Monday, October 17, 2005

"POWER SOURCES: Battery gets bionic charge"

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. 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. 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. 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. The bionic battery was patented through the Wisconsin Alumni Research Foundation and licensed to a startup company, Polyron Inc.