Mt Sinai School of Medicine
A mechanical loading device that induces rapid degeneration of the intervertebral disc using dynamic bending.
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ROLE
Research Engineer CONTRIBUTIONS
SKILLS Rapid prototyping Machine shop tools Arduino User research |
Introduction
Every year, more than 64 million Americans suffer from lower back pain caused by some form of spinal injury. life. A large number of lower back problems are caused by degeneration of the intervertebral disc, that jelly donut that sits in between each of our vertebrates.
Because of this, researchers have put in effort into studying the pathology of disc degeneration. A variety of orthopedic research groups have attempted to simulate characteristics of disc degeneration by inducing disc degeneration in animal models. It was found that disc degeneration ca be induced by either subjective the spin to excessive loads or by disease, such as osteoarthitis. While there do exist prior experiences to study disc degeneration, not many models properly reflect human disc degeneration because loading profiles used in these studies are not representative of the loading experience by the human spine on a daily basis. Most of the loading devices were specialized in applying static compression, dynamic compression or static bending, where human spine experiences dynamic bending on a daily basis. Therefore, it is of great interest to develop a loading device that can induce dynamic bending in the spine of animal subjects while pertaining to environmental conditions.
This device will be able to induce controlled dynamic bending on the spine while maintaining experimental conditions.
Because of this, researchers have put in effort into studying the pathology of disc degeneration. A variety of orthopedic research groups have attempted to simulate characteristics of disc degeneration by inducing disc degeneration in animal models. It was found that disc degeneration ca be induced by either subjective the spin to excessive loads or by disease, such as osteoarthitis. While there do exist prior experiences to study disc degeneration, not many models properly reflect human disc degeneration because loading profiles used in these studies are not representative of the loading experience by the human spine on a daily basis. Most of the loading devices were specialized in applying static compression, dynamic compression or static bending, where human spine experiences dynamic bending on a daily basis. Therefore, it is of great interest to develop a loading device that can induce dynamic bending in the spine of animal subjects while pertaining to environmental conditions.
This device will be able to induce controlled dynamic bending on the spine while maintaining experimental conditions.
Design Specifications
As discussed, different types of loading apparatuses have been used to study IVD degeneration but they do not fully stimulate the loading profile that may be experienced by the human spine. So this device must be capable of inducing IVD degeneration while applying dynamic bending, which is more closely related to loads experienced by the lumbar region of the human spine.
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Physical Dimensions
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Scalable
Weight of the device must be 30-40 grams (10% of rat's body weight) |
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Functionality
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0.01 to 1 Hz cyclic loading
Maintain cyclic loading for up to 8 hours 0 to +45 degrees angular range of motion |
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Durability
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Free motion of rats during device operation
Prevent animal from chewing the device 8 hours of exerting continuous cyclic bending Components follow ASTM standards |
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Biological Requirements
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Biocompatible
Non-toxic to the rat and the researcher Does not induce inflammatory response (non-invasive) Minimal pain (does not require anesthesia) |
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Safety
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Minimal hazards toward researchers and animal subjects
Minimize risk of unintended injuries |
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Total Cost
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Less than $1000 per loading system
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Design Concepts
In order to study the properties of the intervertebral disc after degeneration, many devices have been produced to apply loading onto the disc. The types of loads frequently observed in literature is static compression and dynamic compression, and in one case, static bending. No study has been show to induce dynamic bending. In order to determine which design concept is the more physiologically accurate model, we created these simulations to determine which model would cause the disc to degenerate the fastest.
At our initial meeting, we had to decide whether or not we wanted to fracture the intervertebral disc or vertebral body. Apply to a single disc or multiple. Our proposed designs consisted of shear loading and piston. We created three prototypes in Solidworks in Solidworks then performed FEA analysis using Abaqus on them to evaluate stress on the device in creating axial and transverse to see which would create the most stress. We took MicroCT scans of the rat tails so that we can get lengths and diameters of the vertebral bodies and intervertebral discs in the rat tails.
Intervertebral Disc Connection
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Vertebral Disc Connection
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Stress Analysis: Axial Stress, Transverse Stress, Kinematic Analysis
We took MicroCT scans of rat tails to determine the distance between the vertebral bodies in the tail.
Prototype #1
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Gripper
We verified the position of the gripper with an x-ray, and found that the width of the gripper is much too wide. The width of the gripper should be smaller than the length of the vertebra. For the next prototype, we need to make a thinner gripper that can grab one vertebrae at a time. We also found that the gripper easily damages the tail. Rubber or foam material with larger surface area can be used to increase friction without damaging the tail. |
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Adapter
Because the two pieces of the device are parallel to each other, it restricts the functional angle of the device. By creating more of a u-shaped device, we can increase the range of bending motion. 
