Improved bio-physical performance of hydroxyapatite coatings obtained by electrophoretic deposition at dynamic voltage

This study investigates the effects of the electrophoretic deposition process (EPD) at dynamic voltage on the physical and biological characteristics of hydroxyapatite (HA) coatings. HA powder is synthesized and used for preparation of HA/ethanol suspension which is subsequently characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), zeta potential and particle size analyses. Samples are prepared from commercially pure titanium (CP-Ti) substrates and coated with HA using EPD at dynamic voltage that keeps a constant depositional rate by adjusting the current and electrical field during the process. The HA-coated samples are dried and sintered at 800 °C for 2 h to densify the coatings. The XRD, scanning electron microscopy (SEM), EDS and adhesion tests are used to characterize the coated samples. The cross-sectional SEM images indicate that the thickness of coatings enhances as the current increases from 0.07 to 0.35 mA. The coatings are more uniform, packed and non-cracked at lower currents while HA particles start to arrange in a highly porous structure and show non-uniform, cracked and non-stable coatings as the current increases. The results also demonstrate that the best adhesions for the coatings are obtained at lower currents of 0.07 and 0.15 mA. Morphological studies and cell biological experiments are conducted using MG63 cells cultured on the HA-coated sample with the best overall physical performance. The number of attached and proliferated cells on the selected HA-coated sample is higher than on the non-coated titanium sample and culture plate used as control. There are significantly higher ALP activity and better cytoskeleton organization of cells on the HA-coated sample. This study shows that the EPD process at dynamic voltage can influence the structure and morphology of the coatings; therefore, substrate engineering can be used to improve and control cell-substrate interactions.