Setting Mechanism of a Biomimetic Bone Cement

We have previously shown that gelatin addition to calcium phosphate bone cement improves its mechanical properties. To clarify the role of gelatin on the setting reaction of the cement, we carried out powder X-ray diffraction, DSC, TG, and SEM investigations on samples frozen after different times of soaking in simulated body fluid (SBF). The results indicate that the onset of the setting reaction is under the control of CaHPO4·2H2O, which is contained in small amounts (5 wt %) in the alpha-tricalcium phosphate (alpha-TCP) cement, whereas the accelerating role of gelatin becomes the key factor just in a second step of the setting reaction. Gelatin controls the transformation of alpha-TCP into calcium deficient apatite (CDHA) and produces a composite biomimetic material with a close relationship between gelatin and CDHA crystals, which resembles that between collagen and apatite crystals in bone. With respect to the control cement, which does not contain gelatin, the gelatin-cement after setting exhibits reduced crystallinity, much smaller CDHA crystals, and a more compact microstructure, which can account for the improved mechanical properties.