Hybrid graphene oxide/amorphous carbon coatings and their effect on the viability and toxicity of different cell types

Herein, we explored the possibility to develop hybrid graphene oxide/amorphous carbon (GO/a-C) coatings with different oxidation degree and analysed the influence of surface oxygen composition on biocompatibility. GO/a-C films were obtained by plasma treatment of GO-coated PEEK substrates using different relative amounts of methane and oxygen as gaseous precursors. The chemical surface composition of the coatings, including oxygen abundance and nature of the oxygen-containing groups, was analysed by X-ray photoelectron spectroscopy, and cell response to the sample materials was assessed by viability and cytotoxicity assays on two different cell types, including human osteoblasts (hFOB) and human gingiva fibroblasts (hGF). The cells presented partially decreased viability on plasma-treated samples respect to the untreated PEEK substrate, but no significant evidence of cell toxicity was shown, with LDH release largely below 20% for all the materials. A distinct cell-specific cytotoxicity response was observed. No significant effects were registered on hGF cells, suggesting that hGF cells were not sensitive to the different oxygen surface content of the coatings. On the other side, hFOB showed relatively higher toxicity when cultured on the samples with high surface oxygen concentration. Human osteoblasts cell toxicity increased considerably with increasing content of carbonyl and carboxyl groups on the surface, suggesting that these functional groups had an important role in inducing oxidative stress in hFOB cells.