Light‐Fueled Nonequilibrium and Adaptable Hydrogels for Highly Tunable Autonomous Self‐Oscillating Functions

Abstract

Nonequilibrium oscillation fueled by dissipating chemical energy is ubiquitous in living systems for realizing a broad range of complex functions. The design of synthetic materials that can mimic their biological counterparts in the production of dissipative structures and autonomous oscillations is of great interest but remains challenging. Here, a series of environmentally adaptable hydrogels functionalized with photoswitchable spiropyran derivatives that display a tunable equilibrium‐shifting capability, thus endowing those hydrogels with a high degree of freedom and flexibility is reported. Such nonequilibrium hydrogels are able to responsively adapt their shapes under constant light illumination due to asymmetric deswelling, which in turn generates self‐shadowing and consequently creates autonomous self‐oscillating behaviors through a negative feedback process. Diverse oscillation modes including bending, twisting, and snap‐through buckling with tunable frequency and amplitude are widely observed in three different molecular systems. Density functional theory calculations and finite element simulations further demonstrated the robustness of such a photoadaptable self‐oscillation mechanism. This study provides a useful molecular design strategy for construction of highly adaptable hydrogels with potential applications in self‐sustained soft robots and autonomous devices.

Light-Dissipative and Reprogrammable DNA Hydrogels Enabled by Merocyanine Photoacids

“…However, we failed to obtain the p K a h ν of compound 6 as the irradiation intensity in our experiment is unable to drive the full isomerization of MCH to the cis -MCH and SP isomers (Figure S18). This phenomenon has also been reported previously in the literature, where the electron-donating methoxy substituent in the chromene ring favorably shifts the equilibrium to the protonated MCH form …”

“…This phenomenon has also been reported previously in the literature, where the electrondonating methoxy substituent in the chromene ring favorably shifts the equilibrium to the protonated MCH form. 48 We studied the light-induced pH changes of photoacid 5 by varying its concentrations in an aqueous environment at 25 °C (Figure S19). The solution is incubated in the dark to reach an equilibrium pH value before irradiation with visible light.…”

“…Extending light-fueled DNA dissipative assembly to a larger length scale, for example, to a macroscale solid-like phase, would provide possibilities for the creation of bulk materials with characteristics such as mechanical property and processability. Based on our previous experiences in spiropyran (SP) hydrogels, , in this work, we design new merocyanine photoacids bearing a robust large pH-adjustment capability, which is able to broaden light-fueled DNA dissipative assembly from an aqueous sol to a solid-like gel phase. The presence of such photoacids allows for remote and spatiotemporal manipulation of the photoinactive DNA component to cause an obvious sol–gel transition upon irradiation with light.…”

Bio‐Inspired Far‐From‐Equilibrium Hydrogels: Design Principles and Applications

“…Recently, the researchers designed a photocontrolled non-equilibrium hydrogel with complex actuation behavior by introducing spiropyran into the designed hydrogels. [162] They modified different electron donor groups on spiropyran to regulate the rate of its spontaneous ring-opening processes and create metastable states, Figure 21E. Such design endows the hydrogels with adaptable photo-triggered oscillatory behavior to change shapes through asymmetric deswelling under light irradiation, Figure 21F.…”

“…The combination of two pH‐responsive gels constitutes a jellyfish‐like functional structure with synergistic color change and shape deformation, opening pathways for out‐of‐equilibrium actuators with sophisticated and dynamic functions, Figure 21C–D. Recently, the researchers designed a photo‐controlled non‐equilibrium hydrogel with complex actuation behavior by introducing spiropyran into the designed hydrogels [162] . They modified different electron donor groups on spiropyran to regulate the rate of its spontaneous ring‐opening processes and create metastable states, Figure 21E.…”