| AVS 59th Annual International Symposium and Exhibition | |
| Tribology Focus Topic | Tuesday Sessions |
| Session TR+BI-TuM |
| Session: | Self Healing Coatings, Bio-Inspired Design, and Frictional Properties of Biological Materials |
| Presenter: | S.S. Perry, University of Florida |
| Authors: | S.S. Perry, University of Florida S. Huo, University of Florida A. Rudy, University of Florida |
| Correspondent: | Click to Email |
The surfaces of six types of silicone hydrogel (SH) contact lenses (PureVision®, O2 OPTIX®, ACUVUE® Oasys ®, ACUVUE® TruEye®, Biofinity®, DAILIES TOTAL1®) and the pHEMA-based ACUVUE® 2 have been analyzed using atomic force microscopy (AFM) in aqueous environment. The elastic modulus, frictional, and adhesive properties of each lens were evaluated using calibrated instrumentations, providing a basis for comparing the distinctive surface properties of these lenses. Cantilevers modified with 5-μm (diameter) silica colloidal probes were employed throughout the experiments. Elastic modulus was measured by indenting the probe into the surface of the hydrogel in a controlled manner (i.e. approach speed and maximum applied force), such that the maximum indentation depth was restricted to sub-micron levels. A modulus value was obtained by fitting the characteristic force versus indentation behavior to a mathematical model. The frictional force was measured for the sliding contact of the probe and the surface at the length scale of 500 nm and with applied loads up 20 nN. The friction coefficient was realized by evaluating the linear dependence of friction force on applied normal load. The lenses examined exhibited an order of magnitude difference—from the softest to the stiffest sample—in modulus value, generally reflective of the distinct surface treatments they received during manufacturing. For example, the pHEMA-based ACUVUE® 2 was shown to have a modulus between 100 and 130 kPa, whereas PureVision®’s was an order of magnitude higher in value. The frictional properties of the lenses followed a similar trend in that the lenses with surface treatment, such as PureVision® and O2OPTIX®, generally exhibited coefficients of friction five times greater than that of a non-treated lens such as ACUVUE® OASYS®. The elastic modulus and frictional properties of different lenses evaluated on a nanoscopic level by AFM depict a strong correlation between the surface treatments and the apparent mechanical behaviors of the lenses.