The development of new types of soft robotic structures, and especially materials and methods for the fabrication of such robots, requires and offers rich new opportunities for collaborations involving organic chemistry, soft materials science, and robotics. This project centers on a methodology based on embedded pneumatic networks (EPNs) that enables large amplitude actuation in soft elastomers by pressurizing embedded channels.
Most robotic systems are hard, that is, composed of metallic structures with joints based on conventional bearings. Although hard robots capable of movement often possess limb-like structures similar to those of animals, more often, structures not found in nature – for example, wheels and treads – are used. Mobile elements of hard robots are often modeled on the limbs of animals or insects, and some locomotive systems (hexapods) use the passive compliance of air within pneumatic cylinders to move quickly on rough terrain.
The tentacles of squid, trunks of elephants, and tongues of lizards and mammals are such examples; there structures are muscular hydrostats. Squid and starfish are highly adept locomotors; their modes of movement have not been productively used in conventional hard robotics. These soft actuators rely on elastomeric structures and fibril arrangements of muscles that result in bending, elongation, or contraction without significant changes in the overall volume of the structure.
Using biomimetic principles based on these characteristics we are developing partially or entirely “soft” robots, fabricated in materials (predominantly elastomeric polymers) that do not use a rigid skeleton to provide mechanical strength, and are actuated pneumatically. Soft robots are simpler to make and less expensive than conventional hard robots, and may, in some respects, be more capable of complex motions and “cooperative function” (that is, safe operation around humans). Simple, inexpensive systems will probably not replace more complex and expensive ones, but may have different uses.
Elastomeric Grippers, Tentacles, and Walkers
Our designs use networks of channels in elastomers that inflate like balloons for actuation. Using a series of parallel chambers embedded in elastomers as a repeating component and then stacking or connecting these components enables us to design and test prototype structures providing complex movements by intuition (empirically). Complex motion requires only a single source of pressure and the movement can be designed by appropriate selection of the distribution, configuration, and size of the embedded pneumatic network. Using the techniques described here we have demonstrated soft machines that act as compliant grippers for handling fragile objects (e.g., an uncooked chicken egg, a live mouse) without damaging either (Figure 1), soft robots capable of tethered locomotion (Figure 2), and soft robots that can act as flexible tentacles (Figure 3). -
Camouflaging, Hybrid, Reconfigurable, and Untethered Walking Robots
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. We have developed simple microfluidic networks that enable the change of 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 (Figure 4).
We have also developed hybrid robotics systems that combine hard and soft subsystems. One example (Figure 5) uses a wheeled robot (an iRobot Create; hard) and a four-legged quadruped (soft).  It is capable (using a simple, wireless control system) of rapid locomotion over flat terrain (using the wheeled hard robot) and of gripping and retrieving an object (using the independent locomotive capabilities of the soft robot).
In another work, we have investigated modular magnetic assembly of reconfigurable, pneumatically actuated robots (Figure 6) composed of soft and hard components and materials.  The soft components of these hybrid robots are actuators fabricated from silicone elastomers using soft lithography, and the hard components are structures made using 3D printing. Embedded NdFeB ring magnets enable reversible, rapid reconfiguration of these robots using components made of different materials (soft and hard) that also have different sizes, structures, and functions.
Finally, by using resilient elastomers embedded with glass microspheres, we have also developed soft robots that are large enough to carry their own miniature air compressors, battery, valves, and controller needed for autonomous operation (Figure 7).  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.
Rapid, Programmable, and Explosive Actuation
Our previous designs of pneu-nets have achieved motion with large amplitudes, but only relatively slowly (over seconds). We have developed a new design for pneu-nets that reduces the amount of gas needed for inflation of the pneu-net, and thus increases its speed of actuation.  A simple actuator (Figure 8) can bend from a linear to a quasi- circular shape in 50 ms when pressurized at ΔP = 345 kPa. This actuator can operate over a million cycles without significant degradation of performance.
In other work we have investigated the use of a computer-controlled Braille display as a micropneumatic device to actuate many independent channels in parallel.  The Braille display provides a compact array of 64 piezoelectric actuators that actively close and open elastomeric valves of a micropneumatic device to route pressurized gas within the manifold. As a proof of principle, a pneumatic manifold controlled a soft machine containing 32 independent actuators to move a ball above a flat surface (Figure 9).
Although the combustion of hydrocarbons is ubiquitous in the actuation of hard systems (e.g., in the metal cylinder of a diesel or spark-ignited engine), it has not been used to power soft machines. We have demonstrated that explosive chemical reactions producing pulses of high-temperature gas for pneu-net actuation provides simple, rapid, co-located power generation, and motion in soft robots.  In particular, we used the explosive combustion of hydrocarbons triggered by an electrical spark to cause a soft robot to “jump” (Figure 10)—a gait previously only demonstrated for hard systems.
Pneumatic Origami, Tiles, and Bricks
Beyond purely elastomeric actuators, we have also developed soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible.  Upon pneumatic inflation (Figure 11), these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight.
