A self-propelling liquid?

Video: The scientists placed liquid full of microtubules inside ring-shaped containers. As a result of the microtubules' activity, the liquid moves in the same direction, an example of 'coherent flow.' (The white dots are added so the movement will be visible.)

The researchers work at Brandeis' Materials Research Science and Engineering Center (MRSEC), part of a National Science Foundation initiative to create a revolutionary new class of materials and machines made from biological components. 

The work reported in the journal Science involved reproducing in the lab the complex series of processes that allow cells to change shape and adapt to their environment. Cells can do this because the building blocks of its scaffolding – hollow cylindrical tubes called microtubules – can grow, shrink, bend and stretch, altering the cell’s underlying structure.

The Brandeis researchers extracted microtubules from a cow’s brain and placed them in a watery solution. They then added two other types of molecules found in cells – kinesin and adenosine triphosphate (ATP). The microtubules aligned parallel to each other. A kinesin molecule came between them, connecting them like a tie between rail tracks.

Using the ATP as a fuel source, the kinesin began moving. Its top went in one direction, the bottom in another. The microtubules slid away from each other, and the structure broke apart. But the microtubules didn’t remain free-floating for long. New kinesin came along and bound each to a new partner.

As these microtubules came together then separated, amazing, swirling patterns emerged in the fluid. And for the first time ever, the Brandeis team was able to get the swirls to move in the same direction, creating a 'coherent flow' that pushed the surrounding liquid forward as well.

This microtubule-kinesin-ATP reaction is the same one that goes on in cells, except in cells it is much more complicated. Yet the much more simplified model created by the Brandeis scientists achieved a similar effect. Essentially they harnessed the power of nature to create a microscopic machine capable of pumping fluid.