For decades, metal screws and plates have been surgically implanted to secure broken bones, holding them in place while they heal.
But the metals used—usually titanium or stainless steel—don’t dissolve once their work is done, staying in the body for the life of the patient. In some cases, the body attacks the metal as a foreign object, causing infection and pain. In these cases, the implants must be removed surgically.
“It’s very stiff material that’s in the body and is not needed,” explained Hamdy Ibrahim, assistant professor in mechanical engineering at the University of Tennessee at Chattanooga.
To address the problem, Ibrahim is researching the use of metal alloys such as magnesium and zinc for the implants. They break down and are absorbed by the body, making way for new bone in their place and preventing the need for another invasive surgery to remove them.
Titanium and stainless-steel implants still are stronger than the alloys now being studied, he said. With the current level of research and testing, biodegradable alloys are suitable for hands, feet or facial bones, Ibrahim said, but they’re not strong enough to handle the workload of big bones such as legs or arms.
“There are many goals. One of them that keep increasing the strength. That’s the ultimate goal, for sure,” he said.
Alloys have their own issues, though.
“It’s not straightforward: ‘Let’s put it in the body, it’s going to work,'” he said. “There are some issues with magnesium and zinc alloys. They either degrade very fast as the bone heals or they don’t have enough strength.”
Alloys that degrade too quickly may release potentially dangerous corrosion products into the body as they dissolve.
“That’s one of the areas I’m working on,” Ibrahim said. “First off, starting the degradation, and second, slowing it and controlling it. Treating the material in different manufacturing processes to reduce or control the corrosion rate.”
Without finding solutions to these issues, you’re basically taking the problems with metal implants and replacing them with a different set of problems with alloys, he said.
“We don’t want the alloy to stay permanently. Otherwise, we are contradicting ourselves.”
