Silicate Biomaterials-Stimulated Vascularized Callus Organoids for Bone Tissue Regeneration

Organoids that recapitulate native fracture callus can form spontaneous ossification centers within a bone defect, offering substantial promise for rapid bone regeneration. However, existing callus organoids generally lack a functional vascular network and an appropriate mechanical microenvironment, and their production limits scalability and uniformity. Here, we established a droplet-based microfluidic platform for the high-throughput generation of morphology-dependent magnesium silicate-engineered composite hydrogel microspheres, enabling the uniform construction of vascularized callus organoids. Importantly, morphology-dependent magnesium silicate could regulate both the bulk mechanical performance and internal stress distribution of the composite hydrogels. In vitro, callus organoids modulated by magnesium silicate nanotubes significantly promoted chondrogenic and osteogenic differentiation, developed a stable endothelial network and mineralized structure. Furthermore, magnesium silicate nanotube-engineered composite hydrogel (2NT-GM) offered a favorable mechanical microenvironment for callus organoids, thereby activating the mechanotransduction-related pathway for promoting the development of organoids. In a rat femoral condyle critical-sized defect model, the vascularized callus organoids regulated by 2NT-GM were further found to significantly promote vascular network formation, and facilitate bone regeneration at the bone defect center within 6 weeks of implantation. Together, this study suggests a promising strategy for bone tissue regeneration by developing vascularized callus organoids with the stimulation of inorganic silicate biomaterials.