Materials Properties Chemical and mechanical materials properties including surface adhesion, hardness and friction. Not useful for characterizing chemical and mechanical surface properties. Not useful for characterizing chemical and mechanical surface properties. Sample Damage AFM, particularly TappingMode technique, is non-destructive. The figure at left shows two TappingMode AFM images of commercial soft contact lenses under saline.
Scratches are visible over the entire surface.
The image on the right corresponds to the identical type of contact lens, but the lens had been worn by a 25 year-old male for two weeks. The surface appears to be coated with particulate contaminants that mask the topography of the contact lens. These types of comparisons of AFM images are critical to understanding how the underlying topography of new lenses affects the build-up of proteins and other adsorbates during wear. It is not yet known what size and type of defects or features on contact lens surfaces are critical in prompting unfavorable responses by the eye, but preferential adsorption of protein to local sites is a possible cause. In addition, the etiology of some of the most common problems associated with wearing contact lenses is linked to bacterial contamination.