Jan 29, 2019 | By Cameron
In nature, there are countless examples of motion in organisms that don’t have brains or nervous systems, such as the Venus flytrap. It closes when prey goes inside, but it also opens if it accidentally shuts on something that can’t be digested; all of this motion is caused by tissues that react to pressure and the presence of certain chemicals. Inspired by such systems, researchers at the University of Pennsylvania's School of Engineering and Applied Science have now 3D printed objects that make definable motions when exposed to specific stimuli, all without the use of electronic sensors or microprocessors.
The team designed and 3D printed structures with “embodied logic,” which is a material-driven if/then logic gate. This is possible because of the geometric changes that various materials undergo when exposed to certain stimuli. For example, many materials absorb water and expand. In logic that would translate to: if exposed to water, then expand. "Lots of materials absorb water and expand, for example, but they expand in all directions. That doesn't help us, because it means the ratio between the beams' width and length stays the same," explains Jordan Raney, an assistant professor who led the study. "We needed a way to restrict expansion to one direction only."
They overcame that obstacle by using a multi-material 3D printer to embed glass or cellulose fibers in parallel lines along the length of beams; the fibers restrict elongation of the beams while allowing expansion to occur between the strands, making the beams wider. Raney studies both bistable materials (objects that can hold one of two geometric configurations indefinitely) and responsive materials (objects that change shape under specific conditions), two distinct fields of study that he is marrying together for the study.
"Bistability is determined by geometry, whereas responsiveness comes out of the material's chemical properties," Raney states. "Our approach uses multi-material 3D printing to bridge across these separate fields so that we can harness material responsiveness to change our structures' geometric parameters in just the right ways."
Affecting the beams’ length/width ratio creates predictable motion without motors or servos, as Raney elaborates, “Compressing the lattice stores elastic energy in the material. If we could controllably use the environment to alter the geometry of the beams, the structure would stop being bistable and would necessarily release its stored strain energy. You'd have an actuator that doesn't need electronics to determine if and when actuation should occur."
And that’s exactly what they did. Lead author of the study Yijie Jiang says, "For example, we demonstrated sequential logic by designing a box that, after exposure to a suitable solvent, can autonomously open and then close after a predefined time. We also designed an artificial Venus flytrap that can close only if a mechanical load is applied within a designated time interval, and a box that only opens if both oil and water are present."
These mechanical responses can be used by oil cleanup drones, capturing only water that’s been polluted with oil, and they could do it passively as no energy source is required. Devices that handle microfluids could also benefit from the embodied logic technology, replacing electronic sensors with valves that automatically close when they come in contact with a contaminant. The possibilities are limitless. 3D printing continues to grow from its knickknack infancy into its high-tech business suit.
Posted in 3D Printing Application
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