Joseph Accardo
Northwestern
Physically or chemically crosslinked polymer networks capable of absorbing water to form three dimensional networks (hydrogels) are a promising class of soft materials for applications in tissue engineering and drug delivery systems. The ability to control the physical and dynamic properties of these materials over time by stimuli response enhances their practicality as tools for studying and mimicking non-static systems. Light serves as a practical means for delivering an external stimulus to discrete locations in a time controlled manner (spatiotemporally), allowing for system regulation at the flip of a switch. In recent years light has been used to reversibly crosslink hydrogels by covalent bond formation or host-guest complexes. In this work, a new approach to reversibly tunable hydrogels are achieved by photocontrolling the dynamic covalent boronic acid-diol exchange through azobenzene isomerization. Irradiation with a 365 nm light induces (E to Z) isomerization of the azobenzenes, resulting in an increase in the stiffness of the hydrogel. The reverse reaction (Z to E) isomerization and gel softening is induced by 470 nm blue light. Rheological characterization shows that the hydrogels exhibit viscoelasticity and self-healing properties, and the stiffness of the gels can by ‘cycled’ multiple times without gel failure. These features, as well as the pure reversibility of the system, makes these hydrogels ideal for the development of tunable cell-culture scaffolds and as soft-tissue mimics.