behaviours, such as charged polymer brushes-grafted hollow silica
nanoparticles [7], and poly(3-sulfopropyl methacrylate potassium
salt) brushes grafted poly(N-isopropylacrylamide) microgels [8].
Although low friction coefficient was obtained by these lubricants,
the conditions of the friction pair (i.e., steel-to-steel and PDMS-toSi
in the studies) were greatly different from that in the artificial
joints (i.e., Ti6Al4V-to-UHMWPE). In a research of fabricating
artificial cartilage, mixing 15 wt% polyvinylpyrrolidone (PVP) in
polyvinylalcohol (PVA) hydrogel was found to decrease the friction
coefficient by about 30% [6]. However, it is still unclear whether
some lubricants could improve the tribological properties of the
Ti6Al4V–UHMWPE friction pair