Thin, Softening Epidural Leads for Chronic Arm and Neck Pain

Project Summary BackStop Neural proposes to demonstrate the feasibility of a novel paddle-type epidural stimulation lead to relieve chronic arm and neck pain. To date, spinal cord stimulation (SCS) has been used primarily to treat chronic back and leg pain, which require placement of electrodes in the thoracic region of the spine. Although a few studies have also shown that SCS is effective in treating chronic arm and neck pain, current commercial leads are not well suited to placement in the cervical spine. Percutaneous leads suffer from high lead migration rates, a key issue for cervical placement. Paddle leads offer lower risk of migration but are ~2 mm thick, making placement in the narrow cervical epidural space difficult. In this Phase I SBIR project, BackStop Neural will scale our softening electrode arrays validated in rats to human-sized epidural leads that are 10× thinner than commercially available leads yet stiff enough for established surgical implantation techniques. These leads are capable of softening and conforming to the spinal cord once implanted in the body providing positional stability that limits migration and provides chronic, effective stimulation. We build on preliminary data showing effective cervical stimulation in rats for 4 months using softening electrode arrays, conformation of paddles to rat and human cadaver spinal cords, hydrolytic stability of newly developed softening polymer chemistries, and preliminary biocompatibility and electrode fabrication on these re- formulated softening polymers. The first aim of this grant is to design and fabricate a 16-channel, 0.2 mm thick human-sized softening paddle lead. The main outcomes are a 10× change in modulus from dry, 25 °C conditions to wet, 37 °C conditions, electrode charge storage capacities of at least 2 mC/cm2, and fully packaged lead resistance of < 20 ohms. The second aim will demonstrate the mechanical and electrical stability of the epidural leads using tensile, lead body flex, connector flex, and current pulsing testing. The metrics of success will be a < 20% change in electrode impedance following tensile testing to the earlier of 5N or 20% elongation, 100,000 cycles of lead body bending 90° (+0° / -5°) in each direction, and 100,000 cycles of connector bending 45° ±2° in each direction, and < 20% change in charge injection capacity over a billion stimulation pulses. The third aim will demonstrate the biocompatibility and surgical feasibility of the epidural leads using ISO 10993 cytotoxicity, intracutaneous, systemic toxicity, and ASTM hemolysis studies and a pilot sheep study (n=2) conducted at NAMSA. The main outcomes are passing all ISO biocompatibility tests, minimal inflammation and fibrous capsule formation at 21 days, and confirmation of the mechanical and electrical integrity of leads via visual inspection, cyclic voltammetry, and electrical impedance spectroscopy after explant. Successful completion of Phase I aims will enable Phase II efforts in full SCS system testing with implantable pulse generators, advancing regulatory efforts with the FDA, and full biocompatibility and large animal study testing to demonstrate safety and efficacy for our regulatory submission.