Hydroxyapatite synthesis and the benefits of its blend with calcium aluminate cement

Hydroxyapatite (HA) is a calcium phosphate and the main mineral component of bones and teeth. However, its use as a biomaterial is limited due to the poor mechanical strength presented by this compound. Various techniques have been investigated for HA production, considering its good biocompatibility and chemical stability in the implanted area. In this paper, two methods for hydroxyapatite synthesis (precipitation and mechanosynthesis) were evaluated and compared, in order to select the most viable HA processing route before adding this component to calcium aluminate cement (CAC). The blend of HA+CAC aimed to attain a biomaterial presenting the biological activity of calcium phosphate and the optimized green mechanical strength derived from the selected cement. The obtained HA powders were characterized via XRD, SEM and particle size distribution measurements. The mechanical strength, apparent porosity and pore size distribution of the prepared HA+CAC samples were analyzed. Both studied routes induced hydroxyapatite generation, but the mechanosynthesis was the most suitable one due to the reduced reaction time required. The main advantage of adding HA powders to CAC was associated with the production of a compound with higher mechanical strength, when compared to the original materials. Besides that, the HA favored the bioactivity of the prepared compositions, as observed by the Ca2+ ions release and pH increase of the analyzed aqueous medium, leading to apatite precipitation on the HA+CAC samples׳ surface. This latter transformation also resulted in the decrease of both, apparent porosity and pores diameter, of the samples.