A contact lens-embedded betaine ester polymer for pH-responsive release of an osmoprotectant to the corneal surface

Topical delivery of osmoprotectants to ocular surface has been shown to be a promising solution to ocular discomfort thought to be associated with corneal hyperosmolarity. Currently, most osmoprotectants are administrated by aqueous eyedrops, which are associated with poor bioavailability and short residence time in the tear film, requiring repeated dosing to maintain the osmoprotectant concentration above the effective level. In response to this challenge, this work describes poly(vinyl glycine betaine) (PV-GB), a degradable ester quat polymer which gradually releases the osmoprotectant, glycine betaine (GB), over a period of days to weeks, with release rate strongly dependent on pH of its surroundings. PV-GB was embedded into commercial contact lenses (CLs) alongside a polyanion, hyaluronic acid (HA), to provide extended release of GB during a period reflecting the typical usage of a daily disposable CL wear of 8 - 16 h. A GB release lifetime of ≪48 hrs was achieved from a system comprising PV-GB/HA embedded within an anionic CL using a simple soaking method. Further experiments indicated the polymer was stable to autoclave sterilisation, had a shelf-life of 6 + months (under optimised solution conditions), and was likely to be mucoadhesive, which would be expected to enhance bioavailability of GB at the ocular surface.