Paper BI-TuP14
Biocompatible Hydrogel Materials - Surface Properties and Deposition Comparison of Commercially Available Contact Lenses

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Hydrogel contact lenses are ophthalmic devices designed to correct refractive errors. Wettability, modulus, friction, oxygen permeability, and topography are some of the factors that influence lens comfort and performance. In addition, elimination of deposition of proteins and lipids on the lens surface from the tear fluid is of particular interest as it may influence contact lens surface wettability and impact comfort negatively. Thus, the surface chemistry and morphology of a durable and biocompatible hydrogel material should be carefully fashioned.

The objective of this research was to understand the properties of modern daily disposable contact lens materials. The surface composition, morphology, wettability and protein/lipid uptake of worn and unworn nesofilcon A and delefilcon A hydrogels were examined by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and Captive Bubble (CBCA). Lenses from 5 healthy adults were examined after 4 hours of continuous wearing. A Dimension ICON AFM was used to characterize the unworn and worn hydrogels. Topography, peak to valley, and roughness (RMS) were recorded. AFM phase lag was used to evaluate lipid/protein deposition. Multipoint XPS spectral analysis was performed to establish the spatial distribution of elements over a large area of the hydrogel. CBCA was done to compare the wettability of unworn lenses.

AFM and XPS characterization revealed significant surface chemistry and morphology differences between worn and unworn lens materials. XPS mapping showed a uniform distribution of the identified elements on the surface of unworn nesofilcon A and also detected the presence of a coating on delefilcon A. Unworn nesofilcon A exhibited a smooth featureless surface morphology with RMS of 1.9 ± 0.2 nm while unworn delefilcon A showed clear presence of a branched surface coating (RMS = 14.2 ± 5.5 nm) with peak to valley as deep as 61.4 ± 18.8 nm. It was established that the wear process changes the contact lens material morphology. The changes observed in the case of worn nesofilcon A were minor, while those observed for worn delefilcon A were quite pronounced. Both daily disposable materials attracted lipid/protein deposits. The topography of worn nesofilcon A was uniform and it was not altered by wear. The branched surface coating of delefilcon A collapsed during 4 hours of wear on eye and was no longer detected by AFM. In addition, delefilcon A attracted more deposits than the nesofilcon A. Topography and phase lag AFM imaging of worn deleficon A did not detect any areas that would be lipid/protein deposit free. In terms of stability and lipid/protein deposition nesofilcon A was superior.