A study of the frictional properties of senofilcon-A contact lenses.

The frictional property of soft contact lenses could have a great impact on their clinical performance. However, to date, only a handful of studies have been conducted to understand the friction mechanism(s) of the soft contact lens. In the current paper, the friction of senofilcon-A contact lenses has been studied with a stainless steel ball as the counterface in a saline solution. The load applied was between 0.5 mN and 100 mN and the sliding velocity ranges from 0.01 cm/s to 0.5 cm/s. It was found that the friction force is proportional to normal load as described by Amonton's law and this unexpected behavior can be attributed to the fact that viscous flow contributes little to the overall friction and that solid-solid contact dominates the friction of senofilcon-A. It was also found that the coefficient of the friction increases with the velocity and the quantitative relationship between them can be explained reasonably well with a previously proposed "repulsion-adsorption" model. The impacts of material chemistry, water content, test media, applied load and the sliding velocity on the friction mechanism(s) are also discussed.