WSJournal Harnessing Energy From the Body to Run Devices

WSJournal Harnessing Energy From the Body to Run Devices
http://online.wsj.com/article/SB1000142412788...ljournal_0

The development, still years from becoming a reality, could spare some of the millions of people with implanted devices like pacemakers from undergoing surgery to replace rundown batteries. Other products, including hearing aids, insulin pumps and pain-management devices, could be made to function without changing batteries, or at least sharply extend their power time. Harnessing the body's energy also could spur development of innovative medical technologies that could potentially monitor the body's inner workings.

Researchers harnessed energy from guinea pigs' inner ears to power a chip, which is small enough to be implanted in the animals' ears.

In an experiment this month, researchers from Massachusetts Institute of Technology and Harvard Medical School demonstrated in guinea pigs that it is possible to use energy produced by the inner ear, which is needed for hearing, to power tiny sensors without interfering with the animals' functioning. The researchers say the device, which resembles a semiconductor chip, is small enough to be implanted in the ear one day to monitor problems such as ear infections and hearing loss.

Scientists at other labs are trying to capture and convert energy from heart beats, blood flow, lung contractions and arm and leg movements.

Researchers compare the futuristic devices to solar-powered calculators, which work as long as there is sunlight. Some experts expect the first medical devices that tap the body's energy—known as bioenergy harvesting—could be available within a decade.

Pacemaker batteries typically last for five to 10 years before they wear out and need to be replaced with a new battery using surgery. Currently, there is no way to recharge the pacemaker battery once it's depleted. In the future, the hope is the battery will be continually powered by the energy from one's own heart beat. The ultimate goal "is what I call the perpetual device," says Gene Frantz, an expert in power dissipation and an engineer at semiconductor design and manufacturer Texas Instruments Inc. TXN +0.12% in Dallas. "It doesn't need to be plugged in or operated with" an external battery, he says. Dr. Frantz studies innovation in integrated circuits, including work from many academics and companies researching bioenergy harvesting.

The task is challenging on a number of fronts. Many biological sources of energy tend to emit very low power and often inconsistently, so the energy needs to be captured and stored, such as with batteries, so it can be used by the device, say researchers. Also, energy storage units have to be limited in size if they're going to fit within the body.

An additional hurdle: the devices must not siphon off too much energy, so as to preserve normal body function, says Paul Kohl, a Georgia Tech professor and director of a center that funds researchers, including the MIT group, with grants from the Semiconductor Research Corp., a technology research consortium.

In the work published earlier this month online in the journal Nature Biotechnology, Konstantina Stankovic, an ear surgeon, teamed up with MIT engineering professor Anantha Chandrakasan to figure out a way to tap a reservoir of energy produced by the inner ear to power a medical device. Scientists have been aware of this source of energy, which we need to use in order to hear properly, for some 60 years, but didn't know how to access it.

The researchers designed tiny electrode sensors that could be implanted in the inner ear and would draw just a small bit of current while maintaining normal hearing, says Dr. Chandrakasan, head of MIT's department of electrical engineering and computer science.

It was an engineering feat to design such an ultra-low-power device considering that the ear produces just 70 to 100 millivolts—not even enough juice to power a conventional electronic circuit like a sensor or Wi-Fi chip. A double-A battery generates more than 10 times that amount of voltage, says Dr. Chandrakasan.

The engineers found a way to kick-start a radio-frequency device wirelessly using an external power source initially, but running the device afterward on the output of power generated by the inner ear. To reduce the need for power, they designed a device to wake up and run only when it was taking measurements from the ear.

Dr. Stankovic, an otologic surgeon at the Massachusetts Eye and Ear Infirmary, and a colleague implanted the electrodes into the inner-ear reservoirs of guinea pigs and connected them to the chip outside the animals. The chip, in turn, wirelessly powered a radio-wave device that was located a meter away and measured energy from the ear.

The scientists showed this biological battery was indeed able to be run the radio device and detect the inner-ear environment for about five hours without compromising the guinea pigs' ability to hear. The device is small enough to implant into the middle ear with electrodes connected to the inner ear.

The most immediate application for the device is sensing the inner-ear environment and its vicinity, which can be important to monitor for infection in people with ear disease or a cochlear implant, according to Dr. Stankovic.

Eventually, there may be the possibility that people with some hearing loss could be fitted with these devices to monitor their hearing-loss progression. This could let doctors intervene earlier and possibly help them understand why people lose hearing. The sensors could be used to measure treatment success with those receiving experimental therapies to regrow cells that restore hearing or to deliver drugs.

A University of Michigan team is working on harvesting energy from heart beats to power a pacemaker. M. Amin Karami, an aerospace engineering research fellow, presented data at the American Heart Association annual conference in November showing an experimental energy harvester can convert the energy from the beating of a heart into enough usable electrical energy to, in theory, operate a pacemaker. The harvester hasn't yet been implanted in animals or humans yet.

Their team showed that the device could generate 18 times the amount of energy needed to power a pacemaker using a normal heart beat, according to Dr. Karami. The group measured the vibrations emitted in the chests of pigs and sheep during surgeries, and then used those calculations to estimate how much electrical energy would be generated by the harvester.

"Our next step is to fabricate a complete self-powered pacemaker and examine it with animal tests," wrote Dr. Karami in an email.

At Virginia Polytechnic Institute and State University, electrical engineering professor Dong Ha and his team are in the early stages of studying how to employ body heat to power a circuit. Energy is generated by the body's adjustments to differences in temperature between the skin and the outside air, which can be harvested. If successful, such a device could be implanted just under the skin, or even worn in a jacket, to power a device, says Dr. Ha