Implantation and Control of Wireless, Battery-free Systems for Peripheral Nerve Interfacing

Peripheral nerve injury is quite common. The electrical stimulation showed therapeutic effect on nerve regeneration. So here we showed a generalized method on implanting nerve interface and device utilization.

This technique avoids having leads going through the skin, which can be sites of infection. The implanted stimulator can be powered wirelessly and tuned to treatment needs. This electrical stimulation device has high therapeutic potential to enhance peripheral nerve regeneration after injury or illness, helping restore lost function which might otherwise remain impaired.

Isolating the nerve and achieving good contact with the cuff requires delicacy. Never grab the nerve directly with instruments, but instead manipulate the nerve with blunt tools and maintain tension-free placement. Before starting the surgical procedure, place the rat in a prone position on a prep table and confirm the appropriate depth of anesthesia by checking pinnal reflex.

For the whole surgical duration, keep assessing breathing rate, tissue color, and depth of anesthesia every 15 minutes, and maintain iso fluorine levels accordingly. Monitor the mucus membranes, which should remain pink and moist. Place the rat on the prep table.

Shave the surgical area, including the right leg and lower half of the back. Once done, move the animal to the surgical table and scrub the shaved surgical area with a Betadine pad, followed by a 70%ethanol swab three times. Use tissue scissors to make an incision in the skin parallel to the right femur bone, followed by blunt separation of the subcutaneous connective tissue on the back, directly medial to the incision to clear a subcutaneous pocket for the receiver coil.

Then make a subsequent incision on the right gluteal muscle parallel to the skin incision. With the help of metal dissection probes with blunt ends, isolate the sciatic nerve and then implant the wireless battery-free device on the isolated sciatic nerve by wrapping the cuff around without putting the nerve under tension or distorting its path. Once done, mark out on the skin where the receiver coil is placed for further electrical stimulation.

Suture the gluteal muscle incision using absorbable sutures. Enclose the skin incision with wound clips by matching the skin edges. For one hour post-surgery, deliver continuous 20 hertz electrical stimulation with 200 microseconds pulse width to the animal under anesthesia.

Upon full recovery from anesthesia, return the animal to the home cage. After preparing the wrap for the surgical procedure as described before, shave the surgical area on the ventral aspect of the neck. Move the animal to the surgical table and scrub the shaved surgical area with a Betadine pad, followed by a 70%ethanol swab three times.

Next, make a three centimeter midline incision through the skin in superficial cervical fascia of the anesthetized rat to expose the sterno hyoid and sternocleidomastoid muscles. Use a probe for blood dissection to elevate the sternocleidomastoid muscle before retracting the sternocleidomastoid laterally using a vessel loop. Then, free and retract the omohyoid muscle, followed by freeing and medially retracting the vagus nerve and the carotid bundle beneath the omohyoid muscle.

Isolate the phrenic nerve. Implant the wireless battery-free device on the phrenic nerve by placing the receiver coil of the device on the sterno hyoid, deep relative to the bilateral sternocleidomastoid muscles, with the cuff around the phrenic nerve and the contact electrodes positioned perpendicular to the nerve. Close the skin with inverted absorbable sutures in the deep dermis.

For one hour post-surgery, deliver continuous 20 hertz electrical stimulation with 200 microseconds pulse width to the animal under anesthesia. After full recovery from anesthesia, return the animal to the home cage. For the wireless stimulation, use a waveform function generator to provide electrical power to an external inductive transmission coil.

Match the resonance frequency and positioning of the implanted receiver coil to ensure good inductive coupling. Once the setting is done, deliver monophasic 200 microsecond pulses at 20 hertz for one hour. To verify and quantify electrical stimulation delivery, record the compound muscle action potentials, or CMAPs, from the tibialis anterior muscle while adjusting the stimulation voltage to deliver supra maximal activation of the sciatic nerve.

The complete phrenic nerve transection injury was confirmed in the study by evoking a twitch response. Before transection, electrical stimulation of the phrenic nerve evoked compound muscle action potentials on the ipsilateral diaphragm, which was abolished by the phrenic nerve transection. A maximal CMAP response elicited after delivering a single stimulus pulse to the right sciatic by a wire electrode was compared with a wireless electrode.

It was observed that the wireless nerve stimulation could achieve on average 88%of the CMAP from wire-based nerve stimulation. The representative electromyography analysis shows four sequential spikes at the beginning and the 40 minutes of the one-hour 20 hertz electrical stimulation. At 40 minutes, a slight decrease in peak amplitude was noted.

The degree of peripheral nerve regeneration was assessed using retrograde tracers applied distally to the nerve lesion site. The regenerated subgroups of the tibial nerve or the fibular nerve in the lumbar spinal cord anterior horn were observed. Remember that the transmitting coil must be well aligned to the receiving coil to power the device when maybe to adjust the distance, orientation, or position in order to achieve full efficacy.

The method can be also performed on other preferred nerve interfaces, such as drug release and optogenetics. The technique can be performed to study various mechanisms by which electrical stimulation leads to different effects on different nerves.