F-substituted hydroxyapatite nanopowders: Thermal stability, sintering behaviour and mechanical properties

Fluorine-substituted hydroxyapatites are considered promising materials for bone scaffolding. In this study a systematic investigation on F-half substituted hydroxyapatite (F-HAp, Ca(10)(PO(4))(6)OHF) obtained by precipitation is reported. Results on composition analysis, thermal behaviour, and sinterability are presented for a comparison with the respective pure hydroxyapatite. Samples were characterised by electron microscopy, induced coupled plasma-atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N(2) adsorption measurements, X-ray diffraction and dilatometry. A semicrystalline F-substituted hydroxyapatite powder made up of needle-like nanoparticles was obtained. Notwithstanding that it was thermally stable up to 1300 degrees C, it was sintered at relatively low temperatures obtaining a very fine microstructure with a relevant nanoporosity, beneficial in view of cell adhesion and in-growth. Hardness, elastic modulus and toughness of produced samples were investigated by Vickers-Knoop microhardness testing. Significant improvements of the mechanical properties were observed for the F-substituted hydroxyapatite, in comparison with pure hydroxyapatite. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved