Senior Design

Senior Design: AFO Shoe Donning Assist Device

The AFO Shoe Donning Assist Device is a device that is aimed at helping ankle foot orthosis (AFO) brace wearers place their shoe on. I was part of a team of seven engineering students and one nursing student that designed and fabricated the device during my senior year of bioengineering. We designed a device and documented it through the creation of a DHF file, per FDA guidance. Following the device development, we froze the design and performed verification and validation testing.

Background

Ankle foot orthosis (AFO) braces are used to assist with foot drop, which is a condition in which an individual is unable to lift keep their foot raised when walking. This is common in stroke patients, whom often suffer from hemiparesis - paralysis of half of their body.

The Problem: AFO users commonly have a difficult time donning a shoe over their brace. Because the brace is bulky and rigid, it can be very hard for an individual to get their shoe on over the brace by themselves. This challenge not only limits an individual's independence, it can be a barrier to patients leaving the hospital.

Process

This was a year-long capstone design course during my senior year of bioengineering.

The first semester was focused on ethnography and device development. For the ethnography phase, my team and I went to numerous clinical sites in the Pittsburgh area to find a clinical need that was in need of a medical device.

The second semester focused on verification and validation testing of the frozen design. More details are provided below for the device development and V&V testing.

Individual Contributions

I served two primary roles on my senior design team. Firstly, I was team lead. This meant I took charge of organizing meetings with our professor and clinical sites and served as a high-level organizer for assuring that everything was getting done in terms of prototype development.

Secondly, I served as fabrication lead. As I had been involved in the University of Pittsburgh Makerspaces for the last two years, I had the understanding on how to utilize the materials in the space and operate the machines needed for prototype fabrication. As such, I made it a personal goal of mine to help train the members of my group who had previously not been exposed to such processes.

Fabrication

The low-resolution prototype had us using rapid prototyping techniques to create a model out of foam-core using x-acto knives.

We collaboratively created two main foam-core models, allowing every member to provide input and acting as a medium for us to get our ideas together.

Following their creation, I assisted a subset of my group in setting up and attending visits to occupational therapists to get feedback on the different features of our devices. We used this feedback to drive the design of our second prototype.

Training my team on foam-core for rapid prototyping

Sanding the platform following CNC routing

For the medium-resolution prototype, we made the design out of laser cut and CNC'ed wood.

I used my previous experience of using the machines to work with another member of the team to CAD a model that could be easily fabricated with the devices.

Creation of a sturdy medium-resolution prototype gave us the ability to utilize the device to test out the design. It was quickly revealed that we would need to make an even sturdier design if we wanted to hold our highest expected weight of 280 lbs.

For the high-resolution design, I once again lead the development of the CAD design to create steel parts for the structural components of our design. Use of CAD allowed for us to run simulations to test the stress the parts could withstand. We had to outsource these parts to the machine shop in the engineering building, so another part of my individual contributions was holding discussions with the machinists to determine the best way to create the parts - which involved laser cutting steel sheets and turning the dowels on a lathe.

My render of the CAD file for the final design of the semester. It contains additional spacers which be included in future builds.

Stress simulation on the CAD model to test the strength of the steel parts before committing to fabrication

Through this project, I got exposure to machining on the bandsaw. I also learned how to stain and seal wood to make a device that looked finished and was water-resistant.

Cutting a new dowel rod piece on the bandsaw (pictured above)Staining and sealing the wood platform and bases (pictured right)

FDA Documentation

In parallel to device development, our team created a Design History File (DHF) as per the FDA process for medical device development. The documents we included in the DHF were:

Regulatory Strategy
User Needs and Use Cases
Fault Tree Analysis (FTA)
Failure Modes and Effects Analysis (FMEA)
Risk Summary
Product Documentation Specifications
V&V Plans, V&V Protocols, and V&V Reports
Traceability Matrix
Greenlight Guru electronic Quality System
Document Control Standard Operating Procedures (SOP)
Change Management SOP

An Engineering Change Order was also necessary following a failed verification test. This change is detailed in the Final Design section at the bottom of this page.

CAD files and drawings, assembly instructions, and dxf files for the laser cut parts were included in this file as well to contribute to a "draft" Device Master Record (DMR).

Verification and Validation Testing

Adding plates to the top of the platform.

I was responsible for writing and executing the verification protocol for the tensile and compressive strength testing.

This test involved loading the device incrementally on the platform to characterize its max strength. Our target was 280 lbs, which was the 95th percentile weight for men in the U.S.

To execute the testing, I went to the University's rec center and added plates to the top of the platform while it was raised to the second lowest position, which was the weakest position. Ultimately, the device failed at 225 lbs, which was before it met the acceptance criteria.

While the device failed before the target was hit, this target assumes the user is standing, which would not be recommended by our group. A sitting patient would apply a much smaller mass to the device, very likely under the 225 lbs achieved.

A production level device might be made of a lighter, stronger material, such as bent steel sheet metal, and have a more sophisticated machining processes. I was also limited in resources due to being a student, and was only able to test a single prototype device. In an industry setting, multiple production equivalent devices would be tested prior to gaining approval for market, providing a more thorough analysis.

I also assisted the validation lead in performing usability studies at various clinical sites we had built connections with.

We held a focus group with six occupational therapists and three separate sessions of usability studies with a patient each.

We got great feedback from the OTs, evidencing that the device would benefit the patients when compared to current technologies. The patients were able to use and understand each feature of the device, but due to limitation in the amount of patient's we could recruit, we were unable to get patients that could successfully don the device due to contraindications.

If we were performing this in an industry setting, and not restricted to one semester of testing, more thorough patient recruitment would be performed to hopefully yield better results.

Providing a demo to the patient and OT during a usability study.

Prototype Evolution

The following section will detail each prototype's design and how it evolved throughout the three different resolutions. Image slideshows detail the different features of each prototype, with more supporting text following each section.

Low-Resolution Prototype

The low-resolution prototype was made out of foam-core to lock down the main design features. The production of this low-resolution model allowed for us to bring it to occupational therapists for quick feedback.

Medium-Resolution Prototype

The medium-resolution prototype was made out of plywood and hardboard. The plywood was CNC'ed and the hardboard was laser cut. The development of this prototype provided more structural stability to test the features with our shoes.

High-Resolution Prototype

The high-resolution prototype was made out of plywood, hardboard, and steel. After further defining our user needs and product design specifications, it was indicated that a stronger material would need to be used to support the desired user weight.

Final Design

The final design differed slightly from the high-resolution prototype based on feedback from occupational therapists throughout the development process.

Device Release Mechanism

We decided to use a passive, rather than an active, approach to the release mechanism for the device. With the current method of setting up the device, the device only goes one direction when lifted to prevent backlash when donning the shoe. The passive approach allows gravity to reset the device by simply lifting the end of the platform. This approach keeps the weight low by not needing an active actuator, such as an electronic winch. The video below showcases the release method: