Temporary Actuation of Bilayer Polymer Hydrogels Mediated by the Enzymatic Reaction

Abstract

Most soft actuators have the ability of monotonic responsiveness. That is, there is only one response action after being stimulated once. In this work, a temporarily responsive bilayer hydrogel actuator is designed and fabricated by combining a tertiary amine-containing pH-responsive layer and a urease-containing non-responsive layer. The hydrogel actuator can achieve programed deformation and recovery driven by chemical fuels (i.e., acidic urea solutions), which is essentially regulated by rapid acidification and slow enzymatic production of ammonia for recovering the pH of the system. The actuation extent and duration can be simply controlled by the fuel levels, and the repeated actuations are also possible via refueling. Furthermore, we fabricate several hydrogel devices that can display specific patterns or lift an item. This enzymatic method shows new possibilities to control the temporary actuation of polymer hydrogels potentially useful in many fields such as soft robotics, biomimetic devices, and environmental sensing.

Transient regulation of gel properties by chemical reaction networks

“…In recent years, the temporary actuation of bilayer polymer hydrogels driven by pH changes that can be adjusted spontaneously and temporarily has earned a great deal of study interest. 18,19,43 In a recent study, we used acrylamide and dimethylaminoethyl methacrylate (DMAEMA) as monomers to synthesize responsive hydrogel layers, which combined with the non-responsive PAAm hydrogels containing urease to form bilayer hydrogel actuators (Fig. 7).…”

“…29,44,90,91,111 (v) Temporary actuation of gels: The main changes during the actuation processes are the alterations in the swelling ratio and curvature of the gels. 19,43 (vi) Cascade reaction-based self-reporting of external stimuli: Depending on the alarm signals, different characterization methods such as fluorescence and chemiluminescence spectroscopy can be used. 45,106 Although the common characterization techniques for these six aspects are summarized here, the most appropriate characterization method should be chosen according to the features of the system in practice.…”

“…11,12 Recent works have shown the great potential of nonequilibrium gels in a wide range of applications, including information encryption, [13][14][15] drug release, 16 wound dressings, 17 and smart actuators. 18,19 Therefore, gels with transiently regulated properties are now at the forefront of research in the fields of systems chemistry and dynamic materials. [20][21][22] Inspired by the nonequilibrium dynamic processes in living organisms, researchers have designed many artificial systems that exist far from equilibrium to generate gels with transient structural and functional tunability.…”

“…11,12 Recent works have shown the great potential of nonequilibrium gels in a wide range of applications, including information encryption, 13–15 drug release, 16 wound dressings, 17 and smart actuators. 18,19 Therefore, gels with transiently regulated properties are now at the forefront of research in the fields of systems chemistry and dynamic materials. 20–22…”

Designing Multistimuli-Responsive Anisotropic Bilayer Hydrogel Actuators by Integrating LCST Phase Transition and Photochromic Isomerization

“…In recent years, bilayer hydrogel actuators with different swelling rates have been widely studied [ 21 , 22 , 23 , 24 ]. Due to their asymmetric response characteristics, the shape deformation can be obtained [ 25 , 26 , 27 ]. Bilayer hydrogels can be obtained by layer-by-layer polymerization or macroscopic assembly by host-guest interactions or hydrogen bonds as reversible switches.…”