PBVHx-based microspheres for controlled BMP2 release and enhanced bone regeneration in a disuse osteoporosis mouse model.

Addressing bone defects caused by degenerative diseases, trauma, and cancer through bone tissue engineering remains a significant global health challenge. The osteoinductive properties of bone morphogenetic protein-2 (BMP2) have become a key therapeutic strategy in bone regeneration. However, the development of biodegradable composites that ensure biocompatibility, stability, efficient BMP2 loading, and controlled release remains unresolved. In this study, we designed PBVHx/soy lecithin (SL)/BMP2 controlled-release microspheres (sB2PM) based on the biodegradable material poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PBVHx), incorporating SL to enable sustained BMP2 delivery and enhance capture. sB2PM microspheres exhibited uniform size (approximately 5 μm) and high BMP2 encapsulation efficiency (80.29%) compared to pure PBVHx-based microspheres (pPM). Due to PBVHx's biodegradability, BMP2 release was primarily degradation-driven, resulting in a controlled biphasic release profile. sB2PM achieved 62.79% cumulative BMP2 release over four weeks and continued to release BMP2 sustainably thereafter. Co-culturing sB2PM microspheres with human bone marrow-derived mesenchymal stem cells (hBMSCs) in a Transwell system showed enhanced cell proliferation, biocompatibility, and collagen secretion. Compared with pPM and B2PM, sB2PM significantly promoted osteogenic differentiation, increased alkaline phosphatase (ALP) activity, and upregulated osteogenic gene expression in hBMSCs, outperforming commercial hydroxyapatite microspheres. In a mouse hindlimb unloading osteoporosis model, micro computed tomography and histological evaluations confirmed that injectable sB2PM microspheres significantly enhanced bone regeneration, collagen secretion, and ALP and runt-related transcription factor 2 protein expression. This study highlights the potential of sB2PM microspheres with controlled BMP2 release for future bone regeneration therapies.