Heat-tempered magnesium alloy a strong choice for implants
BROOKLYN, New York – Titanium is the preferred material for surgical fixation procedures ranging from knee replacement to jaw implants. However, since this super-strong metal is not absorbed by the body over time, it can cause complications like infection, fistulization (particularly following radiation therapy), interference with skeletal growth, intolerance, thermal sensitivity, and interference with MRI and other imagining procedures. Additional procedures to remove hardware are among the most common surgeries worldwide and a major cost for hospitals.
A promising alternative is magnesium, a safely biodegradable metal and cofactor for many enzymes in DNA repair that also promotes bone health. But while its physical properties make it suitable for load-bearing sites, such as the temporomandibular region of the jaw, its rapid breakdown in the body sometimes results in the formation of hydrogen bubbles that can lead to serious complications.
In a unique collaboration, researchers at the NYU Tandon School of Engineering, NYU School of Medicine, and NYU Dentistry are developing and testing alloys of magnesium that are treated to improve strength and slow down the degradation process, thereby avoiding the formation of these bubbles.
In research published in the Journal of Cranio-Maxillofacial Surgery, the team, which includes Nikhil Gupta, associate professor of mechanical and aerospace engineering at NYU Tandon; Paulo Coelho, the Dr. Leonard I. Linkow Professor at NYU Dentistry; Eduardo D. Rodriguez, Helen L. Kimmel Professor of Reconstructive Plastic Surgery and chair, Hansjörg Wyss Department of Plastic Surgery at NYU School of Medicine; and Andrea Torroni, MD, associate professor, Wyss Department of Plastic Surgery at NYU School of Medicine, reported on their tests of a magnesium alloy that was subjected in Gupta's lab to a process called T-5 tempering, involving heating at 210 degrees Celsius for 48 hours.
After surgically implanting small samples of the alloy in the fronto-nasal region of study animals, the team examined the accumulation of the element in the lymph nodes, finding no difference between animals with no implants and the study animals. The researchers also implanted untreated — or "as-cast" — alloy, finding that both the as-cast samples and T-5 heat-treated alloys showed good biocompatibility and promoted bone growth in test animals. The T-5 alloy, however, was much more stable, with an eight-fold lower degradation rate than the as-cast alloy.
Gupta said he was not surprised by the positive results, as they mirrored what he had observed during in vitro studies at NYU Tandon.
"In our lab we put both as-cast and the heat-treated alloy in a solution of sodium chloride to simulate body fluid environments. Not surprisingly, the as-cast version corroded a lot. However, the heat-treated version did not corrode at all," he said. "What we have discovered is that by employing heat treatment we can change the alloy completely from a degradable, resorbable structure to one that doesn't degrade over time. In essence, heat treatment makes magnesium behave, in vitro and in vivo, more like titanium."
Torroni thinks the results auger well for eventual clinical applications of T-5 magnesium, whose mechanical properties are comparable to titanium, even in mandibular fractures, where stress on bone is particularly high. "The T-5 is really the best candidate for these high-stress applications. It has superior properties that are very close to those of bone and is very good for fixation of fractures," he explained. "It exhibits lower long-term risks because it resorbs. And it can promote bone formation and bone healing. It is totally biocompatible with no risk of rejection, and limited risk of infection."
The team also discerned no post-surgical morbidity, even in the control animals that received implants of untreated magnesium.
"Because of magnesium's systemic absorbability, this is not a problem," said Coelho. "The key idea is to make an implant that can be either non-absorbable, as a permanent support, or absorbable, like sutures that go away after some time." Gupta said that the research would not have been possible without collaboration between NYU institutions. "The breadth of this research takes it from the lab all the way to a clinical setting," he added.
This work was partially supported by the U.S. Army Research Laboratory.
"Biocompatibility and degradation properties of WE43 Mg alloys with and without heat treatment: in-vivo evaluation and comparison in a cranial bone sheep model" is available at http://www.sciencedirect.com/science/article/pii/S1010518217303256
About the New York University Tandon School of Engineering
The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute (widely known as Brooklyn Poly). A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences, rooted in a tradition of invention and entrepreneurship and dedicated to furthering technology in service to society. In addition to its main location in Brooklyn, NYU Tandon collaborates with other schools within NYU, the country's largest private research university, and is closely connected to engineering programs at NYU Abu Dhabi and NYU Shanghai. It operates Future Labs focused on start-up businesses in downtown Manhattan and Brooklyn and an award-winning online graduate program. For more information, visit http://engineering.nyu.edu.
About NYU School of Medicine
NYU School of Medicine is one of the nation's top-ranked medical schools. For 175 years, NYU School of Medicine has trained thousands of physicians and scientists who have helped to shape the course of medical history and enrich the lives of countless people. An integral part of NYU Langone Health, the School of Medicine at its core is committed to improving the human condition through medical education, scientific research, and direct patient care. The School also maintains academic affiliations with area hospitals, including Bellevue Hospital, one of the nation's finest municipal hospitals. There the School of Medicine's students, residents, and faculty provide clinical and emergency care to New York City's diverse population, which enhances the scope and quality of the School's medical education and training. For more information, go to med.nyu.edu, and interact with us on Facebook, Twitter and Instagram.
About NYU College of Dentistry
Founded in 1865, New York University College of Dentistry (NYU Dentistry) is the third oldest and the largest dental school in the US, educating more than 8 percent of our nation's dentists. NYU Dentistry has a significant global reach with a highly diverse student body. The College's mission is to partner with students in achieving academic excellence, providing the best oral health care, and engaging in research, scholarship, and creative endeavors to improve the health of the highly diverse populations in New York City and around the world. QS World University Rankings, which assess universities in four areas — research, teaching, employability, and internationalization — rank NYU Dentistry 3rd in North America and 3rd in the world for dentistry. For more information, visit dental.nyu.edu.