Fluid confinement within a branched polymer structure enhances tribological performance of a poly(2-methacryloyloxyethyl phosphorylcholine)-surface-modified contact lens.

The poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-modified, silicone hydrogel, contact lens (CL) material has previously been demonstrated to have a lubricious, antifouling and ultra-soft surface. This study provides confirmatory identification of the outer polymer structures on this CL surface as branched PMPC structures. It further aims to understand their role in providing enhanced tribological performance via fluid confinement. A combination of scanning transmission electron microscopy and atomic force microscopy infrared spectroscopy has been used to achieve both morphological and chemical confirmation of branched PMPC structures resembling the polysaccharide species present on the surface of the cornea. Measurements of the fluid-confinement behaviour of this layer, by means of nanoindentation experiments, show it to resist squeeze-out of the interstitial fluid, thereby boosting lubrication by virtue of a fluid-load-support mechanism. Tribological testing of CLs showed this effective lubrication to be maintained after one month of daily wearing.