May 9, 2016 | By Alec
Though it will likely take a few years before we’ll see 3D bioprinted organ implants being used in hospitals, 3D printed titanium orthopedic devices are already a reality. Thanks to the titanium’s excellent mechanical attributes and infection-resistant properties, it’s a perfect 3D printing material for knee and hip implants. And we could be seeing these 3D printed implants a lot more often in the near future, as a research team from Agency for Science, Technology and Research (A*STAR) in Singapore has just found a way to greatly improve their stress absorption levels. Their solution? To use a 3D printable titanium-tantalum alloy mixture, rather than the currently used titanium-aluminum mixture.
This new innovation has been developed by Florencia Edith Wiria, of A*STAR's Singapore Institute of Manufacturing Technology (SIMTech), and Wai Yee Yeong of the Singapore Centre for 3D Printing (SC3DP), which is part of the Nanyang Technological University. Their findings were recently published in the Journal of Alloys and Compounds, in a paper entitled ‘Selective laser melting of titanium alloy with 50 wt% tantalum: Microstructure and mechanical properties’.
Through their collaboration, they sought to find material solutions to improve biomedical titanium products. For while titanium implants (which are actually made from titanium-aluminum powders) have fantastic properties, recent studies have shown that this is not an optimal solution. In particular, concerns have developed over the long-term effects of aluminum on the human neurology. And while titanium could be used as a stand-alone material, mixtures are actually mechanically superior.
These shortcomings led the Singaporean researchers to tantalum. Like titanium, it is biocompatible and has excellent material properties. Its only downside is that it features an absurdly high melting point of over 3,000 degrees Celsius. This means that it wasn’t, and still isn’t, economically viable to turn the rough elongated tantalum particles into the finely dispersed microspheres which are necessary for Selective Laser Melting 3D printing.
But the A*STAR researchers discovered that melting the particles might not even be necessary. After mixing the materials together and leaving them for several hours, they observed that the titanium-tantalum mixture could be spread much more evenly for SLM 3D printing than just a tantalum powder. Several experiments revealed that the mixture was not just 3D printable, but also retained the titanium's spherical shape. “The titanium powder acts as a rolling medium,” Wiria said. “It pushes the tantalum powder along and makes the processing by SLM 3D printing possible.”
What’s more, the resultant mixture proved to be even more potent than titanium-aluminum. For X-ray and imaging technology tests showed that the addition of tantalum promoted and stabilized the formation of strong, laminar titanium grains. This was achieved through a 3D printing process involving a ‘checkerboard’ laser pattern that melted the powder in alternate up/down or side-to-side movements, which greatly reduced thermal stress on the materials.
The researchers believe that this novel titanium-tantalum alloy solution could pave the way towards a far wider range of personalized biocompatible implants, which will be far more resistant to stress than the current generation of 3D printed titanium devices. For while current materials are too elastic and don’t transfer stress to neighboring bones very efficiently, tantalum is expected to greatly strengthen the titanium parts. “These alloys are specifically designed for orthopedic applications, and even have the potential to show a type of 'shape-memory' after being deformed,” says Yeong. “This opens up the possibilities of printing personalized devices to improve patient care.” Could this be the solution the medical world has been waiting for?
Posted in 3D Printing Technology
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