Sandra Shefelbine has always been interested in the human body as a mechanical system: “The lungs are gas exchangers and the heart is a pump,” said the associate professor of engineering.
As an undergraduate simultaneously studying heat transfer and evolutionary biology, she realized that the system of parallel arteries and veins in arctic birds’ legs, which keeps them warm enough to stand on ice, is just an example of counter-flow heat exchange. “I really enjoy seeing the body in terms of mechanical perspectives,” she said.
As a graduate student, this interest became her life’s work. Shefelbine now studies the mechanics of bone—both the unique mechanical properties and the active response of bones to load. The system presents similar questions faced by engineers who study mechanics across length scales, she said. “The equations are still the same, the mechanics are still the same, the graphs are still the same.”
Shefelbine joined the faculty in the Department of Mechanical and Industrial Engineering in the spring after spending eight years at Imperial College London, where her research spanned a broad range of investigations. She uses in vivo experimentation and computational modeling to study topics ranging from how bones adapt to increased mechanical load to what makes the bones of patients with brittle bone disease more susceptible to fractures. According to Shefelbine, bone is generally both tough and strong, two traits not commonly found together.
To understand how different species’ bones have evolved over time, she has studied the bones of animals including elephants and Etruscan shrews, whose thighbones are the size of a fingernail clipping.
She also looks at how bone develops over the course of a single individual’s lifetime; this includes working with emus, which reach full maturity in just 18 month. “During this time they change their bone structure and the way they walk,” she said. “It’s a really interesting model for trying to understand how that process happens.”
This work was inspired by examining the bones of human children with cerebral palsy, a neurological disorder that affects an individual’s ability to control his or her skeletal muscles.
“We asked how does the way the person walks influence the way the bone grows,” Shefelbine said. “The future goal is to provide therapeutic strategies to put the proper loads on the bone to make sure they are growing correctly.”