Protein Rejecting Hyaluronic Acid-Containing Hydrogel Materials

Abstract

Recently new contact lens materials have been introduced which are said to improve comfort by incorporating wetting agents either in a releasable or nonreleasable form. However, there is little information in the literature to demonstrate whether these claims are indeed true. In the present work, model lens materials based on poly(2-hydroxyethyl methacrylate) (pHEMA) and methacryloxypropyltris (trimethylsiloxy) silane(TRIS) were developed which incorporate releasable or crosslinked and therefore physically entrapped hyaluronic acid (HA) of various molecular weights as a wetting agent. Studies showed that uncrosslinked high molecular weight HA exhibited burst release kinetics with 80% release in less than 20 hours. While applicable for use in daily wear cycles, releasable wetting agents certainly would have very little effect on extended wear cycles, a common mode of wear. Protein adsorption results suggest however that the wetting agent resulted in no statistical change over the control material. Crosslinked and therefore physically entrapped HA, despite being only present in very small amounts, showed consistently lower water contact angles over four hours in comparison to controls, indicating that HA is present at the interface and was not being released over time. The presence of HA in the material was further confirmed by increases in the glass transition temperature measured by differential scanning calorimetry, increases in the stiffness as measured by Instron testing, and slight changes observed m both x-ray photoelectron spectroscopy and Fourier transform infrared spectra. This crosslinking procedure appeared to have no effect on optical transparency using 35 kDa HA whereas small decreases in optical transparency at higher wavelength were noted for the 169 kDa HA crosslinked material as measured by UV spectrophotometry. Most importantly, protein adsorption results indicated that the adsorption of all proteins studied was considerably decreased by the presence of the small amount of crosslinked HA. It is hypothesized that HA acts in a similar manner as PEO protein repulsion, where free HA chains are able to produce an environment which highly rejects protein adsorption. Significant decreases in lysozyme adsorption were also observed on model silicone hydrogel materials. The results suggest that these materials have significant potential for application in contact lens applications.