An injectable bioactive magnesium phosphate cement incorporating carboxymethyl chitosan for bone regeneration

Magnesium phosphate cement (MPC) can be injected to form an in situ scaffold to repair bone defects. Here we synthesized novel injectable bioactive cements (CMPCs) by incorporating different ratios of carboxymethyl chitosan (CMC, 0-10%) into MPC. The physiochemical properties, compositions, and microstructures of CMPCs were evaluated. The in vitro cellular responses of pre-osteoblast MC3T3-E1 cells to CMPCs including adhesion, proliferation, and differentiation were quantified and the underlying cellular mechanisms investigated. CMPCs had longer setting times and lower setting temperatures. CMPC injectability was enhanced by the addition of CMC. The CMPC containing 5% CMC had the highest compressive strength and washout resistance. CMPCs had a more neutral pH compared to MPC at four weeks. Furthermore, CMPC samples showed similar degradability and Mg²⁺ release to MPC in Tris-HCl buffer. Osteoblasts (MC3T3-E1) showed significantly greater adherence, proliferation, and differentiation on CMPC specimens than on MPC. Finally, CMPCs effectively increased the adsorption of fibronectin and activated integrin signaling as indicated by enhanced FAK and ERK phosphorylation. Our novel CMPC composites have improved physicochemical properties and cellular responses and represent a promising material for bone regeneration.