Synthesis and biocompatibility of hydroxyapatite in a graphite oxide matrix

Though hydroxyapatite has the ability to promote bone growing, devices based on OHAp are mechanically weak and need to be reinforced for load bearing applications or in the manufacturing of scaffolds for bone regeneration. Graphite (Gr) could provide appropriate reinforcement properties to OHAp without being deleterious for the biocompatibility of the system. This paper describes an accelerated synthesis of the OHAp with ultrasonic agitation in the presence of functionalized graphite (GO). The toxicity of the Graphite and the GO-OHAp system is evaluated. GO-OHAp was produced by a wet chemical reaction involving CaCl2 and Na2HPO4. The calcium salt solution was added first and the solution sonicated for I hour, before repeating the operation with the phosphate solution. Biocompatibility was tested by using a primary cell culture of HOB (ECCAC). The disappearance of the maximum at 2 theta = 26.32 degrees corresponding to the d002 plane of graphite and the appearance of the maximum at 2 theta = 13.2 degrees in the XRD patterns is related with an expansion of the grapheme sheets from 0.34 nm to 0.59 nm and it has been used to assess the graphite oxidation. The OHAP on GO growing has been confirmed by the appearance of a broad peak centred at 2 theta = 31.5 degrees and a sharpened peak at 2 theta = 26.0 degrees characteristic of low crystalline apatites. Although the employed graphite can be considered biocompatible, cellular viability is significantly improved by the presence of apatite.