(154a) Adsorption and Absorption of Polymeric Surfactants onto and into Soft Contact Lenses

Optometrists are trained that reducing the liquid-contact angle (CA) of soft contact lenses (SCLs) can improve pre-lens tear-film stability (PrLTFS) leading to better wear comfort. Consequently, contact-lens care solutions typically contain poly(ethylene oxide)-poly(propylene oxide) block-copolymer surfactants which act as wetting agents. These wetting agents significantly reduce the CA of some SCLs. We hypothesize that the efficacy of the care-solution wetting agents depends upon absorption into the polymer matrix of the SCLs and slow release from the lens during on-eye wear. We examine the kinetics of desorption of two such wetting agents: Tetronic 1304 (T1304) and Pluronic F127 (PF127), from two commercial SCLs: Acuvue 2 (AV2) and O2 Optix (O2O). Tensiometry is used to detect the amount of leached surfactant in the PBS solution. and a captive-bubble apparatus was used to measure the contact angles.

A significant amount of T1304 absorbs into the AV2 lenses. Several days are required for complete desorption. Comparatively little T1304 absorbs into the O2O lenses. This correlates well with the efficacy of the wetting agent on those two lens types. CA data show that T1304 makes AV2 lenses completely water wetting for several days but has little effect on O2O lenses. Comparatively less PF127 was found to absorb into either AV2 lenses or O2O lenses. This also corresponds well with CA data.

We conclude the main mechanism for increase in wettability PEO-PPO-PEO polymeric surfactants is through continual slow desorption of polymeric surfactant from the lens which reduces the liquid-vapor surface tension and in turn reduces the liquid contact angle. Since the main wettability alteration is through the surface tension and not the solid surface energies, better on-eye PrLTFS is unlikely with these wetting agents.