If you grew up around maple trees, you probably spent some time as a child playing with their pods. Their unique structure makes them spin in the air when they fall, like a helicopter landing gently. Various plants use the wind to spread their seeds over long distances, increasing the likelihood that the next generation of trees or dandelions will find fertile ground to grow, but none capture the imagination as successfully as seeds. swirling maple trees. That’s why scientists see them as model structures for airborne passive microflyers, capable of measuring everything from air quality and pollutants to airborne disease.
John Rogers and his colleagues in the Department of Biomedical Engineering at Northwestern University examined the structure of maple seeds as the basis for the development of miniature airborne sensors. The results were published in the journal Nature.
Using computational fluid dynamics, they simulated the movement of hypothetical devices in the air, before building them. Taking into account aerodynamics, gravity, and drag, they found that mimicking the shapes of seeds found in nature maximized the length of time their microfliers could stay aloft. In addition, the helicopter-like shape allows for more controlled flight and reduced fall.
âDepending on the altitude from which they fell, wind flow patterns and other environmental factors, some of the smaller ones could stay in the air for very long periods of time,â Rogers told SYFY WIRE. “I guess it could take tens of minutes.”
The flyers were constructed in two sizes: microfliers measuring about half a millimeter and macroflars measuring two millimeters. The construction involves thin epoxy films and a silicon wafer subjected to a series of reactions that result in a strong bond in some places but not in others. When the process is complete, the varying levels of adhesion across different locations cause the structure to buckle, creating the desired three-dimensional shape.
Once built, the flyers were fitted with color change reagents that react with chemicals in the environment. Consider the color-changing water quality bands used in home aquariums. These reagents could measure the pH, for example, present in water vapor. While an individual sensor may give an above or below average reading, a set of leaflets deployed over an area can paint a compelling picture.
A range of these devices could be deployed in the hundreds or in the thousands from a small craft. A weather balloon or even a small drone is enough to carry the payload. The devices are small and incredibly light, keeping energy costs to a minimum. And, most importantly, they don’t need to be retrieved to provide useful data.
âWireless reading can be achieved with digital image acquisition and algorithmic approaches to extract colors,â says Rogers. âWe have color change reagents that react to heavy metal concentrations in the environment, lead, cadmium and mercury concentrations in groundwater. We can do that. “
Rogers and his team knew that recovering these devices after deployment would be nearly impossible and that their successful use would depend on both the ability to collect data without recovering it and a strategy to minimize or eliminate pollution.
Fortunately for them, and for the planet, they had solved this problem before they even started. The materials used to construct the microfliers come from previous work in electronic devices integrated into the body. Rogers described devices intended for temporary use inside the body, designed to perform a function before breaking down.
âWe have been working for the past 10 years or so on the development of fundamental classes of electronic materials that can support temporary implants. Think of absorbable sutures, but now in the form of fully integrated electronic devices that perform stimulation or diagnostic functionality, âsays Rogers.
Such a device could monitor the healing process of an internal surgical wound or deliver therapies inside the body. Then, when it is no longer needed, it is absorbed. Perhaps the most impressive example of this technology is a temporary pacemaker designed to operate during finite postoperative periods during which a patient may require cardiac stimulation. Rogers’ goal is to use the same technology at work in bioresorbable technology for absorbable sensors in the environment.
The potential capabilities of the sensors increase in macroflars that are two millimeters larger. The technology is still nascent and color change reagents are the most promising application in the short term, but Rogers envisions more advanced leaflets in the future. They demonstrated the potential for integrating miniaturized circuits, radios and digital sensors, all of which could be powered by renewable sources. Macrofliers would measure levels of particulate pollution in the air by measuring the amount of sunlight hitting the device. Sunlight would be measured, but it would also be captured to power the on-board electronics. Future devices could even be configured to measure the spread of airborne disease by measuring aerosols, viruses, bacteria and chemical hazards circulating in the airways.
âThese are difficult to predict and a continuous monitoring capability would be really valuable. It is a direction that excites us. This is going to require additional development work around sensor technologies, âsaid Rogers.
Rogers is careful to point out that the flyers are still mostly in the proof-of-concept stage, describing the underlying physics and potential of the sensors. We shouldn’t expect techno-pollen swarms to fall into our backyards just yet. But sometimes the biggest tech trees grow from the smallest seeds.