Bioactive Silk Fibroin Hydrogel Harnesses BMSCs-EVs to Modulate Inflammatory Microenvironment in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is a common age-related disorder associated with inflammation, pain and impaired mobility. In this study, we developed a therapeutic system using silk fibroin (SF) hydrogel loaded with mRNA-engineered extracellular vesicles derived from murine bone marrow mesenchymal stem cells (BMSCs-EVs) to modulate macrophage polarization and alleviate IVDD. BMSCs were isolated from 6-week-old C57BL/6 mice, and an acute IVDD model was established via 18G needle puncture of the coccygeal discs (Co7-Co10). RAW 264.7 murine macrophages were used for in vitro assays, with M1 polarization induced by LPS and IFN-γ. The SF/EVs complex was characterized by SEM, FTIR and rheology, confirming its structural suitability for EV delivery. Functionally, SF hydrogel not only served as a biocompatible carrier but also enabled sustained release of EVs, enhancing their anti-inflammatory effects. In vitro, SF/EVs inhibited M1 polarization and promoted M2 marker expression. In vivo implantation improved disc histology and reduced inflammatory macrophage infiltration. High-throughput RNA sequencing identified S100B as a key functional cargo within EVs. Lentivirus-mediated overexpression and knockdown experiments confirmed that EV-derived S100B suppresses M1 polarization and mitigates IVDD progression. In summary, SF hydrogel loaded with S100B-enriched BMSCs-EVs offers a promising strategy to reshape the inflammatory microenvironment and promote disc regeneration in IVDD.