Vitrimers/polymeric network with dynamic covalent bonds (paper 1,2,3)

Vitrimer has recently emerged as a polymer combining great processability, self-healing capability and high-temperature mechanical properties. Most of those salient features of a vitrimer originate from the existence of dynamic covalent bonds in the polymer network. We try to understand the nonlinear viscoelasticity and fracture behavior of vitrimer under different loading conditions.

Autonomous and Self-motivated motion (paper 1,2,3)

Self-sustained motion of a structure, driven by steady stimulus, has recently attracted much attention . Continuous and self-sustained motions have been intensively explored for enabling the locomotion of a robot, energy harvesting, self-cleaning, and mass transportation. We explore the systems which can have self-motivated motion and model their dynamics.

3D printing of soft actuator (paper 1,2)

We explore different methods to 3D print various soft actuating materials.

Reprogrammable multimodal soft actuator (paper)

The booming of soft robots has recently motivated myriad designs of soft actuators. New forms of soft actuators have indeed enabled the construction of novel soft robots with various functionalities. Though soft actuators with different actuation modes have been developed in previous researches, their actuation capabilities are often fixed once their fabrication is completed. Herein, a novel soft actuator has been designed and fabricated which is reprogrammable and can be easily electrically controlled. The soft actuator is constructed through combing a recently developed thermally responsive material: disulfide liquid crystal elastomer, and the advancements in fabricating stretchable and flexible electronics. Thanks to the dynamic covalent chemistry and phase transformation in the disulfide liquid crystal elastomer, actuation modes of the soft actuator such as contraction, bending and shearing can be programmed, erased and reprogrammed in a facile way. With the embedded conductive wires of serpentine shape, the actuation of the actuator can be controlled by electricity, so it can be easily integrated with low cost and commonly used electrical control system. With the reprogrammability and easy control, the newly developed general-purpose soft actuator may find its wide applications in making diverse systems and devices.

Soft tubular actuator (paper) (video)

Soft tubular actuators can be widely found both in nature and in engineering applications. The benefits of tubular actuators include (1) multiple actuation modes such as contraction, bending, and expansion; (2) facile fabrication from a planar sheet; and (3) a large interior space for accommodating additional components or for transporting fluids. Most recently developed soft tubular actuators are driven by pneumatics, hydraulics, or tendons. Each of these actuation modes has limitations including complex fabrication, integration, and non-uniform strain. We design and construct soft tubular actuators using an emerging artificial muscle material that can be easily patterned with programmable strain: liquid crystal elastomer. Controlled by an externally applied electrical potential, the tubular actuator can exhibit multidirectional bending as well as large (~40%) homogenous contraction. Using multiple tubular actuators, we build a multifunctional soft gripper and an untethered soft robot.

Human-(soft) machine interface (paper) (videos1,2,3,4,5)

Soft robots or soft machines have been recently explored intensively to work collaboratively with human beings. Most of the previously developed soft robots are either controlled manually or by different prewritten programs. We developed a novel human-machine interface is to use electrooculographic signals generated by eye movements to control the motion and the change of focal length of a biomimetic soft lens. The motion and deformation of the soft lens are achieved by the actuation of different dielectric elastomer films, mimicking the working mechanisms of the eyes of human and most mammals. The system developed in the current study has the potential to be used in visual prostheses, adjustable glasses, and remotely operated robotics in the future.

Light-induced multimodal locomotion of an LCE robot (paper)(videos 1,2,3,4)

Inspired by the movement of caterpillar and fly larva, we demonstrated a bioinspired design of a light-powered untethered soft robot which can crawl on the ground, squeeze itself to pass small channels, and jump over obstacles or onto a step above the ground. For the multimodal locomotion of the soft robot, the associated deformation is elastic, enabling the structural reversibility. Furthermore, we develop a mathematical model to quantitatively understand the multimodal locomotion of the light-powered soft robot.

Hydrogel-based ionic diode and logic gates (paper)

We design and fabricate transparent and highly stretchable hydrogel diode and logic gates, which may potential applications in the field of human machine interface.

Light-powered tensegrity Robot (paper) (videos 1,2,3,4,5,6,7)

We design and construct a tensegrity robot based on LCE artificial muscle. The robot has large deformability, low weight, high load capacity.

Wrinkles Riding Waves in Soft Layered Materials (paper)

We study the formation of wrinkles in a still thin film bonded onto a soft substrate under impact.

Vascular LCE-based artificial muscle (paper) (videos 1,2,3,4)

We introduce fluidic channels into LCE to achieve fast actuation.

Autonomous rolling of LCE rod (paper) (videos 1,2,3,4,5,6,7)

We discovered autonomous rolling phenomenon of a LCE rod on a hot plate of homogeneously elevated temperature.

Daughter cell separation as unstable crack growth (paper)

We model the daughter cell separation as an unstable crack growth process.

Instability of a balloon subject to voltage and pressure (paper 1,2,3)

We analyze electromechanical instability phenomenon in a dielectric elastomer balloon subject to inner pressure and external voltage.

Liquid crystal elastomer with dynamic covalent bond (paper 1,2)

We synthesized disulfide liquid crystal elastomer, with programability, self-healing capability, re-processability etc. We also uncovered living exchange reactions of disulfide bonds.

Contact and adhesion of a stretched elastomer/hydrogel (paper 1,2,3,4)

We conduct both analytical and numerical studies on contact between a rigid probe and prestretched elastomer (with or without surface tension, infinitely large or finite thickness) and hydrogel.

Soft swimming robot (paper1,2) (videos 1,2)

We design and fabricate a soft robot which can swim in water, driven either by light or voltage.

Fracture of liquid crystal elastomer (paper)

We found that the toughening mechanism in liquid crystal elastomer, associated with polydomain-to-monodomain transition.

Voltage-induced wrinkling (paper)(video)

Analytical studies on voltage-induced wrinkling in a DE annulus.

Cell mechanics (paper 1,2)

We collaborate with Prof. Ming Guo (MIT) working on complex mechanics of cytoplasm. We aim to uncover the mechanism associated with large deformation, damping, damage, toughening and self-healing of cells.

Cavitation in soft materials (paper 1,2,3,4,5,6)

We studied cavitation in soft materials.

Fatigue of stretchable elastomer (paper)

We characterized crack growth in stretchable acrylic elastomer under cyclic loading.

Mechanics of nanofibers (paper1,2)

We uncovered very strong size-dependent dynamic mechanical behaviors of both inorganic nanofibers and polymer nanofibers.

Large deformation and instabilities in soft materials (paper 1,2,3,4)

We investigated nonlinear instabilities in soft materials associated with large deformation.