Exploring the potential of hyaluronic acid as a wetting agent in model contact lens materials

A serious problem with contact lenses remains the uptake of tear film components particularly proteins and lipids. These deposits can cause discomfort for the wearer, encourage the adhesion of bacteria, as well as complications including giant papillary conjunctivitis. Surface hydrophilicity is a significant contributing factor to protein deposition and increasing hydrophilicity has been shown to decrease deposition. Previous work has shown that when hyaluronic acid, a hydrophilic muco-polysaccharide. is incorporated into model contact lens materials. hydrophilicity increases leading to a significant decrease in protein uptake. Therefore. based on these promising results. the present research further examines the potential of hyaluronic acid as a wetting agent in model contact lenses.;To decrease the complexity of the synthetic process, all three hydrogel types were prepared using Me-HA in a one pot procedure. The degree of methacrylation as well as the molecular weight of the HA were varied. The presence of the HA was confirmed by XPS and FTIR-ATR. As with the post loaded gels, the presence of the HA was found to increase hydrophilicity. In some cases. the hydrogels prepared using this method were more hydrophilic than those prepared by post loading. Definite effects of degree of methacrylation and HA molecular weight were observed with these materials. although in all cases. a decrease in lysozyme sorption was observed with HA modification.;When HA was incorporated into model contact lens materials as a releasable wetting agent using molecular imprinting techniques where HA was added to the monomer mixture as a template molecular during synthesis. it was released for long periods of time. From pHEMA gels. HA was released for 21 days and from silicone hydrogels for more than 7 weeks. In the pHEMA and pHEMA/TRIS hydrogels. the release of HA significantly decreased lysozyme sorption. In the case of the pHEMA hydrogels. 35 kDa HA was more effective at decreasing sorption than 910 kDa HA Lysozyme sorption increased in DMAA/TRIS hydrogels during the release. surprisingly. but the amount of protein deposited was significantly less than for either of the other materials.;The competing effects of HA and MAA. a polymer found in commercially available lenses. in all three materials prepared using dendrimer crosslinking was examined. The incorporation of MAA alone did not increase the EWC in any of the materials but the combination of MAA and HA increased swelling compared to HA alone. In pHEMA hydrogels. the amount of HA in the materials decreased with the addition of MAA but it increased in the silicone hydrogels. The presence of MAA in the gels decreased surface hydrophobicity and the materials containing both MAA and HA were more hydrophilic that those containing only MAA or only HA The introduction of MAA into the gels substantially increased lysozyme sorption, but the materials containing MAA and HA had significantly lower sorption than those containing only MAA. In the DMAA/TRIS hydrogels, the incorporation of MAA had no effect on sorption in the HA-containing materials. (Abstract shortened by UMI.);Model conventional (pHEMA) and silicone (pHEMA/TRIS, DMAA/TRIS) hydrogel contact lenses were prepared and HA was incorporated using three different methods. In general, the results suggest that with pHEMA hydrogels prepared using the post modification dendrimer incorporation method, lysozyme sorption and denaturation were reduced with the presence of HA in the gels. There did not appear to be a significant molecular weight effect. Similar results were obtained with the pHEMA/TRIS hydrogels and the DMAA/TRIS gels. The latter gels are significant because they have a much higher silicone content than the former and are therefore more representative of commercial materials. Confocal microscopy studies suggest that the location of HA within these gels is impacted by both HA molecular weight and hydrogel type and together with the denaturation results demonstrate the importance of HA mobility in controlling protein interactions. Surprisingly, in the DMAA/TRIS gels, while lysozyme deposition was significantly decreased by the presence of HA, a decrease in denaturation was only observed when the gels were prepared with at least 5% methacrylic acid (MAA), an effect that warrants further investigation.