How will the robots of the future be powered? There are a wide variety of batteries out there, from cylindrical lithium-ion to nickel–metal hydride. Batteries have their pros and cons, but a team of scientists at the Eindhoven University of Technology (TU/e) has taken a different path, one less reliant on metals like lithium. In fact, it’s not reliant on any solid material at all: this robot walks under the influence of light.

The TU/e scientists aren’t using solar panels here. Rather, they’re building off of work from 2017, when the Dutch university’s Department of Chemical Engineering and Chemistry developed light-sensitive polymers. At the time, the polymers could only wiggle around a little bit, with a maximum speed of approximately half an inch per second. But since then, PhD student Marina Pilz da Cunha and master’s student Bas Ambergen, working in collaboration with the research groups of professors Jaap den Toonder and Albert Schenning. They’ve published their findings in the journal Advanced Science.

The polymer owes its locomotion to the fact that when exposed to light, one side contracts and the other side expands. “The robot’s legs stretch when light shines on them and bend as soon as the light goes out. That’s how it takes steps,” says Pilz da Cunha in a press statement.

The strip might look transparent, but it can absorb violet light almost completely, which creates what the 2017 TU/e team called a “shadow.” Combining this “self-shadowing” material with a light-sensitive variant on liquid crystals (LCDs, the same thing found in televisions), the team was able to make a material that immediately distorts itself when exposed to light, and then bend back to its original form when the light is removed. As proof-of-concept, the team was able to make a strip of the polymer, roughly the size of a paperclip, move slightly up and down.

In 2020, the technology has improved to the point where Pilz da Cunha can make a tiny robot running on the material not only walk straight, but also make turns.

It’s arms and legs can also be controlled individually. That’s because, as you might notice, the robot is quite colorful. Each of its body parts consists of a different color, which and in turn they react to different wavelengths of light.

While long strides have been made in three years, the light-activated robots are still a while being seen in daylight outside of the lab. But they’ll keep working on it, because they see a strong upside. “In the future, this application could be used in the human body to deliver medicines to the intestines or the bloodstream, for instance. Another example would be chip machines, in which this little robot can maneuver in order to carry out repairs,” says den Tooder, speaking in the press statement.

As it stands, the tiny robot is too big to be working inside a human body or a computer. So the next steps for the team aren’t to scale up, but rather to shrink down. Their ideal size is under a millimeter. They’re also searching for a better, more accurate, means of controlling the lightbots. In a server, for example, it could be easy to set up a trail of lights for them to follow, like the lights guiding passengers on an airplane. That could get more difficult in a human body. “Perhaps we can then work with heat,” suggests Pilz da Cunha.

It’s certainly an option, but just because there’s no visible light within the human body doesn’t mean scientists can’t sneak it in. Scientists at MIT have been developing medical ingestible devices that are meant to dissolve with ultraviolet rays, or UV light, being pointed at the body from the outside.

Abstract: Mobile organisms with ability for locomotion and transportation, such as humans and other animals, utilize orchestrated actuation to perform actions. Mimicking these functionalities in synthetic, light‐responsive untethered soft‐bodied devices remains a challenge. Inspired by multitasking and mobile biological systems, an untethered soft transporter robot with controlled multidirectional locomotion with the ability of picking up, transporting, and delivering cargo driven entirely by blue light is created. The soft robot design is an ensemble of light‐responsive liquid crystalline polymers that can harness motion either collectively or individually to obtain a high degree of motion control for the execution of advanced tasks in a dry environment. Through orchestrated motion of the device's “legs”, single displacement strides, which exceed 4 mm and can be taken in any direction, allow for locomotion around objects. Untethered cargo transportation is demonstrated by a pickup and release mechanism using the device's “arms”. This strategy demonstrates the constructive harnessing of orchestrated motion in assemblies of established actuators, performing complex functions, mimicking constructive behavior seen in nature.