Evaluation of plasma polymer-coated contact lenses by electrochemical impedance spectroscopy

Abstract

The influence of ultra-thin (i.e., 5-50 nm) plasma polymer coatings on siloxane-based hydrogel contact lenses was investigated by electrochemical impedance spectroscopy (EIS). Impedance measurements as a function of frequency (Bode plots) were taken at regular intervals until steady impedance was obtained, indicating that the lenses were saturated. Appropriate equivalent circuit models were constructed to describe the salt intrusion characteristics of the plasma polymer-coated contact lenses. This provided information pertaining to the resistance and capacitance of interfacial and bulk layers in the plasma polymer-coated lenses. Resistance relates to ion permeability and capacitance for water uptake. This investigation showed that some of an ultra-thin layer of plasma polymer applied onto a dry hydrogel remains a contiguous film after the substrate hydrogel swells upon hydration. In some cases, however, the overall impedance of the coated lens is so low that the state of the plasma polymer layer after the hydration of the substrate hydrogel could not be judged by EIS.

Impact of Ethylene Oxide Butylene Oxide Copolymers on the Composition and Friction of Silicone Hydrogel Surfaces

“…Together, these changes are consistent with their respective formulations and surface treatments. For example, the higher concentration of Si at the surface of senofilcon A is consistent with the absence of the plasma surface treatment presenting an oxidized or carbon-rich top layer, as in the case of balafilcon A and lotrafilcon B, respectively [9,10,33]. Upon solution treatment with the EO-BO diblock copolymer, further changes in composition and differences in each lens' behavior were observed.…”

“…Balafilcon A, for instance, relies on plasma oxidation of the surface for enhanced wettability [1,6,7]. The lotrafilcon lenses, on the other hand, have a thin, uniform coating deposited across the surface through plasma-induced polymerization [9]. A second group of lenses includes ACUVUE Ò OASYS Ò (senofilcon A) and ACUVUE Ò ADVANCE Ò (galyfilcon A), which both incorporate poly(vinylpyrrolidone), or PVP, in their lens chemistry, resulting in greater similarities between the bulk and the surface compositions [7,10].…”

“…In general, these studies have shown that contact lens hydrogels have surfaces that are not usually at thermodynamic equilibrium when used in the ocular environment and, as a result, there can be significant changes in the surface chemistry over time due to the migration of hydrophobic groups to the air/lens interface. To overcome these dynamic changes, the surfaces have been modified through plasma treatment, the inclusion of free polymers into the lenses' matrix, and/or the soaking of lenses in saline solutions containing block copolymers to physically modify the surfaces [1,6,7,9,10,13].…”

Bacterial adhesion to conventional hydrogel and new silicone-hydrogel contact lens materials

“…The surfaces of O2Optix lenses (Lotrafilcon B) are permanently modified in a gas plasma reactive chamber to create a permanent, ultrathin (25 nm), continuous hydrophilic surface [24,30]. PureVision lenses (Balafilcon A) are surface treated in a gas plasma reactive chamber which transforms the silicone components on the surface of the lenses into hydrophilic silicate compounds [31].…”

The role of multi-purpose solutions in prevention and removal of lipid depositions on contact lenses

“…Balafilcon A lenses are plasma oxidized, which purportedly converts the TRIS structure on the surface into islands of hydrophilic silicate [25][26][27]. Lotrafilcon B lenses are reported to be coated with a continuous wettable layer [27][28][29] whose polarity could act as an impediment to lipid sorption. Since these lenses are designed to have a permanently hydrophilic surface, the surfactants in the MPSs may have less additional influence in reducing lipid deposition.…”