A new hollow, pea-sized robot that can roll, flip, and jump to navigate its environment. It can easily transition from dry surfaces to liquid pools, making it fully amphibious. Its ability to use different types of motion in multiple environments–while carrying a cargo–sets it apart from other wee machines, most of which can only move in a single way. It is also able to maneuver around, over, and through obstacles because of its versatility. Its small size and multifunctionality could allow it to navigate the complex environment of the human body and deliver medicine to patients in need.
The robot’s ability overcome physical obstacles is due to a unique design. It has been folded in an origami pattern called a Kresling and topped off with a magnet. The Kresling pattern looks like a series right triangles stacked around the robot’s stomach, creating a ridged and squashed shape. It also has a propeller-like shape that allows it to move through liquid. Renee Zhao, assistant professor of mechanical engineering at Stanford University, says that what she really wanted to find out was whether the geometric features could be combined with the foldability and origami design to enable effective navigation of [robot] and to use its foldability mechanism to deliver drugs. She and her colleagues describe the robot in a paper published on Tuesday in Nature Communications.
A small hole at the robot’s end allows access to its hollow center. This can hold a small payload, such as an object or liquid. The machine can be controlled wirelessly by the magnet at the other end. All the operator needs to do is their own magnet. Zhao explains that the magnetic field used by the researchers is similar to that generated by an MRI machine. She suggests that one strategy is to make the robot compatible with the MRI system. This would allow the robot to be controlled while a patient is inside the imaging machine. Zhao says that there is another option: developing a new type of device that can generate and manipulate the right kind of magnetic field. However, it would need to include medical imaging such as an MRI machine to track the robot’s position within the body.
Some versions of the new robot include a second magnet on either side of its soft, cylindrical body. This makes it pumpable. The magnetic field is controlled by an operator, who creates a small rotational force between magnets that squeezes the robot’s thin plastic body. Repeating this can pump liquid from the robot’s belly to its surroundings.
The device can do more than just deliver liquid payloads. Because it is propeller-like, an operator can spin it by applying a magnetic field to cause it to spin and push liquids through it. The robot’s hollow belly can also be pulled into its hollow stomach by the suction generated by spinning. The robot swims and the spinning motion keeps the sucked-up cargo inside. Once the robot reaches its destination the operator can stop it spinning and the bot will dispose of whatever it has collected. This allows for delivery of small, solid payloads to specific locations.
This process could theoretically transport liquid or solid medication directly to specific areas in a body, such as the digestive tract. Zhao says that the robot was made with soft materials that can avoid tissue damage. She points out that even the magnet is soft. The team created it by embedding tiny glass beads, metal nanoparticles and pliable plastic. Researchers demonstrated that the robot could maneuver in both a dry environment and one with liquid. The robot’s trajectory was controlled by the researchers. However, it did not need to be told how to maneuver around small obstacles. Instead, the magnetic field instructed the robot to move in a particular direction. It then rolled, tumbled, or did any other movement necessary to follow that path. The robot could be made to jump by its operator if it encountered a larger obstacle. The operator could alter the magnetic field to make the robot swim if it was in a deep liquid pool.
This multifunctionality in a simple robot design surprised Siyi Xu (a postdoctoral robotics engineering engineer at Harvard Microrobotics Laboratory), who was not involved with the new study. “It’s very impressive to see them combine many of these abilities into one integrated [design],”,” she said. Xu also said that many small robots are only capable of one type of motion, whether it’s walking, crawling, or flying.
Zhao believes that the new, more skilled origami design could serve as a blueprint for future tiny robots. This could lead to more applications. She says that these functionalities are not restricted to a particular disease or application. Her lab is now looking at ways to make these robots smaller and more capable of traveling in the bloodstream. Smaller bots could be equipped with tiny cameras and forceps that would be useful in minimally invasive procedures. Zhao plans to continue to explore similar devices, adding more capabilities to these microrobots and keeping their simplicity of design.
*Editor’s Note (6/15/22): This sentence was edited after posting to clarify Siyi Xu’s position at the Harvard Microrobotics Laboratory.