Calcium polyphosphate endows silk fibroin hydrogels with enhanced osteogenesis for bone function restoration†

Bone defect repair demands biomaterials that synergize mechanical robustness with osteogenesis potential. The biomaterial performance of conventional crystalline calcium phosphates is often constrained by poor aqueous solubility and slow resorption kinetics. Here, we studied amorphous, hydrophilic and bioactive calcium polyphosphate (CaPP) for the development of regenerated silk fibroin (RSF)-based composite hydrogels to address such challenges. CaPP particles with tunable degrees of polymerization (DP) were synthesized via precursor ratio modulation and ion exchange. The RSF and CaPP mixture was covalently and physically crosslinked through enzyme and ethanol-treatment to yield strong and robust composite hydrogels. The mechanical properties, Ca²⁺ release kinetics and in vitro degradation behaviors of composite hydrogels demonstrated varied DP-dependencies. In vitro and in vivo osteogenesis studies confirmed the enhanced osteogenic performance for RSF–CaPP composites. This work highlights the pivotal role of CaPP with controlled chain length as a bioactive component and proposes RSF–CaPP hydrogels as promising candidates for bone function restoration.