The Use of a Novel Injectable Hydrogel Nucleus Pulposus Replacement in Restoring the Mechanical Properties of Cyclically Fatigued Porcine Intervertebral Discs

Abstract

Repeated flexion and extension of an intervertebral disc has been shown to affect the angular stiffness of spinal motion segments and is a barometer of the mechanical integrity of the disc. A degenerated disc that loses height causes higher levels of stress on the annulus and facet joints which may increase its level of degeneration; restoring disc height may therefore help to slow this degenerative cascade. Previous research has indicated that nucleus implants have the potential to improve the mechanical characteristics of a disc and an implant that is custom-fit to the intervertebral disc yields the best results with respect to decreasing annular degeneration. Two groups of porcine spinal motion segments were exposed to repeated flexion and extension. One group was then injected with a novel hydrogel while the other group was used as a control. Both groups were then exposed to another round of cyclic flexion and extension to examine the effect that the hydrogel had on restoring the original mechanics to the motion segments. Angular stiffness was restored to the group which received the hydrogel injection in addition to a significant improvement in specimen height. No significant changes were seen in the group which did not receive an injection. It would appear that use of the novel injectable hydrogel is able to restore angular stiffness to cyclically fatigued spinal motion segments. It is also important to note that continued repetition of the event causing specimen fatigue after performing hydrogel injection will result in an eventual return to the same fatigued state.

BMP7-Based Functionalized Self-Assembling Peptides for Nucleus Pulposus Tissue Engineering

“…This result indicated that these functionalized self-assembling peptides could be implanted into a disc via a minimally invasive injection, an approach which many studies have shown to be effective. 21,52,53 The results of this study indicated that the designed self-assembling peptides containing short BMP7 motifs have favorable feasibility for clinical applications in NP tissue engineering.…”

Evaluation of an In Situ Gelable and Injectable Hydrogel Treatment to Preserve Human Disc Mechanical Function Undergoing Physiologic Cyclic Loading Followed by Hydrated Recovery

“…Cyclic loading followed by hydrated recovery in human discs mimics this naturally occurring diurnal response [26]. In a previous study that used cyclic loading to evaluate a hydrogel implant in injured porcine discs, the implant demonstrated recovery of angular stiffness and disc height [30]. However, that study did not evaluate the effects of hydrated, unloaded recovery and thus could not evaluate the time-dependent mechanical response.…”

Thermoresponsive, redox-polymerized cellulosic hydrogels undergo in situ gelation and restore intervertebral disc biomechanics post discectomy

“…Moreover, all measured biomechanical parameters (ROM, NZ length, and slow ramp, compressive, tensile and NZ stiffnesses) were restored to intact values upon hydrogel injection, while the Sham samples showed no improvements from their injured values. Although transannular discectomy has been found to measurably alter the compressive and tensile moduli, these parameters are often not restored using an NP replacement alone ( Balkovec et al , 2013 ; Malhotra et al , 2012 ; Smith et al , 2014 ). Therefore, the recovery of these parameters with the CMC 90 MC hydrogel in the current study was unique but must be interpreted with some qualification since the Sham group displayed no statistically significant effect of discectomy on the compressive and tensile moduli.…”

“…However, AF repair strategies alone may not fully restore IVD biomechanics. Recently developed NP replacements include hydrogels, because of their high water-content, tunable material properties, and ability to conform to the intradiscal space ( Balkovec et al , 2013 ; Gan et al , 2017 ; Pérez-San Vicente et al , 2017 ; Showalter et al , 2015 ).…”