As everyone seems to know, our bodies are mostly liquid, so designing tiny robots that can swim may allow new delivery systems for drugs, genes, and other therapies. Traditional propulsion methods used in man-made technologies like propellers are not effective at small scales and microorganisms instead often wiggle their way about.
Researchers at Georgia Tech used computer modeling to design microrobots that have a guiding flap on the front and two power flaps on the back that are attached to the sides of a chunk of gel. The gel can be made responsive to a number of stimuli, like heat or chemical changes of the environment, light, or a magnetic field. The changing shape of the gel due to a stimulus would move the power flaps, propelling the robot forward. Another stimulus can be used to change the shape of the guiding flap, allowing for steering of the robot to its destination.
From Georgia Tech:
Key to the operation of the micro-swimmer would be the latest generation of hydrogels, materials whose volume changes in a cyclical way. The hydrogels would serve as “chemical engines” to provide the motion needed to move the device’s propulsive flaps. Such materials currently exist and are being improved upon for other applications.
As part of their modeling, the researchers examined the effects of flaps of different sizes and properties. They also studied how flexible the micro-swimmer’s body needed to be to produce the kind of movement needed for swimming.
“You can’t swim at the small scale in the same way you swim at the large scale,” Alexeev said. “There is no inertia, which is how you keep moving at the large scale. What happens at the small scale is counterintuitive to what you expect at the large scale.”
The computational fluid modeling the researchers used allowed them to study a wide range of parameters in materials, oscillation rates and flexibility. What they learned, Alexeev said, will give experimentalists a starting point for actually building prototypes of the flexible gel robots.
“We have captured the solid mechanics of the periodically-oscillating body, the fluid dynamics of moving through the viscous liquid, and the coupling between the two,” he said. “From a computational fluid dynamics standpoint, it’s not an easy problem to model at this scale.”
Ultimately, the researchers hope to work with an experimental team to actually build the micro-swimmers. Combining their theoretical work with actual experiments could be a powerful approach to building robots on this size scale.
Abstract in Soft Matter: Designing maneuverable micro-swimmers actuated by responsive gel