Characterization and cytocompatibility of polydopamine on MAO-HA coating supported on Mg-Zn-Ca alloy

Magnesium has been suggested as a potential biodegradable metal for the usage as orthopaedic implants. However, high degradation rate in physiological environment remains the biggest challenge, impeding wide clinical application of magnesium-based biomaterials. In order to reduce its degradation rate and improve the biocompatibility, micro-arc oxidation coating doped with HA particles (MAO-HA) was applied as the inner coating, and polydopamine (PDA) film was synthesized by dopamine self-polymerization as the outer coating. The microstructure evolution of the coating was characterized using scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray diffraction analyses (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results showed that PDA film had covered the entire surface of MAO-HA coating and the pore size of MAO-HA coating decreased. The root mean square (RMS) roughness of PDA/MAO-HA coatings was approximately 106.46nm, which was closer to the optimum surface roughness for cellular attachment as compared with MAO-HA coatings. Contact angle measurement indicated that the surface wettability had been transformed from hydrophobic to hydrophilic due to the introduction of PDA. The PDA/MAO-HA coatings exhibited better corrosion resistance in vitro, with the self-corrosion potential increasing by 150mV and the corrosion current density decreasing from 2.09x10(-5)A/cm(2) to 1.46x10(-6)A/cm(2). In hydrogen evolution tests, the corrosion rates of the samples coated with PDA/MAO-HA and MAO-HA were 4.40 and 5.95mm/y, respectively. MTS assay test and cell-surface interactions experiment demonstrated that PDA/MAO-HA coatings exhibited good cellular compatibility and could promote the adhesion and proliferation of MC3T3-E1 cells.