NU 2018-066
INVENTORS
Julia Kalow*
Joseph Accardo
Boyeong Kang
SHORT DESCRIPTION
Dynamic crosslinkers that offer reversible stiffening and softening of polymer networks by a photoswitch
BACKGROUND
Polymer networks can be linked by weak, reversible physical interactions or strong but irreversible covalent bonds. Dynamic covalent bonds enables strong and reversible linkages, allowing for reprocessing of covalent polymer networks. Existing dynamic covalent materials generally rely on high temperatures to trigger the reversible reactions; thermal stimulus does not provide precise spatiotemporal control, and is incompatible with many applications or materials.
ABSTRACT
Northwestern researchers have developed dynamic linkers wherein the stability and lifetime of the linker is controlled by an adjacent photoswitch. They have demonstrated the application of these photoswitchable dynamic covalent crosslinks in a viscoelastic hydrogel with reversible stiffening and softening using light. Controlling the physical properties of soft materials with external stimuli enables researchers to mimic and study dynamic systems. In particular, hydrogels which are polymer networks swollen by water have broad applicability in biomedicine. Northwestern researchers can now control hydrogel mechanics with light, using an approach that reversibly manipulates the stability of dynamic covalent crosslinks at the molecular level. Specifically, the equilibrium between a boronic acid and diol to form a boronic ester can be altered by the configuration of an adjacent azobenzene photoswitch. By irradiating polymers bearing azobenzene-boronic acid and diol end groups with two different wavelengths of light, they can stiffen or soften the resulting hydrogel. Alternating irradiation induces reversible mechanical changes. Rheological characterization reveals that the hydrogels are viscoelastic, exhibiting stress relaxation on the order of seconds, and the stiffness is tuned independently of the crossover frequency. Further, they have also demonstrated that this approach can be extended to use visible light for both softening and stiffening. These photocontrolled dynamic covalent crosslinks provide a versatile platform for tunable dynamic materials.
APPLICATIONS
ADVANTAGES
IP STATUS
A PCT application has been filed.
PUBLICATIONS
Accardo J and Kalow J (2018). Reversibly tuning hydrogel stiffness through photocontrolled dynamic covalent crosslinks. Chemical Science. 9: 5987-5993.