A Method for Avoiding the Xanthoproteic-associated Discolouration in Reprecipitated (Nitric-acid-digested) Hydroxyapatite Prepared from Mammalian Bone Tissue

A procedure for producing kilogram quantities of a biomedically suitable reprecipitated hydroxyapatite (HAp) powder, which is free of the xanthoproteic-associated discolouration caused by nitric acid interaction with the protein content in bones during digestion, has been developed. Essentially bones were defatted by boiling and then pyrolysed at 1000 °C to burn off the collagenous proteins and produce flakey bleached bones. This bone was then crushed and ground and digested in nitric acid solution to produce digest solutions free of the highly staining orange colouration normally associated with nitric acid digestions of bone material.. Finely divided, white solids could then be reprecipitated as usual from the digests by addition of NaOH solution under a nitrogen atmosphere with heating and stirring at 70 °C of the precipitate to enable its maturation into an HAp phase. The products derived from this procedure were characterised using spectroscopic, microscopic and particle sizing techniques. These analyses showed the resultant powders to be low crystallinity hydroxyapatite of consistent morphology and which possessed either acceptably low or below detection limit levels of heavy metals so rendering it as a potentially valuable source of powder for biomedical applications such as plasma spraying or for implant or prosthesis manufacture.