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Dielectric elastomers (DEs) can act as deformable capacitors that generate mechanical work in response to an electric field. DEs are often based on commercial acrylic and silicone elastomers. Acrylics require prestretching to achieve high actuation strains and lack processing flexibility. Silicones allow for processability and rapid response but produce much lower strains. In this work, a processable, high-performance dielectric elastomer (PHDE) with a bimodal network structure is synthesized, and its electromechanical properties are tailored by adjusting cross-linkers and hydrogen bonding within the elastomer network. The PHDE exhibits a maximum areal strain of 190% and maintains strains higher than 110% at 2 hertz without prestretching. A dry stacking process with high efficiency, scalability, and yield enables multilayer actuators that maintain the high actuation performance of single-layer films.

Variable stiffness materials are an important class of materials that are useful in soft robotics, reconfigurable devices, deployable vehicles, and artificial muscles. Most variable stiffness polym...

Tunable rigidity materials have potentially widespread implications in robotic technologies. They enable morphological shape change while maintaining structural strength, and can reversibly alternate between rigid, load bearing and compliant, flexible states capable of deformation within unstructured environments. In this review, we cover a range of materials with mechanical rigidity that can be reversibly tuned using one of several stimuli (e.g. heat, electrical current, electric field, magnetism, etc.). We explain the mechanisms by which these materials change rigidity and how they have been used for robot tasks. We quantitatively assess the performance in terms of the magnitude of rigidity, variation ratio, response time, and energy consumption, and explore the correlations between these desired characteristics as principles for material design and usage.

Dielectric elastomers have been widely investigated for muscle-like soft actuators and capacitive sensors. Mechanical properties play a central role in the performances of the active material. Most elastomers have specific moduli pre-determined by the polymers' molecular structures, which are not suitable for applications in changing working conditions as natural muscles are capable of. Here new dielectric elastomers are described exhibiting variable moduli controlled via thermal treatment. The elastomers contain furan-maleimide Diels–Alder adduct moieties to administer the crosslinking densities of the elastomeric networks via reversible Diels–Alder/retro-Diels–Alder cycloaddition reaction, resulting in changes in the elastomers' moduli. One of the synthesized elastomers has moduli that can be controlled between 0.17 and 0.52 MPa incrementally and reversibly. Capacitive strain sensors based on this elastomer can be operated in both rigid and soft modes to achieve variable sensing response up to 30% linear strain. Actuators were fabricated and operated in both high strain mode (35% actuation area strain at 65 MV m−1) and high force output mode (0.55 MPa at 104 MV m−1). The elastomers can exhibit a range of stress–strain outputs in similar fashion as muscle.

Understanding the mechanistic pathways underlying the toxicity of chemicals can provide more biologically relevant models to extrapolate adverse outcomes. Mechanistically based models should provide more efficient means to screen untested compounds and predict exposure to untested species. We evaluated the relationship between reproductive outcomes in Daphnia magna and expression of biomarkers after exposure to polyaromatic hydrocarbons (PAHs). These biomarkers include Daphnia magna homologs of ARNT (aryl hydrocarbon nuclear translator), CYP4 (Cytochrome P450 Family 4), COX (cyclooxygenase), retinoid-X-receptor (RXR), and juvenile hormone esterase (JHE). To assess physiological endpoints we monitored reproductive changes in a 14-day chronic exposure. Exposure to benzo(a)pyrene resulted in altered reproduction and was correlated with increases in RXR and decreases in VTG and CYP4 genes. We then conducted exposures with a known cytochrome P450 inhibitor, PBO (piperonyl butoxide and phenanthrene. PBO alone i...