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

Ag+ and Zn2+ or Cu2+ ions were co-doped with β-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 Zn2+ or Cu2+ ions up to 9.09 mol.%, which indicated that Ag+ ions were doped at the Ca(4) site and a vacancy in the β-TCP structure, and Zn2+ or Cu2+ 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 β-TCP (Ag–TCP) and pure β-TCP. These antimicrobial activities suggested that an interaction occurred between bacteria and Ag+, Zn2+ and Cu2+ 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+, Zn2+ and Cu2+ ions in AgZn–TCP and AgCu–TCP by considering both their antimicrobial activities and cytotoxicities, because β-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.