Moving through the world as a microorganism isn’t always easy. Bacteria and other small creatures squirming inside bodies often have to propel themselves through thick, viscous environments. For a human, this would look like someone awkwardly trying to swim their way through a pool of honey. Nature has already come up with creative solutions to this sticky problem. E.coli, for example, uses a corkscrew motion to cut through the muck while flagella contort their frames and whip themselves forward.
Now, using this natural adaptation as inspiration, researchers from Tampere University and Anhui Jianzhu University have created a new doughnut-shaped micro-robot capable of autonomously navigating its way through mucus and other goopy substances. The tiny robot design, which they believe could one day be used to deliver medicine through mucus, made reality a form factor first conceptualized nearly fifty years ago. The researchers published their findings this week in the journal Nature Materials.
Video: Untethered swimming through three-dimensional space in the Stokes regime. Credit: Zixuan Deng, Tampere University
The robot is just one millimeter long and has a “toroidal” (or doughnut) shape which lets thick, viscous materials pass through its exposed center. But the shape alone doesn’t make the robot move. For that, the researchers turned to a synthetic material called liquid crystalline elastomer. Exposure to light or heat stimuli causes this material to begin autonomously rotating. The researchers used a hot plate to apply constant heat to the elastomer-coated robot and found they could get it to propel itself forward through its environment.
Once exposed to light or heat, the robot is in “self-sustained motion,” which the researchers say lets it move autonomously. But it can also be steered. The researchers found they could induce the doughnut bot to move in a certain direction by varying the amount of light or heat exposure. Similarly, they could bring the robot to a stop by cutting off its access to light and heat altogether. The robot can also autonomously alternate between a rolling or self-propulsion mode depending on what’s best for navigating a particular environment.
This doughnut-like design, while a first for small, soft-shaped robots, isn’t an entirely new concept. The idea for the shape is attributed to physicist Edward Purcell in 1977. Purcell believed a toroidal body shape could improve the navigation of microorganisms in the “Stokes regime” which refers to areas where there are viscous forces and little to no inertia. This small robot proves that the general idea was correct.
Video: Terrestrial movement of ZEEM torus walking on land. Credit: Zixuan Deng, Tampere University
Using tiny robots to deliver medicine through snot
Though still early, the tiny doughnut bot could have real-world applications outside of the laboratory. Zixuan Deng, a Doctoral Researcher at Tampere University and one of the paper coauthors believes this underlying technology could be used by future doctors to deliver medication through mucus or even help unblock blood vessels.
“The implications of this research extend beyond robotics, potentially impacting fields such as medicine and environmental monitoring,” Deng said in a statement.
This wouldn’t be the first time scientists have considered sending small robots into humans. For more than a decade, researchers have designed small “nanobots” potentially capable of carrying materials through a body and even to particularly sensitive areas like brains and eyes. More recently, researchers from MIT created a soft, cucumber-inspired robot that can propel itself forward with an inchworm-like motion through blood vessels. The tiny doughnut robot goes a step further by introducing a method for moving through particularly sticky, viscous areas with a low complexity architect that only needs light or heat to get it moving. In other words, snot-traveling medical robots may be one step closer to reality.
