Robert F. Shepherd

Multigait soft robot

This manuscript describes a unique class of locomotive robot: A soft robot, composed exclusively of soft materials (elastomeric polymers), which is inspired by animals (e.g., squid, starfish, worms) that do not have hard internal skeletons. Soft lithography was used to fabricate a pneumatically actuated robot capable of sophisticated locomotion (e.g., fluid movement of limbs and multiple gaits). This robot is quadrupedal; it uses no sensors, only five actuators, and a simple pneumatic valving system that operates at low pressures (< 10 psi). A combination of crawling and undulation gaits allowed this robot to navigate a difficult obstacle. This demonstration illustrates an advantage of soft robotics: They are systems in which simple types of actuation produce complex motion.

A multi-gait soft robot

This manuscript describes a unique class of locomotive robot: A soft robot, composed exclusively of soft materials (elastomeric polymers), which is inspired by animals (e.g., squid, starfish, worms) that do not have hard internal skeletons. Soft lithography was used to fabricate a pneumatically actuated robot capable of sophisticated locomotion (e.g., fluid movement of limbs and multiple gaits). This robot is quadrupedal; it uses no sensors, only five actuators, and a simple pneumatic valving system that operates at low pressures (< 10 psi). A combination of crawling and undulation gaits allowed this robot to navigate a difficult obstacle. This demonstration illustrates an advantage of soft robotics: They are systems in which simple types of actuation produce complex motion.

Soft Robotics for Chemists

In areas from assembly of machines to surgery, and from deactivation of improvised explosive devices (IEDs) to unmanned flight, robotics is an important and rapidly growing field of science and technology. It is currently dominated by robots having hard body plans—constructions largely of metal structural elements and conventional joints—and actuated by electrical motors, or pneumatic or hydraulic systems. Handling fragile objects—from the ordinary (fruit) to the important (internal organs)—is a frequent task whose importance is often overlooked and is difficult for conventional hard robots; moving across unknown, irregular, and shifting terrain is also. Soft robots may provide solutions to both of these classes of problems, and to others. Methods of designing and fabricating soft robots are, however, much less developed than those for hard robots. We wish to expand the methods and materials of chemistry and soft-materials science into applications in fully soft robots. A robot is an automatically controlled, programmable machine. The limbs of animals or insects—structures typically based on rigid segments connected by joints with constrained ranges of motion—often serve as models for mobile elements of robots. Although mobile hard robots sometimes have limb-like structures similar to those of animals (an example is “Big Dog” by Boston Robotics), more often, robots use structures not found in organisms—for example, wheels and treads. The robotics community defines “soft robots” as: 1) machines made of soft—often elastomeric—materials, or 2) machines composed of multiple hard-robotic actuators that operate in concert, and demonstrate soft-robot-like properties; here, we consider only the former. Soft animals offer new models for manipulation and mobility not found, or generated only with difficulty and expense, using hard robots. Because materials from which this class of devices will be fabricated will usually be polymers (especially elastomers), they fall into the realm of organic materials science. The use of soft materials allows for continuous deformation. This type of deformation, in turn, enables structures with ranges of motion limited only by the properties of the materials. Soft robots have the potential to exploit types of structures found, for example, in marine organisms, and in non-skeletal parts of land animals. The tentacles of squid, trunks of elephants, and tongues of lizards and mammals are such examples; their structures are muscular hydrostats. Squid and starfish 14] are highly adept locomotors; their modes of movement have not been productively used, and permit solutions of problems in manipulation, locomotion, and navigation, that are different from those used in conventional hard robotics. The prototypical soft actuator—muscle—developed through the course of evolution. There is currently no technology that can replicate the balanced performance of muscle: it is simultaneously strong and fast, and enables a remarkable range of movements (such as those of a tongue). Muscle-like contraction and dilation occur in ionic polymeric gels on changes in the acidity or salinity of a surrounding ionic solution, but actuation in macroscopic structures is masstransport limited, and typically slow. Other electroactive polymers (EAPs) include dielectric elastomers, electrolytically active polymers, polyelectrolyte gels, and gel-metal composites. Pneumatically-driven McKibben-type actuators are among the most highly developed soft actuators, and have existed for more than fifty years; they consist of a bladder covered in a shell of braided, strong, inextensible fibers. These actuators can be fast, and have a length-load dependence similar to that of muscle but possess only one actuation mode—contraction and extension when pressurization changes. They are, in a sense, an analogue to a single muscle fibril ; using them for complex movements requires multiple actuators acting in series or parallel. Pneumaticallydriven flexible microactuators (FMAs) have been shown to be capable of bending, gripping, and manipulating objects. Roboticists have explored scalable methods for gripping and manipulating objects at the micro and nano scales. The use of compliant materials allows grippers to manipulate objects such as fruit with varied geometry. The field of robotics has not yet caught the attention of soft-materials scientists and chemists. Developing new materials, techniques for fabrication, and principles of design will create new types of soft robots. The objective of this work is to demonstrate a type of design that provides a range of behaviors, and that offers chemists a test bed for new materials and methods of fabrication for soft robots. Our designs use embedded pneumatic networks (PneuNets) of channels in elastomers [*] Prof. G. M. Whitesides Wyss Institute for Biologically Inspired Engineering Harvard University, 3 Blackfan Circle, Boston, MA 02115 (USA) Fax: (+ 1)617-495-9857 and Kavli Institute for Bionano Science & Technology 29 Oxford Street, Cambridge MA (USA) E-mail: gwhitesides@gmwgroup.harvard.edu Homepage: http://gmwgroup.harvard.edu/

