Lightweight, tough and strong, our bones are forces of nature. Ottman Tertuliano joined the faculty of Penn Engineering last year to study bone as both a resilient living tissue and sophisticated organic material. AMA Family Assistant Professor in the Department of Mechanical Engineering and Applied Mechanics, Tertuliano creates new tools to measure tissue mechanics at the smallest scales imaginable.
Thanks to his research, we won’t need to imagine. The Tertuliano Lab is hard at work creating visual data that demonstrates how bones behave under dynamic stress — a significant unknown in healthcare.
Whether it be the everyday stress of walking or a more forceful impact, a healthy bone or one compromised by illness, Tertuliano has fine-tuned methods to visualize and explain it. His research has revealed a rich universe of bone’s protective structural mechanisms and his sights are set on thorough characterization and explanation. After an academic year building a lab, training graduate students and running inventive, labor-intensive experiments at Brookhaven National Laboratory, Tertuliano is ready to reap the rewards.
“I’m excited to get to the point where we are collecting really beautiful data. We’re trying to understand how tissues rearrange under dynamic conditions. In just one year — much quicker than I was expecting — we’ve solved a lot of our hardest problems and are ready to dig into some very complicated experiments,” says Tertuliano.
How does bone tissue rearrange? It depends how closely you look. Tertuliano’s research has revealed that bones respond to stress in vastly different ways at different scales.
For example, apply repetitive stress to a bone sample and examine it at the nanoscale. Fracture may occur, but collagen fibers just a few hundred nanometers wide will rearrange themselves to maintain the tissue’s toughness. (For comparison, a human hair measures about 100,000 nanometers wide). These bone-specific, highly mineralized collagen fibers interrupt an expected mechanical failure, fighting to keep the tissue intact. Where a different material might weaken and crumble, bone acts with surprising resilience.
Now examine the sample at a larger length scale — 100 microns or more — and watch a new world of protection appear. Here, a bone’s self-preservation technique looks more like mineralized obstacles deflecting or even arresting a crack as it grows. These defensive barriers built into the very structure of our bones exist in the tissue to overwhelm and stop the fracture, requiring energy to overcome and giving cellular repair the opportunity to begin.
“These are only some of the levels and variety we see in bone behavior,” says Tertuliano. “There are many, many more we are investigating. What’s exciting is being able to see and understand bone’s unique hierarchical structure. Mechanical force needs to work its way through tiered levels, each displaying distinct protective behaviors. Bone is a material that handles force by switching gears, in a sense, to adapt to stress and contain damage.”
Understanding this material will be as valuable to clinicians as to mechanical engineers and materials scientists. The Tertuliano Lab is currently collaborating with radiation oncologists, bioengineers and materials scientists, pursuing insights into the weakening effects of proton radiation cancer treatment on bone tissue and fatigue fracture in metals. The lab’s first two doctoral students, Riti Sharma and Luc Capaldi, anchor the lab’s fruitful diversity, concentrating on bone biomechanics and metals research, respectively.
Read the full article on Penn Engineering Today.