A Systematic Study of the Effect of pH on the Initialization of Ca-deficient Hydroxyapatite to -TCP Nanoparticles

The formation of -tricalcium phosphate (-TCP) nanoparticles via a wet precipitation technique was studied in a systematical way, taking reaction pH and sintering temperature parameters into account. A full transformation of Ca-deficient hydroxyapatite (CDHA) to -TCP at 750 degrees C in under 3 h from Ca++ and PO43- precursor solutions prepared under a pH of 5.5 was observed. For pH values higher than 6.5, CDHA can only partially transform into -TCP and only at temperatures higher than 750 degrees C confirmed using X-Ray diffraction and Raman spectroscopy. The morphologies of the particles were also examined by Transmission electron microscopy. The lower temperatures and the shorter sintering time allow for a fine needle-like morphology, but with a high crystallinity, likely eliminating the possibility of excessive grain growth that is otherwise expected to occur under high-temperature treatment with long process times. We show that sintering of nanostructured, high crystallinity -TCP at relatively low temperatures is possible via adjustment of the precursor solution parameters. Such an outcome is important for the use of -TCP with a fine morphology imitating that of the skeletal tissues, enhancing the osteointegration of a base, load-bearing alloy to the host tissue. MTT analysis was used to test the effect of the obtained -TCP particles on the viability of MG-63 human osteoblast-like cells.