Synthesis and characterisations of clinoptilolite enriched hydroxyapatite nanoceramics by sol-gel route for bone regeneration

Abstract

Hydroxyapatite (HA) has great bioactive potential in bone tissue engineering (BTE). However, the high crystalline stability of synthetic HA restricts its in-vivo bioresorbability which extends the healing time of bone defects. This study investigates doping HA with biocompatible Clinoptilolite (CLP) mineral rich in silicate and other biomimetic ions (Na+, K+, Ca+2, Mg+2 etc.). Sol-gel-based CLP doped HA nanoceramics are aimed to be exploited as bone filler substitutes with biomimetic morphology, composition, and improved biocompatibility and bioactivity. The pure and CLP (5%, 10% and 20%) doped HA ceramics were synthesised by sol-gel method to provide molecular level interactions of ions and sintered at different temperatures (800 °C, 950 °C, and 1100 °C). Morphological analyses by SEM and S-TEM showed biomimetic nano rod-like HA particles are attached to dispersed CLP sheets. Sintering of composite ceramics led to a cell-friendly interconnected porous microstructure even at 1100 °C, where the pure HA had a compact non-porous structure. The Ca/P ratio of CLP-doped HA samples was lower than the stoichiometric HA which indicates a partial reduction of stability that is supposed to induce bioresorption capacity. Cytotoxicity tests by WST-8 with Saos-2 cell lines showed that CLP addition into HA has significantly improved cell viability. The HA-CLP nanoceramics are expected to promote bone regeneration due to cell-friendly microstructure and biomimetic composition which can be supported by further in-vivo clinical studies.