Researchers proposed a new method to 3D-print metallic alloys for certain medical implants, an alternative to conventional approaches that they said improves the devices' compatibility with cells as well as their integration with the surrounding bone.

The team from Washington State University, Mayo Clinic and Stanford University Medical Center made its case for 3D printing titanium-tantalum alloys for orthopedic and dental applications in a study published Feb. 6 in Materials Today. They said such devices, which were tested in animals and using human cells, are equivalent in performance but better in terms of their compatibility with patients. 

"Various 3D printing, or additive manufacturing, techniques make it relatively easy to design, innovate and manufacture metallic parts with complex shapes on-demand," the study authors wrote. 

They cited the "relative ease" of manufacturing, the patient specificity that may be achieved on an anatomical site and the "'on-the-fly' design flexibility" of 3D printing as reasons that make it "more useful" for metallic implants. 3D printing also helps to "efficiently handle the large difference in melting temperatures" versus conventional techniques of machining these alloys, such as high-temperature furnace melting, the authors wrote. 

Following the enactment of the 21st Century Cures Act and the adoption of U.S. Food and Drug Administration guidance, confidence in 3D printing as a manufacturing platform increased among medical device manufacturers. Part of the $6.3 billion in funding that the 2016 law provided supports medical innovation, including 3D-printing medical devices.

But a knowledge gap regarding the biological response of titanium and tantalum alloys, which is crucial in determining the efficacy of devices made for the human body, has persisted over the years. This, coupled with the unique characteristics that 3D printing can offer in medical devices, such as infection resistance, drove the team to pursue this research project. 

"We will be very excited to see applications," study author Amit Bandyopadhyay, a professor at the School of Mechanical and Materials Engineering at Washington State University, told The Academic Times. "Thousands of patients suffer from infection," and the approach that the study proposed "can be used to make alloys that are inherently infection resistant." 

The FDA has already cleared thousands of 3D-printed medical implants that are on the market and in use, and surgeons and patients often don't even know these implants were 3D-printed, Bandyopadhyay noted. The devices can be 100% tantalum, Bandyopadhyay said; one such example is from Zimmer Biomet. "We showed that between 10% and 25% `tantalum and in titanium is good enough to give you the equivalent performance of 100% tantalum metal," he said.

For the study, the team used 3D printing to create multiscale structural metal implants. Studies in vitro, in human cells and in vivo, in rabbits, then examined whether coming in contact with implants could harm the animal cells and affect bone ingrowth into the medical implants. 

The researchers found that together, the mechanical and biological properties bonded in such a way that improved the implants, including by making them more stable. The nanoscale design elements integrated at the surface of the implants were shown to enhance cell migration and adhesion, and to influence overall bone remodeling.

The question the team had posed was whether titanium-tantalum biomaterials could be designed by "incorporating the excellent biocompatibility of tantalum and good mechanical processability of titanium for biomedical applications." 

Indeed, the researchers observed that different types of porosities bonded with the body faster, resulting in shorter healing times. Osseointegration, or 3D-printed implants' adhesions to surrounding host bones functioning as tissues, was also enhanced. 

The project included rat and rabbit distal femur studies to address reported issues with a poor biological response of titanium alloys. The team highlighted directed energy deposition, a category in 3D-printing techniques, in arguing that their work "shows the design and manufacturing flexibility of 3D printing can help bring the exceptional biocompatibility of [tantalum] together with excellent mechanical properties of [titanium] to innovate the next generation of metallic biomaterials for implants." 

Bandyopadhyay noted that a "great deal of new materials" can be created by mixing materials through 3D printing.

"With the help of 3D printing, we can come up with new alloys where devices can show equivalence, and sometimes an even better performance," he said. 

This means that rather than making 10,000 implants of metals and alloys to only sell 2,000, medical device manufacturers can produce these based on demand. And instead of taking another 10 years to come up with different alloys, they "can come up with different alloys in a few months, if not a few days" Bandyopadhyay said. 

The team plans to pursue additional studies beyond biocompatibility.

The study, "3D Printing in alloy design to improve biocompatibility in metallic implants," published Feb. 6 in Materials Today, was authored by Indranath Mitra, Susmita Rose, William S. Dernell, Nairanjana Dasgupta, Chrissy Eckstrand and Amit Bandyopadhyay, Washington State University; Jim Herrick and Michale J. Yaszemski, Mayo Clinic; and Stuart B. Goodman, Stanford University Medical Center.