Injectable Hydrogel With Nucleus Pulposus-matched Viscoelastic Property Prevents Intervertebral Disc Degeneration

Background:Intervertebral disc(IVD)degeneration(IVDD)that greatly affected by regional biomechanical environment is a major cause of low back pain.Injectable hydrogels have been commonly studied for treatment of IVDD due to their capability of mimicking extracellular matrix structure to support cellular behavior and clinical prospects in minimally invasive treatment.However,most hydrogels suffer from complicated chemistry,potential uncertainty and toxicity from in-situ gelation,and mismatch with IVD mechanical environment that limit their therapeutic effects or clinical translation in IVDD or intervertebral disc defect repair.Objective:For IVD lesion repair,the main purpose of this study is to develop a new model of hydrogel with shear-thinning enabled injectability,high bio-safety,and mechanical properties adaptable to the IVD environment,using a simple chemistry and method.And therapeutic efficacy of the novel hydrogel in the treatment of IVDD or intervertebral disc defect will be revealed.Materials and methods:A glycerol cross-linked PVA gel(GPG)was synthesized based on multiple H-bonds formation between glycerol molecules and PVA chains.The rheological and mechanicalproperties was tested.The swelling ratio was measured.The micro-architecture was observed through scanning and transmission electron microscopes.NP cells were cultured in GPG-coated plate or silicone chambers treated with hydrostatic or dynamic loading in vitro,and examined for proliferation,vitality,apoptosis,the expression of catabolic and anabolic markers by quantitative real-time reverse transcription polymerase chain reaction and Western Blot assay.GPG was injected in needle puncture(IDD)or NP discectomy(NPD)models in vivo,and examined through magnetic resonance imaging,microcomputed tomography scanning and histological staining.Results:GPG had a highly porous structure consisting of interconnected pores.Meanwhile,the GPG was able to withstand the cyclic deformation and exhibited a prominent energydissipating capability.In vitro cell tests demonstrated that,the hydrogel significantly downregulated the expression of catabolic markers,maintained the level of anabolic markers,preserved cell proliferation and vitality,reduced apoptotic rate of NP cells under pathologically hydrostatic and dynamic loading environments compared to cell cultured on plate.In vivo animal studies revealed that injection of GPG efficiently maintained NP structural integrity,IVD height and relative water content in IDD models,and stimulated the fibrous repair in NPD models.Conclusion:This study showed that GPG,with high injectability,NP-like viscoelastic characteristics,good energy-dissipating properties and swelling capacities,preserved NP cells vitality against pathological loading,and had therapeutic effects in IDD and NPD models.The translational potential of this study:Effective clinical strategy for treatment of intervertebral disc degeneration(IVDD)is still lack.This study demonstrates that injection of a hydrogel with nucleus pulposusmatched viscoelastic property could remarkably prevent the IVDD progress.Prepared with simple chemistry and procedure,the cell/drug-free GPG with high bio-safety and shear-thinning enabled injectability bears great translational potential for the clinical treatment of IVDD via a minimally invasive approach.