A high-performance organic-inorganic composite bone cement enabled by a Sr-doped alginate-phosphate ternary system

Conventional calcium sulfate bone cements suffer from rapid degradation, poor anti-washout property, and inadequate bioactivity. To overcome these limitations, we developed an injectable bone cement based on a novel ternary synergistic system of Sr-doped alginate-phosphate (SA/Sr/PO₄^3-) and hydrothermally synthesized α-calcium sulfate hemihydrate (α-CSH). This design leverages the rapid physical crosslinking between Ca²⁺ from α-CSH and the guluronic acid/mannuronic acid blocks of sodium alginate, resulting in a reinforced network with enhanced initial anti-washout property and a wet compressive strength of 2-12 MPa. Simultaneously, the alginate matrix induces the in situ mineralization of Ca²⁺ and PO₄^3- ions, forming a calcium-deficient hydroxyapatite (CDHA) precursor that decelerates the degradation rate (18% in PBS over 60 days) to match new bone formation. In addition, strontium ions (Sr²⁺) sustainably released from the material promote in vitro osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). This work presents a novel composite cement that successfully integrates injectability, robust mechanical properties, controllable degradation, and osteoinductive capability.