Portland, Ore. Surgically implanted pacemakers only last for about five years before their nonrechargeable batteries which draw current of less than a microamp must be replaced. And devices like microstimulators, whose milliamp-current flows require bulky rechargeable batteries, must be reimplanted surgically far more often.
Now a consortium of government, industry and academic organizations has developed a microstimulator with a tiny battery that can be recharged through the skin, enabling nonsurgical implantation for much longer periods of time.
The microstimulator is used to bridge broken nerve connections resulting from Parkinson's, epilepsy and spinal chord injuries and other conditions. "Any place you have a broken nerve connection, our device can supply the electrical impulse to complete the circuit," said emeritus professor Robert West. The microstimulator was enabled by a battery with a organosilicon core designed by West and his colleagues at the University of Wisconsin.
The consortium includes the University of Wisconsin's (Madison) Organosilicon Research Center, Argonne National Laboratory, Advanced Bionics, the Alfred Mann Foundation and Quallion.
"We estimate that the battery will last up to 15 years, because it's rechargeable by virtue of an induction coil built into it by Advanced Bionics," West said. "You simply place an external coil over the part of the body where the implant is, run current through it, and that is picked up by the implant's coil and recharges the battery."
The bionic device also has a wireless transceiver that permits doctors to monitor the battery's state from outside the body. By building battery-monitoring and -charging functions into the external electronics, the bionic device can selectively monitor and direct the recharging of multiple microstimulators.
The lithium-ion rechargeable battery was created with organic liquids, called organosilicon compounds, specifically for bionic implants.
"Our part was developing the electrolytes for the battery," said West. "We discovered that organosilicon compounds can make a big difference they can really extend the lifetime of lith-ium-ion batteries. They are also stable, nonflammable, nontoxic and pose no threat to the environment."
Organosilicons enable bionic batteries by using compounds composed of silicon and other natural materials, here designed to be electrolytes the electricity-conducting liquid that stores charge in a battery.
"We tweaked our organosilicon molecules for high conductivity and stability, enabling ions to go through it very easily," said West.
Today's microstimulators are so large that they have to be implanted and removed periodically to have their batteries replaced. These batteries are rechargeable through the skin, since nonrechargeables can't supply enough current, but they have be encapsulated to prevent them from leaking harmful chemicals. In contrast, the organosilicon-based bionic batteries contain no harmful chemicals and thus do not require a bulky case. In fact, the resulting implant is so small that it does not even require surgery to be inserted inside the body.
"Our device is so small that it can be implanted without surgery using an instrument that's like a needle," said West. "It's just a little thicker than pencil lead and about an inch long."
The bionic battery was patented through the Wisconsin Alumni Research Foundation and licensed to a startup company, Polyron Inc. Funding for developing the organosilicon compounds was provided by the National Institute of Standards and Technology.