Light-controllable viscoelastic properties of a photolabile carboxybetaine ester-based polymer with mucus and cellulose sulfate

In this study, the interaction of a photoswitchable carboxybetaine ester-based polymer with mucus and cellulose sulfate was elucidated, showing light-controllable viscoelastic properties. This polymer contains photolabile o-nitrobenzyl ester moieties, allowing transformation from its polycationic form to a charge-balanced nontoxic polyzwitterionic form upon photolysis by irradiation at 365 nm. Rheological studies revealed that the polycationic form of the polymer interacts with mucus and cellulose sulfate to create a physically crosslinked hydrogel based primarily on polyionic complexation and partially on hydrogen bonding. In these cases, a dramatic change in the rheological synergism was confirmed for mucus-based and cellulose sulfate-based systems. Rheological synergism with the polycationic carboxybetaine ester sample reached nearly 4 and 3.8, while it decreased with the charge-balanced zwitterionic sample to 0.3 and 0.7 after irradiation of the mucus-based and cellulose sulfate-based systems, respectively. Disruption of the interaction during light-induced transformation was on-line monitored and showed a 3 and 3.3 times decrease in the elastic modulus for the mucus-based and cellulose sulfate-based systems, respectively. These properties suggest possible biomedical applications, such as spatially controlled drug release or laparoscopic utilization.