Growth Mechanism and Structural Correlations of Hydroxyapatites on Surface Functionalized Carbon Fibers

In this study, hydroxyapatites were deposited on surface modified carbon fibers using a simulated body fluid; different amounts of COOH functional group were formed on the fiber surfaces by different degrees of KOH pretreatment. The effect of the surface functional group on the growth features of the hydroxyapatite crystals was analyzed, and the detailed stacking and structural correlations of the grown crystals to the substrate carbon fibers were examined to realize the mineralization mechanism. It was observed that hydroxyapatite nanocrystallites longitudinally constructed a crystal chain along [211] direction; several aligned crystal chains were then bundled to form a spindle structure which ultimately composed differently featured coatings. A mild KOH pretreatment created a small amount of functional group that activated few sites for hydroxyapatite nucleation compliant to the COOH bond structure, yielding a horizontally oriented olive structure under an orientation correlation HAP [112] or [211]//C [100]. A severer treatment induced more nucleation sites; attributed to the repulsion between the close COO- ligands, the bond structure was bent, leading to the radially aligned and ball-featured growth of hydroxyapatites with a different correlation HAP [112] or [211] //C [002]. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.064201jes]