In-vivodemonstration of a self-contained ultrasound-based battery charging approach for medical implants

Ultrasound electrical recharging (USER^TM) has been developed to demonstrate application-specific charging of a 200 mA-h Li-ion battery currently used in a clinical device for lower esophageal sphincter stimulation. In refining earlier developments [JASA 134(5) 4121, 2013], the receiver transducer and charging chip circuitry was miniaturized by an order of magnitude to a volume of 1.1 cc, the transducer attached directly to the 0.4 mm thick titanium device casing. Transmitter was a 1 MHz, 25 mm diameter piezo-composite disk, while the 1 MHz frequency matched receiver was either a 15 mm diameter disk or a 15 mm square tile. During a series of acute in vivo porcine experiments, the titanium prototype was implanted 10—15 mm deep in the subcutaneous tissue, the battery being successfully charged at a current of up to 75 mA, whereby the nominal transmitted RF power was 2 W. Maximum tissue temperature increase during the 4-hour charging cycle was 2.5 0C, directly in front of the receiver face, with no histologic thermal changes noted in the tissue post-mortem. The ultrasound approach with 10-15% system efficiency is a potentially favorable option for charging a Li-ion battery for next generation gastric stimulation implants. [Work supported by the NIH/NIBIB R43EB019225.]