Graphene oxide based coatings on nitinol for biomedical implant applications: effectively promote mammalian cell growth but kill bacteria

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Abstract
An important clinical challenge is the development of implant surfaces which have good integration with the surrounding tissues and simultaneously inhibit bacterial colonization thus preventing infection. Recently, graphene oxide (GO) a derivative of graphene, has gained considerable attention in the biomedical field owing to its biocompatibility, surface functionalizability and promising antimicrobial activity. In this study gelatin-functionalized graphene oxide (GOGel) was synthesized by a simple one step modification where GO and GOGel were used to develop surface coatings on nitinol substrates. Mouse osteoblastic cell (MC3T3-E1) functions including cell attachment, proliferation and differentiation were investigated on GO-based coatings. The results indicated that MC3T3-E1 cell functions were significantly enhanced on both GO coated nitinol (GO@NiTi) and GOGel coated nitinol (GOGel@NiTi) compared with the control nitinol without coating (NiTi). Especially, the GOGel@NiTi surface exhibited the best performance for cell adhesion, proliferation and differentiation. Additionally the antimicrobial property of GO-based coatings against E. coli was studied with the evaluation of colony forming units (CFU) counting, live/dead fluorescent staining and scanning electron microscope (SEM). We found that the growth of E. coli was inhibited on GOGel@NiTi and particularly on GO@NiTi. SEM images revealed that the cell membrane of bacteria lost their integrity and live/dead fluorescent images confirmed the low live/dead ratio of E. coli after incubation on GOGel@NiTi and GO@NiTi. We conclude that GO-based coatings on NiTi combine the antimicrobial activity and improved biocompatibility and therefore present a remarkable potential in biomedical implant applications.

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