Phosphate and buffer capacity effects on biomimetic carbonate apatite

With the increasing use of carbonated apatite (CAp) in biomedical devices, it has become necessary to understand how this thermodynamically unstable mineral interacts with varying surrounding body fluids. Despite existing knowledge about the evolution of other calcium phosphates in bio-like fluids, it is unknown how CAp reacts in these solutions. Therefore, our goal was to determine how solution phosphate concentration and the buffer capacity (BC) affects CAp dissolution/recrystallization. To do so, CAp powder was first synthesized through an aqueous precipitation reaction and then exposed to one of the following solutions for 3 days: (1) 0 mM PO4, (2) 8 mM PO4, (3) 16 mM PO4, (4) low BC, or (5) high BC. Afterwards, the powders were analyzed for mass loss, composition via Raman, crystal structure via XRD, and size via TEM. The solutions were evaluated for Ca, P, Na, and K through ICPOES. Our results suggest that increased phosphate in the solution, regardless of BC, created larger, more crystalline CAp crystals, indicating crystal maturation. In addition, the crystals had fewer carbonate substitutions and more phosphate ion uptake from the solution after pH equilibrium. This data offers insight on how CAp in biomaterials may mature and change composition and material properties in the body after implantation.