The chaotic motion of a collection of actively moving molecular rods can be harnessed to rotate millimeter-sized propellers and pinwheels, according to new experiments [1]. The rod motion was driven by chemically powered molecular motors that cause neighboring rods to connect and pull past one another. The ability to convert the energy of these microscopic machines into large-scale motion might eventually be used to drive small pumps that work without external power.

Active matter refers to a collection of objects that can move on their own via some energy-consuming process. It is often characterized by its ability to create order from disorder. For example, certain bacteria in isolation swim in no particular direction, but researchers have shown that these bacteria can collectively turn a microscopic gear by preferentially bumping into one side of the gear notches [2].

Other types of active matter exhibit collective motion through an alignment of rod-like elements. This so-called active nematic behavior is common in certain types of biological tissues, such as layers of elongated epithelial cells (see Synopsis: Extending and Contracting Cells). The active elements normally align with each other, but their individual motions can lead to regions of misalignment called defects. These regions form and move around in an unpredictable fashion. “One of the intriguing aspects [of active nematics] is that we can harness this internally generated chaos to create some kind of coherent motion,” says Zvonimir Dogic from the University of California, Santa Barbara.