Bioactivity enhancement of hydroxyapatite by silicon substitution

Objective: Silicon is an effective element in bone biomineralization; hence Si-substituted hydroxyapatite can be a relevant bioceramic as bone materials substitution.
Materials and Methods: Stoichiometric hydroxyapatite (HA) and Si-substituted hydroxyapatite (Si-HA) with different contents of Si substitution were synthesized successfully by a hydrothermal method using Ca(NO3)2, (NH4)3PO4 or (NH4)2HPO4 and Si(OCH2CH3)4 (TEOS) as starting materials.
Results: Crystalline Phases, chemical composition, microstructure and morphology of synthesized powders were investigated using X-ray diffraction (XRD), Fourier transform IR spectroscopy (FTIR), inductively coupled plasma AES (ICP-AES) and scanning electron microscopy (SEM) techniques. The results proved silicon substitution in hydroxyapatite structure and revealed that the substitution of phosphate groups by silicate groups caused some OH- loss to maintain charge balance and the lattice parameters slightly changed with respect to stoichiometric HA.
Conclusion: Si-incorporation reduces the crystallites size of Si-HA and crystallinity, thus the solubility of Si-HA powders increases, and as a result Si- substitution has improved bioactivity behavior of HA. Based on in-vitro tests; soaking and incubating the specimens in simulated body fluid (SBF) and MTT assays (Dimethylthiazol assay), Si-substituted hydroxyapatite is more bioactive than pure hydroxyapatite.