title: Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol-gel method. Optimisation, characterisation and rheology.
abstract: OBJECTIVE
  Currently, most titanium implant coatings are made using hydroxyapatite and a plasma spraying technique. There are however limitations associated with plasma spraying processes including poor adherence, high porosity and cost. An alternative method utilising the sol-gel technique offers many potential advantages but is currently lacking research data for this application. It was the objective of this study to characterise and optimise the production of Hydroxyapatite (HA), fluorhydroxyapatite (FHA) and fluorapatite (FA) using a sol-gel technique and assess the rheological properties of these materials.
  
  
  METHODS
  HA, FHA and FA were synthesised by a sol-gel method. Calcium nitrate and triethylphosphite were used as precursors under an ethanol-water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the sol-gel derived FHA and FA. Optimisation of the chemistry and subsequent characterisation of the sol-gel derived materials was carried out using X-ray Diffraction (XRD) and Differential Thermal Analysis (DTA). Rheology of the sol-gels was investigated using a viscometer and contact angle measurement.
  
  
  RESULTS
  A protocol was established that allowed synthesis of HA, FHA and FA that were at least 99% phase pure. The more fluoride incorporated into the apatite structure; the lower the crystallisation temperature, the smaller the unit cell size (changes in the a-axis), the higher the viscosity and contact angle of the sol-gel derived apatite.
  
  
  CONCLUSIONS
  A technique has been developed for the production of HA, FHA and FA by the sol-gel technique. Increasing fluoride substitution in the apatite structure alters the potential coating properties.
authors.affiliation: Plymouth University Peninsula Schools of Medicine and Dentistry, Universities of Exeter & Plymouth, Research Way, Plymouth, United Kingdom.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Tredwin
authors.forename: Anne M
authors.initials: AM
authors.lastname: Young
authors.forename: George
authors.initials: G
authors.lastname: Georgiou
authors.forename: Song-Hee
authors.initials: SH
authors.lastname: Shin
authors.forename: Hae-Won
authors.initials: HW
authors.lastname: Kim
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Knowles
mesh_terms: D001031:Apatites / Q000138:chemical synthesis*; D004055:Differential Thermal Analysis / Q000379:methods*; D017886:Durapatite / Q000138:chemical synthesis*; D005459:Fluorides / Q000737:chemistry*; D006882:Hydroxyapatites / Q000138:chemical synthesis*; D044367:Phase Transition; D012212:Rheology / Q000379:methods*; D013499:Surface Properties; D014783:Viscosity; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D001031:Apatites; D006882:Hydroxyapatites; C028869:fluor-hydroxylapatite; D017886:Durapatite; C025105:fluorapatite; D005459:Fluorides