Calcium phosphate ceramics with a (CazZn)/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 b or a 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 1150uC. 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.MST/6206

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Zinc-containing calcium phosphate ceramics with a (Ca+Zn)/P molar ratio of 1.67 (ZnHAP ceramics) were synthesized to clarify the main phase for zinc release. ZnHAP ceramics with a zinc content at or more than 0.20 wt% contained zinc-containing tricalcium phosphate. The ion activity product of monophasic ZnHAP ceramic containing at or less than 0.13 wt% of zinc corresponded to that of pure HAP ceramic. The presence of tricalcium phosphate (TCP) phases was necessary condition for ZnHAP ceramics to release zinc. The coexistence of TCP phases in the ZnHAP ceramics meant that a phase with a (Ca+Zn)/P molar ratio higher than 1.67 also coexisted. Although the phase was assumed to be zinc oxide, zinc was not concentrated anywhere in the ZnHAP ceramics including grain boundaries.

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