Mechanically robust nitrogen-rich plasma polymers: Biofunctional interfaces for surface engineering of biomedical implants

Surface bio-functionalization through covalent attachment of bioactive molecules is a promising approach to facilitate rapid bone-implant integration. Radical-rich plasma polymer interlayers are highly attractive as platforms that enable covalent biofunctionalization in a single-step, reagent-free manner. However, fabrication of mechanically robust plasma polymer films, particularly for biomedical devices that operate in corrosive body fluids, is not trivial. Here we show a facile approach to tune the robustness of ion-assisted plasma polymer (IPP) films via simply varying the nitrogen atomic concentration incorporated into their structure. X-ray photoelectron spectroscopy data indicated that the total sp3/sp2 ratio of carbon atoms decreases in the films with increasing nitrogen atomic concentration. Electron recoil detection analysis data provided evidence that the hydrogen content decreases as the nitrogen atomic concentration increases. Nano-indentation and nano-scratch tests, together with long-term stability studies in simulated body fluid, showed a strong correlation between the nitrogen atomic concentration and the robustness and stability of the films. We confirmed the potential of the optimized, nitrogen-rich IPP film to regulate osseointegration by covalent attachment of fibronectin followed by quantifying primary osteoblast attachment and proliferation. The IPP films developed here hold great potential as robust interfaces for biomimetic surface engineering of implantable biomedical devices, in particular bone implants.