"We have developed a direct-current nanogenerator that is driven by ultrasonic waves," said lead researcher Dr Zhong Lin Wang, Regents' Professor at Georgia Tech.

"The basic principle is to use piezoelectric and semiconducting coupled nanowires, such as zinc oxide, to convert mechanical energy into electricity.

"This nanogenerator has the potential to directly convert hydraulic energy in the human body, such as blood flow, heart beat, and contraction of blood vessels, into electric energy."

Wang and his team have developed a prototype which generated electricity continuously for four hours.

"We expect the lifetime of the nanogenerator is much longer than the time we have tested," said Wang.

It is envisaged that the technology could be used to power a new generation of nanoscale medical implants to aid patients with conditions requiring constant monitoring.

For example, diabetics currently monitor blood sugar levels manually by taking a small blood sample which is analysed using a handheld electronic meter.

The new implants would be inserted surgically into the body where they could continually measure blood sugar and automatically alert patients and doctors to problems over a wireless link.

Wang and his team are confident that their work represents a real breakthrough in enabling the deployment of nanoscale devices in medicine.

"It sets a solid foundation for self-powering implantable and wireless nanodevices and nanosystems in biofluid and any other type of liquid," he said.