In situ synthesis of polysaccharide-stabilized amorphous calcium Phosphate: Mechanical performance and In vitro biological assessment

The short lifetime and the weak mechanical properties of amorphous calcium phosphate-based materials (ACP) constitute the most relevant drawbacks prohibiting their use for orthopedic application. The current study focuses on the in-situ synthesis of ACP composite using sodium alginate and/or chitosan as biopolymers to address these drawbacks. The prepared composites were characterized using XRD, FTIR, SEM, and TGA-DTA. The formulated composites using alginate (ACP_Alg), chitosan (ACP_CS), and alginate-chitosan (ACP_Alg-CS) exhibited an amorphous structure typical of the amorphous nature of the ACP phase. The evolution of the precipitated amorphous phase as a function of the maturation time indicated that polymer-free ACP is stable only for 5 min. However, adding the polysaccharides increases the amorphous phase lifetime from 5 min to 2 h, thus raising its stability. The TGA-DTA analysis demonstrated that the presence of polymers significantly delayed the crystallization of ACP, confirming their stabilization effect. Furthermore, the polymer content in the amorphous composites estimated using TGA analysis revealed that only 6.7 wt% and 7.2 wt% of the polymeric phase were associated with the amorphous matrix in ACP_Alg and ACP_Alg-CS, respectively. Nevertheless, 19 wt% of chitosan polymer was successfully associated with the ACP_CS matrix. The three-dimensional composites elaborated from ACP_CS and ACP_Alg-CS and using acetic acid as a liquid phase exhibited high compressive strength, achieving a value of 98 MPa for ACP_CS-based composite. The in vitro bioactivity and biodegradability of the prepared biocomposites in the SBF solution were confirmed. Moreover, the cytotoxicity test of the selected composites highlighted their high biocompatibility.