Fabrication of Zn containing apatite cement and its initial evaluation using human osteoblastic cells

Recently, the effects of Zn²⁺ on osteogenesis stimulation have become major topics in the research fields of bone formation and organism essential elements. Based on the fundamental finding of Zn²⁺ with respect to osteogenesis stimulation, Ito et al. have prepared Zn doped β-tricalcium phosphate (ZnTCP) and have reported that ZnTCP enhances the proliferation of MC3T3-E1 cells. In this investigation, we studied the effects of ZnTCP added to apatite cement (AC) with respect to its setting reaction and proliferation of human osteoblastic cells as an initial evaluation for the feasibility of AC containing ZnTCP. Compositional analysis using powder X-ray diffractometer revealed that ZnTCP shows no reactivity with the setting reaction of AC. As a result, the mechanical strength of set AC decreased increasing amounts of added ZnTCP as if ZnTCP acts as a pore in AC. The setting time of AC was not affected by addition of ZnTCP up to 10%. When AC containing ZnTCP was immersed in α-MEM containing 10% bovine serum, Zn²⁺ was released from AC. Larger amounts of Zn²⁺ were released from AC containing larger amounts of ZnTCP. When human osteoblastic cells were incubated on the surface of AC discs, proliferation of human osteoblastic cells was significantly increased on the surface of AC that contained 5% ZnTCP when compared with that containing no ZnTCP. In contrast, proliferation of human osteoblastic cells decreased on the surface of AC that contained 10% ZnTCP when compared with that free from ZnTCP; indicating cytotoxicity. We concluded therefore, that addition of ZnTCP to AC is useful to enhance the osteoconductivity of AC when release of Zn²⁺ can be carefully regulated.