Home

For the project's Executive Summary, please click here.

Background:

Dr. Sameer B. Shah is a professor for the Departments of Orthopaedic Surgery & Bioengineering at UC San Diego's School of Medicine. His work in the Neuromuscular Bioengineering Laboratory includes research on the function and dysfunction of nervous and muscular systems. One research focus of the laboratory is to develop strategies for peripheral nerve regeneration using biomedical devices. 

Peripheral Nerve Damage

The peripheral nervous system connects the central nervous system to sensory organs, essentially allowing the brain to communicate with limbs. Repetitive stresses on limbs, sports accidents, car crashes, and other forms of trauma can sever a nerve which results in a gap between the proximal stump (the end of the nerve closest to the spinal cord) and the distal stump (the end closest to the limb). This gap causes a loss of both sensory and motor function. This type of nerve damage is of great importance as there are more than 50,000 annual peripheral nerve repair procedures performed in the United States, piling a cost of 7 billion dollars per year. Although there are readily available methods to bridge short nerve gaps, there is yet to be an effective strategy for repairing nerves across large gaps spanning more than 10 millimeters. The Nerve Gripping Project Team is assisting Dr. Shah in developing a mechanical device to stimulate nerve growth over large distances. 

Objective:

The objective of the Nerve Gripping Project Team is to improve on the initial prototype of Dr. Shah and his research group's nerve lengthening plan on laboratory rats' sciatic nerves. The method revolves around the science of imposing mechanical loads onto the proximal nerve stump to stimulate regeneration. Dr. Shah and his group developed a device with a spiral cuff that grips onto the proximal stump and is then actuated by a guidewire to pull the cuff towards the distal stump, which in turn, applies a tensile load onto the proximal end.

However, there are problems that exist, mainly with the spiral cuff often slipping on itself when being pulled by the guidewire. As a result of the slippage, the proximal nerve does not experience the tensile load, and the nerve stump will not grow. To prevent slippage, the project team has decided to replace the spiral cuff with a different gripping mechanism. This new mechanism is designed to securely clamp the proximal stump, while also distributing the radial compressive load along the nerve's surface to ensure no damage is done to the nerve. 

Functional Requirements

In redesigning the nerve gripping mechanism, the functional requirements that must be followed are:

• Reliable Clamping - Gripping mechanism must reliably clamp onto the nerve stump and not slip when actuated

• The Backbone - Mechanism must be able to interface with the stainless-steel backbone system for actuation 

• Biocompatibility - Materials employed must be biocompatible for human implantation

• In Situ - Mechanism must be able to fit within nerve injury setting of a laboratory test rat

Final Design:

Design Overview

The Nerve Gripping Project Team developed two final design solutions to achieve the objective of securely gripping the nerve. The two designs are named the Screw-Clamp and the Strap-Down. 

Screw - Clamp Gripping Mechanism

• One screw to tighten for easy user-interface

• Slotted insert to allow for proper alignment of the screw

• 3 rows of directional micro-barbs to increase friction

• A guide channel for interfacing with backbone system

• Cubic dimensions: 5.0 x 7.0 x 5.0 mm

Strap - Down Gripping Mechanism

• • Capability for suture-induced compression of the nerve on the clamp channel

  • Micro-barb lined channel to secure nerve on device by increasing surface friction

  • A guide channel for interfacing with backbone system

  • Cubic dimensions: 4.0 x 6.1 x 4.6 mm

Performance 

Screw - Clamp Gripping Mechanism

Performance summary:

• Minimum of 0.5 screw revolutions to ensure proper clamping

• Nerve elongation of 9.1% without slippage

• Stress relaxation after each actuation

Strap - Down Gripping Mechanism

Performance summary:

• Constant increasing tensile force with elongation with 0.42 N of compressive force on nerve

• Slight dips in tensile stress in between elongations is attributed to stress relaxation of visco-elastic nerve

• No significant, sharp decreases in tensile force, thus the device did not slip off from nerve during process of 10.3% elongation