Researchers at the National University of Science and Technology MISiS (NUST MISiS) in collaboration with their Canadian colleagues published an article in the journal Materials Science and Engineering: A, in which they told about new shape memory alloy, which can significantly increase the service life of medical implants.
Human bone tissue remained unique in its characteristics for a long time: it is both durable and elastic, which allows it to stay functional for decades despite constant cyclic stress. Sometimes, however, bones suffer so much damage that they need to be replaced.
Titanium implants, which are compatible with the human body’s natural tissues, became the most popular bone replacements in recent years. But even they have a disadvantage, being not as flexible as actual bones. This often leads to a disruption of mechanical-biological balance in the human body. The bone tissue stops receiving the loads once the implant’s more rigid material takes over. As a result, bone tissue cells die, as the body does not need them anymore. Therefore, the implant loses its connection with the bone; it comes loose and requires further replacement.
Just like the previous titanium alloy, this new titanium-zirconium-niobium alloy is very resilient to an aggressive environment, such as the human body. Since its elasticity matches that of human bone, implants made from this alloy are much more durable.
“Together with our industrial partner, Conmet, our international research team is now developing an industrial technology to produce billets, or round bars for implants. In order to form an internal structure inside the long products made from this alloy, which will ensure the best possible combination of the alloy’s functional properties, you need a well-defined sequence of procedures that include various kinds of processing the billet with pressures at high temperatures. We are planning to make bars for systems of transpedicular fixation of the spine. These systems are attached to the spine through the pedicle of the vertebra, and that is where the name of this procedure comes from. They are used to treat bad cases of scoliosis. Bars made from the titanium-zirconium-niobium alloy will have high functional durability under conditions of increased operational deformation; and due to its low rigidity, the risk of injuring a patient will be reduced, while the quality of his or her life will improve,” said Vadim Sheremetyev, one of the researchers and a senior research fellow at NUST MISiS’ Department of Pressure Metal Processing.
The new superelastic alloy can also be used in personalized medicine. Researchers have already learned how to turn it into a powder of a predetermined composition. This made the new material suitable for additive technologies, which is why now one can make personalized metal implants with a predetermined degree of porosity using a 3D printer.
“The new material has a low value of Young’s modulus (between 30 to 50 GPa), which is why it is considered to be superelastic, and it will not prevent the bone tissue from receiving the necessary load. The alloy has high corrosion resistance. It can be used as an alternative to foreign inventions (such as Dynesis and PEEK), which are widely used in medicine today. Perhaps, technologies based on the new material will be used as a functional method of stabilization in the treatment of degenerative diseases and spine deformations. I believe that this new alloy has great prospects in traumatology, orthopedics and vertebrology,” said Alexander Kuleshov, head of the vertebrology group at the Priorov Central Research Institute of Traumatology and Orthopedics.