Xuxu Yang

Supramolecular Lego Assembly Towards Three‐Dimensional Multi‐Responsive Hydrogels

Inspired by the assembly of Lego toys, hydrogel building blocks with heterogeneous responsiveness are assembled utilizing macroscopic supramolecular recognition as the adhesion force. The Lego hydrogel provides 3D transformation upon pH variation. After disassembly of the building blocks by changing the oxidation state, they can be re-assembled into a completely new shape.

Fast-moving soft electronic fish

A soft robotic fish can quickly swim and turn with a fully integrated onboard system for power and remote control. Soft robots driven by stimuli-responsive materials have unique advantages over conventional rigid robots, especially in their high adaptability for field exploration and seamless interaction with humans. The grand challenge lies in achieving self-powered soft robots with high mobility, environmental tolerance, and long endurance. We are able to advance a soft electronic fish with a fully integrated onboard system for power and remote control. Without any motor, the fish is driven solely by a soft electroactive structure made of dielectric elastomer and ionically conductive hydrogel. The electronic fish can swim at a speed of 6.4 cm/s (0.69 body length per second), which is much faster than previously reported untethered soft robotic fish driven by soft responsive materials. The fish shows consistent performance in a wide temperature range and permits stealth sailing due to its nearly transparent nature. Furthermore, the fish is robust, as it uses the surrounding water as the electric ground and can operate for 3 hours with one single charge. The design principle can be potentially extended to a variety of flexible devices and soft robots.

A bioinspired reversible snapping hydrogel assembly

Controlling the response for stimuli-responsive shape changing polymers is critically important for their device applications. The snapping transformation of the Venus Flytrap has inspired the design of shape changing devices with a unique controlling mechanism in mechanical instability, yet their practical potential has been quite limited due to the irreversible nature. Herein, we report an approach to achieve an unprecedented reversible snapping. The material system is a hydrogel assembly that can be mechanically programmed to exhibit instability based bi-stable states. Taking advantages of the multi-responsiveness of the hydrogels allows reversible switching between the two stable states in an abrupt non-continuous (snap) fashion, with unique benefits in precise time-delayed deployment, accelerated deployment speed, and enhanced output force. The mechanism behind our design can be readily extended beyond hydrogels to enhance the performances of diverse multifunctional smart devices.

Thermoplastic Dielectric Elastomer of Triblock Copolymer with High Electromechanical Performance

Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single-component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene-b-butyl acrylate-b-styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g-1 within the excitation frequency range of 300-800 Hz.

Electromechanical behavior of fiber-reinforced dielectric elastomer membrane

Based on its large deformation, light weight, and high energy density, dielectric elastomer (DE) has been used as driven muscle in many areas. We design the fiber-reinforced DE membrane by adding fibers in the membrane. The deformation and driven force direction of the membrane can be tuned by changing the fiber arrangements. The actuation in the perpendicular direction of the DE membrane with long fibers first increases and then decreases by the increasing of the fiber spacing in the perpendicular direction. The horizontal actuation of the membrane decreases by decreasing the spacing of short fibers. In the membrane-inflating structure, the radially arranged fibers will break the axisymmetric behavior of the structure. The top area of the inflated balloon without fiber will buckle up when the voltage reaches a certain level. Finite element simulations based on nonlinear field theory are conducted to investigate the effects of fiber arrangement and verify the experimental results. This work can guide the design of fiber-reinforced DE.

Soft Artificial Bladder Detrusor

Developing soft devices for invasive procedures bears great importance for human health. The softness and large strain actuation of responsive hydrogels promise the potential to fabricate soft devices, which can attach on and assist to the function of organs. The key challenges lie in the fabrication of soft devices with robust actuating ability and biocompatibility to the attached organ. This paper presents a solution that integrates the thermoresponsive hydrogel membrane with flexible electronics and silk scaffold into a balloon-like soft device. As an example, the actuation assisting function of this soft device for shrinking an animal bladder is presented. The mechanical behaviors of the balloon-like soft device are experimentally and theoretically investigated. The concepts are applicable to other applications such as soft implants, soft robotics, and microfluidics.

Three dimensional responsive structure of tough hydrogels

Three dimensional responsive structures have high value for the application of responsive hydrogels in various fields such as micro fluid control, tissue engineering and micro robot. Whereas various hydrogels with stimuli-responsive behaviors have been developed, designing and fabricating of the three dimensional responsive structures remain challenging. We develop a temperature responsive double network hydrogel with novel fabrication methods to assemble the complex three dimensional responsive structures. The shape changing behavior of the structures can be significantly increased by building blocks with various responsiveness. Mechanical instability is built into the structure with the proper design and enhance the performance of the structure. Finite element simulation are conducted to guide the design and investigate the responsive behavior of the hydrogel structures

Fiber-reinforced dielectric elastomer laminates with integrated function of actuating and sensing

The natural limbs of animals and insects integrate muscles, skins and neurons, providing both the actuating and sensing functions simultaneously. Inspired by the natural structure, we present a novel structure with integrated function of actuating and sensing with dielectric elastomer (DE) laminates. The structure can deform when subjected to high voltage loading and generate corresponding output signal in return. We investigate the basic physical phenomenon of dielectric elastomer experimentally. It is noted that when applying high voltage, the actuating dielectric elastomer membrane deforms and the sensing dielectric elastomer membrane changes the capacitance in return. Based on the concept, finite element method (FEM) simulation has been conducted to further investigate the electromechanical behavior of the structure.

Highly stretchable, transparent, and colorless electrodes from a diblock copolymer electrolyte

Herein, highly stretchable, transparent, and colorless, electrodes free of liquid and non-volatile components were fabricated for the first time. Crosslinkable diblock copolymers of poly[(ethylene glycol)9 methyl ether acrylate-b-n-butyl acrylate] with preset molecular weights and compositions were synthesized via reversible addition–fragmentation chain transfer polymerization in solution. The electrodes were made of diblock copolymer/LiClO4 composites. It was found that the dielectric elastomer actuators (DEAs) made of an acrylic dielectric elastomer (VHBTM4910) and the electrodes of the crosslinked poly[(ethylene glycol)9 methyl ether acrylate140-b-n-butyl acrylate80]/LiClO4 could exhibit actuation area strains over 100% when driven by voltage. The DEAs showed over 90% light transmittance in the entire range of the visible wavelengths. The block architecture and composition were crucial for the electrode performance although only the block of poly[(ethylene glycol)9 methyl ether acrylate] contributed to ionic conductivity. The presence of poly(butyl acrylate) blocks avoided dewetting during electrode fabrication such that a transparent electrode was achieved.

The behavior of dielectric elastomer actuators connected in series and parallel

Dielectric elastomer membrane has the ability of shrinking the thickness and expanding surface area when a voltage is applied through its thickness. Dielectric elastomer has been widely studied and used as dielectric elastomer actuator (DEA), dielectric elastomer generator (DEG) and dielectric elastomer sensor (DES). We study the behavior of several DEAs connected in series and parallel, and find that the different connecting models can achieve different responses of the DEAs. DEAs connected in series can enhance the actuation, while DEA connected in parallel can enhance the actuation force. In our experiment, DEAs connected in series and parallel are loaded in actuation direction under a dead load providing pre-stretch. We discuss the results of the experiments and give the conclusions.