Heartbeats tapped for power generator implant [图片]
A minuscule electricity generator implanted in the body could power an early-warning system for hypoglycaemia – or other medical conditions –
from a heartbeat. A "nanogenerator" has been implanted in a live rat and has generated electricity from the animal's beating heart. In future it could run in-vivo sensors.
Zhong Lin Wang at the Georgia Institute of Technology in Atlanta knew that at the nanoscale carefully constructed wires of zinc oxide could act as
piezoelectric materials – materials that convert mechanical energy into
electricity. So with colleagues he set about creating a flexible generator that could harvest energy from natural actions such as breathing or heartbeats.
The team deposited zinc-oxide nanowires on a flexible polymer substrate that allows the nanowires to bend in a variety of ways. They sealed the device in a polymer to shield it from body fluids and to ensure that any electricity they measured was generated by the device, not background interference.
This 2 millimetre by 5 millimetre rectangular device was then attached
to a rat's diaphragm muscle using tissue adhesive. "The device is so tiny, you can barely see it by eye," says Wang.
With each breath, the rat's implant stretched and twisted, deforming the nanowires and generating up to 4 picoamps of current at a potential of
2 millivolts. Wang then implanted a similar device on a different rat's heart, generating around 30 picoamps at 3 millivolts.
While the amount of energy generated is small, Wang thinks he can scale up its output enough to power simple implantable nanosensors – blood
pressure or glucose sensors, for instance – that have modest power
requirements and don't need a continuous supply.
Wang says that the device can capture motion in any direction, so it does not have to be fixed in a particular alignment. "Any deformation can drive the device," says Wang.
Other devices have already been used to generate power from body movements. For example, last year researchers at NASA's Glenn Research
Center in Cleveland, Ohio, implanted a ceramic piezoelectric generator into a rabbit's quadriceps muscle. The device generated enough
electricity to continuously power a stimulator attached to the same muscle – but required large movements to generate power.
The Georgia Tech work "is very creative" because it uses involuntary natural actions whose movements are small, says Xudong Wang a nanoengineer
at the University of Wisconsin-Madison who was not involved with the
research. "It's the first time a nanogenerator has been tied to muscle movements in vivo."
Journal reference: Advanced Materials, DOI: 10.1002/adma.200904355