The Surface Tribological and Mechanical Behaviors of Silicone-Based Hydrogel Materials

Abstract

In recent years, the study of the surface properties of compliant materials (especially synthetic and biological hydrogels) has emerged as an urgent need for both industrial and academic fields. Silicone-based contact lens materials are a practical application of hydrogels used in daily life, on which the investigation of surface frictional and mechanical behaviors could contribute to the improvement of their clinical performance. In this study, the tribological and mechanical properties of senofilcon-A contact lenses were systematically studied through nanotribology and nanoindentation methods in both liquid and dehydrated conditions. In the tribological study, a stainless steel counterpart was employed to wear the lens surface with various load and velocity conditions. It was found that the friction force is proportional to normal load and solid-solid contact dominates the friction of silicon hydrogel. It was also found that the coefficient of friction increases with the velocity which follows the power law fashion. The stiffness of the hydrogel lens was also measured by nanoindentation with direct compensation for thermal fluctuation and surface adhesive force. It was interesting to observe the dramatic change of gel stiffness during the dehydration process. The dehydration also had a great influence on the material time dependent properties, such as creep degree.