Bacteria-Killing Metals Developed for Implants

Scientists have developed a surgical implant made with a new combination of metals that can kill harmful bacteria, paving the way for the development of improved infection control for common joint replacement surgeries.

Researchers at Washington State University added the corrosion-resistant metal tantalum and copper to the titanium alloy typically used in hip and knee replacement surgeries. The alloy has served these operations well for more than 50 years but traditionally is not well-suited to overcoming dangerous infections that can plague patients after surgeries.

A team that included Amit Bandyopadhyay, a Boeing distinguished professor in WSU’s School of Mechanical and Materials Engineering, added 10% tantalum and 3% copper to the alloy, creating a new metal that can prevent infection. 

Bacteria-Busting Metal

When bacteria come into contact with the material’s copper surface, almost all of their cell walls rupture, while the tantalum encourages healthy cell growth with surrounding bone and tissue leading to expedited healing for the patient, the researchers said.

“In most cases, the implant has no defensive power from the infection," Bandyopadhyay explained. "We need to find something where the device material itself offers some inherent resistance—more than just providing drug-based infection control."

Related:Understanding the Hardness of Metals

Indeed, surgeons often treat patients preemptively with antibiotics; however, life-threatening infection still can occur right after surgery or weeks or months later as a secondary infection. 

Antibiotics often are prescribed again, but in some cases they still don't eliminate infection and in about 7% of cases further surgeries are needed. This is why the team decided to attack the problem from a preventative material perspective rather than treating infections when they occur, Bandyopadhyay said.

"Here we’re saying, why not change the material itself and have inherent antibacterial response from the material itself?” he noted.

Careful Development and Testing of Metal Implants

The team used 3D-printing technology to develop the implant, which was studied for three years to assess its mechanical properties, biology, and antibacterial response both in the lab and in animal models. The researchers also studied how the implant wears over time to ensure that metal ions from the implant won’t move into nearby tissue,causing toxicity.

In lab tests, the implant behaved on par with current implants, remaining strong and compatible with surrounding tissue, while also killing 87% of the bacteria that cause staph infections, the researchers reported in a paper published in the International Journal of Extreme Manufacturing.

Related:National Metals Lab Helps Technology Transfer of New Alloys

“The biggest advantage for this type of multifunctional device is that one can use it for infection control as well as for good bone tissue integration,” noted Susmita Bose, Westinghouse Distinguished Professor at the university, who also worked on the project. “Because infection is such a big issue in today’s surgical world, if any multifunctional device can do both things, there’s nothing like it.”

The researchers plan to continue their work with a goal of improving the bacterial death rate to the standard of more than 99% without compromising tissue integration. They are working with WSU's Office of Commercialization and have filed a provisional patent for the technology.

Future plans include making sure new iterations of the implant create replacement joints with performance that can withstand real-world load conditions that patients might use. This might include, for example, a knee that can allow the patient to continue to go hiking, the researchers said.