Living cell yields blueprint for nano engine
Here are live Vorticella cells. The big ones are only 625 microns long (including stalk), with one micron measuring a millionth of a meter. France told Earth & Sky that because these cells have already been "engineered by nature to move very dramatically and very quickly on that very small length scale, we think that it could be useful to take the same principles and put them into . . . nanoscale to microscale machinery." Image courtesy of Michael Shribak and Grant B. Harris, Marine Biological Laboratory.
JB: This is Earth & Sky. Scientists often look to nature for inspiration. That’s true in nanotechnology, where scientists hope to build extremely small machines.
DB: Danielle France is a biological engineer at MIT. She’s studying microbes called Vorticella. These tiny freshwater organisms hang on to surfaces with long stalks. The stalks can stretch straight out or quickly contract and coil up like telephone cords.
JB: France and her team wanted to know how strong—and how fast—these contractions are. So they put Vorticella in a rotating chamber under a microscope and started it spinning 11,000 RPM.
Danielle France: So the camera is stationary and what it does is it uses a laser pulse to synchronize the camera shutter with the specimen every time it comes around to the exact same spot.
JB: France said the Vorticella experienced about 10,000 times the normal force of gravity on Earth—and yet they were still able to contract. Relative to their size, Vorticella are more powerful than car engines.
JB: France envisions “nanomachines” that mimic this natural engine. One example might be a tiny implantable device that delivers a precise dose of a drug at regular intervals from inside the human body.
DB: To see videos of Vorticella stretching and contracting, come to earthsky.org. With thanks to the National Science Foundation, we’re Block and Byrd for Earth & Sky.
Vorticella move extremely quickly. For comparison, they move a thousand times faster than human body cells involved in the healing process called fibroblasts.
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. France says, “usually when you see somebody’s movie that they’ve made in cell biology, it’s almost always sped up—it’s almost always a time lapse movie. And I think we have the only movies where you have to slow it down to show people.”
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).
More Vorticella images and videos.
Imagine yourself hanging on to a spinning merry–go–round and trying to pull yourself in. It takes some effort. This is akin to what the Vorticella experienced in France’s experiment. Although the Vorticella cells experienced 10,000 times the normal force of Earth’s gravity. On a merry–go–round, you would only experience a few times the normal force of gravity.
Using laws of physics, France’s team could calculate how strong the Vorticella had to be to contract against the centrifugal force of the spinning chamber. They found that it could pull with over 300 nano–Newtons of force. That’s an extremely small amount of force by human standards, but in biological terms, it’s quite powerful.
A Newton is the amount of force that it takes to push a one kilogram (2.2 pound) object for one second and get it to move at a speed of one meter (3.28 feet) per second. In everyday terms, imagine you held a hamburger in your hand that weighed half a kilogram (or a quarter pound). A Newton is the amount of force that the hamburger would be pushing down on your hand with due to gravity’s tug on it. (That’s assuming you’re at sea level!) Now a nano–Newton would be one billionth as much force.
France says another feature that makes these tiny engines useful for nanomachines is that they can be forced to contract and stretch out by simply adding or removing calcium. Danielle France said, “So we can actually take these cells and extract just the stalk material and just by exposing it to calcium, we can make that stalk contract and re–extend and we can cycle it through just by adding and taking away calcium. So from an engineering perspective, it’s already . . . a small micromachine that we can play with.”
Our thanks to:
Danielle France
Ph.D. Candidate in Biological Engineering
Massachusetts Institute of Technology
