Researchers from Ontario-based Mohawk College and McMaster University have become the first to investigate the suitability of a titanium alloy, Ti-5553, for 3D printed bone implants. As it stands, most 3D printed implants are created using Ti64 powder, but the research team wanted to see if the unconventional alloy’s topography, coupled with complete design freedom, could encourage osseointegration – the ingrowth of bone into an implant.
Improving osseointegration
According to the study, certain compositional, topographical, and morphological modifications to bone implants have been known to increase the chances of osseointegration. When osseointegration occurs, bone implants are more likely to be successful in the long term as the growth of the bone cements them and improves structural integrity. With this in mind, the researchers moved forward, comparing Ti-5553 to the long-established Ti64 alloy.
Titanium alloy bone implants
An EOS metal 3D printer was used to manufacture geometrically simple samples of both titanium alloys with the SLM process. After fabrication, the researchers cleaned the samples in alcohol with the aid of ultrasound, removing all of the powder without altering the surface of the prints.
The Ti-5553 samples were first subjected to tensile strength testing using a universal testing machine. Cyclic loading was performed until the samples eventually fractured and the results were recorded in triplicate. Averages for the elastic modulus, yield strength, ultimate tensile strength, and ductility were calculated for the alloy. The results showed tensile strengths almost identical to those of additively manufactured Ti64 parts, which were known prior to testing. The Ti-5553 specimens also displayed ductile fractures, indicating that the process parameters that the researchers tested were successful in producing a uniform structure in the build direction.
After confirming their method of 3D printing the titanium alloy was mechanically suitable for medical implants, the team tested the new alloy’s biological compatibility. Saos-2 (human bone) cells were cultured on both the Ti64 and Ti-5553 specimens after anodization at 40V for 30 minutes. After a whole day, the cells were stained, dried, and prepped for SEM observation to determine the level of biological activity on the surface of the alloys. The cells displayed extension and growth on both the flatter areas of the specimens and the nanotubes found within the parts. The researchers concluded that the Ti-5553 specimens performed very similarly to the established Ti64 specimens, suggesting a strong potential for Ti-5553 as a 3D printed bone implant material.
Further details of the study can be found in the paper titled ‘Ti-5Al-5Mo-5V-3Cr Bone Implants with Dual-Scale Topography: A Promising Alternative to Ti-6Al-4V’. It is co-authored by Chiara Micheletti, Bryan E. J. Lee, Joseph Deering, Dakota M. Binkley, Simon Coulson, Asad Hussanain, Hatem Zurob and Kathryn Grandfield.
The 3D printing of medical implants is not limited to engineering-grade metal alloys. Last year, FossiLabs, a US-based medical 3D printing start-up, commenced work on its FFF 3D printed bone-like scaffolding structures using the high-performance engineering polymer, PEEK. Elsewhere, on the ISS, 3D Bioprinting Solutions, a Russian bio-technical research laboratory, 3D bioprinted bone tissue in zero gravity. Using the Organ.Aut 3D bioprinter, the lab’s researchers hope to one day create real bone implants for astronaut transplantation on long interplanetary missions.
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Featured image shows the particles on the surface of the as-printed titanium samples. Image via McMaster University.
