The management of contact lens discomfort remains a challenge leading to the increased contact lens dropout rates. Tear protein accumulates on the lens surfaces with different configurations observed are correlated to the lens friction, with the improved comfort experienced by reduced surface friction in the eye. However, protein adsorption is a complex process with the combined protein-protein interactions (PPI) and protein-surface interactions (PSI) involved, which is difficult to explain the complicated tribological behavior in terms of protein structural shifts alone on lens surfaces. On the other hand, the type of solvent-exposed side chains from specific protein conformations on lens surfaces should be more important to the lens friction involved. We aim to investigate the correlation between the structure-related side-chain exposure and corresponding lens friction of adsorbed tear proteins on lens surfaces under varied PPI and PSI. Albumin was the model protein adsorbed onto the conventional lens material. Such as polymethylmethacrylate (PMMA) or the poly-2-hydroxyethyl methacrylate (PHEMA) surfaces applied here. Adsorption was conducted under varying protein solution concentrations to saturate the model surface to change the PPI effects over a wide range. Our results indicate that PPI effects help stabilize protein structures on both surfaces. When PPI is minimized, a distinct correlation was observed between the surface friction and the hydrophobicity of structure-related side-chain exposure of albumin on lens surfaces depending on the different PSI involved. At a fundamental understanding, our results would provide insights for developing new lens materials or the lens care solution designs to reduce the lens discomfort.
Keywords: Albumin; Conformational changes; Friction coefficient; PHEMA; PMMA; Protein-protein interactions; Protein-surface interactions; Solvent-exposed side chains.
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