Effect of chloride ions in Tris buffer solution on bioactive glass apatite mineralization

Degradation and apatite precipitation of Bioglass 45S5 were characterized in two different tris(hydroxymethyl)aminomethane (Tris) buffer solutions. In the conventional one, pH was adjusted to 7.4 using hydrochloric acid (Tris-HCl buffer). In the other one, acetic acid was used instead, thereby obtaining a Tris buffer solution, which was virtually free of chloride ions (Tris-HAc). EDX results showed that chloride ions present in Tris-HCl buffer solution were incorporated into the apatite formed during immersion experiments, forming a (partially) substituted chlorapatite. No chloride ions were detected in apatite precipitated in Tris-HAc. Although no significant differences in the rate of apatite formation were observed during the time points studied here (6 hours to 7 days), the presence of chloride ions may affect very early stages of apatite formation. It may therefore be advantageous to use modified Tris buffer solutions, which do not contain high concentrations of ions involved in apatite formation, when studying early time point release kinetics or apatite precipitation of bioactive glasses.