Biomimetic 4D‐Printed Breathing Hydrogel Actuators by Nanothylakoid and Thermoresponsive Polymer Networks

Abstract

Shape-morphing actuators, which can breathe with the accompany of morphology changes to mimic botanical events, are challenging to fabricate with soft hydrogel materials. Herein, 4D printed-smart hydrogel actuators are reported that can not only dynamically deform but also generate oxygen (O 2 ) upon external stimulations. The printed breathing actuators featured with spinach leaf-derived thylakoid membrane (nanothylakoid) for photothermal conversion and catalytical O 2 evolution, a poly(N-isopropylacrylamide) (PNIPA) thermoresponsive polymer network for generating deformation forces by swelling/shrinkage (rehydration/dehydration), and an asymmetric bilayer poly(N-isopropylacrylamide)/polyacrylamide (PNIPA/PAA) structure to amplify the mechanical motions. Upon thermal stimulation or laser irradiation, the actuator can reversibly bend/unbend because of the photothermal conversion of nanothylakoid and the printed thermoresponsive asymmetric bilayer structure. Additionally, the catalase-like property of nanothylakoid imparts the actuator with O 2 evolution capability to breathe for further mimicking botanical systems. Notably, 4D printing can greatly facilitate and simplify the actuator fabrication process, including adjusting the size and layer compositions. This artificial breathing actuator with photothermal and catalytical properties provides a strategy in designing intelligent hydrogel systems and proves to be a highly promising material candidates in the fields of 3D/4D printing, automated robotics, and smart biomedical devices.

A Shift from Efficiency to Adaptability: Recent Progress in Biomimetic Interactive Soft Robotics in Wet Environments

“…The reversible swelling‐deswelling property of hydrogels by stimuli can be exploited to produce macroscopic actuation for soft robots. A large variety of stimuli, such as heat, [ 142 , 143 , 144 , 145 , 146 , 147 , 148 , 149 ] light, [ 150 , 151 , 152 , 153 ] water, [ 154 , 155 ] pH, [ 156 , 157 , 158 ] biomolecules, [ 159 , 160 ] and electric field, [ 157 , 161 , 162 , 163 ] can change the osmotic pressure of solvents in hydrogels and/or environments, resulting in water diffusion in or out of the hydrogels, corresponding to their expansion or contraction, respectively. [ 164 ] Other than common physical stimuli, a recent study showed that a hydrogel robot could locomote on water surface for 3.5 h by the Marangoni effect (Figure 5e ).…”

Multicompartment Hydrogels

“…Recently, Wang and co‐workers fabricated a photoactive actuator via 3D printing ( Figure ). [ 322 ] A thermoresponsive PNIPAM‐based layer loaded with spinach‐leaf‐derived nanothylakoid was combined with a PAA layer. The nanothylakoid was introduced to enable photothermal conversion and oxygen evolution.…”

“…a) Formation via 3D printing, b) final flower-shaped two-layer hydrogel (crosslinked PNIPAM/PAA with 3:1-layer ratio),and c) movement of the flower-shaped actuator to grab a moving object. Reproduced with permission [322]. Copyright 2021, Wiley-VCH GmbH.…”

Multiresponsive Ti3C2Tx MXene-Based Actuators Enabled by Dual-Mechanism Synergism for Soft Robotics

“…Smart actuators that can transform other forms of energy into mechanical deformation from external stimuli such as heat, light, electricity, magnetism, solvent, pH, and humidity have been widely studied due to their potential applications in soft robotics, biomedical devices, haptic feedback systems, and so on. − To date, substantial efforts have been devoted to developing flexible actuators based on various active materials such as electroactive polymers (EAPs), ,,− shape memory polymers (SMPs), − liquid crystal elastomers (LCEs), , hydrogels, ,− and bimorph nanocomposites. ,,− Among these actuating materials, stimuli-responsive bimorph nanocomposite-based flexible actuators have recently come to the fore due to their simple structure, low production cost, high stability, and so on. ,− Unlike other previously mentioned flexible and soft actuators, the principal actuation mechanism for these bimorph actuators is attributed to asymmetric deformation at the interfaces due to their mismatched thermal, mechanical, and electrical properties . To date, many materials such as carbon nanotubes (CNTs), ,,, graphene, ,, graphene oxide, , and poly­(3,4-ethylene­dioxythiophene):polystyrene sulfonate (PEDOT:PSS) , have been utilized in bimorph flexible actuators.…”