Most complex cells, and even a few bacterial ones, contain a network of microtubule fibres collectively called a cytoskeleton, which is responsible for giving the cell its shape and transporting materials around as they twist, bend, shrink, and stretch.
These fibres are made up of a string of proteins called tubulin, which spirals around on itself to form a cylinder about 25 nanometres across. In this case, the researchers used the microtubules found inside the nerves of a cow's brain.
The researchers found they could turn a watery mixture of cow microtubules into molecular motors by adding kinesin, a protein which naturally attaches to the microtubule and 'walks' along its length in a molecular waddle. Another added component was adenosine triphosphate (ATP), which provides energy whenever it donates one of its three phosphates to proteins such as kinesin.
This combination of cells resulted in turbulent dynamics like those of bulk active fluids. The composition of the microtubules tore apart as the movement went on but new kinesin cells matched them to a new partner. This splitting and combining cycle of microtubules resulted into swirling patterns in the liquid and the Brandeis team managed to manipulate this motion into a uniform or ‘coherent flow’. This swirl of fibres produced small whirlpools in the gel-like mixture.
This turbulence could be harnessed to push the fluid in the same direction simply by choosing the right shape for the container, such as discs and doughnut shaped 'toroids'. By picking the right dimensions of the container the churning of the fibres became a steady current in a single direction.
While this only works in containers with precisely the right dimensions, it does scale up, meaning liquids can be encouraged to flow over several metres.
One potential application is in the oil and gas industry. With this kind of technology in hand, oil may not need to be pumped through pipelines to flow. Especially for pipelines that stretch hundreds of miles from the point of origin to its destination. Moreover, this research could also lead to self-propelling gels that would benefit the field of mechanical engineering.
However, once the ATP runs out of phosphate to hand over to the kinesin, the flow stops, making it unlikely for large scale transport of liquids. But the researchers say their work provides insight into the dynamics of moving fluids inside our own cells.
The researchers said: “From a technology perspective, self-pumping active fluids set the stage for the engineering of soft self-organised machines that directly transform chemical energy into mechanical work.”
Perhaps, in future, ‘wet’ robotics could power cybernetic body parts with self-propelled fluids fed by the body’s own reserves of ATP.