Light-activated capillaries that can propel a range of liquids along winding paths and even uphill are described in this week’s Nature. The tiny tubes could be used in technologies ranging from biomedical devices to micro-pumps.

Systems that manipulate small amounts of fluids to perform reactions or analyses are important in underpinning many laboratory investigations and also have more immediate practical applications. Light energy can be used to trigger the motion of liquids, but existing light-driven technologies can limit this motion to simple trajectories over short distances, as well as limiting the range of liquids that are able to be transported.

Yanlei Yu and colleagues have designed a light-activated tubular system that is inspired by the structure of artery walls, in particular their strength and ability to change shape to pump blood through the body. The tubes deform when exposed to light, and this configuration change propels liquid over long distances with controllable speed and direction. The system can drive liquids through ‘S’-shaped and helical trajectories, an achievement that has not previously been reported for closed microchannels. Various liquids and mixtures can pass through the tubes, including complex fluids, such as emulsions and petrol, which have not been handled by existing light-driven methods. In addition, the system can handle biomedical liquids, such as cell suspensions and buffer solutions, indicating that it could be used to make laboratory-on-a-chip devices.