Supplementary material from "Fluid Confinement Within a Branched Polymer Structure Enhances Tribological Performance of a PMPC-Surface-Modified Contact Lens"

The poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC)-modified, silicone hydrogel, contact-lens material lehfilcon A 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 contact-lens 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 (AFM-IR) 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 behavior 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 contact lenses showed this effective lubrication to be maintained after one month of daily wearing.