|Title||XPS CHARACTERIZATION OF SOFT CONTACT LENS MATERIALS|
|Author, Co-Author||Caroline Karlgard, Lyndon Jones, Dilip Sarkar, K. Tong Leung, Christine Moresoli|
|Abstract|| PURPOSE: Contact lenses (CL) interact with a variety of chemicals, both synthetic (drugs) and natural (tear components). The understanding of surface interactions is critical for insight into CL behavior. X-ray Photoelectron Spectroscopy (XPS) is a powerful technique with a small sampling depth (10-300Ĺ) that has provided surface information for certain CLs. For example, the effect of spoilage after wear, bacterial adhesion, and manufacturing processes. However, there has not been a systematic study of the sample preparation procedures, thus this work will evaluate the effect of CL drying on the XPS results. In addition, base-values of the surface composition of different soft CL materials will be measured.
METHODS: Novel hydrogel contact lenses that contain silicon (Si), PureVision™ and Focus® Night&Day™, and several conventional hydrogel (CH) and daily disposable (DD) hydrogel lenses based on polyhydroxyethyl methacrylate (pHEMA) were studied. Triplicates of all lenses were washed and dehydrated by three different methods: (1) drying in air, (2) drying in nitrogen and (3) freezing with subsequent freeze-drying, before analysis by XPS (VG Scientific ESCALab 250). Statistical treatment included ANOVA/MANOVA, contrast tests and Shefffe’s post-hoc comparison test (significance at p<0.05).
RESULTS: All lenses had Si contamination on the surface. However, the DD and CH lenses had higher amounts of other impurities than Si-based lenses (p<0.00001). The lenses dried in air had more impurities on the surface (p<0.012), and the lenses that were freeze-dried lost transparency, suggesting that drying lenses in nitrogen is the preferred preparation for XPS analysis. Si-based lenses were more robust and less affected by the drying technique than the DD and CH lenses.
CONCLUSIONS: Surface compositions for all lens materials (Si-based, CH and DD lenses) were obtained and can serve as a control/base-value for analysis of contact lenses with drugs/tear components.
ADDITIONAL COMMENTS: This work was supported by the Natural Sciences and Engineering Research Council of Canada.
|Affiliation of Co-Authors||University of Waterloo, School of Optometry and Vision Science, University of Waterloo, School of Optometry and Vision Science, University of Waterloo, School of Optometry and Vision Science, University of Waterloo, School of Optometry and Vision Science|