Injectable photosensitive bone cement enhancing angiogenesis and osteogenic differentiation for the treatment of bone nonunion

Nonunion fractures present a significant clinical challenge because of their complex microenvironment, which includes poor vascularization, insufficient osteogenesis, infection, and separation of fracture ends. The current clinical treatments have certain limitations. Inspired by this phenomenon, sandcastle worms secrete adhesive proteins that bind sand grains, shell fragments, and mineral particles, thereby constructing their "castles." In this study, we developed an injectable bone cement using methacryloyl chitosan (CSMA) combined with a specific concentration of oyster shell nanoparticles (OS-np) to treat nonunion fractures. Oyster shells are composed primarily of calcium carbonate, which releases ions that promote angiogenesis and osteogenesis. The <i>in vivo</i> results at 8 weeks showed that the expression of BMP2, RUNX2, and VEGF in the OS-np/CSMA group was increased by 5.47, 4.38, and 3.54 times, respectively, compared to the control group, significantly enhancing vascularization and bone repair in the bone nonunion model. The injectability of the OS-np/CSMA bone cement ensures that it can adapt well to the complex structures of nonunion sites, providing a supportive matrix for new bone formation. Both <i>in vivo</i> and <i>in vitro</i> osteogenesis experiments demonstrated that the OS-np/CSMA bone cement significantly enhanced vascularization and bone repair in nonunion models, which was because of the synergistic effects of ion release and the bioactive properties of the oyster shell nanoparticles. This study highlights the potential of OS-np/CSMA injectable bone cement as a promising treatment strategy for complex nonunion fractures that effectively promotes angiogenesis and osteogenesis.