Surface analysis of hydrogel contact lenses by ESCA.

We used electron spectroscopy for chemical analysis (ESCA) to examine the surface chemistry of polymacon, tefilcon, and bufilcon hydrogel contact lenses. Worn and unworn water-cleaned and surfactant-cleaned lenses were compared. The surface chemistry of unworn lenses, which were used as controls, consisted of approximately 70% carbon, 25% oxygen, and < 10% other elements (i.e., silicon, sulfur, sodium, nitrogen, and zinc). In general, surfactant cleaning removed silicon contamination, but left a residue containing sulfur and zinc. The increase in the nitrogen/carbon (N/C) ratio for worn bufilcon and polymacon lenses was significantly greater than the N/C ratio for unworn bufilcon and polymacon lenses. As a group the worn ionic lenses (bufilcon) showed a greater N/C ratio than the worn nonionic lenses (polymacon, tefilcon). The nitrogen that appears on all worn lenses probably represents adherent as well as adsorbed surface proteins. The highest N/C ratios were found on a pair of pathologically deposited lenses and on the lens with the longest wearing time (2 years). For the bufilcon and polymacon lenses, the differences observed in the ESCA data for the unworn and worn lenses suggest that contact lenses begin interacting with the tear film within 1 minute (the shortest wearing time in this study).

Relating the surface properties of intraocular lens materials to endothelial cell adhesion damage.

Relationships between corneal endothelial cell adhesion and intraocular lens (IOL) surface properties were studied to develop a lens surface with a lower potential to damage the corneal endothelium. The surfaces examined were poly(methyl methacrylate) (PMMA) and four types of plasma-deposited coatings on PMMA. These four films were prepared from perfluoropropane, ethylene oxide, 2-hydroxyethyl methacrylate (HEMA), and N-vinyl-2-pyrrolidone (NVP). These "monomers" were chosen to produce surfaces with a range in surface chemistry and surface energy. Each type of coating was characterized by electron spectroscopy for chemical analysis (ESCA) and contact angle techniques. In addition, these surfaces were contacted with rabbit corneal endothelium over a force range of 4000-20,000 dynes. The extent of endothelial cell damage was measured. Over the force range investigated, each modified surface was found to induce a significantly different degree of cell adhesion than that caused by PMMA. The perfluoropropane plasma film induced a constant lower degree of adhesion damage than the PMMA for all forces of contact. Although the HEMA and NVP hydrogel surfaces also induced lower adhesion damage than PMMA, the cell loss associated with each did increase as a function of force. The ethylene oxide film caused a significant increase in cell loss compared to the PMMA-induced losses. Based upon the correlation between the surface analysis data and the cell-surface contacting results, we suggest that a "soft" high-energy surface or a "rigid" low-energy surface is favorable for reduced cell adhesion. Also, the results indicate that cell adhesion increases for materials with increased hydrocarbon enrichment and for materials with lower (ether bonding)/(ester and ketone linkages) ratios.