For athletes from pee-wee to pro, cartilage plays a crucial role in protecting joints during activities such as running and jumping.
All too often, however, we read reports of high-profile players forced to make an early exit from sports such as football or basketball because their cartilage has crumbled.
The tough but flexible tissue that covers the ends of bones at joints in the human body is quite effective at dissipating energy—but if enough force is applied, cartilage will fracture.
“Once there is a structural failure in cartilage, the cells can’t rebuild it,” says Corinne Henak, an assistant professor of mechanical engineering at the University of Wisconsin-Madison. “So we want to understand how those structural failures occur so that ultimately we can prevent them, or reduce the effects of that failure.”
Now, thanks to the work of Henak’s graduate student Guebum Han (PhDME ’19), who was co-advised by Mechanical Engineering Associate Professor Melih Eriten, we have a better understanding of how fractures occur in cartilage.
This important information could eventually help clinicians more accurately predict an individual patient’s risk of developing incurable osteoarthritis. And it could have implications for training regimes in a variety of high-impact sports by providing insight into which athletes might be predisposed to injuring their cartilage.
“For example, if we had some information about the state of a patient’s cartilage, that could give us insight into whether that patient should do swimming rather than basketball to keep active,” Henak says.
Han’s research has provided some much-needed experimental data showing how much loading cartilage can handle before it fails. He studied differences in how cartilage fractures when a load is applied quickly, and when it’s applied at a slow rate.
The researchers found that a fast impact significantly reduces the cartilage’s strength. In comparison, when they slowly applied the displacement, they found the cartilage could withstand about 10 times the mechanical work before fracturing.
A state-of-the-art experimental setup that Han developed with Henak and Eriten enabled him to make these research advances. He conducted well-controlled experiments using a technique that involved poking cartilage samples with a very small indenter to take measurements.
“A big advantage of this micro-indention technique is that we can perform many more tests on each sample because of the very small size of the indenter tip, and that gives us better, more consistent data. That, in turn, helps us better understand the trends,” says Han, who is taking a postdoctoral position at the University of Minnesota after earning his PhD in August 2019.
Han says mentoring from his co-advisors was instrumental to his success, and that combining their different perspectives and areas of expertise opened up unique and fruitful research directions for his PhD work.
Henak’s background is in biomechanics, and she is an expert in cartilage mechanics, whereas Eriten’s expertise is in fundamental mechanics. Their collaboration formed around a shared interest in studying failure mechanisms in soft materials—cartilage, for example—although they were approaching the problem from different angles. Eriten was eyeing applications for synthetic soft materials, while Henak was interested in biomedical and clinical applications.
“We started collaborating to investigate these mechanisms from both perspectives, looking at cartilage, and by merging our expertise and research techniques we were able to do things that others couldn’t,” Eriten says. “It propelled us to the forefront of this research field.”
Inspired by his advisors, Han’s advances in this area could have applications not only in improving human health but also for designing tough, soft materials for a variety of uses, including soft robots.
Han’s work has attracted much interest in the mechanics and biomechanics research communities, especially from computational mechanics researchers. As these researchers work to build computational models that aim to predict, for example, when a patient will develop cartilage disease as a result of an ACL tear, Han’s experimental data will enable them to build more accurate models.
“There isn’t a lot of published research in this area, so there is a lot more potential to dig into these mechanisms of failure,” Henak says. “Guebum has done very good work that’s making an impact and that’s also opening up some exciting future research directions.”
Author: Adam Malecek