Antimicrobial Properties and Synthesis of Tricalcium Phosphate Doped with Alkali Metal and Silver Ions

Abstract

In order to prepare an inorganic antimicrobial agent with a biocompatibility, we have attempted synthesis of beta-tricalcium phosphate(β-TCP) doped with silver using a solid-state reaction method, and have investigated the solubility and the bactericidal activity to Escherichia coli or Staphylococcus aureus of the obtained products. TCP solid solutions were formed by reaction of the mixture of β-TCP and silver ion. The Ca²⁺ ion in β-TCP was replaced with silver ion of up to 10 mol%. It was considered that Ca²⁺ ion and vacancy located Ca(4) site in β-TCP structure were displaced by two silver ions. The products doped with silver ion showed a high bactericidal activity and their antimicrobial effects increased with increase of the amount of silver ion. In order to change the bactericidal activity of a TCP doped with silver ion, further more, alkali metal ion was added to β-TCP together with silver ion. As the result, alkali metal ion also replaced Ca²⁺ ion, and formed the substituted solid solution that is similar to silver ion. The bactericidal activity of β-TCP doped with silver and potassium ions was increased and that of β-TCP doped with silver and lithium ions was decreased. This depended on the solubility of the obtained β-TCP solid solution. By means of ESR evaluation using a spin-trap reagent, we found that superoxide radicals was generated from β-TCP doped with silver ion by UV irradiation, and considered that β-TCP doped with silver ion has both an antimicrobial effect that was generated by photo irradiation and an antimicrobial effect that was caused by the dissolved silver ion.