A dynamic self-regulation actuator combined double network gel with gradient structure driven by chemical oscillating reaction

Region-dependent volumetric oscillation of self-oscillating gels with gradient transducers

Heartbeats with different ventricular contractions vary with heart regions, which can be described as anisotropy. Herein, we report self-oscillating gels which exhibit region-dependent anisotropic volumetric oscillation behavior similar to that of the heart. We installed a (Ru(bpy)₃) gradient transducer on self-oscillating gels by employing slow and unidirectional diffusion in the gels and dipping part of the gel into a Ru(bpy)₃-NHS solution. We found that the spatial distribution of Ru(bpy)₃ in the gel caused region-dependent swelling/deswelling behavior depending on the redox state. We also confirmed that gel regions with smaller Ru(bpy)₃ amounts exhibit lower amplitudes than those with larger amounts of Ru(bpy)₃ during the Belousov-Zhabotinsky (BZ) reaction. These results are important in the design of self-oscillating soft actuators or machines, such as a biomimetic pump with desirable anisotropic oscillating behavior.

Oxidation-degree-dependent moisture-induced actuation of a graphene oxide film

Multilayered films prepared from graphene oxide (GO) subjected to a single oxidation process (1GO) can actuate in response to moisture, whereas those prepared from GO subjected to two oxidation processes (2GO) lose this ability. To elucidate the origin of this difference, the structures and properties of various multilayered films and their contents were analyzed. According to atomic force microscopy images, the lateral size of the GO monolayer in 2GO (2.0 ± 0.4 μm) was smaller than that in 1GO (3.2 ± 0.4 μm), although this size difference did not affect actuation. Scanning electron microscopy images of the cross sections of both films showed fine multilayered structures and X-ray diffraction measurements showed the moisture sensitive reversible change in the interlayer distances for both films. Both films adsorbed 30 wt% moisture in 60 s with different water contents at the bottom moist sides and top air sides of the films. Nanoindentation experiments showed hardness values (1GO: 156 ± 67 MPa; 2GO: 189 ± 97 MPa) and elastic modulus values (1GO: 4.7 ± 1.7 GPa; 2GO: 5.8 ± 3.2 GPa) typical of GO, with no substantial difference between the films. On the contrary, the 1GO film bent when subjected to a weight equal to its own weight, whereas the 2GO film did not. Such differences in the macroscopic hardness of GO films can affect their moisture-induced actuation ability.

Fuel-Driven and Enzyme-Regulated Redox-Responsive Supramolecular Hydrogels

Chemical reaction networks (CRN) embedded in hydrogels can transform responsive materials into complex self-regulating materials that generate feedback to counter the effect of external stimuli. This study presents hydrogels containing the β-cyclodextrin (CD) and ferrocene (Fc) host-guest pair as supramolecular crosslinks where redox-responsive behavior is driven by the enzyme-fuel couples horse radish peroxidase (HRP)-H2 O2 and glucose oxidase (GOx)-d-glucose. The hydrogel can be tuned from a responsive to a self-regulating supramolecular system by varying the concentration of added reduction fuel d-glucose. The onset of self-regulating behavior is due to formation of oxidation fuel in the hydrogel by a cofactor intermediate GOx[FADH2 ]. UV/Vis spectroscopy, rheology, and kinetic modeling were employed to understand the emergence of out-of-equilibrium behavior and reveal the programmable negative feedback response of the hydrogel, including the adaptation of its elastic modulus and its potential as a glucose sensor.