Hydroxybutyl chitosan-based thermosensitive hydrogel enhanced osteoporotic bone regeneration through sustained release of alendronate and BMP-2.

Osteoporotic patients face an elevated risk of fractures and bone defects due to impaired repair mechanisms stemming from imbalanced osteoclast and osteoblast activity. In this context, we present an injectable thermo-responsive hydrogel/microgel platform based on Hydroxybutyl Chitosan, which exhibits long-term anti-osteoporotic and osteogenic efficacy aimed at enhancing bone regeneration in osteoporotic conditions. The hydrogel demonstrated excellent thermo-responsive properties, injectability, and an optimal degradation rate. It facilitated the sustained release of anti-osteoclastogenic alendronate (ALN) for six weeks from gelatin methacrylate (GelMA) microgels and BMP-2 for over 35 days from nanoscale decellularized bone matrix (nDBM). The HBC-nDBM-GelMA@ALN system effectively inhibited osteoclastogenesis in bone marrow macrophages (BMMs) while simultaneously enhancing proliferation, osteogenic biomarker expression, and matrix mineralization in MC3T3-E1 cells. Transcriptome sequencing analysis indicated that osteogenesis was associated with the activation of the BMP-Smad signaling pathway, whereas the anti-osteoporotic mechanism involved the NF-κB and MAPK/P38 signaling pathways. The hydrogel's enhanced efficacy in osteoporotic bone regeneration was validated using an osteoporotic rat calvarial defect model. This hydrogel demonstrated the convenience of injectability, dual-release functionality, and long-term controlled release characteristics, underscoring its translational potential for treating osteoporotic bone defects.