A team of engineers has developed the smallest-ever remote-controlled walking robot in the form of a tiny crab, coming one step closer to the idea of micro-sized robots performing minimally invasive surgeries. Just a half-millimeter wide, the tiny crabs can bend, twist, crawl, walk, turn and even jump. The researchers also developed millimeter-sized robots resembling inchworms, crickets and beetles. Although the research is exploratory at this point, the researchers believe their technology might bring the field closer to realizing micro-sized robots that can perform practical tasks inside tightly confined spaces. Last September, the same team had introduced a winged microchip that was the smallest-ever human-made flying structure.

Smaller than a flea, the crab is not powered by complex hardware, hydraulics or electricity. Instead, its power lies within the elastic resilience of its body. To construct the robot, the researchers at Northwestern University (Evanston, IL, USA) used a shape-memory alloy material that transforms to its “remembered” shape when heated. In this case, the researchers used a scanned laser beam to rapidly heat the robot at different targeted locations across its body. A thin coating of glass elastically returns that corresponding part of structure to its deformed shape upon cooling.

As the robot changes from one phase to another - deformed to remembered shape and back again - it creates locomotion. Not only does the laser remotely control the robot to activate it, the laser scanning direction also determines the robot’s walking direction. Scanning from left to right, for example, causes the robot to move from right to left. To manufacture such a tiny critter, the team turned to a technique they introduced eight years ago - a pop-up assembly method inspired by a child’s pop-up book.

First, the team fabricated precursors to the walking crab structures in flat, planar geometries. Then, they bonded these precursors onto a slightly stretched rubber substrate. When the stretched substrate is relaxed, a controlled buckling process occurs that causes the crab to “pop up” into precisely defined three-dimensional forms. With this manufacturing method, the Northwestern team could develop robots of various shapes and sizes.

“Robotics is an exciting field of research, and the development of microscale robots is a fun topic for academic exploration,” said John A. Rogers, who led the experimental work. “You might imagine micro-robots as agents to repair or assemble small structures or machines in industry or as surgical assistants to clear clogged arteries, to stop internal bleeding or to eliminate cancerous tumors - all in minimally invasive procedures.”

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