Barrier Graphene Oxide on a CoCr Alloy via Silane/GO Covalent Bonding and Its Electrochemical Behavior in a Simulated Synovial Fluid Electrolyte

In this work, impermeable and ultrathin surface nanomodifications for joint applications based on graphene oxide (GO) are assembled on CoCr surfaces via covalent immobilization between GO nanosheets and silane monolayers. Two silane curing temperatures, 45 °C for 24 h and 75 °C for 30 min, on CoCr surfaces and two incubation times for GO suspension, 12 h and 24 h, on silanized CoCr surfaces are prepared. Electrochemical characterization is performed using electrochemical impedance spectroscopy (EIS) in a 3 g/L hyaluronic acid solution. Results show that GO nanosheets immobilized with silane covalent bonding confer impermeability of sp2 networks on GO and strong interfacial adhesion of GO sheets anchored to silanized CoCr via organosilane chemistry, which prevents the permeation of oxidant species at the metal interface. At short GO incubation times (12 h), the Rs values decrease with the immersion time, indicating that small species, such as metal ions, are able to diffuse through the interlayer gaps of nanolayers. Longer GO incubation times (24 h) favor the formation of bonds between the GO and the silane, thus slowing downdiffusion and metal ion release into the medium. EIS data confirm the impermeability of GO nanocoatings with lengthening GO incubation time for medical application of metallic implants.