Remote-controlled miniature valves designed by US scientists can deliver tracers into the brain. 

Real-time neuroimaging studies on small animals such as mice are needed to understand the relationship between behavioural events and brain function, says Ellis Meng, leader of the team at the University of Southern California, Los Angeles. Standard techniques such as MRI require the animal to be immobilised which severely limits the events that can be studied. Radiotracers selectively label areas of the brain with elevated blood flow and have been used in larger animals without the need for sedation. Imaging the labelled areas can link areas of increased brain activity with a particular behaviour. 

Existing valves are too heavy to use in small animals without affecting their mobility. So, Meng's team have created a small, light, valve which can be remotely operated for fast, on-demand tracer delivery. They made the valve using a very thin omega-shaped metal wire attached to a thin plastic film. Passing a low-power current through the wire makes the plastic next to it melt - freeing a section of film which forms a flap and releases the contents.     

'It's the shape that really allows us to minimise the power required to open it, and makes [the opening time] very, very fast,' says Meng. 

The system could also be used for other drug delivery applications as Meng indicates, 'Anywhere, where you need very rapid release of a compound from a reservoir - this is the perfect device for that.' 

'They tackled a real immediate problem,' says Michel Maharbiz, a micromachine engineer at the University of California, Berkeley, US. 'Flowing all the drug in at one time; it has to be a robust structure and very reliable,' he adds.    

The team are now building the other side of the system - a cage that is wirelessly hooked up to talk to the implant. Maharbiz seemed in no doubt that the USC group would perfect their device: 'They are very close, they have done a nice analysis job and it is very nice engineering,' he says.    

Matthew Batchelor 

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