Flexible Multielectrode Array for Skeletal Muscle Conditioning, Acetylcholine Receptor Stabilization and Epimysial Recording After Critical Peripheral Nerve Injury

Abstract

Complete re-innervation after a traumatic injury severing a muscle's peripheral nerve may take years. During this time, the denervated muscle atrophies and loses acetylcholine receptors, a vital component of the neuromuscular junction, limiting functional recovery. One common clinical treatment for atrophy is electrical stimulation; however, epimysial electrodes currently used are bulky and often fail due to an excessive inflammatory response. Additionally, there remains a need for a device providing in vivo monitoring of neuromuscular regeneration and the maintenance of acetylcholine receptors. Here, an implantable, flexible microelectrode array (MEA) was developed that provides surface neuromuscular stimulation and recording during long-term denervation.Methods: The MEA uses a flexible polyimide elastomer and an array of gold-based microelectrodes featuring Peano curve motifs, which together maintain electrode flexibility. The devices were implanted along the denervated gastrocnemius muscles of 5 rats. These rats underwent therapeutic stimulation using the MEA daily beginning on post-operative day 2. Another 5 rats underwent tibial nerve resection without implantation of MEA. Tissues were harvested on post-operative day 14 and evaluated for quantification of acetylcholine receptors and muscle fiber area using immunofluorescence and histological staining.Results: The Young's modulus was 1.67 GPa, which is comparable to native tendon and muscle. The devices successfully recorded electromyogram data when implanted in rats. When compared to untreated denervated muscles, MEA therapy attenuated atrophy by maintaining larger muscle fiber cross-sectional areas (p < 0.05). Furthermore, the acetylcholine receptor areas were markedly larger with MEA treatment (p < 0.05).Conclusions: This proof-of-concept work successfully demonstrates the ability to combine conformability, tensile strength-enhancing metal micropatterning, electrical stimulation and recording into a functional implant for both epimysial stimulation and recording.

Vascularized Muscle Flap to Reduce Wound Breakdown During Flexible Electrode-Mediated Functional Electrical Stimulation After Peripheral Nerve Injury

“…The fabrication of this polyimide-based electrode has been published previously in detail ( 5 ). Briefly, the electrodes consist of two 5 μm layers of polyimide (PI 2674, HD Microsystems, Parlin, New Jersey), a base layer and a top layer.…”

“…All animals ( n = 10) with electrode implants were stimulated 5 times per week beginning on postoperative day 2 and ending on postoperative day 13 for 45 minute sessions per day using 400 ms of 100 Hz frequency, 200 μs per phase biphasic pulses followed by 6 seconds of rest. Stimulus amplitudes were adjusted to maintain a strong contraction evident visually and/or by palpation between 2 and 5 mA as described previously ( 4 , 5 , 33 ). The rats were anesthetized using 3% isoflurane in oxygen and maintained at the same rate.…”

“…Generation of the critical peripheral nerve injury model and implantation of the flexible electrode along the dorsal surface of the gastrocnemius muscle has been described and implemented previously (5). A 2 cm skin incision was made using a scalpel along the dorsal surface of the right hindlimb parallel with the tibia.…”

“…Devices delivering functional electrical stimulation (FES) have been developed to prevent muscle atrophy and enhance functional recovery during peripheral nerve injury (4,5). Electrical stimulation of the proximal nerve stump accelerates nerve outgrowth across the injury site but the distal denervated muscles for extended periods of time become atrophied, diminishing the potential for optimal functional recovery (6)(7)(8)(9)(10).…”

“…Epimysial electrodes may allow for targeted treatment of muscles while minimizing the invasiveness of the electrode itself. Because of the combination of current density and minimized invasiveness, our group has focused on the development of epimysial interventions ( 5 , 20 – 22 ).…”