Tiny winged microchips that ride the wind like plant seeds are the smallest flying devices ever made by humans, a new study reports.
The bio-inspired robots are about the size of sand grains and could be deployed in swarms with far-ranging applications, such as monitoring air pollution, tracking the spread of disease, or collecting scientific data. The fliers could also be constructed from biodegradable materials that are reabsorbed into environments upon landing to prevent contamination.
A team led by John A. Rogers, who serves as the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at Northwestern University, developed these artificial versions of wind-dispersed seeds.
The tiny flying platforms “establish a set of unusual capabilities in aerial dispersal of advanced device technologies” that “may offer enhanced levels of performance, beyond those observed in nature,” according to a study published on Wednesday in Nature.
“Plants and trees have some pretty unique and innovative schemes for transmitting their genetic material in the form of seeds using passive means: wind and air currents,” said Rogers, who is also the director of Northwestern’s Querrey Simpson Institute for Bioelectronics, in a call.
“We decided that that might be an interesting direction to pursue and began to ask questions like: what are the fundamental physics concepts that are behind the way that plants do dispersal? Could we leverage, downscale, and apply them to emerging miniaturized classes of electronics?”' he continued. “That's what got us started down this path of thinking about bio-resorption in the context of environmentally degradable devices that could be dispersed, but in a way that you wouldn't have to worry about associated electronic waste streams.”
Rogers and his colleagues are currently studying the full gamut of nature’s innovative seed dispersal techniques, from dandelion-style parachutes, to gliders used by the Javan cucumber, to the flutterers and spinners of the jacaranda tree. But the new study focuses in particular on the spinning helicopter-style seeds dispersed by maple trees or woody vines.
You’ve probably seen these natural propellers falling from trees and maximizing their time in the air—and therefore their ability to travel from their parent plant—by spinning in the wind. Rogers’ team emulated this ingenious design by running simulations of the flight dynamics and controlled rotation of three-winged tristellateia helicopter seeds, which guided the construction of the tiny artificial rotors.
The researchers were able to shrink their robotic fliers down to the millimeter scale, which is much smaller than their natural seed counterparts, but still big enough to carry miniaturized instruments, computer chips, power sources, and other components. The team experimented with even smaller concepts, but things started to get funky beyond the millimeter scale.
“The aerodynamics start to break down as you decrease sizes below about a millimeter,” Rogers said. “Below that size scale, everything looks and falls like a sphere. There's really no flow-driven rotational motions. All of the advantages of the helicopter design begin to disappear below a certain length scale, so we pushed it all the way, as far as you can go or as physics would allow, and that size is, in fact, much smaller than you would see with seeds.”
Despite hitting this miniaturization threshold, Rogers and his colleagues were still able to test multiple versions of the winged devices that carried versatile payloads, such as antennae that can wirelessly communicate with a smartphone or environmental sensors that can monitor pH, water quality, or solar wavelengths.
Though there are numerous potential applications for these devices, perhaps the most topical is the possible deployment of disease-sniffing swarms that could flag early warning signs of epidemics and pandemics or track them as they progress.
“One future that we are intrigued by is the idea of using these devices to monitor biohazards like pathogens, aerosols, and all the kinds of things that people are thinking about these days,” Rogers said. “This is just a concept and we don't have a proof-of-principle yet, but if you start thinking about what possibilities would open up if you add sensing capabilities, I think pathogen-monitoring could be interesting, so that's something we're exploring.”
To build on their findings, the researchers plan to construct new fliers based on other types of seeds that could be optimized for different functions. The winged robots could eventually be released in batches that collect information for a short time before biodegrading into their dispersal environments. Rogers and his team have already spent years developing transient medical implants that harmlessly dissolve in the body, so they’ve already laid the practical groundwork for these airborne designs.
“We don't think about these devices, in most cases anyway, as a permanent monitoring componentry but rather temporary ones that are addressing a particular need that’s of finite time duration,” Rogers said. “That's not the way that it would have to work, but that's the way that we're envisioning things currently: you monitor for a month and then the devices die out, dissolve, and disappear, and maybe you have to redeploy them.”
“We have an idea for applications and some ways that these ideas could have practical utility,” he concluded, “but just at the base academic level, it's kind of fun to think about.”