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Wirelessly Charged Microchip Opens Doors into 'Electroceutical’ Devices'

Tue, 07/29/2014 - 11:58am
Melissa Barnes, Associate Editor

Stanford's novel method safely delivers wireless power to devices as small as a grain of rice for medical implants deep within the body.

A batteryless electrostimulator next to grains of rice. All Photo Credit: Austin YeeIn their quest to integrate microchip technology with internal medical devices, a team of Stanford engineers, led by Professor Ada Poon, and John Ho, an electrical engineering student, have invented a groundbreaking solution for wirelessly charging devices implanted in the body.

There has long been a disparity between the level of microchip capabilities and medical integration, as medical electronic devices remain cumbersome, having to rely on batteries and external power sources. While the rest of the wireless electronics world has been getting smaller and more powerful, the medical world has lagged behind, with inherent regulatory and biological barriers holding technology back.

"We need to make these devices as small as possible to more easily implant them deep in the body and create new ways to treat illness and alleviate pain," says Poon.

Poon and Ho were inspired by this challenge to explore possible methods of wirelessly transferring power within the body.

“The project began as a highly theoretical study where we examined the behavior of electromagnetic field in biological tissues,” recalls Ho. “We identified a method that could reach tiny devices implanted nearly anywhere in the body, which is not possible with conventional wireless powering techniques.”

The Discovery of Mid-Field Wireless Transfer

After nearly two years of trial and error, Ho and Poon found an electromagnetic structure capable of generating the particular type of waves necessary to make their idea work.

The key to breaking the technology barrier was in revisiting the differences between far-field and near-field waves. Far-field waves have not typically been involved in medical applications, as they are usually reflected away from the body or completely absorbed. Near-field waves, on the other hand, are able to transfer power over shorter distances and have been safely used in such medical devices as hearing implants. However, like their name implies, these waves are not useful for deep within the body.

“Miniaturized devices have previously been possible only at very superficial depths in the body, rendering locations such as the heart or the brain inaccessible,” says Ho.

Thus, the best solution for the disparity was found through a combination of the two wave-field types. So, Poon developed an entirely new method, known as mid-field wireless transfer. Like a field-wave hybrid, the mid-field wireless transfer makes use of the far-reaching far-field characteristics, while preserving the level of safety inherent in near-field waves.

Taking into consideration that waves travel differently through different material, Poon investigated how these waves would move through the body. With clear understanding of this concept, she was able to design a power source, which generates a particular wave that changes its characteristics when moving from air to skin. Poon was then able to successfully test her mid-field transfer method by sending power directly to implanted medical devices.

The device demonstrated by Poon and Ho was a tiny electrostimulater the size of a grain of rice. A miniature coil within the electrostimulator extracts power from the incident electromagnetic field. The signal is then processed by integrated circuits into electrical pulses and precisely delivered by electrodes.

“The innovation is actually not in the device itself but in the way that it is powered,” explains Ho. “The device does not have a battery and, once implanted deep in the body, can be powered by a flat metal plate placed outside the body, above the surface.”

Overcoming Design Hurdles

A batteryless electrostimulator next to a U.S. penny for size comparison. The new powering method allows the device to be wirelessly powered deep inside the body, in locations such as the heart or brain.As with any novel approach to an old problem, Poon and her team had to overcome several design challenges. Developing a wireless power source was a feat in and of itself.

“The structure needed to control electromagnetic waves in far more precise ways than conventional wireless powering coils did,” recalls Poon. “We addressed this problem through extensive experimentation, both through numerical simulations and physical prototyping.”

Another challenge, typical to the medical industry, was the issue of safety and size. The device was forced to undergo vigorous testing before it could be considered a viable system. In preliminary trials, Poon’s lab tested the charging system on a pig, as well as a miniature pacemaker implanted in a rabbit. Now, the scientists must continue to prepare for testing in humans.

“We are in the process of initiating human clinical tests for our system… commercial use may require another 5 to 10 years,” foresees Ho.

Though the entire process is likely to take several years under the stringent standards of the medical industry, Poon is already on her way toward completely revolutionizing the field. 

The Possibility of ‘Electroceutical’ Devices

Poon’s discovery is on the cusp of an exciting new generation of microimplants and other nano-sized electrostimulators. The significance of the new device is in its so-called ‘electroceutical’ capabilities, which could completely change the administration of drugs in the body and the alleviation of pain.

“We envision that the powering method could pave the way for new generations of sensors and stimulators that can electrically treat some disorders in ways more effective than drugs.”

Through integrated circuit technology, specific nerves can be targeted and stimulated, and drugs can be administered in precise locations and doses.

“Implantable electronic devices that directly modulate activity in the nervous system could provide more effective treatments for some disorders than drugs,” explains Ho. “The 'midfield' powering method may play a part in making these treatments practical by miniaturizing the devices and powering them deep in the human body.”

The wireless transfer of energy means that there is no longer the need for bulky batteries. Devices can now be made even smaller, with the ability of being implanted anywhere in the body, including the brain. Though the wireless powering system will have great value in the medical community, Poon and Ho hope that it may have wider technological applications.

“We believe that the powering method will find broader applications in sensors, treatments, and other yet to be developed applications," concludes Ho.

This article originally appeared in the January/February print issue. Click here to read the full issue.

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