Introduction: In medicine there is a need for wireless data and power transfer from implanted medical devices. One useful application in particular could be direct nerve stimulation. In patients with peripheral nerve injury, monitoring their recovery is important. By stimulating an injured nerve directly, it is possible to more easily quantify functional nerve recovery. Doing so wirelessly with an implant could be less invasive and lower the risk of infection. Inductive coupling was the method used for power transfer with the thin film wireless power receivers. Models for nerve stimulation to possibly aid in nerve recovery were examined in rats. Materials and Methods: Wireless power transmission was achieved using Red Rock Laboratories WiRe product. It is a small implantable wireless power receiver coil that was equipped with tuning capacitors and a diode. A class E oscillator controlled the transmitter coil, and a signal frequency was established by either a function generator or a 555 timer circuit. The transmitter and receiver coils must be within a few centimeters of each other and in the proper orientation to transfer a significant amount of energy. Determining voltages based on rats’ position was found using a receiver coil attached to a small PCB with an XBee for data transfer. A receiver XBee was attached to an arduino microcontroller to process data. The PCB also contained components to make up a low pass filter and a voltage cap. Receiver coils were incased in silicone and implanted in rats. Medwire platinum-iridium lead wires were attached to the rats’ sciatic nerves. Sciatic nerves were crushed or cut to simulate injury. The rat’s nerves were stimulated at various frequencies (up to about 80 Hz when tetanus occurs). Rats’ reaction to nerve stimulation was observed at several intervals post operatively.

Results and Discussion: The 14 mm receiver coils are able to receive about 27 volts while under no load. This is too large for the XBee chip so a voltage cap was implemented before the signal was sent to the XBee. There is also a low pass filter to eliminate noise from the circuit and the carrier frequency from being transferred. The XBee system gives data about how much voltage is being induced on the receiver coil. When the rats’ sciatic nerves are stimulated from an implanted receiver coil and XBee circuit it is possible to determine the exact voltage at which they are being stimulated with the proper implanted circuit. Conclusions: Given the simplicity of the receiver coil’s design, they could also be applied to powering and charging other implantable medical devices. Using the XBee chips as a model, wireless data transfer out of implants is also possible in a clinical setting.

Figure 1. Schematic diagram of the backpack and implant circuit containing an XBee for data transfer.

Figure 2. Rat walked under a transmitter coil with backpack containing XBee circuit.

Figure 3. 14 mm receiver coil compared to penny.