Programmable microfluidic devices could help reduce animal testing, according to scientists in the US.

David Beebe and colleagues from the University of Wisconsin have developed microfluidic components that can act in the same way as logic gates, timers and rheostats, essentially the basic building blocks of a computer. They created a system that uses various channel geometries and the presence/absence of droplets on access points to indicate a 1 or a 0. This makes the devices essentially digital and therefore programmable. The fluid is moved via passive pumping: 'the pressure created in a droplet is a function of the size of the droplet, and fluid flow can be created in a microchannel positioned between droplets of different sizes,' explained Beebe.

The idea of these devices is to take the complexity out of the microfluidics and cut down the amount of connections to the chip, which could all be built in to the device. One potential application is in cell culture and biological assays that have many staining and washing stages. Ideally, you could design a device that can be pre-programmed by the appropriate placement of droplets, placed in an incubator and left for the duration of the experiment.

Another advantage is the reduction in reagents; often microfluidic devices require large reservoirs of reagents. These new chips have very little dead volume, so reagent and cell quantities can be reduced dramatically. 'For example, in some cases it is possible to reduce the number of cells required by 100 fold (that is, running an experiment that now requires 100 mice with just one),' said Beebe.

In the future, 'controlling evaporation and making devices out of alternative materials, such as polystyrene, are areas that will be explored so that the platform can be used with a variety of different liquids,' added Michael Toepke, a colleague of Beebe's.

Michèle Zgraggen