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Saad Bhamla, Claire Elkins, David Bergsman, Gerald Fuller; Effect of Protein Adsorption on Dewetting and Corneal cell adhesion on Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2013;54(15):488.
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© ARVO (1962-2015); The Authors (2016-present)
We discuss the influence of lysozyme adsorption on contact lenses using two different experimental approaches - dewetting on lenses and adhesion of corneal cells to a contact lens substrate.
Dewetting is studied by stretching a contact lens flat on an elevation stage built on a miniature Langmuir trough. By raising the stage, the lens surface captures a sessile droplet coated with DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) at surface pressure of the eye (20-25 mN/m). Liquid is slowly drained and dewetting dynamics captured using a CCD camera. Corneal cell adhesion is studied using an apparatus developed in the Fuller lab. A contact lens is descended upon a cultured monolayer of live epithelial cells. After a waiting period, the contact lens is sheared laterally relative to the bottom plate, subjecting the cells to a controlled strain while a force transducer measures the applied stress. Our rheometer-based design allows precise control over the strain down to 0.001 strain units, as well as highly sensitive measurement of the applied stress. The entire apparatus is mounted on a DIC microscope, allowing live cell imaging.
Two commercial lenses are tested for both experimental approaches. In the absence of DPPC, clean contact lenses were highly hydrophilic and resisted dewetting, whereas when soaked overnight in 1 mg/ml lysozyme showed substantial dewetting. Standard deviation across 4 samples was about 10%. In the presence of DPPC, dewetting is stabilized on the lysozyme adsorbed contact lens surface. For clean lenses, a 200% step-strain produces a low force response indicating no attachment of cells to the lens substrate. Whereas for contact lens soaked overnight in 1 mg/ml lysozyme solution, a higher maximum force is exhibited, indicating relatively greater cell adhesion to the contact lens. This stress relaxes quickly to a new equilibrium value, likely due to the re-organization and relaxation of the adhered corneal cells.
Our findings show that adsorbed lysozyme decreases the hydrophilicity of the lens surface leading to dewetting. Deposition of lysozyme also makes the lens surface more attractive to cell adhesion.
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