Surface chemical structure for soft contact lenses as a function of polymer processing

Abstract

The surface chemistry and topography of cast-molded Etafilcon-A and doubled-sided lathed Etafilcon-A soft contact lenses were determined to be significantly different. The variations in surface chemical and morphologic structure between the two lenses were the result of contact lens manufacturing methods. The surface of the cast-molded Etafilcon-A had a consistently less rough surface compared to the doubled sided lathed Etafilcon-A as determined by atomic force microscopy. The surface of the doubled sided lathed Etafilcon-A contained primarily silicone and wax contamination in addition to minute amounts of HEMA. The cast-molded Etafilcon-A had an elemental and chemical content which was consistent with the polymer stoichiometry. Contact angle wettability profiles revealed inherent wettability differences between the two lenses types. The cast-molded Etafilcon-A had an inherently greater water wettability, polarity, and critical surface tension. This means that these two lenses cannot be compared as similar or identical lens materials in terms of surface composition. The manufacturing method used to produce a soft contact lens directly determines the surface elemental and chemical structure as well as the morphology of the finished lens material. These results suggest possible differences in the clinical comfort, spoilage, and lubricity felt during patient wear.

AFM in mode Peak Force applied to the study of un-worn contact lenses

“…Polymacon lenses values of Rq ranging from 7 to 28 nm, Grobe et al [2] reported for Etafilcon-A lenses values of Rq ranging from 5.0 to 25.2 nm, and Maldonado et al [8] reported values of Rq ranging from 3.9 to 12.3 nm, which depend in all of these studies on the fabrication method and on the face of the lenses. These studies clearly show that the fabrication technique has a notable influence on the lens roughness, being the cast-molded lenses those showing lower Rq values.…”

“…The Atomic Force Microscopy (AFM) is a technique that becomes useful to determine these properties, as was pointed out in an earlier work by Rabke et al [1]. Consequently, several authors [2][3][4][5][6][7][8][9][10][11][12][13][14][15] performed studies on CLs and using the AFM technique, but none of them used the Peak Force Quantitative Nanomechanics mode to determine the nanomechanical properties, such as the adhesion or the Young modulus, also named elastic modulus.…”

“…Grobe et al [2] studied the surface chemistry and topography of Etafilcon-A hydrogel CLs as a function of polymer processing, by using AFM, and concluded that the processing technique has influence in both the surface chemistry (surface composition, wettability) and the topography. Maldonado et al [8] examined the impact of manufacturing and material composition on the surface topographic characteristics of five types of hydrogel CLs.…”

“…Maldonado et al [8] examined the impact of manufacturing and material composition on the surface topographic characteristics of five types of hydrogel CLs. Observations were made using both Scanning Electron Microscopy (SEM) and AFM, indicating that cast-molded lenses show lower root-meansquare (RMS) roughness values, in agreement with the results of Rabke et al [1] and Grobe et al [2]. Kim et al [4,5] investigated the surface of hydrogel pHEMA-based CLs by using AFM and measuring the friction and adhesive forces.…”

Hydrogel Contact Lenses Surface Roughness and Bacterial Adhesion

“…The spin casting method generates contact lenses with the smoothest surfaces, followed by cast-molding and then lathe-cut lenses (Guryca et al, 2007;Grobe, 1996). All the lenses presented here were cast-molded, and their roughness parameters were similar to the ranges reported for other non surface-treated cast-molded lenses (Guryca et al, 2007).…”