Sol-Gel Derived Hydroxyapatite, Fluorhydroxyapatite and Fluorapatite

Objectives: To characterise, optimise and investigate the properties of Hydroxyapatite (HA), Fluorhydroxyapatite (FHA) and Fluorapatite (FA) produced via a sol-gel technique for potential future use as implant coating and bone grafting materials. Methods: HA, FHA and FA were synthesised using Calcium nitrate and triethyl phosphite as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH₄F) were incorporated for the preparation of the FHA and FA sol-gels. Optimisation of the chemistry and subsequent characterisation of the sol-gels was carried out using, X-ray Diffraction (XRD) and Differential Thermal Analysis (DTA). Following crystallisation the sol-gels produced were further investigated using Scanning Electron Microscopy (SEM) and Ion Chromotography. Bond strengths to Ti were investigated using an Instron Universal Load Testing machine and biological behaviour was assessed using cellular proliferation with human osteosarcoma cells and alamarBlue^TM assay. Statistical analysis where applicable was performed with a two way analysis of variance and post hoc testing with a Bonferroni correction. Results: (1) 99% phase pure HA, FHA and FA were produced. (2) Increasing fluoride incorporation; (a) lowered the crystallisation temperature, unit cell size and dissolution rate; (b) increased the coating thickness of the sol-gel and cellular proliferation (p<0.01). (3) Coating speed inversely influenced the coating thickness. (4) Increasing fluoride ion substitution and heating temperature significantly increased bond strength to Ti (p<0.01). (5) Increasing the firing temperature of the HA, FHA and FA sol gels decreased the dissolution rate. Conclusion: A refined method has been developed for the production of HA, FHA and FA by the sol-gel technique. These materials offer great possibilities as implant coatings and bone grafting materials which can be potentially tailored to meet different clinical requirements.