TINY electronic devices known as a “lab-on-a-chip” are now routinely used to analyse small biological samples, sometimes a few microlitres or less, and to carry out out other tasks such as purifying proteins and DNA. Some even reproduce the functions of a complete organ, like a kidney or lung, so that they can be used to test drugs reliably and cheaply. Many of these devices, though, end up not so little because of the bulky ancillary parts and chunky bits of tubing required to pump fluids in and out of the chips. This can limit their application. What would be good is a way to make the complete system more portable—or, indeed, wearable so that the devices can be used to test patients regularly. That means shrinking the external paraphernalia down to a size more comparable to the chip itself.

Yu Yanlei at Fudan University in Shanghai and her colleagues think they have found a way to do that. They used fine tubes (pictured) made from a new material that allows small quantities of fluid to be moved around precisely simply by aiming a beam of light at them—in effect creating tiny, light-activated pumps (see video below).

Dr Yu turned to liquid-crystal polymers, a class of materials that includes Kevlar. Bonds between the chemical chains in these plastics can make them pack together tightly. That is what makes Kevlar famously tough, allowing its use in armour. But it can also create polymers that are difficult to work with: once they bond together, the chains are hard to prise apart and the polymer cannot easily be dissolved or melted.

To overcome this obstacle, the researchers drew inspiration from one of nature’s most robust fluid-transport networks, the circulatory system. Specifically, they looked at arteries which are composed of alternating layers of muscle and elastic tissue and carry blood at high pressure away from the heart. To imitate this structure, Dr Yu designed a new liquid-crystal polymer consisting of a long flexible carbon backbone and azobenzene, a chemical compound made up of two hexagonal rings linked together. This has two properties that Dr Yu’s team exploited. First, the flat faces of the rings on neighbouring chains should stack together. The chains in the polymer would thus assemble into layers, like the arterial walls the researchers hoped to copy, rather than strongly linked chains of some other liquid-crystal polymers. Second, azobenzene’s rings are known to line up with each other when visible light is shone on it, a movement that should make the polymer expand a little.

To make their micro pumps, the researchers dissolved the polymer in dichloromethane, a solvent, and filled glass capillary tubes with the solution. When the solvent evaporated the inside of the capillary was left evenly coated with the polymer. These were then soaked in hydrofluoric acid, which dissolves glass, leaving behind hollow polymer tubes about half a millimetre in diameter.

Shining blue light on a tube makes it expand enough to propel any liquid inside towards the narrower, unilluminated end—a consequence of surface tension differences between the two ends. As the researchers report in Nature, they have been able to make a variety of structures including coils and “Y” shapes using the same technique, and to propel a variety of fluids along them including oils, ethanol and a suspension of human pancreatic cells.

The team has a number of hurdles to overcome before the tubes can be hooked up to a lab-on-a-chip. One problem is how to manipulate the fluid in one tube with light without also accidentally affecting a neighbouring tube feeding the same device. Dr Yu suggests that optical fibres might provide an effective way of channelling light to the correct tube. Her next step, however, will be to use the material to craft a “microreactor” device that would allow small biological or chemical samples to be mixed and studied at the flick of a light switch.