Camouflage and Display for Soft Machines

Mechanical Chameleon A wide range of animals can adapt their color patterns as a means of camouflage or otherwise changing their appearance. This is accomplished through changes in coloration, contrast, patterning, or shape. Morin et al. (p. 828) show at a basic level that some of these features can be added as microfluidic layers attached to mobile, flexible, soft machines. By pumping different fluids through the channels, the robots were able to change their coloration or overall contrast and could thus blend into the background of the surface they were lying upon. Conversely, by pumping through fluids of different temperature, the infrared profile of the robot could be changed without changing its visible coloration. Soft robots with microfluidic channels in a skin layer show camouflaging abilities. Synthetic systems cannot easily mimic the color-changing abilities of animals such as cephalopods. Soft machines—machines fabricated from soft polymers and flexible reinforcing sheets—are rapidly increasing in functionality. This manuscript describes simple microfluidic networks that can change the color, contrast, pattern, apparent shape, luminescence, and surface temperature of soft machines for camouflage and display. The color of these microfluidic networks can be changed simultaneously in the visible and infrared—a capability that organisms do not have. These strategies begin to imitate the functions, although not the anatomies, of color-changing animals.

Robotic Tentacles with Three‐Dimensional Mobility Based on Flexible Elastomers

Soft robotic tentacles that move in three dimensions upon pressurization are fabricated by composing flexible elastomers with different tensile strengths using soft lithographic molding. These actuators are able to grip complex shapes and manipulate delicate objects. Embedding functional components into these actuators (for example, a needle for delivering fluid, a video camera, and a suction cup) extends their capabilities.

Highly stretchable electroluminescent skin for optical signaling and tactile sensing.

Make it stretch, make it glow The skins of some cephalopods, such as the octopus, are highly flexible and contain color-changing cells. These cells are loaded with pigments that enable rapid and detailed camouflaging abilities. Larson et al. developed a stretchable electroluminescent actuator. The material could be highly stretched, could emit light, and could also sense internal and external pressure. A soft robot demonstrated these combined capabilities by stretching and emitting light as it moved. Science, this issue p. 1071 Light emission, actuation, and sensing are combined in a stretchable electronic material suitable for soft robotics. Cephalopods such as octopuses have a combination of a stretchable skin and color-tuning organs to control both posture and color for visual communication and disguise. We present an electroluminescent material that is capable of large uniaxial stretching and surface area changes while actively emitting light. Layers of transparent hydrogel electrodes sandwich a ZnS phosphor-doped dielectric elastomer layer, creating thin rubber sheets that change illuminance and capacitance under deformation. Arrays of individually controllable pixels in thin rubber sheets were fabricated using replica molding and were subjected to stretching, folding, and rolling to demonstrate their use as stretchable displays. These sheets were then integrated into the skin of a soft robot, providing it with dynamic coloration and sensory feedback from external and internal stimuli.

A Resilient, Untethered Soft Robot

A pneumatically powered, fully untethered mobile soft robot is described. Composites consisting of silicone elastomer, polyaramid fabric, and hollow glass microspheres were used to fabricate a sufficiently large soft robot to carry the miniature air compressors, battery, valves, and controller needed for autonomous operation. Fabrication techniques were developed to mold a 0.65-meter-long soft body with modified Pneu-Net actuators capable of operating at the elevated pressures (up to 138kPa) required to actuate the legs of the robot and hold payloads of up to 8kg. The soft robot is safe to interact with during operation, and its silicone body is innately resilient to a variety of adverse environmental conditions including snow, puddles of water, direct (albeit limited) exposure to flames, and the crushing force of being run over by an automobile.

Using Explosions to Power a Soft Robot

grasping and walking. Despite their advantages(simplicity of fabrication, actuation, and control; low cost;light weight), pneu-nets have the disadvantage that actuationusing them is slow, in part because the viscosity of air limitsthe rate at which the gas can be delivered through tubes to filland expand the microchannels. Herein, we demonstrate therapid actuation of pneu-nets using a chemical reaction (thecombustion of methane) to generate explosive bursts ofpressure.Althoughthecombustionofhydrocarbonsisubiquitousinthe actuation of hard systems (e.g., in the metal cylinder ofa diesel or spark-ignited engine

Soft Machines That are Resistant to Puncture, and That Self Seal

A soft machine composed of a composite of elastomer and fibers resists puncture from sharp objects, and continues to operate even if punctured.

Optoelectronically innervated soft prosthetic hand via stretchable optical waveguides

Stretchable optical waveguides can sense curvature, elongation, and force in a prosthetic hand. Because of their continuous and natural motion, fluidically powered soft actuators have shown potential in a range of robotic applications, including prosthetics and orthotics. Despite these advantages, robots using these actuators require stretchable sensors that can be embedded in their bodies for sophisticated functions. Presently, stretchable sensors usually rely on the electrical properties of materials and composites for measuring a signal; many of these sensors suffer from hysteresis, fabrication complexity, chemical safety and environmental instability, and material incompatibility with soft actuators. Many of these issues are solved if the optical properties of materials are used for signal transduction. We report the use of stretchable optical waveguides for strain sensing in a prosthetic hand. These optoelectronic strain sensors are easy to fabricate, are chemically inert, and demonstrate low hysteresis and high precision in their output signals. As a demonstration of their potential, the photonic strain sensors were used as curvature, elongation, and force sensors integrated into a fiber-reinforced soft prosthetic hand. The optoelectronically innervated prosthetic hand was used to conduct various active sensation experiments inspired by the capabilities of a real hand. Our final demonstration used the prosthesis to feel the shape and softness of three tomatoes and select the ripe one.