Effect of frequency on the structure and cell response of Ca- and P-containing MAO films

The Ca- and P-containing MAO films were prepared on titanium substrate at different frequencies (100-5000 Hz) and were characterized by SEM, XRD, XPS and contact angle goniometer. For in vitro test, the rat bone marrow mesenchymal stem cells (rMSCs) were seeded on the films. The fluorescence microscopy and the PicoGreen assay were used to determine the cell initial adhesion and proliferation. It shows that the frequency of the MAO affected the crystallinity, composition, morphology and wetting ability of the oxidation film. At a high frequency, the crystallinity decreased, and the content of Ca and P increased. The structure formed at a high frequency - there were many smaller pores on the wall of the larger ones and many inner pores in the film - could improve the connectivity of the film. The wetting ability of the film was also improved by increasing the frequency. The mechanism of how the frequency of the MAO process could influence the oxidation film was discussed. It could be explained by the theory of electron avalanche and the phenomenon of secondary breakdown. In vitro test showed that the film formed at 5000 Hz was more favorable for the initial cell attachment and proliferation.