Transparent, photothermal and stretchable alginate-based hydrogels for remote actuation and human motion sensing.

Multifunctional hydrogels show potential applications in actuators and wearable sensors. However, it is still a challenge to develop a photothermal responsive conductive hydrogel with high transparency, mechanical properties, broad sensing range, and low-temperature resistance. In this work, a transparent, photothermal responsive, and highly stretchable alginate-based hydrogels was feasibly constructed by adding two-dimensional non-layered molybdenum dioxide nanosheets (2D-MoO2) to sodium alginate/polyacrylamide mixture and then soaking into the calcium chloride solution. The introduction of 2D-MoO2 renders the hydrogels excellent photothermal properties and controllable photomechanical deformation under near-infrared irradiation, while maintaining high transparency (~60 %).The calcium ions give the hydrogel excellent mechanics, conductivity, and freezing tolerance concurrently. The transparent hydrogel-based sensor shows wide sensing range (0-1800 %) and cycling stability in detecting deformations and real-time human motions even in harsh environments. Therefore, this work provides a new route for generating transparent multifunctional hydrogels towards the applications of remote actuation and strain sensing.

Rapid Photothermal Responsive Conductive MXene Nanocomposite Hydrogels for Soft Manipulators and Sensitive Strain Sensors.

Stimulus-responsive hydrogels are of great significance in soft robotics, wearable electronic devices, and sensors. Near-infrared (NIR) light is considered an ideal stimulus as it can trigger the response behavior remotely and precisely. In this work, a smart flexible stimuli-responsive hydrogel with excellent photothermal property and decent conductivity are prepared by incorporating MXene nanosheets into the physically cross-linked poly(N-isopropyl acrylamide) hydrogel matrix. Because of outstanding photothermal effect and dispersion of MXene, the composite hydrogel exhibits rapid photothermal responsiveness and excellent photothermal stability under the NIR irradiation. Furthermore, the anisotropic bilayer hydrogel actuator shows fast and controllable light-driven bending behavior, which can be used as a light-controlled soft manipulator. Meanwhile, the hydrogel sensor exhibits cycling stability and good durability in detecting various deformation and real-time human activities. Therefore, the present study involving the fabrication of MXene nanocomposite hydrogels for potential applications in remotely controlled actuator and wearable electronic device provides a new method for the development of photothermal responsive conductive hydrogels.

Arbitrarily Reconfigurable and Thermadapt Reversible Two-Way Shape Memory Poly(thiourethane) Accomplished by Multiple Dynamic Covalent Bonds.

The fabrication of a single polymer network that exhibits a good reversible two-way shape memory effect (2W-SME), can be formed into arbitrarily complex three-dimensional (3D) shapes, and is recyclable remains a challenge. Herein, we design and fabricate poly(thiourethane) (PTU) networks with an excellent thermadapt reversible 2W-SME, arbitrary reconfigurability, and good recyclability via the synergistic effects of multiple dynamic covalent bonds (i.e., ester, urethane, and thiourethane bonds). The PTU samples with good mechanical performance simultaneously demonstrate a maximum tensile stress of 29.7 ± 1.1 MPa and a high strain of 474.8 ± 7.5%. In addition, the fraction of reversible strain of the PTU with 20 wt % hard segment reaches 22.4% during the reversible 2W-SME, where the fraction of reversible strain is enhanced by self-nucleated crystallization of the PTU. A sample with arbitrarily complex permanent 3D shapes can be realized via the solid-state plasticity, and that sample also exhibits excellent reversible 2W-SME. A smart light-responsive actuator with a double control switch is fabricated using a reversible two-way shape memory PTU/MXene film. In addition, the PTU networks are de-cross-linked by alcohol solvolysis, enabling the recovery of monomers and the realization of recyclability. Therefore, the present study involving the design and fabrication of a PTU network for potential applications in intelligent actuators and multifunctional shape-shifting devices provides a new strategy for the development of thermadapt reversible two-way shape memory polymers.

Thermal/Near-Infrared Light Dual-Responsive Reversible Two-Way Shape Memory cEVA/2D-MoO2 Composite for Multifunctional Applications.

Light-responsive reversible two-way shape memory polymers (2W-SMPs) are highly promising for many fields due to indirect heating, clean, and remote control. In this work, a composite with both thermal- and near-infrared (NIR) light-induced reversible two-way shape memory effect (2W-SME) is prepared by doping extremely little quantities of 2D non-layered molybdenum dioxide nanosheets (2D-MoO2 ) into semicrystalline poly(ethylene-co-vinyl acetate) (EVA) networks. This is the first report on light-induced reversible two-way shape memory composites employing 2D-MoO2 as photothermal fillers. Upon switching the NIR light on and off, due to the excellent photothermal feature and stability of 2D-MoO2 , the composite exhibits remarkable light-induced reversible 2W-SME. A light-driven actuator for sensing applications is designed based on the composite and the circuit, where the lamp acting as an alarm can raise and fade upon responding to NIR light. A completely flexible, fuel-free self-walking soft robot is designed based on the advantages of the light-responsive reversible 2W-SMPs. Additionally, the composite acting as a light-fueled crane is able to lift and lower a load that is 3846 times its own weight. The results demonstrate that the prepared composite has a promising prospect for applications as actuators, self-walking soft robot and crane.