The Mechanical Design and Control of Lower Limb Prosthetics

An Interview with Max Shepherd


Max Shepherd is a PhD candidate in the Department of Biomedical Engineering at the McCormick School of Engineering. His research focuses on the mechanical design and control of lower limb prosthetics and how prosthetic foot behavior affects the biomechanics of walking.  Max was recently named a Presidential Fellow, the most prestigious fellowship awarded to graduate students by Northwestern University.  

How would you describe your research and/or work to a non-academic audience? 
My work focuses on designing robotic prosthetic feet that can change their behavior according to the task. For instance, most prosthetic feet are designed for walking, but feel too stiff when walking up and down stairs, like ski boots. With the foot I designed, an onboard computer can command a small motor to change the foot stiffness when it senses that the task has changed. Recently, I've used this robotic prosthetic foot as a research platform to conduct experiments on how well people with amputation can sense changes in stiffness. This research is a crossover between the fields of rehabilitation engineering and psychophysics, which is understanding how people with amputation perceive physical stimuli from the prosthetic foot.

What do you find both rewarding and challenging about your research and/or work? 
I perform my research at the Shirley Ryan AbilityLab, a rehabilitation hospital, and it has been highly rewarding to work with patients and clinicians to develop a deeper understanding of their challenges. For an engineer, this is a unique and special environment. Keeping the patient in the loop has its challenges as well. Experiments never quite go as planned, and factors such as subject comfort and safety often require on-the-fly accommodation of experimental methods. 

What is the biggest potential impact or implication of your work? 
My hope is that a better understanding of how people with amputation can sense changes in the mechanical behavior of their prosthetic feet will lead to changes in the prescription process. Currently, it's common for patients to try on only one or two feet during their visit to the clinic, and then use that foot for years. My research is showing that many patients are very sensitive to this mechanical behavior, but first need to experience the effects of it changing to develop and communicate their preferences. Hopefully, this research will cause a shift toward the use of robotic prosthetic testing devices in the clinic, to fully incorporate patients' feedback in the prescription process.

Why Northwestern? 
The Department of Biomedical Engineering has a strong track record of preparing students for academia and has a unique relationship with the Shirley Ryan Ability Lab. These factors and the ability to perform research in a clinical setting in downtown Chicago made Northwestern a perfect choice for me.

Tell us about a current achievement or something you're working on that excites you. 
I'm currently visiting and working with Össur, a prosthetics manufacturer in Reyjkavik, Iceland, developing a new framework for designing running prosthetics. I've been diving head first into finite element modeling, a field that I know very little about, and I feel like I'm adding a new dimension to my understanding of design. I'm hoping we will be able to build a new foot and have someone run on it!

What are you most proud of in your career to date? 
I think the proudest moment I've had in my career so far was when my advisor and I visited a prosthetics manufacturer, with whom we were beginning to work on potentially commercializing a prosthetic ankle I designed. It had been about two years since I had the idea for the ankle and it validated my belief in the project and the hard work I put in to make a working prototype.

This article originally appeared as part of The Graduate School spotlight series.



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