Kinetic study of citric acid influence on calcium phosphate bone cements as water-reducing agent

Most of the research performed on calcium phosphate bone cements (CPBCs) has dealt with the improvement of bone cement formulations for new, demanding bone-filling applications. In particular, the development of injectable bone cements is of real interest for the biomedical community. The aim of this work was to study the effect of citric acid on the injectability and the setting properties of alpha-tricalcium phosphate-based cements. A comparative kinetic study was performed on cements with and without citric acid relating the hardening curves and the hydration rates using a mathematical approach. Citric acid behaved as a fluidificant during the first stages of the cement mixing. The dissolution-precipitation reactions of the alpha-tricalcium phosphate were retarded with the addition of citric acid and the compressive strength at saturation increased. In conclusion, citric acid can behave as a water-reducing admixture.