Experimental testing of bionic peripheral nerve and muscle interfaces: animal model considerations

Introduction: Man-machine interfacing remains the main challenge for accurate and reliable control of bionic prostheses. Implantable electrodes in nerves and muscles may overcome some of the limitations by significantly increasing the interface's reliability and bandwidth. Before human application, experimental preclinical testing is essential to assess chronic in-vivo biocompatibility and functionality. Here, we analyze available animal models, their costs and ethical challenges in special regards to simulating a potentially life-long application in a short period of time and in non-biped animals. Methods: We performed a literature analysis following the PRISMA guidelines including all animal models used to record neural or muscular activity via implantable electrodes, evaluating animal models, group size, duration, origin of publication as well as type of interface. Furthermore, behavioral, ethical, and economic considerations of these models were analyzed. Additionally, we discuss experience and surgical approaches with rat, sheep, and primate models and an approach for international standardized testing. Results: Overall, 343 studies matched the search terms, dominantly originating from the US (55%) and Europe (34%), using mainly small animal models (rat: 40%). Electrode placement was dominantly neural (77%) compared to muscular (23%). Large animal models had a mean duration of 135 ± 87.2 days, with a mean of 5.3 ± 3.4 animals per trial. Small animal models had a mean duration of 85 ± 11.2 days, with a mean of 12.4 ± 1.7 animals. Discussion: Only 37% animal models were by definition chronic tests (>3 months) and thus potentially provide information on long-term performance. Costs for large animals were up to 45 times higher than small animals. However, costs are relatively small compared to complication costs in human long-term applications. Overall, we believe a combination of small animals for preliminary primary electrode testing and large animals to investigate long-term biocompatibility, impedance, and tissue regeneration parameters provides sufficient data to ensure long-term human applications

Functional electrical stimulation-supported interval training following sensorimotor-complete spinal cord injury : a case series

Objective. To investigate the effect of interval training supported by Functional Electrical Stimulation (FES) on ambulation ability in complete spinal cord injury (SCI). Methods. We trained four men with sensorimotor-complete (ASIA A) SCI, who achieved gait through FES of the quadriceps femoris, gluteus maximus, and common peroneal nerve on each side on a motorized treadmill. Training involved progressive interval walking exercise, consisting of periods of activity followed by equal periods of rest, repeated until muscle fatigue. We used time to muscle fatigue during continuous treadmill ambulation as the primary outcome measure. We also recorded the patterns of incremental stimulation for all training and testing sessions. Results. All subjects increased their ambulation capacity; however, the responses varied from subject to subject. Some subjects increased the total distance walked by as much as 300% with progressive improvement over the entire training period; however, others made more modest gains and appeared to reach a performance plateau within a few training sessions. Conclusions. FES-supported interval training offers a useful and effective strategy for strength-endurance improvement in the large muscle groups of the lower limb in motor-complete SCI. We believe that this training protocol offers a viable alternative to that of continuous walking training in people with SCI using FES to aid ambulation

SPEXOR: Towards a passive spinal exoskeleton

Most assistive robotic devices are exoskeletons which assist or augment the motion of the limbs and neglect the role of the spinal column in transferring load from the upper body and arms to the legs. In this part of the SPEXOR project we will fill this gap and design a novel, passive spinal exoskeleton to prevent low-back pain in able bodied workers and to support workers with low-back pain in vocational rehabilitation