Jill Middendorf, an assistant professor of mechanical engineering, is researching the mechanics of soft tissues in the spine and joints, with the goal of understanding mechanisms of disease and developing new therapies.
She received her BS in mechanical engineering from Iowa State University, and her MS and PhD from Cornell University. Prior to joining Johns Hopkins, she was a postdoctoral associate in the Department of Biomedical Engineering at the University of Minnesota.
What problems are you tackling through your research?
My goal is to understand the degeneration process of multiple joint tissues, and how we can potentially repair them with tissue engineering. The tissues I’m particularly interested in are articular cartilage, ligaments, and the intervertebral disc in the spine and knee.
We study the degeneration process using advanced mechanics techniques. In my lab, we look at local changes in mechanical properties, with the goal of relating that information back to clinical measures of biochemical properties or clinical measures of pain . By doing this, we can get an idea of why this degeneration is happening across the board. And if we can understand why joint tissues are degrading, we hope to someday be able to mend damaged tissues or even create new ones.
For example, in a recent study we chose to look at the mechanics of the facet capsular ligament in the lumbar spine, which is known to cause people lower back pain and compared the ligament mechanics to the overall health of the spine measured through MRI. This correlation furthered our understanding of the mechanisms associated with spinal degeneration and could potentially lead to improved therapeutic techniques in the future.
How is your approach to the problem better, more innovative, more promising, or just different than the approach others in your field are using?
We take a combined experimental and computational approach to understanding the mechanics of tissue degeneration. In the body, our cartilage, ligaments, and intervertebral discs are undergoing multiaxial loading processes, such as pulling, shear, and compression, from multiple directions. In our work, we can model this real-world mechanical behavior, and use this data to potentially design treatment therapies to target the areas in the tissue that may be degrading first.
More specifically, we look at localized regions within tissues to understand how that region may be affecting the overall joint. For example, consider an ACL injury. There’s initially a high impact load between bones, meaning two bones hit each other and one slides, causing the ACL to tear. During this process the articular cartilage is also damaged. The impact causes localized cracks to the articular cartilage in that joint, which leads to further degeneration. In this case, using our combined experimental and computational approach we can uncover really useful mechanical information about that localized area of damage, better understand why the damage is happening, and inform ways to fix it.
Where do you see your work heading in the next few years?
The next steps are to enhance the diagnosis of joint degeneration then find targeted methods to repair the joint tissues. We have plans to further diagnostic techniques associated with evaluating joint tissue degeneration and plans to repair damaged tissues using cell based therapies and tissue engineering. This future work could change the way that knee degeneration and spinal degeneration are evaluated and treated.
One specific concern with cell based therapies and engineered cartilage, or really any engineered tissue, is that it can be difficult to integrate successfully with the surrounding native tissues. What if there is a mismatch in mechanical properties, how do you adhere them to each other, and how do you make sure they stay adhered? This is an area where advanced mechanics can really enhance the long term success of engineered tissue in human patients. So these future experiments will be able to potentially predict which patients will have better long-term success with engineered cartilage because we would really understand the integration and performance of the engineered tissue with the surrounding tissues in the joint prior to implantation.
What influenced you to get into this particular field?
Understanding joint disease, degeneration, and repair is an important problem area where I felt like I could combine my interest in healthcare and engineering. Everyone knows someone that has undergone and dealt with joint problems. I personally know many people with joint issues partially because of the farming and construction community I grew up in. This population is at more risk for joint degeneration that any other occupation. Studies have attributed this to several factors, but one may be exposure to machinery vibrations while driving tractors. Are there ways that we can study mechanical problems related to small vibrations or large loads that can, over time, cause tissue damage in the joint? Finding answers to those kinds of questions, along with helping people in pain, motivates my work.
What excites you most about being at Johns Hopkins?
What really stood out to me was how excited people are about science in general. Every professor and student is excited about their research but also really excited to learn about your research, even if it doesn’t necessarily overlap with theirs. I think this is an environment that makes you feel like your ideas are really great.
I’m also looking forward to building new collaborations with the orthopedic group at the hospital. I want to continue building on my joint and spine research and learn more about the clinical issues they encounter.
What classes are you teaching?
I’m teaching Biosolid Mechanics this spring for upper-level undergraduates and graduate students. We cover a range of mechanical principles and how they can help us to understand biological tissues.
Outside of work, what are some of your other hobbies and passions?
I enjoy running and am planning on getting back into biking when the days get longer. I listen to podcasts on my way to work. I also really like reading biographies and autobiographies – I’ve always found it fascinating to hear about lives that are so different than mine.