Grants We Funded

Abstract

Impact Summary: Almost 2 million people in the United States are currently living with upper or lower limb amputations. Despite major advances in modern prosthetic devices, patients with limb loss continue to struggle in their activities of daily living since reliable control of these devices with signals obtained from residual nerves is still not possible. In addition, the lack of sensory feedback availability from neuroprosthetic devices remains a significant deterrent to their adoption by an amputee. The major impact of the proposed research is the development of an accurate, simple to implement, and reliable, peripheral nerve interface that provides simultaneous transmission of both afferent somatosensory and efferent motor information, thereby closing the sensorimotor feedback loop for the end-user.

Project Summary: Current advanced prosthetic devices share many attributes with the limb they replace. Although these devices are equipped with multiple joint actuators, the ideal interface to integrate the human nervous system with the machine remains the primary challenge. Lack of reliable and intuitive motor control, and most importantly, insufficient sensory feedback often leads to prosthetic abandonment in the overwhelming majority of patients. Also, most of the current technologies either need extensive microsurgical expertise or expensive implantable electrodes which makes them financially limiting to most patients. Previously, our lab has developed the Regenerative Peripheral Nerve Interface (RPNI) as a biologic nerve interface designed for stable integration of a prosthetic device with transected peripheral nerves in a residual limb. The RPNI is surgically created by implanting a residual nerve into a free muscle graft. Here, the reinnervated muscle will directly serve as a myoelectric signal amplifier. However, these signals can currently only be captured through implantable electrodes. An attractive alternative to this problem is to fabricate RPNIs directly underneath the defatted skin to record compound muscle action potentials (CMAPs) using surface electrodes. Preliminary data from our lab in rats showed that when a mixed nerve is implanted into the superficially located RPNI, not only the motor fibers reinnervate the muscle, but also sensory axons reach the overlying skin, creating a sensory interface at the same time. Therefore, our overall objective for this study are to develop a simple, reliable, and yet widely available biologic interface to simultaneously control prosthetic movements and transfer sensory feedback to the central nervous system. The central hypothesis is that the motor and sensory fibers within a transected mixed nerve will preferentially reinnervate their respective end-organs of the denervated muscle and skin. This hypothesis will be assessed by pursing the following two aims: (1) Determine the viability and accessibility of superficial RPNIs for acquiring efferent CMAPs using surface electrodes. (2) Elicit afferent sensory signaling in the peripheral nerve during electrical and mechanical stimulation of the overlying skin. Successful development and safe implementation of this peripheral nerve interface would be a step forward toward our long term goal of restoring the natural sensorimotor functions of the lost limb.

Biography
Amir Dehdashtian, MD, MPH, joined the Neuromuscular lab at the University of Michigan as a plastic surgery research fellow. Previously, he attended a combined MD-MPH program and graduated cum laude from the Tehran University of Medical Sciences. During his research fellowship, Dr. Dehdashtian investigated the differences in neuroma pain behaviors and signaling between genders in rats, developed neural interfaces for controlling prosthetic devices, and studied fat grafting in peripheral nerve regeneration and neuropathic pain. Dr. Dehdashtian has demonstrated a long-standing interest in medical and surgical research. His focus has been in the application of clinically translatable interventions for congenital malformations, burn, limb loss trauma, and neuropathic pain, especially in regions lacking adequate medical infrastructure. He has published several manuscripts and abstracts in high-impact scientific journals, some of which were recognized as best papers. He also enjoys drawing, and has published several of his medical illustrations. In the future, Dr. Dehdashtian plans to pursue a residency in the field of plastic surgery. His ultimate career goal is to become a surgeon scientist, combining his love for medicine, specifically helping patients suffering from debilitating trauma and nerve injuries, with running a laboratory researching nerve regeneration and prosthetic interfaces.