Stability and cellular responses to fluorapatite–collagen composites

Fluorapatite (FA)–collagen composites were synthesized via a biomimetic coprecipitation method in order to improve the structural stability and cellular responses. Different amounts of ammonium fluoride (NH4F), acting as a fluorine source for FA, were added to the precipitation of the composites. The precipitated composites were freeze-dried and isostatically pressed in a dense body. The added fluorine was incorporated nearly fully into the apatite structure (fluoridation), and a near stoichiometric FA–collagen composite was obtained with complete fluoridation. The freeze-dried composites had a typical biomimetic network, consisting of collagen fibers and precipitates of nano-sized apatite crystals. The human osteoblast-like cells on the FA–collagen composites exhibited significantly higher proliferation and differentiation (according to alkaline phosphatase activity) than those on the hydroxyapatite–collagen composite. These enhanced osteoblastic cell responses were attributed to the fluorine release and the reduced dissolution rate.