Focus on new faculty: Assistant Professor Kevin Turner
eyond their circular shape, semiconductor wafers and red blood cells seemingly have little in common. But studying the two isn’t really so different, says new Assistant Professor Kevin Turner. “The common theme is materials, mechanics and microsystems,” he says. Turner began pursuing this theme as a graduate student at the Massachusetts Institute of Technology, where he studied the materials and mechanics involved in a microelectronics manufacturing process called wafer bonding. He continued to follow it during a postdoctoral fellowship, also at MIT, in which he probed the mechanical properties of red blood cells.
He will now carry on these dual avenues of research at UW-Madison, and here the breadth of the university’s research facilities and expertise serve his interests well. In addition to being a member of the Computational Mechanics Center and a user of the Wisconsin Center for Applied Microelectronics (WCAM), Turner plans to collaborate with biologists from other schools and colleges on campus.“That’s one of the things that attracted me to Madison: a great mechanical engineering department that is surrounded by great programs in the medical and life sciences,” he says.
Turner, who arrived in Madison in mid-August, is a newcomer to the Midwest. A native of New Jersey, he earned a bachelor’s degree in mechanical engineering from Johns Hopkins University in Baltimore, Md., and master’s and doctoral degrees in mechanical engineering from MIT in Cambridge, Mass. From an early age, he knew he wanted to be an engineer. “Either that or a carpenter when I was little,” he says. “Mechanical engineering interested me because the systems you work on are concrete and physical. It was the best fit for my interests.”
During his doctorate, Turner studied new materials and manufacturing processes for making microelectromechanical systems (MEMS). These tiny, silicon-based machines are produced with many of the same techniques used to manufacture semiconductor chips. But unlike flat, two-dimensional chips, MEMS possess a 3-D structure that is hard to construct with traditional methods.
Engineers have instead begun bonding one or more wafers together to build 3-D structures. Bonding sounds simple, says Turner, but it often yields very few usable wafers. Problems arise primarily from other manufacturing steps, such as etching and deposition processes, which create waviness and roughness on the wafer surface that can interfere with bonding.
To address this, Turner has developed models describing the mechanics of bonding and the effects of treatments, such as the clamping together of wafers, to enhance it. With this fundamental scientific understanding in hand, engineers can then make appropriate changes to the design and tooling involved in bonding, he says.
He has also applied his knowledge of mechanics to the study of biological cells. As a postdoc at MIT, he investigated how red blood cells carry mechanical load and was interested in changes in stiffness and deformability that occur with disease—specifically malaria.
To measure their mechanical properties, Turner bent, twisted and pulled on the tiny cells one by one, a process he jokes was “remarkably painful”—for him, not the cells. And because of the cells’ natural variability, many need to be tested in order to obtain an accurate measurement.
Now, he and his graduate student want to design and build a MEMS device that can do the same thing much more quickly and efficiently. Eventually, such a device might test the stiffness of red blood cells in order to monitor the health of the blood supply or to reveal the effects of a drug.
But even with the help of a MEMS device, the mechanical properties of cells will still be tricky to measure. Red blood cells are among the simplest of the body’s cell types. Still, as living entities, they can reshape their cellular skeletons and change their structures right in the middle of testing, says Turner.
With non-living substances, too, engineers usually isolate and test a piece of material with a well-defined geometry. But with a cell, says Turner, “You’re testing an entire structure. It’s not as if you’re peeling off a piece of cell membrane and measuring just that. It’s more like you’re testing the whole building.”