Reversible Modulation of Elasticity in Fluoroazobenzene-Containing Hydrogels Using Green and Blue Light.

Hydrogels are soft materials that have found multiple applications in biomedicine and represent a good platform for the introduction of molecular switches and synthetic machines into macromolecular networks. Tuning their mechanical properties reversibly with light is appealing for a variety of advanced applications and has been demonstrated in the past; however, their activation typically requires the use of UV light, which displays several drawbacks related to its damaging character and limited penetration in tissues and materials. This study circumvents this limitation by introducing all-visible ortho-fluoroazobenzene switches into a hydrophilic network, which, as a result, can be activated with green or blue light. Photoisomerization of the photochromic moieties is accompanied by a reversible tuning of the elastic modulus. The translation of molecular isomerization within the network into macroscopic modulation of its mechanical properties is attributed to different aggregation tendencies of the E and Z isomers of the azobenzene derivatives.