ORIGINS OF THE LOW FRICTION EXHIBITED BY BIOCOMPATIBLE ZWITTERIONIC POLYMER BRUSHES

Surface grafted polymer brushes comprised of poly(2-(methacryloyloxy)ethyl phosphorylcholine) (pMPC) have a attracted the attention of researchers due to their unique lubricating properties. These biocompatible materials exhibit friction coeffcients orders of magnitude lower than those used in current artificial joints yet also readily withstand wear. is property is believed to arise from a mechanism called hydration lubrication where the polymer brushes tightly bind surrounding water molecules yet still offer a fluid-like response to shear. However, the molecular origins of this behavior, specifically where and how the water molecules bind, remain unknown. Here, we use molecular dynamics simulation to study a pMPC brush in aqueous solution. Our results show that the phosphate group is the predominant contributor to the hydration lubrication mechanism but that the choline group may also serve a stabilizing role, which potentially contributes to the brush’s remarkable durability.