German and Swiss researchers have found a simple method for making very long lipid tubes for use in tailor-made microfluidic networks.

The team, led by Petra Dittrich of the Institute for Analytical Sciences in Dortmund, Germany, forced lipid membranes through small holes in a microfluidic device to form tubes, cylinders and spheres. 

The device works by forming a lipid membrane over a series of micrometre-sized holes, and then pumping liquid towards the holes to force the membrane through. The membrane reorganises into tubes as it is extruded through the holes. 

Dittrich described the process as 'reminiscent of a children's toy for making soap bubbles'. By changing the pumping rate, the device can produce tubes or varying lengths of cylinders. 

Lipids are long hydrocarbons with a hydrophilic head and a hydrophobic tail, which causes them to self-assemble into spheres or bilayer membranes when put in water. Because cell walls are based on lipid bilayers, it should be possible to connect them seamlessly into microfluidic networks using lipid tubes, said Dittrich. Structures made out of lipids could also be used as pipes, storage chambers and reaction vessels in these networks.

The team made perfectly uniform tubes 1.5 cm long, and as the reservoir of lipids can be refilled easily they foresee the automated production of much longer tubes. They also found that the tubes can twist into helices, though they admit that more work is needed to understand how and why these helices form. 

They were able to regulate the movement of lipid tubes through the device, and hope to build on this to make more complicated structures and to control connections between them. Dittrich's vision is 'complicated networks where connections between different tubes could be realised reversibly and on demand.'

Clare E Boothby