A new battery — lauded as the smallest implantable battery in the world — may soon be powering tiny bionic neurons, devices that emit electrical micropulses to stimulate damaged nerves and muscles.

The battery measures 2.9 mm in diameter and 13 mm in length — about the size of a pencil tip.

The tiny powerhouse helps keep the bionic neurons small. Even with the battery, the cylindrical devices are only 1/35 the size of a standard AA battery. The small size allows doctors to use minimally invasive techniques when implanting the bionic neurons, reducing surgical trauma and the risk of infection.

While the battery may be small, it makes up in staying power what it lacks in size. California-based Quallion’s battery can, with recharging, last up to 10 years.

The team at Quallion, which developed the battery in conjunction with Argonne National Laboratory, says the key to the lifespan of the battery is its chemistry.

The researchers isolated a phase of a polysiloxane polymer, a material that has the highest conductivity ever reported for an electrical conductor.

Recharging is done wirelessly by an external electrical field, meaning implants no longer have to be surgically removed and replaced when the battery runs out of juice.

The new battery may power implantables that could help millions of stroke victims and people suffering from urinary-urge incontinence and neurological disorders such as Parkinson’s disease.

Electrical pulses are already used for muscle stimulation as part of physical therapy, but current methods are not without their drawbacks.

The most common treatment method uses an electrical stimulator on the surface of the skin. But the electrical jolts can prove painful and the pulses may not hit the muscle in the right place.

Implants, which are less commonly employed, currently are powered by large, relatively short-lived batteries, which cannot be recharged. Consequently, only a few implantable devices, such as cardiac pacemakers, are in use.

“Current ones sometimes last three or at most five years,” said Wendy Fong, senior manager in business development at Quallion.

“This is a concern for doctors, especially for those treating patients who are not so healthy, because (the patients) have to be subjected to surgical intrusion when the implant needs replacing,” Fong said.

Bionic neurons have the advantage of being small and can be implanted near the target muscle. They work by mimicking nerve impulses from the brain: They reanimate the paralyzed muscles through electrical stimulation, just like the frog in Frankenstein.

Other research into bionic neurons has experimented with external power supplies. One such project is being conducted at the University of Southern California’s biomedical engineering department.

“If you have a complicated set of control parameters (for the stimulator), they can’t fit into the implant. If you have to have the control system outside the body, then you may as well have the power source outside, too,” said Dr. Gerald Loeb, professor of biomedical engineering at USC. “This way you can keep your implant smaller.”

Loeb’s device is powered by an external transmitter coil that emits a magnetic field. He admits that needing to be constantly in proximity to the coil to power the stimulation means the method would not be feasible for all applications.

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