Preparation and characterization of beta-tricalcium phosphate co-doped with monovalent and divalent antibacterial metal ions.

Ag(+) and Zn(2+) or Cu(2+) ions were co-doped with beta-tricalcium phosphate (AgZn-TCP and AgCu-TCP), and their substitution models, antimicrobial activities, mechanisms and cytotoxicities were investigated. The lattice constants (a-axis and c-axis) of AgZn-TCP and AgCu-TCP decreased linearly with the amount of Zn(2+) or Cu(2+) ions up to 9.09 mol.%, which indicated that Ag(+) ions were doped at the Ca(4) site and a vacancy in the beta-TCP structure, and Zn(2+) or Cu(2+) ions were doped at the Ca(5) site. Antibacterial activities of AgZn-TCP and AgCu-TCP on Escherichia coli and Staphylococcus aureus were higher than those of Ag(+) ions-doped beta-TCP (Ag-TCP) and pure beta-TCP. These antimicrobial activities suggested that an interaction occurred between bacteria and Ag(+), Zn(2+) and Cu(2+) ions eluted from AgZn-TCP and AgCu-TCP and between bacteria and the free radicals generated by antibacterial agents or in bacterial cells. AgZn-TCP and AgCu-TCP can be used over long periods of time with high antimicrobial activity, because the rate at which Ag(+) ions are released from AgZn-TCP and AgCu-TCP is slower than that at which Ag(+) ions are released from Ag-TCP. However, it is necessary to determine the suitable amounts of Ag(+), Zn(2+) and Cu(2+) ions in AgZn-TCP and AgCu-TCP by considering both their antimicrobial activities and cytotoxicities, because beta-TCP doped with a large amount of these metal ions exhibits cytotoxicity. Furthermore, AgZn-TCP and AgCu-TCP are considered to be promising materials for use in various fields.