The carnivorous plant known as the Venus flytrap catches its prey through a sophisticated mechanism: The flytrap’s sensitive hairs, when touched, trigger two leaf lobes to snap shut and ensnare any insect inside.
Using stimuli-responsive materials and geometric principles, researchers created an artificial Venus flytrap with its own “embodied logic.”
The flytrap-like system closes only if a mechanical load is applied and an actuator is exposed to a solvent.
A team at the University of Pennsylvania’s School of Engineering and Applied Science used multi-materials 3D printers to make the active structure. With simple changes in the environment, controllable “if/then” logic gates activate the complicated mechanical behaviors.
The study was led by Jordan Raney, assistant professor in Penn Engineering’s Department of Mechanical Engineering and Applied Mechanics, and Yijie Jiang, a postdoctoral researcher in his lab. Lucia Korpas, a graduate student in Raney’s lab, also contributed to the study.
Professor Raney spoke with Tech Briefs, via email, about how his team's flytrap works, and what’s possible when you can embody 3D-printed objects with logic.
Tech Briefs: What inspired this idea?
Prof. Jordan Raney: This work was inspired by observing how efficiently and effectively natural systems can respond to their environment. Many of these systems (such as the Venus flytrap) can use relatively simple cues from the environment to do complex things. Of course, robotic systems can be built to perform similar actions, but these typically require microprocessors, batteries, sensors, and actuators. Natural systems respond intelligently to their environment without any of those.
Tech Briefs: What is “embodied logic?”
Prof. Raney: Natural systems respond to their environment in sophisticated ways without needing microprocessors, batteries, sensors, or actuators. Instead, all of these sensing, processing, and actuating functions are "embodied" by the material and structural features of which the system is composed. This is what we mean by embodied logic.
Tech Briefs: How did the systems that you developed “embody” this kind of logic?
Prof. Raney: The systems we developed "embodied" all necessary sensing, logic, and actuation capabilities in the material/structure combination of which the system was composed. We did not have wires, batteries, microprocessors, or other electronics that you would typically expect in systems that respond in programmed ways to their environment. Instead, we used materials that partly swell in response to particular cues in the environment (like moisture), and we used this swelling to trigger instabilities and rapid rearrangement in the structure (like flipping a switch). We can also control when these instabilities are triggered, allowing us to produce controlled sequences of logic.
Tech Briefs: How do your 3D printed smart objects enable a kind of “fine-grained control? ”
Prof. Raney: By "fine-grained control" we are really referring to two unique aspects of this technology. First, 3D printable materials can be developed that respond to a large variety of specific cues, like moisture, temperature, pH, and light.
In principle any number of these could be printed, integrated into a single system, and programmed with very complex logic (e.g., "actuate if the temperature is between 300 and 312 K and the pH > 8, or if exposed to sunlight").
Second, we are able to control the time of actuation, which is a fairly unique attribute in the realm of stimuli-responsive materials. This allows us to pre-program a sequence of events, or to require a sequence of stimuli be encountered to actuate.
Tech Briefs: How does your artificial Venus Fly Trap work, and how does the trap embody logic?
Prof. Raney: We used two different kinds of materials in our work: a silicone elastomer, which is like a "sensor" for hydrophobic things (certain solvents or oils), and a hydrogel, which swells in the presence of water.
We devised a couple types of artificial Venus flytraps that would only enclose after certain pre-defined cues (oil, water, etc.) were introduced. For example, to test the principles of embodied logic, we made a Venus flytrap that only closes if exposed to solvents. That is, you can set a mass inside the trap, but the trap does not close unless a solvent is introduced, which causes one of our bistable switches to flip.
At that point the mass is able to trigger closure of the trap. We made more complex versions as well, such as traps that would only activate for a period of, say, 10 seconds, and then deactivate. If a mass was not introduced within that precise 10 second window it would never close. This control over timing can be difficult to achieve in engineering without using electronics.
Tech Briefs: What are the most exciting applications that you can envision with this type of technology?
Prof. Raney: To me one of the most interesting features of this technology is its ability to monitor its environment for a very long period of time without needing continued input of energy. For example, with a microfluidic chip you might be interested in confirming that there is no contaminant entering into one of its inputs. Rather than continuously monitoring the input with a solid-state sensor and a constant power source, this technology could passively wait for weeks or months without power, and then suddenly close off the channel as soon as contaminant was detected. Similar applications could be envisioned in remote monitoring or deployable structures.
What do you think? What kind of applications do you envision? Share your comments and questions below.