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Biomaterials $73.9bn


Amount the US implantable medical device market was estimated to be worth in 2018.


$20.73bn The projected value of the


active implantable medical device market in 2025. Transparency Market Research


neurological implants, cardiovascular implants and hearing implants – is set to grow in value to $20.73bn by 2025.


“For the most part, companies have copied the technology that already existed,” Bandyopadhyay adds. “They are using 3D printing just for the ease of manufacturing. On-demand manufacturing is certainly one of its key benefits, but there has been little innovation in design or composition.”


That is all about to change, however, as novel techniques are emerging that will have a far-reaching impact on biocompatibility and performance. Bandyopadhyay was heavily involved in a new study by researchers at Washington State University, the Mayo Clinic and Stanford University Medical Centre, which has shown the value of using 3D printing to identify new alloys that could greatly improve the performance of medical implants. The metals most commonly used in implanted devices were developed for other industrial applications, notably in the aviation and automotive sectors. They were not chosen for their biocompatibility. Stainless steel (SAE 316) is commonly used in fracture repair, titanium (Ti64) for load-bearing implants such as hip replacements, and cobalt-chrome alloys for applications requiring articulation, such as joints and dental implants.


“Back in 2001, we were talking about 3D printing porous metal coatings for implanted medical devices and people were telling us not to bother, because 3D printing would never achieve the required strength.”


Amit Bandyopadhyay


“None of these were designed for medical use, so they are not tailored to bone biology, which can be different in people of different ages,” says Bandyopadhyay. “The bone biology in a child may not be the same as in an elderly person who is more prone to osteoporosis. [But] biocompatibility has not been an issue because there were no options.” In the knowledge that more than half of all commercial biomedical implants contain metal, Bandyopadhyay and his team decided to ask whether it was possible to improve biocompatibility by creating new alloys better suited to implantation in the body without the long lead-times usually required for spinal, dental and craniomaxillofacial devices. The team used 3D-printing techniques to assess various alloys to see whether they could perform better than standard metal components with biocompatible coatings. While coatings are effective to some degree,


104


they do not always bond well with the base metal, which can result in failures and remedial surgeries. “The solution today is to develop a coating rather than focusing on alloy chemistry,” Bandyopadhyay observes. “So, we did biology-based work to increase the biocompatibility of alloys rather than coatings.


As Bandyopadhyay explains, the most biocompatible metal is tantalum, which forms a stable oxide layer that prevents an exchange of electrons, allowing it to recruit proteins and enabling osteoblast molecules to form. Its lack of reactivity makes it highly suitable for use in the body, but it’s high melting point and density make it hard to work with, and it is very expensive in its pure form. What the team discovered, however, was that adding a small amount of tantalum to titanium provided the same biocompatibility as pure tantalum, along with the load-bearing and corrosion-resistant qualities of titanium. Combining 3D printing, which enables the fabrication of complex designs that can be customised to the needs of each patient, with the properties of new alloys could greatly improve the body’s acceptance of an implant.


“Though the alloy can be cast or forged, 3D printing is already used in device manufacturing, so it is the way forward,” says Bandyopadhyay. “We used laser-based processes because tantalum has such a high melting point. It is hard to melt it, but it absorbs the laser, which enables us to melt and mix a small amount of tantalum powder as we do the 3D printing. Because we are using 3D printing, the processing can be done at the point of manufacture.” The team’s paper is one of the first to examine the application of 3D printing to alloy design and, having come out in February 2020, the concepts it lays out are still very new. Medical device manufacturers and regulators will need time to absorb the opportunity that it presents.


“A tantalum-titanium alloy is very simple and 3D printing is already widely used, so we are looking at other applications,” says Bandyopadhyay. “We are now working on identifying infection-resistant alloys using 3D printing techniques. This is not a solution looking for a problem. It is the opposite.”


Supersonic synthesis


Elsewhere, researchers have been working to improve the 3D printing process itself. A team led by Atieh Moridi, assistant professor at Cornell University’s Sibley School of Mechanical and Aerospace Engineering, is revolutionising the printing of implants by doing it without heating metal to its melting point. They achieve this by blasting powder particles together through a supersonic nozzle. The work of Moridi and her


Medical Device Developments / www.nsmedicaldevices.com


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