Sometimes inspiration comes from looking at nature. The Venus flytrap (Dionaea muscipula), for example, can perform very complex actions—even releasing a prey that isn't edible—without having a nervous system. Based on that ability, a group of researchers from the School of Engineering and Applied Science at the University of Pennsylvania created a series of logical objects that respond to external stimuli without relying on traditional resources like motors or batteries.
Inspiration from everyday mechanisms
Of course, motors and portable energy sources aren't necessary for something to work. A common example is the mousetrap. All we do is inject a bit of our energy into the spring and set it in balance until the rodent comes along and trips the arc. This also makes us think of mechanical calculators, formidable machines both inside and out, but useless without a human willing to turn the crank. What this team of engineers achieved, however, is integrating an equivalent of IF/THEN logic gates into their new structures, giving rise to advanced mechanical behaviors with a simple change in the environment.
The artificial Venus flytrap
For example, the animated GIF shows an artificial Venus flytrap that only activates when an object is inside it and its "actuator" is exposed to a solvent. There are no computers in the background, nor hidden motors. The action isn't very fast—about 30 seconds in real time—but it opens up a wide range of possibilities. One application the experts mention is creating a device that measures water pollution, prepared to take a sample only when it detects the presence of a petroleum-derived chemical at a certain temperature. The objects were designed with multi-material 3D printers and stem from an interest in bistability (maintaining one of two configurations indefinitely) and sensitivity (that is, changing shape under the right conditions).
How it works
Professor and project leader Jordan Raney explains that bistability is determined by geometry, while sensitivity or responsiveness depends on chemical properties. By using 3D printers that combine several materials at once, it's possible to create a kind of bridge or link between these two properties. The real breakthrough of the experts is their precise control over the transformation process. In other words, a material that expands when absorbing water isn't so strange, but its expansion happens in all directions at the same time. The key is to limit that expansion to specific directions.
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