Metal-organic coordination is widely used to design responsive polymers and soft devices. However, preparing redox-responsive actuators with complex structures is still a challenge, limiting their advanced applications in the fields of materials and engineering. Recently, researchers reported a photoredox-mediated design and regulation strategy to prepare metal-coordinated hydrogels through Ru(II)/Co(III) catalysis in a few seconds under visible light irradiation. At the same time, multiple polymer networks form and penetrate each other, giving the prepared hydrogel excellent mechanical properties and toughness. This fast, one-step, controllable process is highly compatible with standard photography and printing techniques and can produce layered 2D/3D structures. Importantly, the oxidative decomposition of Co(III) favors the formation of a redox-responsive network based on cobalt cation , which has the potential to design shape memory materials and actuators by modulating the Co3+/2+ state by adjusting redox environmental conditions. potential. As a proof-of-concept, a programmable air-driven actuator was successfully demonstrated to control cargo capture/release by designing a complex asymmetric structure and optimizing its performance in conjunction with typical extrusion 3D printing methods. The team reports a simple and versatile metal-organic coordination strategy for designing high-performance actuators, which shows promising applications in smart soft devices and electronics.
Figure 1. Schematic representation of the preparation of MCTH in a short time by the developed PMDR strategy under visible light (452 nm) irradiation.
Figure 2. (a) In situ rheological properties of PVI aqueous solutions with different cobalt cations. (b) UV-visible spectra of PVI/Ru(II)/Co(III) solution under different irradiation times. (c) EPR (top) spectrum of Ru(II)/Co(III) aqueous solution and FT-IR (bottom) spectrum of AAm/Ru(II)/Co(III) under continuous irradiation. (d) In situ rheological characterization of hydrogel precursors with Ru(II)/Co(III) and Ru(II)/APS photocatalytic systems, respectively. (e) Measurement of gel time of hydrogel precursors with , phenol, and phenol-free ALG. (f) Digital image of the 3D printed hydrogel with the corresponding precursor in (e).
Figure 3. (a) Stress-strain curves of MCTH and other control hydrogels. (b) Digital image of 5 kg cargo loaded with MCTH and Co2+ coordinated hydrogel. (c) XPS spectrum of cobalt cations in MCTH. (d) Stress, strain, and Young’s modulus (E) of MCTH with different molar ratios of Co(III) and imidazole units in PVI. (e) Stress-strain curves of MCTH-, acid-, and alkali-treated hydrogels. (f) Cyclic stretching of MCTH, Co2+ coordinated hydrogel, and PAAm, strained to 200%. Recycling processes of (g) MCTHs and (h) Co2+ coordinated hydrogels with different waiting times at 25 and 80 °C, respectively. (i) Continuous cyclic tensile and compression tests on MCTH and Co2+ coordinated hydrogels, respectively.
Figure 4. (a) Stress-strain curves of samples treated with MCTH and reducing agent. (b) Effect of oxidant chemicals on the mechanical properties of ASC-reduced hydrogels. (c) In situ rheological characterization of hydrogels treated sequentially with ASC and PMDR strategies with different reaction times. (d) Change in Young’s modulus of hydrogels treated with alternative ASC and PMDR. (e) SEM image of the corresponding hydrogel sample in (d). White and red bars are 100 and 25 μm, respectively. (f) Digital image of a hydrogel with reversible redox treatment capable of loading 100 g of cargo. (g) Demonstrating the shape memory properties of MCTH and (h) the recovery process of the fixed sample in water, respectively.
Figure 5. (a, b) Surface morphology and cross-section of patterned hydrogel using coating reaction solution and selective irradiation method, respectively. (c) Digital images of 3D MCTH with one- and two-time patterning by shadow masking technique. (d) Digital image of patterned MCTH and expansion-driven curling of patterned MCTH ribbons in water. (e) Schematic illustration of shape changes of different pneumatic 3D actuators.Digital images of (f) standard and (g) asymmetrically processed zigzag actuators for capturing and releasing cargos under certain air pressures, respectively.
A related paper titled Photoredox-Mediated Designing and Regulating Metal-Coordinate Hydrogels for Programmable Soft 3D-Printed Actuators was published in "ACS Macro Letters". The corresponding authors are Dr. Zhang Ping of Northwest University and Professor Yu You.
Reference:
doi.org/10.1021/acsmacrolett.2c00362
