion following a single off‐axis compression; however, it is not known whether this step affected expulsion risk in either the preformed or in situ case disproportionately.…”