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Electromechanical Properties of Regenerative Peripheral Nerve Interfaces
Ziya Baghmanli, MD; Christopher M. Frost, Student; Benjamin Wei, MD; Kristoffer B. Sugg, MD; Paul S. Cederna, MD; Melanie G. Urbanchek, PhD
University of Michigan, Ann Arbor, MI, USA
Introduction: Our ultimate goal is the development of a regenerative peripheral nerve interface for closed loop neural control of prostheses. This interface integrates amputee's residual peripheral nerves with transferred skeletal muscle. The purpose of this study is a) to determine the nature of electrical and mechanical muscle properties 3 months after standard free muscle transfer with implantation of a residual nerve and b) to determine if successful neurotization takes place.
Methods: Rats (n = 18) were divided into three groups: sham, standard free muscle transfer (Trans), and muscle transfer with residual nerve implantation (Trans+RN). During sham surgeries, the right leg was dissected to expose the soleus muscle and then sutured closed. For both Trans and Trans+RN groups the right soleus muscle was transferred between interstitial tissues of the left thigh, beneath the m. biceps femoris and parallel with the femur. In both Trans and Trans+RN groups the right tibial nerve was dissected free and divided. In the Trans+RN group the left peroneal nerve was divided and the proximal end sutured within the transferred muscle. After 90 days of implantation the transferred muscles were tested using both nerve conduction studies (NCS) and muscle force testing. For both NCS and muscle force testing, the peroneal nerve was stimulated at the sciatic notch. NCS testing measured stimulus threshold, amplitude, and number of active motor units. Muscle force testing measured maximal tetanic force generated. Specific force was calculated by dividing the tetanic force by the muscle cross sectional area.
Results: All transferred muscles survived throughout the entire study. Muscle mass for Sham was significantly higher than for Trans but not Trans+RN (Table 1). The stimulus threshold for Trans+RN was significantly lower than for Trans alone indicating increased muscle responsiveness to lower levels of current. The stimulus threshold for Trans+RN however was still higher than Sham. CMAP amplitude and duration for Sham were higher than both Trans and Trans+RN. Nerve implantation increased the tetanic force production of soleus muscle when compared to transferred muscle alone at POD 90. Histology is in progress.
Conclusion: Nerve implantation into transferred muscle is the basis for our biotic-abiotic, peripheral nerve interface. With this interface, we found increased sensitivity to electrical stimulation and tetanic force capacity when compared with transferred muscle alone. These data imply that nerve implantation promoted successful neurotization. Successful neurotization of the peripheral nerve interface has significant implications for the design of biocompatible, long-lasting neural interfaces.
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