Purpose:
To develop a process to measure the biological activity of an intact layer of adsorbed lysozyme at the surface of hydrogel contact lens materials.
Methods:
We use this technique to measure the time dependent amount and activity of adsorbed lysozyme on a number of commercial contact lens biomaterials during the first 2 hours of protein interaction with the material surface. The quantity of adsorbed lysozyme is measured using standard radiolabeled protein. The activity of the surface adsorbed protein is measured using a standard micrococcal activity assay, with extra steps to distinguish between protein on the surface and protein in solution. We use the measured quantities in our experiment to estimate a total layer activity.
Results:
The amount of active protein is essentially independent of the total protein, and is similar to what one would expect from monolayer coverage. We calculate the amount for a theoretical monolayer of lysozyme on a contact lens to be 692-1035ng, depending on the orientation of lysozyme, and thus can calculate a percentage of active lysozyme in a surface layer for each lens type. The percent of active lysozyme for senofilcon A, lotrafilcon B, and comfilcon A were 3-4, 4-5, and 2-3 percent respectively. Balafilcon A had the highest percent activity in a surface layer for all the silicone hydrogels tested at 30-45 percent. Etafilcon A was the only conventional hydrogel tested and showed 78-117 percent activity in a surface layer of lysozyme, which was the highest of all lens materials tested.
Conclusions:
This study has established an effective technique to evaluate the activity of an intact lysozyme coating on a biomaterial. Our results show that protein can rapidly deposit and can rapidly lose its biological function on biomaterials in as little as 10 seconds of protein-surface interaction. Despite the simplicity of the technique, to the best of our knowledge this is the first report quantifying the biological activity of an intact layer of surface-adsorbed protein on hydrogel materials.
Keywords: contact lens • protein structure/function