Rheological properties of an apatitic bone cement during initial setting

One scientific and technological aspect of main importance to the medical profession is to develop injectable calcium phosphate cements (CPCs) to be used through minimally invasive surgery techniques with still suitable mechanical and biodegradable properties. The objective of this research was to study the influence of several technological factors on the injectability of CPCs. This was performed by studying the rheological behavior of the cement pastes during their initial setting. Cement rheology was approached by looking at the creep response of apatitic cements as a function of the shear stress, the liquid-to-solid (L/S) ratio, the temperature and the addition of organic admixtures. Results showed creep experiments to be a finer method to detect characteristic setting times than other established subjective procedures. However, of all transition times detected none but the dough time seems to be of relevant importance when injectability of cement is concerned. Creep experiments also showed that the addition of organic admixtures such as citric acid increased injectability by retarding the hydration time.