Science News

Translucent soft robots driven by frameless fluid electrode dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) are a promising enabling technology for a wide range of emerging applications, including robotics, artificial muscles, and microfluidics. This is due to their large actuation strains, rapid response rate, low cost and low noise, high energy density, and high efficiency when compared with alternative actuators. These properties make DEAs ideal for the actuation of soft submersible devices, although their use has been limited because of three main challenges: (i) developing suitable, compliant electrode materials; (ii) the need to effectively insulate the actuator electrodes from the surrounding fluid; and (iii) the rigid frames typically required to prestrain the dielectric layers. We explored the use of a frameless, submersible DEA design that uses an internal chamber filled with liquid as one of the electrodes and the surrounding environmental liquid as the second electrode, thus simplifying the implementation of soft, actuated submersible devices. We demonstrated the feasibility of this approach with a prototype swimming robot composed of transparent bimorph actuator segments and inspired by transparent eel larvae, leptocephali. This design achieved undulatory swimming with a maximum forward swimming speed of 1.9 millimeters per second and a Froude efficiency of 52%. We also demonstrated the capability for camouflage and display through the body of the robot, which has an average transmittance of 94% across the visible spectrum, similar to a leptocephalus. These results suggest a potential for DEAs with fluid electrodes to serve as artificial muscles for quiet, translucent, swimming soft robots for applications including surveillance and the unobtrusive study of marine life.

Source: Sciencemag.org – Science Robotics Latest Content

Geometric constraints and optimization in externally driven propulsion

Micro/nanomachines capable of propulsion through fluidic environments provide diverse opportunities in important biomedical applications. In this paper, we present a theoretical study on micromotors steered through liquid by an external rotating magnetic field. A purely geometric tight upper bound on the propulsion speed normalized with field frequency, known as propulsion efficiency, , for an arbitrarily shaped object is derived. Using this bound, we estimate the maximum propulsion efficiency of previously reported random magnetic aggregates. We introduce a complementary definition of the propulsion efficiency, *, that ranks propellers according to their maximal speed in body lengths per unit time and that appears to be preferable over the standard definition in a search for fastest machines. Using a bead-based hydrodynamic model combined with genetic algorithms, we determine that *-optimal propeller deviates strongly from the bioinspired slim helix and has a surprising chubby skew-symmetric shape. It is also shown that optimized propellers with preprogrammed shape are substantially more efficient than random magnetic aggregates. We anticipate that the results of the present study will provide guidance toward prospective experimental design of more efficient magnetic micro/nanomachines.

Source: Sciencemag.org – Science Robotics Latest Content

Bioinspired living structural color hydrogels

Structural color materials from existing natural organisms have been widely studied to enable artificial manufacture. Variable iridescence has attracted particular interest because of the displays of various brilliant examples. Existing synthetic, variable, structural color materials require external stimuli to provide changing displays, despite autonomous regulation being widespread among natural organisms, and therefore suffer from inherent limitations. Inspired by the structural color regulation mechanism of chameleons, we present a conceptually different structural color material that has autonomic regulation capability by assembling engineered cardiomyocyte tissues on synthetic inverse opal hydrogel films. The cell elongation and contraction in the beating processes of the cardiomyocytes caused the inverse opal structure of the substrate film to follow the same cycle of volume or morphology changes. This was observed as the synchronous shifting of its photonic band gap and structural colors. Such biohybrid structural color hydrogels can be used to construct a variety of living materials, such as two-dimensional self-regulating structural color patterns and three-dimensional dynamic Morpho butterflies. These examples indicated that the stratagem could provide an intrinsic color-sensing feedback to modify the system behavior/action for future biohybrid robots. In addition, by integrating the biohybrid structural color hydrogels into microfluidics, we developed a “heart-on-a-chip” platform featuring microphysiological visuality for biological research and drug screening. This biohybrid, living, structural color hydrogel may be widely used in the design of a variety of intelligent actuators and soft robotic devices.

Source: Sciencemag.org – Science Robotics Latest Content

A soft, bistable valve for autonomous control of soft actuators

Almost all pneumatic and hydraulic actuators useful for mesoscale functions rely on hard valves for control. This article describes a soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow. A structural instability—often called “snap-through”—enables rapid transition between two stable states of the membrane. The snap-upward pressure, P1 (kilopascals), of the membrane differs from the snap-downward pressure, P2 (kilopascals). The values P1 and P2 can be designed by changing the geometry and the material of the membrane. The valve does not require power to remain in either “open” or “closed” states (although switching does require energy), can be designed to be bistable, and can remain in either state without further applied pressure. When integrated in a feedback pneumatic circuit, the valve functions as a pneumatic oscillator (between the pressures P1 and P2), generating periodic motion using air from a single source of constant pressure. The valve, as a component of pneumatic circuits, enables (i) a gripper to grasp a ball autonomously and (ii) autonomous earthworm-like locomotion using an air source of constant pressure. These valves are fabricated using straightforward molding and offer a way of integrating simple control and logic functions directly into soft actuators and robots.

Source: Sciencemag.org – Science Robotics Latest Content