Tiny Implants Run on Wirelessly Transmitted Power

Stanford University assistant professor of electrical engineering Ada Poon, PhD, and her research team have developed a way to wirelessly transmit electromagnetic energy to implanted devices within the body.

Their paper, "Wireless Power Transfer to Deep-Tissue Microimplants," is published in the Proceedings of the National Academy of Sciences. In the paper's abstract the team says they have developed a wireless powering method that induces "spatially focused and adaptive electromagnetic energy transport." This publication marks the next step in Poon's developmental work, which we first described in September 2012.

Termed midfield powering, the technique creates a high-energy density region deep in tissue. The power-harvesting structure can be made extremely small, the team says. "Unlike conventional near-field (inductively coupled) coils, for which coupling is limited by exponential field decay," the paper's abstract continues, "a patterned metal plate is used to induce spatially confined and adaptive energy transport through propagating modes in tissue."

Poon and her team have used this method to power a 2 mm microimplant capable of functioning as a pacemaker. An independent laboratory has found that her system fell well below the danger levels for human exposure levels, and milliwatt levels of power can be transferred to a deep-tissue (>5cm) microimplant capable of both complex electronic function and physiological stimulation.

Poon's team has built a pacemaker that is smaller than a grain of rice. It can be powered or recharged wirelessly by holding a power source, about the size of a credit card, near the device.

"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," Poon told the Stanford Report's Tom Abate. Poon's lab has tested their wireless charging system in a pig, Abate wrote,  and used it to power a tiny pacemaker in a rabbit.

According to Abate, "She is currently preparing the system for testing in humans. Should such tests be approved and prove successful, it would still take several years to satisfy the safety and efficacy requirements for using this wireless charging system in commercial medical devices."

The team hopes their approach will enable new generations of implantable systems that can be integrated into the body at minimal cost and risk. Poon told Abate that she believes "this discovery will spawn a new generation of programmable microimplants - sensors to monitor vital functions deep inside the body; electrostimulators to change neural signals in the brain; and drug delivery systems to apply medicines directly to affected areas."

Brian Buntz is the editor-in-chief of MPMN. Follow him on Twitter at @brian_buntz and Google+.