MECHANICALLY MATCHED INJECTABLE PHOTOCROSSLINKABLE HYDROGEL LOADED WITH EXOSOMES REPAIR ANNULUS FIBROSUS-NUCLEUS PULPOSUS COMPLEX DEFECT

Low back pain has become the leading cause of disability, resulting in enormous labor loss and economic losses, while intervertebral disc degeneration (IVDD) is one of the main causes of low back pain. Annulus fibrosus-nucleus pulposus complex defect is known to precipitate severe intervertebral disc degeneration and disc herniation. Hydrogels are promising materials for disc regeneration, we designed novel mechanically matched injectable photocro-sslinkable poly(lactide-co-propylene glycol-co-lactide) dimethacrylates (P7L2DMA) and methacrylated hyaluronic acid (MeHA), which are loaded with bone marrow mesenchymal stem cells-derived exosomes (Exos), and evaluated the therapeutic efficacy on intervertebral disc degeneration in vivo and in vitro. Exosomes isolated via differential ultracentrifugation were characterized by TEM, NTA, and WB. Hydrogels P7L2DMA and MeHA underwent FTIR, ^1H NMR, and SEM characterization. Their mechanical properties were evaluated through compression tests. P7L2DMA@Exo and MeHA@Exo constructs were assessed for exosome release and internalization. Effects of MeHA@Exo, MeHA, and PBS on nucleus pulposus cell (NPC) regeneration and RAW 264.7 cell inflammation were analyzed using PCR, ELISA, flow cytometry, and immunofluorescence. Animal study groups: Sham, P7L2DMA@Exo-MeHA@Exo (PME), P7L2DMA-MeHA (PM), and Defect groups, in a rabbit disc defect model, with radiological and histological evaluations at 2, 4, and 12 weeks. Characterization confirmed exomes and hydrogels met specifications. MeHA@Exo showed concentration-dependent effects in restoring type II collagen and reducing MMP3 in LPS-induced NPCs, reducing apoptosis and pyroptosis. PCR, ELISA, and immunofluorescence showed MeHA@Exo decreased IL-6 and TNF-α, and increased IL-10 in LPS-induced RAW 264.7 cells, with reduced M1 macrophage marker CD86. MRI and histological assessments showed that, compared to the Defect group, both the PME Group and the PM Group significantly alleviated intervertebral disc degeneration within 4 weeks. Moreover, the PME Group continued to exhibit recovery in type II collagen expression and reduced apoptosis of NPCs up to 12 weeks. The combined application of P7L2DMA@Exo and MeHA@Exo demonstrates significant potential in repairing the annulus fibrosus-nucleus pulposus complex defect, alleviating inflammation, and decelerating degenerative processes.