Effect of strontium and gelatin on the reactivity of α-tricalcium phosphate

The hydrolysis reaction of α-tricalcium phosphate (α-TCP) is of great interest because of its widespread use in the preparation of biomaterials for hard tissue repair. The aim of this study was to investigate how this reaction is influenced by the presence of a bioactive ion, Sr2+, and of a biopolymer, gelatin, which were previously reported to affect the setting reaction of α-TCP-based cements. Hydrolysis experiments were carried out at different Sr2+ concentrations (0, 5, 10, 20 at.%) in solutions at different gelatin concentrations (0, 0.1, 0.5, 1.0 wt.%). The results indicate that Sr2+ delays the conversion of α-TCP into calcium-deficient hydroxyapatite (CDHA). The structural and morphological modifications of CDHA obtained from solutions at increasing Sr2+ concentrations indicate that during hydrolysis strontium enters the structure of CDHA, where it partially substitutes for calcium. On the contrary, α-TCP hydrolysis rate increases on increasing gelatin concentration. Gelatin promotes conversion of α-TCP into octacalcium phosphate, and strongly interacts with the nucleating and growing crystals.