Cell culture medium as an alternative to conventional simulated body fluid

Simulated body fluid (SBF) has been widely used for bioactivity assessment of biomaterials. Many different recipes have been developed, but there is still room for improvement. We have suggested the use of cell culture medium to overcome the drawbacks of conventional SBF. Compared with conventional SBF, cell culture medium is easy to prepare. The normal practices in cell culturing, such as filtering, can eliminate insoluble precipitates in the medium and incubation at 37 °C in an atmosphere with 5% CO(2) also better simulates the in vivo environment. After 4 days immersion in carbonate buffered Dulbecco's modified Eagle's medium (DMEM), precipitates were found to have formed on the surfaces of hydroxyapatite (HA), α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). In order to further verify the use of cell culture medium for SBF studies, we carried out computational thermodynamic and kinetic analyses of the precipitation reaction to reveal the effect of pH and ion concentrations on the driving force and nucleation rate of precipitation of different calcium phosphates (CaP). In general, a slight increase in pH of the cell culture medium from physiological pH (pH 7.4) would favor CaP precipitation thermodynamically and increase the rate, as in the case of r-SBF reported previously. [Ca] and [P] have more impact on precipitation compared with other ions, but the effect is consistent among different materials, indicating that other cell culture media with slightly different compositions may also be used. This study also shows that matching the buffer with the environment is required and fetal bovine serum (FBS) slows down surface CaP precipitation on HA.