Nano-morphology, crystallinity and surface potential of anatase on micro-arc oxidized titanium affect its protein adsorption, cell proliferation and cell differentiation

Using a novel microwave-assisted hydrothermal (MW) process we created nano-scale anatase on micro-arc-oxidized (MAO) titanium surface. The morphology/crystallinity and surface potential of the anatase which altered by Ca/P ions concentrations and pH in the MW medium were characterized by atomic force microscopy, Kelvin probe force microscopy, Raman spectrometer, and x-ray photoelectron spectroscopy. The surface of MWDD (processed in DD water) and MWCP (in neutral pH medium with Ca/P ions) are covered with anatase spikes, which enhance their nano-roughness, hydrophilicity, and possess lower surface potential than other groups. The nano-precipitates on surface of MWCP9 and MWCP11 (processed in medium containing Ca/P ions at pH 9 or pH 11) were mainly amorphous anatase with less P ions. The protein adsorption of negatively charged bovine serum albumin was higher in MWDD and MWCP groups which possess lower surface potential. The adsorption of positively charged histones on the surface of MWCP11 was higher compared to the other groups. The osteogenic characterizations of D1 mice bone marrow mesenchymal stem cells co-cultured for 1, 7, and 14 days were measured by ALP and osteopontin assays. Although MW groups revealed comparable viability of D1 mice bone marrow mesenchymal stem cells to MAO group, their superior hydrophilicity and higher protein adsorption, thus regulating the differentiation of osteoprogenitor stem cells demonstrating higher ALP and osteopontin secretion after 7 days and 14 days. The nanoscale topography, crystallinity and surface potential change the hydrophilicity and protein adsorption on the MW treated titanium surface, thus regulating the differentiation of osteoprogenitor stem cells in vitro.