The bioactive glass developed firstly in 1969, has been used clinically to regenerate bone since the mid-1980s. Bioactive glasses degrade when in contact with body fluids, release ions and mineralise a surface layer of biomimetic apatite. One key part of early stage bioactive glass characterisation is immersion in simulated physiological solutions, to investigate in vitro ion release and apatite surface mineralisation. The most well-known of the solutions for this purpose is simulated body fluid (SBF), which mimics the inorganic composition of blood plasma; buffering is obtained by including tris(hydroxymethyl)aminomethane(Tris). This Tris-buffered SBF has recently been recommended in a proposed unified in vitro dissolution test for bioactive glasses.

Tris buffer is commonly used for in vitro studies in life sciences to maintain solution pH at the physiological one of 7.3. For this purpose, pH is usually adjusted using hydrochloric acid (Tris-HCl), resulting in relatively high concentrations of chloride ions in the solution. It is well known that chloride ions can be incorporated into the apatite lattice, forming a fully or partially substituted chlorapatite. Kriste et al. (doi: 10.1111/ijag.12288) investigated if the presence of chloride ions in a Tris buffer solution affected bioactive glass ion release and apatite precipitation, by performing immersion experiments in a conventional Tris-HCl and a Tris-acetate solution.

Based on the experimental results from pH changes, the differences in immersion fluid composition did not seem to affect glass degradation at the time points (6 hours to 7 days) studied, as recorded pH values were the same for both solutions within the error limits. EDX results showed that the 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. And the rate of apatite formation is not affected significantly during the times studied using Tris-HCl or Tris-Acetate buffer solution.

Although no significant differences were observed in the rate of apatite formation, Kriste et al. mentioned that the presence of chloride ions may affect apatite formation at very early time points. So their suggestion is that it may be advantageous to use modified Tris buffer without high concentrations of ions involved in apatite formation, when studying early stage ion release or apatite formation. 

Edited by Suzhou Yacoo Science Co., Ltd.