Dissolution of dense carbonate apatite subcutaneously implanted in Wistar rats

Hydroxyapatite (HA) is used as a biomaterial in orthopedic applications bec ause it is similar in composition to bone mineral; however, carbonate apati te (CHA) is closer in chemical composition to bone mineral because bone min eral contains significant amounts of carbonate, yet there have been few rep orts comparing biological responses to HA and CHA. It is generally agreed t hat bone forms a bond of some kind to HA, and there is conflicting evidence as to whether HA is resorbed in vivo or not. However, comparative reports generally agree that beta-tricalcium phosphate (beta-TCP) is removed faster than HA from an implant site by an undetermined combination of resorption and/or dissolution. The work reported here attempts to provide the first di rectly comparable subcutaneous dissolution data for dense sintered HA, beta -TCP, and CHA in rats. The weight losses of HA, beta-TCP, and 3.2 wt % CHA were approximately 60, 520, and 320 mg m(-2) day(-1), respectively. Histolo gical sections did not show any evidence of giant cells, and all of the sam ples were encapsulated with fibrous tissue. beta-TCP and (to a lesser degre e) CHA were found to be resistant to dissolution around the edges of the sa mple. An X-ray analysis did not indicate that any phase transformation had occurred in the dissolution resistant region. (C) 2000 John Wiley & Sons, I nc.