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James W. Davis, Robert E. Baier, Anne E. Meyer, Howard Ketelson; A New Mechanism for Facilitated Re-wetting of Silicone Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6502.
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© ARVO (1962-2015); The Authors (2016-present)
Current methods used to determine advancing contact angles (ACA) have some ambiguity in regards to the interpretation of wettability for lens surfaces. Low contact angles can stem from the eluted surfactants. Captive Bubble (CB), Sessile Droplet (SD) and Multiple Attenuated Internal Reflection InfraRed (MAIR-IR) Spectroscopy were used to investigate the means by which novel block copolymers of ethylene oxide and butylene oxide (EOBO) enhance the ability for Silicone Hydrogel (SiH) to be re-wetted by water after short duration air exposures of EOBO-based disinfectant treated contact lenses (PureVision® (PV)).
ACA data were collected from CB videos using OCA20-Beta software. In vitro, SD contact angle data on referenced Teflon foil and SiH lenses supported by MAIR-IR were used to study the water wettability.
The apparent mechanism of sustained wettability improvement was believed to operate through embedment of the BO copolymer segments into hydrophobic domains of the SiH lenses, exposing the water-loving EO copolymer segments at the lens/air interface. This was demonstrated by the low ACA’s of PV treated lenses with the EOBO formulation in CB: initial ACA of 32° at 160 seconds with surface tension (SFT) of the air bubble was 72.1mN/m; after 10 UNISOL 4® rinse cycles with 90 second air exposure an ACA of 60° at 160 seconds with SFT at 71.9mN/m. Rinsing demonstrated the substantivity of the EOBO formulations where EOBO eluted slowly from the hydrophobic PV lenses.
This mechanism of action supplements simple adsorption, absorption and reservoir/depot effects that can also take place with EOBO block copolymers. The data showed that block copolymers lacking EOBO’s molecular geometry, molecular weight and hydrophilic-lipophilic balance may not be as effective and efficient to preferentially wet and re-wet hydrophobic contact lenses.
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