Researchers at the Georgia Institute of Technology have worked out how to create tiny robots, just a few microns long, that can swim through liquids such as water and could one day be used for everything from drug delivery to construction.
It's not as straightforward as it seems - at this scale, the viscosity of water is more like that of honey, and momentum can't necessarily maintain forward motion.
"We believe that our simulations will give experimentalists a reason to pursue development of these micro-swimmers to go beyond what is available now," says assistant mecahnical engineering professor Alexander Alexeev.
"We wanted to demonstrate the principle of how robots this small could move by determining what is important and what would need to be used to build a real system."
The team's swimmer consists of a responsive gel body about ten microns long with two propulsive flaps attached to opposite sides. A steering flap sensitive to specific stimuli would be located at the front of the swimmer.
The responsive gel body would undergo periodic expansions and contractions triggered by oscillatory chemical reactions, oscillating magnetic or electric fields, or by cycles of temperature change. These expansions and contractions would create a beating motion in the flaps attached to each side, moving the micro-swimmer forward.
It could be steered by a flexible steering flap on its front, made of a material that deforms based on changes in light intensity, temperature or magnetic field.
"The combination of these flaps and the oscillating body creates a very nice motion that we believe can be used to propel the swimmer," says Alexeev. "To build a device that is autonomous and self-propelling at the micron-scale, we cannot build a tiny submarine. We have to keep it simple."
The researchers envision groups of micro-swimmers carrying cargo through microfluidic chips or other devices. Swarms of them could one day work together as tiny construction robots moving materials to desired locations for assembly - albeit rather slowly.
"If your body is micrometers in size, that kind of speed is really not too bad," says Alexeev. "The swimming speed will be rather slow, but at that size scale, you don't really need to go very fast since you only need to go short distances."