Zinc containing hydroxyapatite ceramics to promote osteoblastic cell activity

Calcium phosphate ceramics with a (Ca + Zn)/P molar ratio of 1(.)67 containing various amounts of zinc (ZnHAP ceramics) were synthesised and their effect on promoting osteoblastic cell proliferation was examined. Above 0(.)13 wt-%Zn, which is the solid solution limit of zinc in hydroxyapatite (HAP), zinc containing tricalcium phosphate (ZnTCP) phases appeared in the ZnHAP ceramics. The TCP phases were in beta or alpha form, or both, depending on the sintering temperatures and zinc content. A monophasic ZnHAP ceramic was obtained only when ZnHAP with a zinc content of less than 0(.)13 wt-% was sintered from 1050 to 1150degreesC. When zinc was incorporated only in HAP crystal lattice, thereby having no TCP phases, no marked release of zinc from ZnHAP ceramics was observed in either the cell culture medium or in the acetic acid-sodium acetate buffer solution at pH 5. Without TCP phases, ZnHAP ceramics showed no influence on the proliferation of MC3T3-E1 cells in vitro. The optimum zinc content of ZnHAP ceramics for promoting osteoblastic cell proliferation was 0(.)34 wt-%. The present study demonstrated that the incorporation of zinc beyond the solid solution limit converted the HAP ceramic into a zinc releasing calcium phosphate material.