Micromechanical measurement of adhesion of dehydrating silicone hydrogel contact lenses to corneal tissue

Adhesion properties, which can vary with multiple factors, of silicone hydrogel contact lenses are important to their performance and comfort in the eye. In this study, we developed and used a simple, representative testing system and method to study the adhesive interactions of different silicone contact lenses (balafilcon A and senofilcon A) on polished titanium alloy and porcine whole eye cornea under dehydrating conditions. Adhesive interactions for senofilcon A varied by hydration state for both corneal and titanium adhesion, starting low, rising to a maximum and falling with dehydration time and dehydration state. Balafilcon A showed a rise and fall against titanium, but retained a relatively constant adhesive interaction with corneal tissue over dehydration time. Senofilcon A reached the highest adhesion forces (400 mN) within 5 to 10 min of testing against cornea, then dropped with time after that. Johnson-Kendall-Roberts (JKR) theory was applied to determine the surface energy of the lenses, and work of adhesion (WOA) was also determined for both lenses. Similar trends as observed with the force-hydration curves were seen with surface energy and work of adhesion as well (peak surface energy of 8 N/m and work of adhesion of 80 µJ for senofilcon A). Video imaging of the adhesive interactions showed significant corneal deformation taking place during testing, and post-test analysis shows damage to the corneal tissue. This method could be used to assess pre-clinical performance of long-lasting contact lenses and the role of hydration state. STATEMENT OF SIGNIFICANCE: Adhesion properties of contact lenses play significant roles in their performance and comfort in the eye. Adhesion is influenced by polymer chemistry, counterface materials and hydration state of the contact lenses. However, no test method has been developed to directly study the adhesion properties between contact lenses and corneal tissue during the dehydration process. Our work aims to fill this gap by developing testing and analysis methods for evaluating the adhesive interactions in vitro between contact lenses of different chemistries and properties and different counter surfaces under dehydrating conditions over time. Our study shows that adhesive interactions of contact lenses are highly dependent on polymer type, surface treatment, counterface material and hydration state.