MechE professor receives NSF CAREER award for work in developing "virtual mechanical test"

Broken bones have a unique capacity to heal. The new bone that forms along the fracture line, called callus, starts out as a soft tissue and, over time, it hardens into bone that is just as strong—or stronger—than before the break.

But in some cases, the healing process goes awry. This failure to heal is called a nonunion, a painful and often debilitating condition that requires further medical intervention.

“We know that nonunions happen in about 10 percent of fractures of the shinbone, and it’s impossible to predict who will have one,” says Hannah Dailey, an assistant professor of mechanical engineering and mechanics at Lehigh University’s P.C. Rossin College of Engineering and Applied Science. “But patients who get a diagnosis of a nonunion can have higher rates of depression, opioid use, and addiction. They might be unable to return to work. So we want to be able to identify very early on when healing is not progressing well  so surgeons can intervene sooner. The problem is that right now, you can’t make that early determination."

Dailey recently received a prestigious grant from the National Science Foundation’s Faculty Early Career Development (CAREER) Program that will help her develop a virtual mechanical test that will make that determination possible. 

CAREER awards are granted annually by the NSF in support of junior faculty members across the U.S. who exemplify the role of teacher-scholars through outstanding research, excellent education, and the integration of education and research. Each award provides stable support at the level of approximately $500,000 for a five-year period.

Using specialized software on low-dose computed tomography (CT) scans of patients who have sustained tibial fractures, Dailey and her team build 3-D mechanical structural models that identify regions of bone and new bone, or callus. They run the models through finite element analysis software that divides the bone model into tiny zones that all have a mathematical relationship to each other. They then simulate different types of loads that mimic the conditions during healing . The technique is called virtual mechanical testing. The less the bone flexes under load, the more healed it is.

Using the same CT scans, they then digitally re-create a healthy version of each person’s leg and perform the same virtual mechanical tests. When they measure the flex of the unbroken leg against the fractured leg, the resulting percentage helps them determine how stiff the broken bone is compared with the healthy one. The stiffer a bone is early in the healing process, the quicker the patient can bear weight. 

Preliminary results have found that the virtual mechanical test significantly correlates with how long it takes patients to heal, and could successfully identify a nonunion. It is the first such test of its kind to do so.

“But there are some fundamentals that we don’t totally understand,” says Dailey. “This project is about understanding the structural mechanics of bones while they’re healing. If they’re healing well, what does that new material look like and how does it behave under loading during the early stage of healing? And if there’s a problem with healing, how do we better understand the behavior around the defect site using imaging from humans? If we can understand the mechanical properties of early-stage tissue, we can refine our mechanical modeling, and intervene earlier to reduce the tremendous burden on these patients.”

Dailey’s CAREER award will also support the educational mission of the Perry Initiative, a nonprofit dedicated to inspiring women to enter the fields of orthopedic surgery and engineering. The organization conducts one-day outreach programs to high school and first- and second-year medical students across the country. Participants perform mock orthopedic surgeries and biomechanical engineering experiments.

“Women are underrepresented in these disciplines,” says Dailey. “Only about 6 percent of practicing orthopedic surgeons are women, and just over 12 percent of faculty at engineering schools are women, so there’s a pipeline problem. These students get to meet women in these fields, and the idea is if you can see yourself represented in these careers and get to engage in these realistic simulations, it builds your confidence and ability to visualize yourself on that path. For medical students, it can get them to think seriously about trying to match for orthopedic residencies.” 

Dailey is partnering with the Perry Initiative and serving as a liaison with Lehigh’s interdisciplinary capstone design experience, the Integrated Product Development (IPD) courses to create a hands-on learning module  the organization can use during its outreach. Over two semesters, a team of five female Lehigh engineering students will design a mock orthopedic implant system, specifically an intramedullary (or IM) nail, which is the same implant used in patients with tibial fractures. The Lehigh students will learn how to design a mechanical system that must be lightweight, robust, and easy for the outreach students to use. The goal, says Dailey, is to empower participants in the Perry Initiative programs to see themselves doing hands-on things and show some of the many career possibilities at the intersection of engineering and health care.

“The stereotype of the mechanical engineer is that they’re someone who works on cars or planes, and we love that so many of our students are into that,” says Dailey. “But not every student wants to do that. This kind of outreach helps them see that fields like mechanical engineering, bioengineering, and materials science give them tools that apply to intersectional fields like medical device design and tissue engineering, and to do work that is really important for the human good.”

Hannah Dailey

The NSF CAREER award will support further research by MechE professor Hannah Dailey into the structural mechanics of bones as they heal, as well as her efforts to encourage women to pursue orthopedics and engineering. Photo: Christa Neu

If we can understand the mechanical properties of early-stage tissue, we can refine our mechanical modeling, and intervene earlier to reduce the tremendous burden on these patients.
Hannah Dailey, assistant professor, mechanical engineering and mechanics