A squishy octopus-shaped machine less than 2 centimetres tall is making waves in the field of soft robotics. The ‘octobot’ described today in Nature1 is the first self-contained robot made exclusively of soft, flexible parts.
Interest in soft robots has taken off in recent years, as engineers look beyond rigid Terminator-type machines to designs that can squeeze into tight spaces, mould to their surroundings, or handle delicate objects safely. But engineering soft versions of key parts has challenged researchers. “The brains, the electronics, the batteries — those components were all hard,” says roboticist Daniela Rus at the Massachusetts Institute of Technology in Cambridge. “This work is new and really exciting.”
The octobot is made of silicone rubber. Its ‘brain’ is a flexible microfluidic circuit that directs the flow of liquid fuel through channels using pressure-activated valves and switches. “It’s an analogy of what would be an electrical circuit normally,” says engineer Robert Wood at Harvard University in Cambridge, Massachusetts, one of the study’s leaders. “Instead of passing electrons around, we’re passing liquids and gases.”
Valves and switches in the robot’s brain are positioned to extend the arms in two alternating groups. The process starts when researchers inject fuel into two reservoirs, each dedicated to one group of four arms. These reservoirs expand like balloons and push fuel through the microfluidic circuit. As fuel travels through the circuit, changes in pressure close off some control points and open others, restricting flow to only one half of the system at a time. As that side consumes fuel, its internal pressure decreases, allowing fuel to enter the other side — which then pinches off the first side, and so on.
The robot’s brain talks to its limbs through 3D-printed channels embedded in the body. To create the body, researchers poured silicone polymers into an octopus-shaped mould. Then, using a 3D printer, they injected special inks that maintained their form and position in the surrounding polymer. The scientists heated the octobot to cure its structure, which also caused the ink to evaporate — leaving behind a hollow network that infiltrates the octobot’s limbs and links to its brain.