Electrical medical devices like pacemakers and cochlear implants are capable of remarkable things once they’re put in the body, but the devices can only be as small as the batteries and wiring needed to power them. To open up new applications in other parts of the body, including the brain, researchers are seeking ways to make implantable devices even tinier.

Making Waves

Today, replacing the batteries in medical implants like pacemakers requires surgery. That’s not the case with devices that can be recharged wirelessly, but that won’t work if they are placed too deep in the body. Stanford researcher Ada Poon is trying to solve that problem with a charging system that produces a type of electromagnetic wave better at reaching inside the body than the ones in use today. This could open up new possibilities for recharging heart or brain implants or tiny devices that deliver drugs to specific places in the body. Poon has tested the system on animals with a pacemaker implant smaller than a grain of rice. The charging system, which is outside the body, has a power source no bigger than a credit card. Poon explains the system in this video and describes the charging method in a paper published in Proceedings of the National Academy of Sciences.

Sound Approach

Other Stanford researchers are trying a different kind of energy for wireless charging. They have developed a tiny implant that receives power from ultrasound waves aimed at the device. The implant, which measures only a few millimeters long and wide, can convert the sound waves into electricity. It could someday be used with hardware that would have applications in the brain, including recording the activity from individual neurons. The prototype device was unveiled at the IEEE Custom Integrated Circuits Conference in September and explained in this paper.

Heartbeat Harvester

Northwestern University researchers have created an implant that could one day power pacemakers with the energy produced by heartbeats and the motion of the lungs and diaphragm. The implant uses a film that is piezoelectric, which means it can generate electricity from the mechanical energy created when it is strained. It also includes a rechargeable battery, but it is small—all these components fit into a device just over a couple of centimeters tall and wide, whereas most pacemakers today are the size of half-dollar coins. A description of the device can be found in the Proceedings of the National Academy of Sciences.

Invisible Implant

A drawback of cochlear implants, which restore a person’s hearing by stimulating the auditory nerve, is that they require wires to connect several pieces of hardware together. Scientists at MIT and Harvard have minimized this footprint significantly by designing an implant that houses its hardware inside the ear, making it virtually invisible. The researchers say this will fix problems with today’s models, like the fact that the outside components can’t get wet. Another perk is that the device can be recharged wirelessly by a charger that plugs into a smartphone, which allows it to remain within the body at all times. The implant is described in a paper presented at the International Solid-State Circuits Conference in February.

The Takeaway:

Someday new kinds of implants could treat conditions like Alzheimer’s and traumatic brain injury, but it will take years to convince regulators that the necessary powering and sensing mechanisms are safe.

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