Development of hydroxyapatite thin film on titanium substrate by electrophoretic deposition

Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO₂-CaO-P₂O₅-B₂O₃ bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO ₃ for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10-20 V for 1∼20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 μm (0.5 %, 20 V, 10 min) to 4∼5 μm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a codeposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.