Saltwater-Induced Rapid Gelation of Photoredox-Responsive Mucomimetic Hydrogels.

Shear-thinning hydrogels represent an important class of injectable soft materials that are often used in a wide range of biomedical applications. Typically, the hydrogel network is formed prior to injection and "heals" once the shearing forces have been removed. However, creation of new shear-thinning materials often requires that factors such as viscosity, injection rate/force, and needle gauge be evaluated to achieve efficient delivery, while simultaneously protecting potentially sensitive cargo (e.g., cells). Here, a new approach to establishing shear-thinning hydrogels is reported where a host-guest crosslinked network initially remains soluble in deionized water but is kinetically trapped as a viscous hydrogel once exposed to a high ionic strength solution. The shear-thinning properties of the viscous hydrogel may then be "switched on" in response to heating or exposure to visible light. These hydrogels consist of polynorbornene-based bottlebrush copolymers with porphyrin- and oligoviologen-containing side chains that are crosslinked through the reversible formation of β-cyclodextrin-adamantane host-guest inclusion complexes. The resultant viscous hydrogels displayed broad adhesive properties across polar and non-polar substrates, mimicking that of natural mucous and thus making it easier to distribute onto a wide range of surfaces. Additional control over the hydrogel's mechanical properties (storage/loss moduli) and performance (adhesion) was achieved post-injection using a low-energy (blue light) photoinduced electron-transfer process. We envision these injectable copolymers and corresponding multimodal viscous hydrogels can serve as versatile next-generation biomaterials capable of light-based mechanical manipulation post-injection. This article is protected by copyright. All rights reserved.