Microbe muses
Danielle France uses living microbes as inspiration for nano engines.
A budding scientist thinks that “nano engines” – too small for the eye to see – will someday provide the power source for a myriad of futuristic machines. She’s looking to a tiny creature – a freshwater microbe called Vorticella – to learn how to build these engines. Earth & Sky’s Marc Airhart spoke with Danielle France in January, 2006.
Airhart: Vorticella have bell–like bodies with long “stalks” extending from them, which can coil and release. This coiling motion lets Vorticella move at blinding speeds and with great power. As an engineer, why does this ability of Vorticella excite you?
France: From an engineering perspective, a Vorticella cell is already a small micromachine that we can play with.
We can actually take these Vorticella cells and extract just the stalk material. By exposing it to calcium, we can make that stalk contract and re–extend.
Airhart: But then what?? How does that help you?
France: A Vorticella cell has been engineered by nature to move very dramatically and very quickly on a very small length scale.
We think that it could be useful to take the same principles and put them into contracting fibers or in small devices called MEMS, which stands for Microelectromechanical Systems. Or they might be useful in nanoscale to microscale machinery – machines so small, they’re measured in millionths or billionths of a meter.
So, we could take what we learn from Vorticella and use that same principle in a very small micromachine. Suppose you want it to be biocompatible – in other words, something that the human body won’t reject. Examples would be a drug delivery device or anywhere you might need a small gate or door opened in a small device. These are the places where you could deliver a calcium pulse, like those we used with the Vorticella cells to make them contract and re–extend. In that way, we could generate movement.
So, you figure out what you need done from a biological or medical perspective. And, once you’ve figured out which cells you need to target inside your body, this is the machinery that could make it happen.
This technology could help you make your car, but you would still need a driver to actually make the decisions.
Airhart: How powerful are Vorticella?
France: In one experiment, we put Vorticella cells under a special microscope where the entire stage of the microscope spins. And it’s spinning really, really fast to over 10,000 rpms (revolutions per minute) and that means that cells are actually feeling a centrifugal force that’s 10,000 times the force of gravity that holds us on to Earth’s surface.
At those speeds and forces, a Vorticella stalk can still contract. In that situation, we can calculate how much force the stalk has to exert to move the cell against that opposing acceleration.
Vorticella stalks are much smaller than human muscles, but if you scaled them up, they would be more powerful and faster than human muscles.
Airhart: How fast are Vorticella contractions?
France: Fast. They move thousands of times faster than fibroblasts – cells in your body that crawl into wounds to help with the healing process.
Usually when you see a movie that someone has made in cell biology, it’s almost always sped up. In other words, it’s a time lapse movie. I think we have the only cell biology movies where you have to slow the action down to show people. We show our movies at 150 times slower than real time.
Airhart: Thank you for speaking with me today, Ms. France.
Danielle France is a doctoral student in biological engineering at the Massachusetts Institute of Technology.
Watch videos of Vorticella cells in motion:
Don’t blink or you’ll miss it. In this video, a live Vorticella cell contracts with blinding speed, stretches back out and contracts again. The cell is inside a chamber spinning at over 10,000 times per minute. It’s experiencing over 10,000 times the normal force of Earth’s gravity.
The Vorticella contraction in this video happens right at the beginning, followed by a slow stretching out. Watch carefully. Video courtesy of Arpita Upadhyaya and Alexander van Oudenaarden, MIT.
In another video, a Vorticella cell contracts and re–extends under a slight centrifugal force, at about 21g’s (21 times the acceleration due to Earth’s gravity).
