Bio-engineered thermo-sensitive alginate/PNIA-g-CS co-polymeric injectable hydrogel laden with GDF-5 to stimulate nucleus pulposus for IVD regeneration.

Chronic back pain and disability are primarily caused by intervertebral disc degeneration (IDD) that requires novel therapies to regenerate the nucleus pulposus (NP) and restore disc function. In this study, a bioengineered thermo-sensitive injectable hydrogel composed of co-polymeric poly-N-isopropyl acrylamide-grafted-chondroitin sulfate cross-linked with sodium alginate microspheres (PNIA-g-CS-NaA Ms: denote HMs) loaded with growth differentiation factor 5 (GDF-5), to stimulate Nucleus Pulposus cells (NPCs) activity and promote intervertebral disc (IVD) regeneration. The Low critical solution temperature (LCST) of PNIA-g-CS was 31.8 and 32.3 °C at 5% (w/v) and 15% (w/v), respectively. In the in vitro study, GDF-5-loaded hydrogel (1 mg/mL) marginally enhanced NPC proliferation and reduced inflammatory cytokines (TNF-α, IL-6, IL-1β) after 24 h. HMs-GDF-5 combined with Adipose-Derived Mesenchymal Stem Cells (ADMSCs) was delivered to NP tissue using a minimally invasive technique, promoting NP regeneration in rats. At 8 weeks, significant upregulation of COL-II and ACAN proteins and mRNA expressions was observed. X-ray imaging showed disc height recovery and increased water content, while histology revealed partial restoration of NPCs and matrix. The outcomes show that the biodegradable hydrogel could be used as a potential therapeutic agent for IVD repair.