A small robotic crab, controlled by lasers, can run, twist and jump

Just fractions of a millimeter in diameter, a new bio-inspired robot can perform a complex range of movements when hit with a sequence of laser pulses. The Crab’s structure is much more sophisticated than many existing robots of the same size, but can still be crafted using a relatively simple process. Its design could open up promising prospects in research and medicine.

Small robots: Robot designs have advanced at a breakneck pace over the past few years. Often inspired by the evolutionary adaptations of animals, many modern robots feature complex structures, advanced materials, and intricate electrical circuits that allow them to perceive their surroundings, communicate with neighbors, and navigate difficult terrain.

By miniaturizing these designs, researchers hope to extend these applications to spaces that would otherwise be impossible to reach, including the many passageways and chambers found inside our own bodies.

By bending 2D materials in the right way, more complex 3D structures can emerge.

The challenge: With most existing manufacturing techniques, it is not yet possible to recreate robot complexity on a larger scale in sub-millimeter robots. This mostly limited tiny robots to very simple structures, like spheres, rods, and tubes.

There is one exception: by folding 2D materials in the right way, more complex 3D structures can emerge – much like paper from a pop-up book.

So far, these designs have demonstrated an ability to swim in liquid, but are still not able to walk on flat, solid surfaces.

Design: A team of researchers in China and the United States, led by John Rogers of Northwestern University, has now overcome this challenge with a new robot design, inspired by the peekytoe crab.

To build their robot, the team printed its components on a flat surface, then transferred them to a piece of stretched silicone.

This first “2D” print contained a rigid skeleton, consisting of a central body and six legs, connected by joints made of deformable material.

Using this same knuckle material, the team attached two claws and a pair of hind legs to the central body. They also used sticky pads to stick the feet and claws to the silicone surface.

When they released the stretched silicone, the joints deformed under the compressive stress and the structure transformed into a self-contained 3D structure: a robot crab.

At this point, Rogers’ team covered the entire crab with a thin glass shell. This kept the gasket material in its new shape, even after the robot was removed from the unstretched silicone.

With this technique, the researchers made a robot measuring just 200 micrometers in diameter. At about 1/150e actual size of a peekytoe crab, their design was small enough to stand on the edge of a coin.

Programming movement: When heated by a laser, the crab’s joint material returned to its original 2D shape, allowing the robot to straighten its legs and claws. Yet, as it cooled, the glass shell pushed this material back into its folded state.

This behavior allowed Rogers’ team to stimulate a wide range of motion in their crab: by heating its entire body with laser pulses, the structure could bend, twist and expand. By targeting specific sets of joints in pre-programmed sequences of laser pulses, the robot could be instructed to crawl, run, turn and jump.

Unlike previous submillimeter robot designs, the crab’s tiny size worked to its advantage. After heating and straightening, the gasket material took very little time to cool and bend, allowing the robot’s legs and claws to move quickly through their full range of motion.

The crab has a sensing ability that allows its users to gain useful information about the robot’s surroundings.

In total, this allowed the crab to move at speeds close to half its body length per second, significantly faster than existing submillimeter robots.

To further improve their design, Rogers and his colleagues fitted their crab with a pair of “eyes” made from retroreflective material – which direct incoming light to its source. This provided a simple wireless system for the team to monitor and locate their robot.

Additionally, they coated these retroreflectors with a material that absorbs particular wavelengths of light, which vary with the humidity of the surrounding air. This added sensing capability to the robot, allowing its users to gain useful information about its surroundings.

Performing delicate tasks: Already, the team’s robot capabilities present promising opportunities in a wide range of tasks.

For biologists, such a design could be an ideal vehicle for manipulating tissue, or even transporting individual cells: performing programmed maneuvers that would be far too delicate for larger-scale robots to handle.

Elsewhere, tiny robots could be programmed to deliver drugs to targeted sites inside the body or help doctors perform minimally invasive surgery.

By adapting their approach, Rogers and his colleagues ultimately hope to manufacture submillimeter robots spanning a diverse range of shapes and sizes in the future, further expanding the scope of their potential uses.

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