Nerve cuffs for nerve repair and regeneration

Bioelectric interfaces for the peripheral nervous system

The peripheral nervous system (PNS) is an attractive target for those developing neural interfaces as an access point to the information flow coursing within our bodies. A successful neural interface could not only offer the means to understand basic neurophysiological mechanisms, such as how the body accomplishes complex coordinated control of multi degree of freedom body segments, but also could serve as the means of delivering treatment or therapies to restore physiological functions lost due to injury or disease. Our work in the development of such a neural interface focuses upon multi-microelectrode devices that are placed within the body of the nerve fascicle; mulit-channel intra-fascicular devices called the thin-film Longitudinal Intra-Fascicular Electrode (tfLIFE) and the Transversely Implanted Multi-Electrode (TIME). These structures provide high resolution access to the PNS and have demonstrated promise in animal work as well as in preliminary sub-acute work in human volunteers. However, work remains to improve upon their longevity and biocompatibility before full translation to clinical work can occur.

Coordinated, multi-joint, fatigue-resistant feline stance produced with intrafascicular hind limb nerve stimulation

The production of graceful skeletal movements requires coordinated activation of multiple muscles that produce torques around multiple joints. The work described herein is focused on one such movement, stance, that requires coordinated activation of extensor muscles acting around the hip, knee and ankle joints. The forces evoked in these muscles by external stimulation all have a complex dependence on muscle length and shortening velocities, and some of these muscles are biarticular. In order to recreate sit-to-stand maneuvers in the anesthetized feline, we excited the hind limb musculature using intrafascicular multielectrode stimulation (IFMS) of the muscular branch of the sciatic nerve, the femoral nerve and the main branch of the sciatic nerve. Stimulation was achieved with either acutely or chronically implanted Utah Slanted Electrode Arrays (USEAs) via subsets of electrodes (1) that activated motor units in the extensor muscles of the hip, knee and ankle joints, (2) that were able to evoke large extension forces and (3) that manifested minimal coactivation of the targeted motor units. Three hind limb force-generation strategies were investigated, including sequential activation of independent motor units to increase force, and interleaved or simultaneous IFMS of three sets of six or more USEA electrodes that excited the hip, knee and ankle extensors. All force-generation strategies evoked stance, but the interleaved IFMS strategy also reduced muscle fatigue produced by repeated sit-to-stand maneuvers compared with fatigue produced by simultaneous activation of different motor neuron pools. These results demonstrate the use of interleaved IFMS as a means to recreate coordinated, fatigue-resistant multi-joint muscle forces in the unilateral hind limb. This muscle activation paradigm could provide a promising neuroprosthetic approach for the restoration of sit-to-stand transitions in individuals who are paralyzed by spinal cord injury, stroke or disease.

A fully implanted drug delivery system for peripheral nerve blocks in behaving animals

Inhibiting peripheral nerve function can be useful for many studies of the nervous system or motor control. Accomplishing this in a temporary fashion in animal models by using peripheral nerve blocks permits studies of the immediate effects of the loss, and/or any resulting short-term changes and adaptations in behavior or motor control, while avoiding the complications commonly associated with permanent lesions, such as sores or self-mutilation. We have developed a method of quickly and repeatedly inducing temporary, controlled motor deficits in rhesus macaque monkeys via a chronically implanted drug delivery system. This assembly consists of a nerve cuff and a subdermal injection dome, and has proved effective for delivering local anesthetics directly to peripheral nerves for many months. Using this assembly for median and ulnar nerve blocks routinely resulted in over 80% losses in hand and wrist strength for rhesus monkeys. The assembly was also effective for inducing ambulatory motor deficits in rabbits through blocks of the sciatic nerve. Interestingly, while standard anesthetics were sufficient for the rabbit nerve blocks, the inclusion of epinephrine was essential for achieving significant motor blockade in the monkeys.

Selective motor unit recruitment via intrafascicular multielectrode stimulation

Recruitment of force via independent asynchronous firing of large numbers of motor units produces the grace and endurance of physiological motion. We have investigated the possibility of reproducing this physiological recruitment strategy by determining the selectivity of access to large numbers of independent motor units through intrafascicular multielectrode stimulation (IFMS) of the peripheral nerve. A Utah Slanted Electrode Array containing 100, 0.5–1.5 mm-long penetrating electrodes was inserted into the sciatic nerve of a cat, and forces generated by the 3 heads of triceps surea in response to electrical stimulation of the nerve were monitored via force transducers attached to their tendons. We found a mean of 17.4 ± 4.9 (mean ± SEM) electrodes selectively excited maximal forces in medial gastrocnemius before exciting another muscle. Among electrodes demonstrating selectivity at threshold, a mean of 7.3 ± 2.7 electrodes were shown to recruit independent populations of motor units innervating medial gastrocnemius (overlap < 20%). Corresponding numbers of electrodes were reported for lateral gastrocnemius and soleus, as well. We used these stimulation data to emulate physiological recruitment strategies, and found that independent motor unit pool recruitment approximates physiological activation more closely than does intensity-based recruitment or frequency-based recruitment.Key words: functional neuromuscular stimulation (FNS), microelectrode array, neuroprosthesis, intrafascicular multielectrode stimulation (IFMS).

Chronically implanted epineural electrodes for repeated assessment of nerve conduction velocity and compound action potential amplitude in rodents

Implanted epineural electrodes were used for the longitudinal assessment of peripheral nerve conduction velocity (NCV) and compound action potential (CAP) amplitude in rats. Custom-fabricated stimulating and recording electrodes were sutured over the tibial and sciatic nerves, respectively, and were used for weekly recordings of CAP latency and amplitude. Intra-day variability of nerve conduction velocity measurements had coefficients of variation of less than 2% for same day recordings from individual subjects. A clear trend in recovery of the NCV values following implant was observed over the 7-week trial period. These results demonstrate that implanted epineural electrodes provide a reliable method for chronic, in vivo monitoring of nerve conduction parameters in rodents.