Modulating the crystallinity of biphasic calcium phosphate composites balances surface and ionic cues to enhance osteogenesis via integrin-mediated cytoskeletal signaling

Biphasic calcium phosphate (BCP) composites are widely employed for bone repair, with osteogenic performance governed by both the HA:β-TCP ratio and crystallinity. While compositional tuning has been extensively investigated, the role of crystallinity as a multiscale regulator of composite properties remains insufficiently explored. Here, BCP composites with controlled crystallinity were fabricated by adjusting calcination temperature, and systematically characterized across multiple length scales. Reducing crystallinity decreased calcium ion release but enhanced surface roughness, hydrophilicity, and protein adsorption, while maintaining mechanical competence sufficient for load-bearing environments. These physicochemical changes synergistically promoted cytoskeletal extension, integrin-mediated signaling, and osteogenic gene expression in bone marrow stromal cells. Among the tested BCP composites, BCP2, with moderately low crystallinity, showed the best osteogenic outcomes both in vitro and in vivo, due to its balanced combination of favorable surface properties and moderate ion release. In contrast, BCP1, with the lowest crystallinity and superior surface properties, exhibited slightly lower osteogenesis than BCP2, likely due to insufficient calcium release. BCP3, although highly crystalline with abundant calcium release, showed the lowest osteogenic performance, possibly due to insufficient stimulation of surface characteristics during cell-material interactions in vitro and in vivo. Transcriptomic profiling further confirmed that BCP2 activated integrin-mediated cytoskeletal pathways to drive osteogenesis. Overall, this study identifies crystallinity as a key tunable design parameter that indirectly regulates osteogenesis through its coupled effects on surface and ionic cues, providing strategic insights for the rational development of BCP composites for bone regeneration.