Movement and morphing in biological systems provide insights into the materials and mechanisms that may enable the development of advanced engineering structures. The nastic motion of plants in response to environmental stimuli, e.g., the rapid closure of the Venus flytrap's leaves, utilizes snap-through instabilities originating from anisotropic deformation of plant tissues. In contrast, ballistic tongue projection of chameleon is attributed to direct mechanical energy transformation by stretching elastic tissues in advance of rapid projection to achieve higher speed and power output. Here, a bioinspired trilayered bistable all-polymer laminate containing dielectric elastomers (DEs) is reported, which double as both structural and active materials. It is demonstrated that the prestress and laminating strategy induces tunable bistability, while the electromechanical response of the DE film enables reversible shape transition and morphing. Electrical actuation of bistable structures obviates the need for continuous application of electric field to sustain their transformed state. The experimental results are qualitatively consistent with our theoretical analyses of prestrain-dependent shape and bistability.

Although Ti 3 C 2 T x MXene/fabric composites have shown promise as flexible pressure sensors, the effects of MXene composition and structure on piezoresistive properties and the effects of the textile structure on sensitivity have not been systematically studied. Herein, impregnation at room temperature was used as a cost-effective and scalable method to prepare composite materials using different fabrics [plain-woven fabric, twill-woven fabric, weft plain-knitted fabric, jersey cross-tuck fabric, and nonwoven fabric (NWF)] and MXene nanosheets (Ti 3 C 2 T x , Ti 2 CT x , Ti 3 CNT x , Mo 2 CT x , Nb 2 CT x , and Mo 2 TiC 2 T x ). The MXene nanosheets adhered to the fabric surface through hydrogen bonding, resulting in a conductive network structure. The Ti 3 C 2 T x @NWF composite was found to be the optimal flexible pressure sensor, demonstrating high sensitivity (6.31 kPa −1 ), a wide sensing range (up to 150 kPa), fast response/recovery times (300 ms/260 ms), and excellent durability (2000 cycles). Furthermore, the sensor was successfully used to monitor full-scale human motion, including pulse, and a 4 × 4 pixel flexible sensor array was shown to accurately locate pressure and recognize the pressure magnitude. These findings provide a basis for the rational design of MXene/textile composites as wearable pressure sensors for medical diagnosis, human−computer interactions, and electronic skin applications.

Abstract:Interface issues urgently need to be addressed in high-performance fiber reinforced composites. In this study, different periods of O 2 plasma treatment are proposed to modify twist-free polyimide (PI) filaments to improve hydrophilicity and mechanical and interfacial properties. Feeding O 2 produces chemically active particles to modify the filament surface via chemical reactions and physical etching. According to the X-ray photoelectron spectroscopy (XPS) results, the PI filaments exhibit an 87.16% increase in O/C atomic ratio and a 135.71% increase in the C-O functional group after 180 s O 2 plasma treatment. The atomic force microscope (AFM) results show that the root mean square roughness (Rq) of the treated PI filaments increases by 105.34%, from 38.41 to 78.87 nm. Owing to the increased surface oxygenic functional groups and roughness after O 2 plasma treatment, the contact angle between treated PI filaments and water reduces drastically from the pristine state of 105.08 • to 56.15 • . The O 2 plasma treated PI filaments also demonstrate better mechanical properties than the pristine PI filaments. Moreover, after O 2 plasma treatment, the adhesion between PI filaments and poly(amic acid) (PAA) is enhanced, and the tensile strength of the polyimide/poly(amic acid) (PI/PAA) self-reinforced composites increases from 136 to 234 MPa, even causing the failure mode of the composite changes from adhesive failure to partly cohesive failure.

Bistable shells can reversibly change between two stable configurations with very little energetic input. Understanding what governs the shape and snap-through criteria of these structures is crucial for designing devices that utilize instability for functionality. Bistable cylindrical shells fabricated by stretching and bonding multiple layers of elastic plates will contain residual stress that will impact the shell's shape and the magnitude of stimulus necessary to induce snapping. Using the framework of non-Euclidean shell theory, we first predict the mean curvature of a nearly cylindrical shell formed by arbitrarily prestretching one layer of a bilayer plate with respect to another. Then, beginning with a residually stressed cylinder, we determine the amount of the stimuli needed to trigger the snapping between two configurations through a combination of numerical simulations and theory. We demonstrate the role of prestress on the snap-through criteria, and highlight the important role that the Gaussian curvature in the boundary layer of the shell plays in dictating shell stability.Multistable structures made with soft materials can reversibly change between stable configurations through a snapthrough elastic instability. Snap-through is a limit point instability [1] that is commonly observed in the eversion of an umbrella on a windy day, or in the jumping of a toy popper [2]. Such structures have utility in engineering and material systems due to their ability to remain in an alternate configuration following the removal of the applied stimulus. Bistable structures have been used in the design of biomedical devices [3], micro-electromechanical systems [4,5], energy harvesters [6,7], morphing structures [8][9][10], and architected materials that trap strain energy [11]. The snap-through of these bistable systems can be triggered by a wide range of stimuli, including temperature [12], light [13] and swelling [14][15][16].Recent research has focused on the snap-through of shells induced by non-mechanical stimuli, such as an evolving natural curvature [16,17]. Such structures often do not possess a stress-free equilibrium configuration, and are therefore modeled using a non-Euclidean shell theory [18]. The critical natural curvature needed to induce snapping of a bistable, stress-free cylindrical shell was recently shown to be proportional to the shell's initial curvature [17]. The snap-through of prestressed cylindrical shells in response to a mechanical force is commonly encountered in structures such as tape springs, tape measures, and toy snap-bracelets [19], but little is understood about the response of these shells to non-mechanical stimuli. Non-mechanical loading of prestressed shells is particularly relevant to electrically active polymers (EAP) wherein dielectric elastomers are deformed in response to an applied voltage [20].The voltage-induced stretching of EAPs is inversely proportional to the material's thickness [21], which has led researchers to significantly prestretch the nearly incompressible d...

Soft robots are those that can move like living organisms and adapt to the surrounding environment. Compared with traditional rigid robots, the advantages of soft robots, in terms of material flexibility, human–computer interaction, and biological adaptability, have received extensive attention. Flexible actuators based on light response are one of the most promising ways to promote the field of cordless soft robots, and they have attracted the attention of scientists in bionic design, actuation implementation, and application. First, the three working principles and the commonly used light-responsive materials for light-responsive actuators are introduced. Then, the characteristics of light-responsive soft actuators are sequentially presented, emphasizing the structure strategy, actuation performance, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research frontier.