A Stanford engineer has invented a way to wirelessly recharge electronic medical devices such as pacemakers and spinal cord stimulators. The engineering breakthrough creates a new type of wireless power system – using roughly the same power as a cell phone – that can safely penetrate deep inside the body.
The wireless system, first reported in the Proceedings of the National Academy of Sciences, could eliminate the need for bulky batteries and clumsy recharging systems that prevent medical devices from being more widely used. It could also lead toward a new type of medicine that allows physicians to treat diseases with electronics rather than drugs.
“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,” said Ada Poon, an assistant professor of electrical engineering at Stanford.
Spinal cord stimulators surgically implanted in the spine give relief to pain patients by sending electrical pulses to a specific nerve, turning pain signals to the brain into a tingling sensation.
The stimulators are often considered the treatment of last resort after narcotic painkillers and other types of treatment fail. Many patients are also reluctant to have the devices surgically implanted because of their size.
Poon and her colleagues built an electronic device smaller than a grain of rice that acts as a pacemaker. It can be powered or recharged wirelessly by holding a power source about the size of a credit card above the device, but outside the body.
Researchers tested this wireless charging system in a pig and used it to power a tiny pacemaker in a rabbit. They are currently preparing the system for testing in humans. If the tests are successful, it could still take several more years before the system is approved by regulators for use in medical devices.
Poon believes her discovery will spawn a new generation of programmable micro implants that can be used to power stimulators, pacemakers and other medical devices.
William Newsome, director of the Stanford Neurosciences Institute, says Poon’s work also creates the potential to develop “electroceutical” treatments as alternatives to drug therapies. He believes they could be more effective than drugs for some disorders because electroceutical approaches would use implantable devices to directly modulate activity in specific brain circuits.
“To make electroceuticals practical, devices must be miniaturized, and ways must be found to power them wirelessly, deep in the brain, many centimeters from the surface,” said Newsome, the Harman Family Provostial Professor and professor of neurobiology at Stanford.
“The Poon lab has solved a significant piece of the puzzle for safely powering implantable micro-devices, paving the way for new innovation in this field.”
Poon’s discovery involves a new way to control the two main types of electromagnetic waves inside the body: far-field waves and near-field waves.
Far-field waves, such as those broadcast from radio towers, can travel over long distances. But when they encounter biological tissue, they either reflect off the body harmlessly or get absorbed by the skin as heat. Because of that, far-field waves have not been used as a wireless power source for medical devices.
Near-field waves are used to power some medical devices such as hearing implants. But they can only transfer power only over short distances, limiting their usefulness deep inside the body.
What Poon did was find a way to blend the safety of near-field waves with the reach of far-field waves. She designed a power source that uses a “mid-field” wave to send power directly to medical implants or to recharge the batteries that power them.
“With this method, we can safely transmit power to tiny implants in organs like the heart or brain, well beyond the range of current near-field systems,” said John Ho, a graduate student in Poon’s lab and a co-author of the study.