Silicon substituted hydroxyapatite: Preparation with Solid-State Reaction, Characterization and Dissolution Properties

Silicon substituted hydroxyapatite (Ca₁₀(PO₄)₅.₅(SiO4)₀.₅(OH)₁.₅; Si-HAP) and unsubstituted hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HAP) are prepared by solid-solid reaction at 1100°C from intimate mixtures of tricalcium phosphate (β-Ca₃(PO₄)₂), calcium carbonate (CaCO₃) with or without silicon dioxide (SiO₂). The prepared ceramics were characterized by Fourier Transform Infrared spectroscopy (FTIR) and X- ray Diffraction (XRD). There dissolution was carried out in a buffer solution (pH = 4.8) at 37°C. From the analysis of the XRD patterns, HAP and Si-HAP, have been identified as single phase. The results of FTIR and the structural refinement show and confirm the incorporation of the silicate ion in the HAP structure. The substitution of PO₄³⁻ by SiO₄⁴⁻ groups causes a reduction of the hydroxyl groups and increase the lattice distortion index (Dind = 4.682 ) compared to the pure HAP value (Dind =4.156) and the theoretical HAP value (Dind = 3.079). This structural change increases the dissolution of HAP which would lead to an improvement of its biological activity.