Protein-lipid interaction on the surface of a rigid gas-permeable contact lens in vitro.

PURPOSE: To investigate the mechanism of protein-lipid interactions responsible for biofilm formation on the surface of rigid gas-permeable contact lenses in vitro.
METHODS: Two types of new, never-worn rigid gas-permeable contact lenses (siloxanyl alkyl acrylate and fluorosiloxanyl alkyl acrylate) were individually incubated in a protein only, lipid only, or combination protein-lipid artificial tear solution for 24 h at 37 degrees C with constant stirring. Deposited lipids were removed with a methanol based extraction procedure, separated using high performance thin layer chromatography and quantitatively analyzed densitometrically. Deposited proteins were extracted with 4M urea, separated using gel electrophoresis and quantitatively analyzed densitometrically.
RESULTS: Lipid deposition on rigid gas-permeable contact lenses is dependent on lens matrix hydrophobicity while protein deposition is minimal and not material-dependent. The presence of lipid in the artificial tear solution enhances protein deposition on both types of rigid gas-permeable materials examined. The presence of protein in the artificial tear solution decreases lipid deposition on a siloxanyl alkyl acrylate lens.
CONCLUSIONS: The hydrophobic nature of rigid gas-permeable contact lenses causes them to be more prone to lipid than to protein deposition. When both types of molecule are present in an artificial tear solution, the hydrophobic sites of the lipid molecules are attracted to the lens matrix while the more hydrophilic sites are repelled by the matrix and, thereby, exposed to the aqueous surroundings. Thus, lipid binding to rigid gas-permeable contact lenses reduces the hydrophobicity of the lens surface allowing protein to bind. The bound deposited hydrophilic protein then alters subsequent binding of both protein and lipid.