Peek behind the paper: using ultrasound to strengthen 3D-printed titanium alloys
In this exclusive interview with Ma Qian (RMIT University; Melbourne, Australia), 3DMedNet takes a closer look at a novel 3D printing technique using ultrasound to strengthen 3D-printed alloys, which could be applied to the manufacture of medical devices and implants.
I am Ma Qian, a Distinguished Professor at the Royal Melbourne Institute of Technology (RMIT) University and Deputy Director of the RMIT Centre for Additive Manufacturing (both Melbourne, Australia). One of my major research interests is additive manufacturing of metal implants.
With my PhD students, research fellows and collaborators, I have published 245 peer reviewed journal papers and co-authored and/or co-edited four books published by Elsevier, including Titanium in Medical and Dental Applications.
Could you please tell us about the project covered in the recent 3DMedNet news piece, as well as any other related projects you may currently be working on?
The project covered in the recent 3DMedNet news piece is concerned with improving both the strength and structural homogeneity of 3D-printed titanium alloys by applying high-intensity ultrasound to the printing process. The work was funded by the Australian Research Council. It aims to improve the performance of 3D-pritned titanium alloys and other metallic materials for broad applications, including medical devices. Currently, I also work on a range of other projects, including the design and manufacture of potent antimicrobial metal surfaces; design of bone-like implants for additive manufacturing; fabrication of micro-to-nano-porous tantalum structures; and additive manufacturing of titanium materials for aerospace and defence applications.
How do you envision your work benefitting the medical field? Could the use of ultrasound in the 3D printing of titanium alloys benefit implants or other medical devices, for example?
The titanium alloy Ti-6Al-4V (in wt.%) studied in the project is a premier bone implant alloy by both conventional manufacturing and metal 3D printing. It was invented from 1952 to 1954 by Stanley Abkowitz in the US and first evaluated for implant applications in 1957, also in the US. Since 2007, custom-made Ti-6Al-4V implants by metal 3D printing have served patients worldwide, in excess of about 250,000 patients so far. The use of ultrasound can help to improve the performance of the 3D-printed Ti-6Al-4V implants and possibly the performance of other metal implants as well such as tantalum and cobalt-chromium alloys.
The incorporation of ultrasound into metal 3D printing is currently limited to the manufacture of small parts. In that regard, it could be easily applicable to the manufacture of a number of implants.
For example, in 2016, RMIT designed and printed Australia’s first Ti-6Al-4V humerus implant, which was successfully implanted in 2016. Technically, this implant can be printed with the assistance of ultrasound today. In addition, I think most dental implants can be printed in the same way.
What challenges have you faced with including ultrasound into your 3D printing technique?
The main challenge is how to introduce the ultrasound energy into the molten metal during the printing process.
Currently, the metal is deposited or printed directly on the radiating face of the sonotrode, which is made of Ti-6Al-4V (it can be made of other metals such as stainless steel or niobium). This appears to be the most direct way of introducing the ultrasound energy into the molten metal. We are in the process of exploring other options in order to make the process more flexible.
What challenges with 3D printing does ultrasound help to overcome?
To help to overcome two major challenges:
(i) to convert the long and coarse columnar crystals along the build direction during 3D printing into fine, uniform and randomly distributed crystals,
(ii) to improve the performance consistency of the printed parts.
The third potential challenge to overcome, which we need to confirm experimentally in the future, is that the process may be able to reduce the residual stress in the as-printed part, which has been a concern for many applications.
What’s next for you and your research?
We are in the process of designing a more powerful ultrasound system for our 3D printing process, the power of which would be four times what we have used. In addition, we aim to increase the part size to 100 mm in diameter for more detailed evaluations. At the same time, we intend to apply the process to 3D printing of a variety of non-metallic materials.
Where do you see medical 3D printing in 5–10 years time? How could research such as yours affect this?
I think we will see more and more breakthroughs in the design of implants for 3D printing towards achieving both real bone-like structures and functionalities in order to better serve those who need bone replacements or repairs so that we can minimize or even avoid revision surgeries in the future. This is particularly important for those who have their primary procedures in their 60s. Statistics from the Australian Orthopaedic Association released in 2018 indicate that the cumulative percentage survival of patients aged 80 years with primary procedure and their first revision procedure can be noticeably different. For example, the 90-day mortality for this group of patients is 43/1000 for revision procedures and 11/1000 for primary procedures. The former is almost four times the latter! I think eventually we may be able to avoid revision procedures.
We will get there. I would be over the moon if my research were somehow useful in the course of realising this goal.