Photoresponsive Double Cross‐Linked Supramolecular Hydrogels Based on A‐Cyclodextrin/Azobenzene Host–Guest Complex

Abstract

Smart hydrogels are interesting materials as they can change their dimensions upon an external trigger. Herein, a photoresponsive double cross-linked hydrogel system based on polyacrylamide (AAm) with grafted poly(2-methyl-2-oxazoline) (PMOXA) chains with a 𝜶-cyclodextrin/azobenzene host-guest complex is present. Switching azobenzene from the trans to the cis-conformation through irradiation with UV light breaks the complex reversibly. Well-defined PMOXA macromonomers have been synthesized and functionalized with the respective host and guest functionalities as well as double bonds for the incorporation into the polymer network as grafted side chains. The chemical structure of the macromonomers and the complex is confirmed by 1 H NMR, 2D NOESY NMR, GPC, and UV-VIS measurements. Hydrogels with different ratios of permanent and photoresponsive cross-linkers as well as different chain lengths of the PMOXA macromonomers are analyzed toward differences in their swelling/deswelling and elastic properties. Successive irradiation of supramolecular hydrogels with UV and VIS light allowed for a repeated swelling and de-swelling of the hydrogels. This system is studied at both macro and micro scales, showing similar swelling tendencies. The tuned properties of photoresponsive double cross-linked hydrogel makes this system a promising tool for various applications, for example, as in situ controllable valves in microfluidic flow cells.

Stimuli-responsive dynamic hydrogels: design, properties and tissue engineering applications

“…42 Liubimtsev et al developed a double cross-linked hydrogel with changes in the cross-linking density on demand. 43 The authors developed a polyacrylamide hydrogel with azobenzene and cyclodextrin (CD) moieties as reversible cross-linkers and N , N ′-methylenebis(acrylamide) as an irreversible cross-linker. Cross-linking density of the hydrogel changed with successive irradiation of the hydrogel with UV ( λ = 365 nm) and visible ( λ = 400 to 500 nm) light.…”

Photoresponsive Smart Hydrogels and Their Versatile Applications: A Review

“…Stability of these complexes depend on cis-or trans-form of azobenzene. Many research groups utilized cyclodextrin-azobenzene host-guest complexes to develop photoresponsive hydrogels [31][32][33][34]. Spiropyran is another popular unit to induce photo-responsiveness as its two isomers are hugely different.…”

Pillar[5]arene-based dually crosslinked supramolecular gel as a sensor for the detection of adiponitrile

“…32,33 Utilization of dual reversible crosslinking, for instance, was shown to endow the networks with multi-stimuli-responsiveness as well as shape memory behavior. [34][35][36][37] Furthermore, incorporation of a covalent and a non-covalent linkage types in a single gel was demonstrated to be highly promising since it receives the advantages of both types: 38,39 the former provides an integrity of structure to the system, whereas the latter is responsible for the reversibility and responsiveness. Such combination proved to be beneficial for the fabrication of reusable devices, which is especially important in sensing applications.…”