ToF-SIMS and AFM Characterization of Brown Cosmetic Contact Lenses: From Structural Analysis to the Identification of Pigments

Abstract

Over the years, soft contact lenses for vision correction and cosmetic and therapeutic purposes have been greatly improved. For cosmetic contact lenses, the pigments need to be nontoxic, and the position of the pigment layer is particularly important because of the risks posed by pigment elution and the roughness of the lens surface. In this paper, we characterized the properties of brown cosmetic contact lenses made by three different manufacturers using surface analytical techniques. The surface topographies of the noncolored and colored parts were obtained by atomic force microscopy (AFM), and the position and composition of the pigment layer were determined by analyzing the cross section of the contact lenses using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). The influence of pigment location on surface roughness was also examined. In addition, to find the method of the evaluation for the risk of surface elution of the pigments in the colored parts, the mass spectra and ion images of the surfaces were obtained by time-of-flight secondary ion mass spectrometry (ToF-SIMS) with a new sample preparation. From the ToF-SIMS spectra, we observed specific fragment ions of the poly(hydroxyethyl methacrylate) (PHEMA) polymer and found differences in the composition of the pigment layer depending on the manufacturers. The cross-sectioned image and 3D chemical characterizations of metallic and specific ions in the brown cosmetic contact lenses clearly indicated the spatial distribution and location of the pigment layer that can be used for the evaluation of pigment elution.

Figure 1

Schematic drawing of (a) analysis area of a cosmetic lens and (b) preparation procedure of a cross-sectioned sample.

Figure 2

Comparison of surface topographies in images (20 μm × 20 μm) measured by AFM.

Figure 3

Cross-sectional BSE images and analyses of compositions by SEM-EDX. The crosses represent the EDX analysis points, with red crosses for colored layer points and yellow crosses for the noncolored layer.

Figure 4

Positive-ion ToF-SIMS spectra of cosmetic contact lens revealed the presence of the bulk polymer PHEMA at all surfaces of three lenses. (a) Noncolored part: (1) central clear zone. (b) Colored part: (2) front surface. (c) Colored part: (3) back surface.

Figure 5

Optical images of the analysis area and ToF-SIMS 2D image mapping on the front surface of the colored part. (a) Overlay image of Cu⁺ and PHEMA for CCL-B. (b) Cl⁻ mapping images normalized by total intensity for lenses CCL-A, CCL-B, and CCL-C.

Figure 6

ToF-SIMS results of cross-sectional 2D image mapping and line scan of the surface layer for lenses CCL-A, CCL-B, and CCL-C.

Figure 7

Optical images of the analysis area and 3D chemical images by ToF-SIMS.