An in situ-forming zwitterionic hydrogel as vitreous substitute

Zwitterionic polymers have shown ultra-low biofouling properties at surfaces and excellent biocompatibility as implant. In this study, an in situ-forming zwitterionic hydrogel was designed and evaluated, both in vitro and in vivo, as a long-term vitreous substitute. The zwitterionic polymer poly(MPDSA-co-AC) was designed as a copolymer of the sulfobetaine methacrylamide and acryloyl cystamine monomers, providing the zwitterionic components and the thiol functional groups, respectively. The in situ gelation was via the thiol-ene Michael addition reaction with α-PEG-MA as the crosslinker. The gelation time, rheological properties, swelling profiles, and the transparency of zwitterionic hydrogels were studied in detail. Two systems with different crosslinker concentrations were tested in a rabbit model, and the one with the thiol-ene ratio of 2 : 1 showed excellent biocompatibility in vivo, formed space-filling hydrogels and remained transparent in the vitreous cavity for the 2 month implantation period. Therefore, in situ-forming zwitterionic hydrogels represent a promising material system as a vitreous substitute and possibly for other soft tissue replacements.