Microfliers: Polymers on a mission for the environment

They are the size of a grain of sand and resemble trundling maple seeds: the flying microchips that researchers at Northwestern University have now developed. In the future, they should make it possible to monitor air pollution or airborne diseases. Polymers play a fundamental role in this. John Rogers tells us more in an interview with K-MAG.

You have developed winged microchips. What are they exactly?

John Rogers: These devices combine collections of three-dimensional (3D) wing structures in helicopter-like geometries with integrated circuit chips. During free-fall, interactions between these winged microchips with patterns of wind lead to rotational flight behaviors that increase the time for interaction with the atmosphere and maximize the total distances for dispersal across a targeted environment. The devices can be released from a drone or an airplane; alternatively, they can be launched directly from the ground into the air in housings that open at certain altitudes.

What principle do they work on? What are they inspired by?

Rogers: The aerodynamics of these devices lead to controlled, passive modes of flight, similar to mechanisms associated with Maple seeds, Tristellateia seeds and certain other types of wind-dispersed seeds. Our designs take inspiration from these seeds, although in smaller and more optimized layouts guided by computational modeling and controlled experimental studies in wind tunnels. To create these devices, we use a process that relies on principles adapted from those in children’s pop-up books to convert planar, 2D precursors into 3D collections of wings, in spiral type configurations. The microchips serve as payloads in these systems much like the plant embryos of wind-dispersed seeds.

What role do polymers play here? Why did you decide to use them?

Rogers: We use polymer materials for the wings. Polymers are attractive because they are lightweight and physically tough and because they can be designed chemically to bond to the surfaces of the microchips. We can also mold and manipulate these materials to form 3D wings with tiny dimensions, less than one millimeter in length scale, suitable for integration with even the smallest forms of microchip technologies.

What contribution do they make to environmental protection?

Rogers: We envision the use of these devices in distributed, wireless networks to monitor environmental processes or to track efforts to clean-up chemical spills. Passive flight forms the basis for dispersing these devices in a simple manner, over large areas. Color-changing chemical reagents that respond to an environmental species of interest or digital electronic sensors that capture changes in weather parameters provide quantitative sources of information, in a wireless fashion.