Another approach to assembly of soft robots uses elastomeric bricks (Figures 12–13)—universal construction elements fabricated from elastomeric polymers—that can be clicked together to assemble many different elastomeric structures.  We focused, for illustration, on rectilinear elastomeric bricks that had pegs and recesses similar to those used by Lego bricks: these features ensured the bricks were properly aligned. We fabricated the click-fit elastomeric bricks (“click-e-bricks”) using a single master, and assembled them into structures by hand.
Yet another approach to constructing soft robots uses 3D soft, inflatable structures constructed from thin, 2D tiles (Figure 14) fabricated from elastomeric polymers.  The tiles are connected using soft joints that increase the surface area available for gluing them together, and mechanically reinforce the structures to withstand the tensile forces associated with pneumatic actuation. The ability of the elastomeric polymer to withstand large deformations without failure makes it possible to explore and implement new joint designs, for example “double-taper dovetail joints,” that cannot be used with hard materials. This approach simplifies the fabrication of soft structures comprising materials with different physical properties (e.g., stiffness, electrical conductivity, optical transparency), and provides the methods required to “program” the response of these structures to mechanical (e.g., pneumatic pressurization) and other physical (e.g., electrical) stimuli.
 F. Ilievski, A. D. Mazzeo, R. F. Shepherd, X. Chen, and G. M. Whitesides, “Soft Robotics for Chemists,” Angew. Chem. Int. Ed., vol. 50, no. 8, pp. 1890–1895, 2011.
 R. F. Shepherd, F. Ilievski, W. Choi, S. A. Morin, A. A. Stokes, A. D. Mazzeo, X. Chen, M. Wang, and G. M. Whitesides, “Multigait Soft Robot.,” Proc. Natl. Acad. Sci. U.S.A., vol. 108, no. 51, pp. 20400–20403, Dec. 2011.
 R. V. Martinez, J. L. Branch, C. R. Fish, L. Jin, R. F. Shepherd, R. M. D. Nunes, Z. Suo, and G. M. Whitesides, “Robotic tentacles with three-dimensional mobility based on flexible elastomers.,” Adv. Mater., vol. 25, no. 2, pp. 205–212, Jan. 2013.
 S. A. Morin, R. F. Shepherd, S. W. Kwok, A. A. Stokes, A. Nemiroski, and G. M. Whitesides, “Camouflage and Display for Soft Machines.,” Science, vol. 337, no. 6096, pp. 828–832, Aug. 2012.
 A. A. Stokes, R. F. Shepherd, S. A. Morin, F. Ilievski, and G. M. Whitesides, “A Hybrid Combining Hard and Soft Robots,” Soft Robotics, vol. 1, no. 1, pp. 70–74, 2014.
 Sen W Kwok, S. A. Morin, B. Mosadegh, J.-H. So, R. F. Shepherd, R. V. Martinez, B. Smith, F. C. Simeone, A. A. Stokes, and G. M. Whitesides, “Magnetic Assembly of Soft Robots with Hard Components,” Adv. Funct. Mater., vol. 24, no. 15, pp. 2180–2187, 2013.
 M. T. Tolley, R. F. Shepherd, B. Mosadegh, K. C. Galloway, M. Wehner, M. Karpelson, R. J. Wood, and G. M. Whitesides, “A Resilient, Untethered Soft Robot,” Soft Robotics, vol. 1, no. 3, pp. 213–223, 2014.
 B. Mosadegh, P. Polygerinos, C. Keplinger, S. Wennstedt, R. F. Shepherd, U. Gupta, J. Shim, K. Bertoldi, C. J. Walsh, and G. M. Whitesides, “Pneumatic Networks for Soft Robotics that Actuate Rapidly,” vol. 24, no. 15, pp. 2163–2170, Apr. 2014.
 B. Mosadegh, A. D. Mazzeo, R. F. Shepherd, S. A. Morin, U. Gupta, I. Z. Sani, D. Lai, S. Takayama, and G. M. Whitesides, “Control of Soft Machines using Actuators Operated by a Braille Display.,” Lab Chip, vol. 14, no. 1, pp. 189–199, Jan. 2014.
 R. F. Shepherd, A. A. Stokes, J. Freake, J. Barber, P. W. Snyder, A. D. Mazzeo, L. Cademartiri, S. A. Morin, and G. M. Whitesides, “Using Explosions to Power a Soft Robot,” Angew. Chem., vol. 125, no. 10, pp. 2964–2968, Feb. 2013.
 R. V. Martinez, C. R. Fish, X. Chen, and G. M. Whitesides, “Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators,” Adv. Funct. Mater., vol. 22, no. 7, pp. 1376–1384, 2012.
 S. A. Morin, Y. Shevchenko, J. Lessing, S. W. Kwok, R. F. Shepherd, A. A. Stokes, and G. M. Whitesides, “Using ‘Click-e-Bricks’ to Make 3D Elastomeric Structures,” Adv. Mater., vol. 26, no. 34, pp. 5991–+, 2014.
 S. A. Morin, S. W. Kwok, J. Lessing, J. Ting, R. F. Shepherd, A. A. Stokes, and G. M. Whitesides, “Elastomeric Tiles for the Fabrication of Inflatable Structures,” Adv. Funct. Mater., vol. 24, no. 35, pp. 5541–5549, 2014.