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Nerve Lengthening Device for Peripheral Nerve Regeneration

Wesley Cheung, William Lee, Andrew Wang, Kevin Wei

Sponsored by Dr. Sameer Shah

Project Overview

    Nerve damage occurs when the nervous system sustains physical trauma that severs a nerve from the primary base of the nervous system, the spinal cord. In order to recover from nerve damage, the severed nerve stump connected to the spine must regrow out towards to dead nerve stump and replace it. While the minor nerve damages can easily be healed over time by the body itself, major nerve damages that require a severed nerve stump to grow large distances often fail to recover naturally and usually require the surgical care to repair. One of the most recently developed and promising solution to treating nerve damage is the idea of nerve lengthening. which revolves around the idea of slowly stretching a severed nerve stump to simulate growth until it recovers its original length. However, current implementation of this procedure is a crude and imprecise method that involves attaching a guide to the severed nerve stump and manually pulling on it by hand. Thus, a nerve lengthening device has been proposed as an mechanized implementation of this treatment. This device be attached to the site of the damaged nerve stump and, over the course of several weeks, lengthen the nerve by the slowly stretching it towards the dead nerve stump. Having a device that can implement this procedure rather than having a doctor perform it provides the primary benefits of having a controlled and precise method to lengthen of the nerve.

Figure 1: This illustration quickly summarizes the idea and procedure behind the nerve lengthening device

Objectives

• The primary objective of the project is to design, fabricate, and deliver a device that can implement the nerve lengthening procedure. A successful device should be able to lengthen a nerve by around 20-30mm over the course of 2-3 weeks.

• Device must be able to actuate nerve at 1-3 mm increments and index the nerve actuation.

• The secondary objective of the project is to further optimize the device to be fully self-contained with implemented wireless capabilities, thus having the device be fully contained within a body and be able to be controlled with a wireless remote. 

 Design Solution

        The final design solution for this project was a tiny motor-powered spool device enclosed in a stainless-steel enclosure that would reel in a guide wire that attaches the the proximal nerve stump to the distal nerve stump. The device is mounted along a bone that is in close proximity to the distal nerve. From this position, motor torque would allow the spool to rotate and slowly stretch the proximal nerve towards the distal nerve. Between the motor and spool, there is a driveshaft used to transmit torque from the motor to the spool as well utilize mechanical stops designed into the enclosure. These enclosure ensure that the spool is never rotated more than a certain amount, therefore ensuring that the nerve is never stretched  more than the distance set by the mechanical stops. Then, a one-way bearing mechanism consisting of two bearings is utilized to index the distance actuated as well as retain the tension of the stretch nerve when the device is not powered. The device has wire that safely extrude from the patient's body so that it can connect to an external controller. This controller acts as a power supply and control when the motor is running. This controller mainly consists of an Arduino Mega 2560 powered by a 9V battery and other components to operate the device. A cross section of the device and its components as well as the controller can be seen in Figure 2. A simulation of how the device functions can be seen in the video below.

Figure 2: (Left) Cross section of nerve lengthening device with labeled components. (Right) Prototype controller box for nerve lengthening device.

Video 1: CAD simulation of prototype performing nerve lengthening procedure,