Silicon-doped calcium phosphates; the critical effect of synthesis routes on the biological performance

In this study, the effect of using different types of fuel and various amounts of Si⁴⁺ ions on the biological properties of silicon-doped calcium phosphates (CaPs), which were synthesized using solution combustion method were investigated. X-ray diffraction (XRD) patterns showed that hydroxyapatite/beta-tricalcium phosphate (HA/βTCP) was crystallized in all synthesized samples. The synthesized sample using glycine as fuel, which doped with 0.1 mol Si⁴⁺ ions exhibited the most desirable properties. Consecutively, the zeta potential and specific surface area were enhanced from -20 to -27 mV and 38 to 146 m²/g, respectively, by increasing the amount of Si⁴⁺ ions from 0 to 0.1 mol. The bioactivity of the samples immersed in simulated body fluid (SBF) was innovatively determined by the joint analyses of the tensiometer, inductively coupled plasma (ICP), field emission scanning electron microscopy (FESEM), and XRD data. These findings plus theoretical calculations demonstrate, for the first time, that the Si⁴⁺ doping could improve the bioactivity of the powders up to ~155%. The results of in vitro cell-based experiments, including cell viability, alizarin red staining, and cell attachment, confirmed the positive effects of Si-doped powders in the biological systems. Furthermore, Si-doped powders were able to improve the migration ability of mammalian cells in vitro; they could be considered good candidates in angiogenesis-based therapeutic strategies.