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There's also a limited distance between adapters. This can be fixed by creating an adjustable link. 
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Transmission
Wires sometimes gets loose while bending. This can be fixed can implementing tuning knobs that can tighten the wires. It was also easy to restrain bending. This can be fixed by modifying with a stronger motor and stronger wires.
Wires sometimes gets loose while bending. This can be fixed can implementing tuning knobs that can tighten the wires. It was also easy to restrain bending. This can be fixed by modifying with a stronger motor and stronger wires.
Next Steps...
Lots of improvements to be made! The overall design should be much simplier, easier to install, and can be adjustable to the size of the rat tail without damaging it.
Lots of improvements to be made! The overall design should be much simplier, easier to install, and can be adjustable to the size of the rat tail without damaging it.
Prototype #2
Prototype #3
Prototype #4
Prototype #5
Verification and Validation Testing
Multiple tests were designed to validate the functionality of the device and how well it fulfills our specifications.
In vitro tests are comprised of a few preliminary tests to validate how well the device fits onto the vertebral body, and how well it bends the spine, and the amount of slippage resulting from the bending, using X-ray imaging of the rat tail. Afterwards, the device undergoes a series of reliability tests comprised of the following: time tests, frequency tests and angle tests.
In vitro tests are comprised of a few preliminary tests to validate how well the device fits onto the vertebral body, and how well it bends the spine, and the amount of slippage resulting from the bending, using X-ray imaging of the rat tail. Afterwards, the device undergoes a series of reliability tests comprised of the following: time tests, frequency tests and angle tests.
Device Functionality Testing
Fit Test
The most basic of the test is the Fit Test. For each prototype, we put the device onto the neighboring vertebral bodies, and used x-rays to check that they are actually on the vertebral body.
The most basic of the test is the Fit Test. For each prototype, we put the device onto the neighboring vertebral bodies, and used x-rays to check that they are actually on the vertebral body.
Slip Evaluation Test
For the Slip Evaluation Test, we put two ends to create the most extreme angle and to see how much the device slips from the vertebral body.
For the Slip Evaluation Test, we put two ends to create the most extreme angle and to see how much the device slips from the vertebral body.
Bending Test
The purpose of this test is to see how much the device itself can bend.
The purpose of this test is to see how much the device itself can bend.
Device Functionality Testing : Fit Test
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Device Functionality Testing: Slip Evaluation Test
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Device Functionality Testing: Bending Test
System Reliability Testing
We want to test how well the device does as a testing system.
Time Test
The device ran successfully in a series of timed trial runs of 1 hour, 30 minutes and 10 minutes.
The device ran successfully in a series of timed trial runs of 1 hour, 30 minutes and 10 minutes.
Angular Position Test
For the Angular Position Test, we evaluate if each of the prototypes have the ability to bend at specific angles:
For the Angular Position Test, we evaluate if each of the prototypes have the ability to bend at specific angles:
System Reliability Testing: Angular Position Test
Kinematics Test
For the Kinematics Test, we evaluate how well the device is able to bend the rat tail in dynamic motion.
For the Kinematics Test, we evaluate how well the device is able to bend the rat tail in dynamic motion.
System Reliability Testing: Kinematics Test
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System Reliability Testing: Kinematics Test
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Opportunities for Design
While we made adjustments for each prototype that will better define the requirements of the device itself, there were many opportunities for design. It's important to be mindful of the end user when designing any product. In this case, the end user will be the researcher, as well as the test subjects themselves. The device would be safe to use for the researcher and not cause any harm during the testing procedure.
One of the issues we had was the fact that the rat tail would slip away from the device during the test. Since we wanted this test to be non-invasive, we knew this was going to be an issue because no other researchers have done a non-invasive testing procedure. Most use needles and k-wires to hold the device in place. In order for it to hold, we knew we had to create a layer between the device and the rat tail for increase the grip. The other thing to consider is that it should also be comfortable for the rat to be wearing. The researcher intended to use this device on a live rat for 8 hours a day, so it is crucial that the device is comfortable for the rat.
Final Design
The electronic system is comprised of the Arduino Uno microcontroller and a computer running Windows operating system. With this the user has control over the function of the whole device: the frequency, bending angle, and duration of cyclic bending.
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Group photo at CCNY's BME Day