Investigating Molecular\nInteractions between Mucin\nand Contact Lens Thin Films Using Nuclear Magnetic Resonance

Poly(2-hydroxyethyl methacrylate) (PHEMA) and polyvinyl­pyrrolidone\n(PVP) are common polymers used in contact lens materials. In these\nsystems, PHEMA forms the hydrogel network and PVP is used as a wetting\nagent. These lens materials, like other implantable devices, suffer\nfrom interactions with biological macromolecules that ultimately foul\nthe surface of the lens. Despite the widespread adoption of contact\nlenses, the mechanisms of protein adsorption onto lenses are not well\nunderstood. To investigate the interactions responsible for fouling\non contact lens materials, we developed a spin-coating apparatus to\ndeposit thin polymer films onto NMR tube surfaces. We then used direct\nsaturation compensated (DISCO) NMR on PHEMA-coated NMR tubes to investigate\nmucin binding at the surface of the coatings and the effect of varying\nPVP concentrations. Using this technique, this study was able to characterize\nthe binding profiles of PHEMA-only and PHEMA+PVP hydrogels. The results\nshow that the mucin-binding profile of PHEMA evolves as the PVP content\nincreases. In the absence of PVP, the protons in the PHEMA backbone\ninteract with mucin. However, when PHEMA and PVP form a hydrogel network,\nthe protons on the PHEMA side chain become mucoadhesive in addition\nto the backbone. When the PVP content is further increased, only the\nside chain protons retain their interaction. Interestingly, the NMR\nspectra of PHEMA+PVP hydrogels suggest that PVP preferentially accumulates\nwithin the PHEMA matrix, with relatively little presenting at the\nsurface of the hydrogels. In conjunction, SEM imaging of the PHEMA\nand PHEMA+PVP hydrogels shows that an increase in porosity accompanies\nthe change in mucin-binding behavior, indicating that the change in\nmorphology is correlated to the change in mucin-binding behavior rather\nthan solely the change in composition. Overall, this study develops\na tool to study the interactions between macromolecules and polymeric\nsurfaces with atomic precision, uncovering structure–activity\nrelationships that govern mucoadhesion of polymeric hydrogels.