Multivalent ion-based in situ gelling polysaccharide hydrogel as an injectable bone graft

We prepared in situ gelling alginate (ALG)/hyaluronic acid (HA) hydrogels with a controllable gelation rate using CaSO₄ as a crosslinking agent and Na₂HPO₄ as a crosslinking retardation agent. The ALG/HA hydrogels provided sustained release of bone morphogenetic protein-2 (BMP-2) immobilized in the hydrogels over 5 weeks. The BMP-2-immobilized ALG/HA hydrogels with different ALG/HA ratios were investigated for their in vitro osteogenic differentiation behavior of human bone marrow stem cells (hBMSCs) and in vivo bone regeneration behavior using an animal model (mandibular defect model of miniature pigs). Our findings from cell culture and animal study demonstrated that the osteogenic differentiation of hBMSCs was improved with increasing HA composition in the hydrogel. The hBMSCs/BMP-2-immobilized ALG/HA hydrogel allowed greatly enhanced osteogenic differentiation of hBMSCs (in vitro) and bone regeneration (in vivo) compared with the ALG/HA hydrogel itself and single hBMSCs- or BMP-2-immobilized hydrogel groups.