Articular Cartilage-Inspired Surface Functionalization for Enhanced Lubrication

Natural articular cartilage has excellent superlubrication property, and it is attributed to the hydration lubrication mechanism of the charged biomacromolecules which extend from the cartilage surface to form a brush-like layer. In this study, a bioinspired brush-like polyelectrolyte, namely poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), is grafted onto the SiO2 wafer and polystyrene (PS) microsphere via surface-initiated polymerization to enhance the lubrication performance. The characterization of Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, water contact angle, and scanning electron microscopy demonstrates that the PMPC polymer brushes are successfully modified onto the substrates. Furthermore, the lubrication test performed using atomic force microscope, with the PMPC-grafted SiO2 wafer and PMPC-grafted PS microsphere as the contact tribopair, shows that the PMPC-functionalized surfaces significantly reduce friction coefficient under different test conditions. The tenacious water hydration shells formed surrounding the zwitterionic charges of PMPC polymer brushes are responsible for the reduced friction coefficient, which could support high pressures without being squeezed out under loading. In summary, the articular cartilage-inspired surface functionalization method can be used to modify various substrates for enhanced lubrication.