Microwave Assisted Synthesis of Ion Substituted Bioactive Ceramics

Objectives: The bioperformance of hydroxyapatite (HA) can be improved by doping of ions such as magnesium (Mg) and zinc (Zn). Doping of iron (Fe) ions can make HA magnetic and suitable for hyperthermia treatment of cancer. Traditional synthesis methods are time consuming (24 hours or more) and require strict reaction parameter control. The objectives of this study were to explore extent of ion (Mg, Zn, Fe) doping into HA and its effect on thermal stability of HA using microwave assisted (for reduced synthesis times) wet chemical synthesis. Methods: Typical reactions involved mixing of dopant ion nitrate salts (Mg, Zn, Fe respectively) into calcium nitrate solution. Diammonium hydrogen phosphate solution was added drop-wise into the calcium and dopant ion containing solution. Resulting suspension was exposed to 600 Watts microwave irradiation for 5 minutes prior to filtration, oven drying and heat treatment. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infra Red spectroscopy (FTIR) were carried out for characterization. Results: SEM images for Mg doping revealed porous agglomerates (pore size ≤ 10 microns). For all ions (Mg, Zn, Fe) XRD results showed heat treated samples to be phase pure HA at low level dopings (0.1 wt% for Mg, 1 wt% for Zn and 0.5 wt% for Fe). Further increase in dopant levels resulted in appearance of tricalcium (TCP) phase in all the cases and additionally Fe₂O₃ in the case of Fe doping. FTIR spectroscopy revealed presence of carbonate ions in as-precipitated samples. Conclusions: Microwave irradiation facilitated the lowering of reaction time to only ~ 3 hours. Reduced thermal stability (i.e. formation of TCP phases) with increasing dopant levels suggests that dopant ions were doped into HA lattice. This work showcases the versatility of microwave assisted synthesis wherein bioactive ceramics with tailorable properties (phase-composition and solubility) can be synthesized.