Wavelength‐Orthogonal Stiffening of Hydrogel Networks with Visible Light

Abstract

Herein, we introduce the wavelength‐orthogonal crosslinking of hydrogel networks using two red‐shifted chromophores, i.e. acrylpyerene (AP, λactivation=410–490 nm) and styrylpyrido[2,3‐b]pyrazine (SPP, λactivation=400–550 nm), able to undergo [2+2] photocycloaddition in the visible‐light regime. The photoreactivity of the SPP moiety is pH‐dependent, whereby an acidic environment inhibits the cycloaddition. By employing a spiropyran‐based photoacid generator with suitable absorption wavelength, we are able to restrict the activation wavelength of the SPP moiety to the green light region (λactivation=520–550 nm), enabling wavelength‐orthogonal activation of the AP group. Our wavelength‐orthogonal photochemical system was successfully applied in the design of hydrogels whose stiffness can be tuned independently by either green or blue light.

Basic-to-acidic reversible pH switching with a merocyanine photoacid

“…1) 1 has been used for a wide-spread range of applications in supramolecular 2 and materials chemistry. 3 Recently developed merocyanines demonstrated increased pH jumps ranging from 2.5 (R 1 = H, R 2 = H, R 3 = (CH 2 ) 4 SO 3 − (ref. 4) and R 1 = H, R 2 = polymer, R 3 = (CH 2 ) 3 SO 3 − (ref.…”

Fluorescence turn-on by photoligation – bright opportunities for soft matter materials

“…Nevertheless, redshifting the activation wavelength of photochemical ligations is an ongoing challenge in the realm of photochemical pericyclic reactions, where the current maximum ligation wavelength is close to 550 nm. 128,129 We have recently introduced tetrazoles with activation wavelengths exceeding 500 nm 69 and further efforts should concentrate on making such long wavelength activated systems available in aqueous environments through suitable hydrophilic handles. Similarly, the use of up-conversion nanoparticles can be an attractive option to push activation wavelengths in tetrazole systems.…”

4D Materials with Photoadaptable Properties Instruct and Enhance Intestinal Organoid Development

“…Moreover, emerging hydrogel technologies present new opportunities for sequential or repeatable degradation and cross-linking in a spatiotemporal manner. 34,37,38 While many advanced photochemistries that enable these properties have yet to reach the intestinal organoid community, unique mechanical conditioning involving both softening and stiffening will be made newly accessible by next-generation biomaterials incorporating this orthogonal responsiveness. These technologies are also challenging to apply in a highthroughput manner to intestinal organoids.…”