As a kid, Michael Sealy was tall. A little clumsy, he says. And he has lasting proof: two metal screws in his left elbow. The southpaw underwent surgery after tripping and fracturing that elbow in the fifth grade. Surgeons inserted the screws to hold his ulna bone together. The bone healed. The screws remained.
"It starts to hurt," Sealy said of the elbow. "Sometimes it seems to be correlated with cold weather or a storm front moving in. Other times, it hurts — and of course my wife doesn't believe me — when I'm doing chores, like carrying in the jug of milk or lifting clothes out of the washing machine."
Now an assistant professor at the University of Nebraska-Lincoln, Sealy has mixed business with that displeasure by pioneering a novel approach to a decades-long quest.
"Instead of having these permanent metal implants, let's have one that degrades over time," he said. "Let's eliminate this whole idea of a second surgery to have these implants removed."
It's a major challenge for multiple reasons. But the university has equipped Nebraska Engineering with technology commensurate to that challenge: the first 3D printer in the world that can integrate multiple materials and manufacturing processes while also printing highly reactive metals such as magnesium.
That combination of familiarity and reactivity, Sealy said, makes magnesium a prime candidate to become the primary ingredient in dissolvable screws, plates and other medical implants that could eliminate follow-up surgeries or a lifetime of aches during snowstorms.
To reinforce magnesium against the rigors of the body long enough to serve as an implant, Sealy began experimenting with a technique called laser shock peening as a graduate student.
The laser shock peening helped magnesium withstand initial corrosion tests so well that Sealy began thinking of his dissertation results as "lake-house data, because it was so good that I was going to commercialize the technology and buy a lake house off those results."
Sealy then began testing the long-term corrosion of magnesium parts in a fluid that simulated the aqueous environment of the body. This time, the results were more sobering: The screws lost 50% of their strength after just one week and 80% after two weeks. Sealy quickly realized that peening only the surface of the magnesium parts wouldn't suffice.
State-of-the-art 3D printers
Not just any 3D printer would do. He needed access to the sort of technology that was only just beginning to emerge. Nebraska Engineering offered him the opportunity to help direct its purchase of three state-of-the-art 3D printers.
Those printers eliminate virtually all of the oxygen, moisture and other impurities that could react with magnesium — a fairly rare capability in itself. But they also allow Nebraska engineers to construct components layer by layer, which enables Sealy and his colleagues to incorporate multiple materials or build intricate internal structures.
"What's unique about our printer is that it's the first one where they actually combined these hybrid- and reactive-printing capabilities. I would argue this is probably the most advanced hybrid-additive manufacturing facility in the world, just because our equipment is so rare."
Ultimately, Sealy said, the print-and-peen approach should help him design and construct magnesium implants that degrade at different rates inside the body. One model of clavicle plate or knee pin might degrade within a year, whereas another might dissolve over three or five years.