Drops of gel full of a protein mix can move themselves, mimicking a key feature of life
. The mobile drops could one day have medical uses, and might help untangle the laws that govern how patterns emerge from chaos.
The drops are made from a special gel containing ingredients extracted from real cells: nano-sized protein tubes from cow brains and motor proteins from bacteria. The motor proteins can "walk" along the tubes at a rate of about 8 nanometres per step, feeding on adenosine triphosphate (ATP), the same energy source they use in living bodies.
"This is a little bit of a Frankenstein experiment," says Zvonimir Dogic of Brandeis University in Waltham, Massachusetts. "We're taking biological materials and putting them together to make totally new materials."
Van Gogh in motion
Previous research used these proteins to make self-assembling structures, but once assembled they didn't move.
"That system formed a pattern and then stopped, while this system keeps going," says biomaterials expert M. Cristina Marchetti of Syracuse University in New York, who was not involved in the new work.
The key to making the blob mobile was to add nanometre-sized polymers to the solution, which helped draw the tubes into bundles. A motor protein could then span the tight spaces between tubes and cause them to slide past each other in opposite directions. When Dogic and colleagues crammed enough tubes in a small space, they flowed and churned in patterns that resemble a Van Gogh painting in motion.
Creating drops of the active gel about 30 to 100 micrometres across resulted in something akin to cells that crawled across a microscope slide. "It mimics a little bit what might happen in a living system," Marchetti says. But the researchers can control how their artificial cells behave. Adjusting the amount of ATP dictates how long the drops stay in motion, while changing the concentration of tubes affects the way they churn.
Swarm lab
Daniel Chen, a post-doc in Dogic's lab, imagines that someday the droplets could be controlled well enough to deliver drugs or seek out cancer cells. Because the gel is made of biological material, bodies are less likely to reject it, he says. The gel can also self-heal, so it could help make liquid-crystal displays more robust.
But all of that is a long way off, Dogic cautions. At the moment, the cells tend to turn circles and only cover about 250 micrometres in 33 minutes. The more immediate promise lies in using the way the tubes move to understand swarm behaviour ? how patterns form spontaneously in flocks of birds and schools of fish.
"Most of nature is out of equilibrium inherently," Dogic says. "But it's hard to get a tunable model system to compare to theory ? you can't do experiments on flocks of birds. This is a model system."
Journal reference: Nature, doi.org/jp3
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