In Vitro Friction of Contact Lenses & Model Contact Lens Biomaterials: Effect of Proteoglycan 4

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Abstract

Contact lenses are associated with discomfort and dry eye in many users. Friction is currently the only variable known to correlate with contact lens discomfort. Therefore, one approach to improve the performance of contact lenses could be to reduce their friction. Proteoglycan 4 (PRG4) is a mucin-like glycoprotein that is naturally produced at, and lubricates, the ocular surface. Hyaluronan (HA) is a repeating disaccharide produced in the body that has also been shown to function as a boundary lubricant at biological interfaces. It is possible that PRG4 and HA could be used as boundary lubricants for contact lenses. The interaction between these molecules and contact lens materials have not been thoroughly characterized.

The motivation of this thesis was to contribute to the development and use of PRG4 and HA for contact lens hydrogels using physiologically relevant in vitro friction testing techniques.

Novel and previously characterized methods were used to synthesize model contact lens hydrogels. in vitro friction testing was used to evaluate the boundary lubrication of PRG4 and HA for model contact lens materials (conventional: pHEMA; silicone hydrogel: pHEMA/TRIS, DMAA/TRIS), and commercially available contact lenses. PRG4 solutions were effective lubricants for model and commercial silicone hydrogels. PRG4, immobilized on the surface, was an effective lubricant for pHEMA/TRIS, but not pHEMA. HA incorporated into bulk materials was only effective for pHEMA/TRIS. HA immobilized on the surface of hydrogels did not effect friction. PRG4+HA combinations were effective for DMAA/TRIS and pHEMA/TRIS. There was evidence for PRG4+HA synergistic lubrication for pHEMA/TRIS, both when HA was incorporated and when PRG4+HA were in solution. A novel lid wiper - commercial contact lens in vitro friction test was developed and could resolve differences between lenses tested in saline, ATS, and worn vs. fresh lenses.

These results demonstrate that PRG4 and HA lubrication of contact lens materials is dependent on the composition of surfaces, and is effective for certain hydrogels. Additionally, a physiologically relevant lid wiper - contact lens test was developed and characterized. This work provides a foundation and framework for use of these natural lubricants for current and future contact lens materials.

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