Radiopaque 3D printing

Our ‘radiopaque material’ paper has been published in 3D Printing and Additive Manufacturing journal (and here is the link). The X-ray of the hands was printed on a full page within the journal, just before the article. If that wasn’t enough for us, they used our work on the front cover for the December edition which is still sinking in months later!

December 2020 edition of 3D Printing and Additive Manufacturing journal cover showing our 3D printed hands

The term ‘radiopaque‘ describes a material that is visible under X-ray imaging. ‘Radiolucent’ describes a material that is invisible to X-rays.

Background

First, I will give some background as to why we developed this material.

In general, plastic-based 3D printing materials are not clearly radiopaque. This can cause issues if 3D printed anatomical models are being X-rayed/CT scanned or instruments are being used under X-ray/fluoroscopy.

The paper details how we created and 3D printed a plastic-based radiopaque material. This material shows up under regular X-ray imaging as well as CT imaging, and could potentially be visible using fluoroscopy and MRI, but have not checked these experimentally.

One point that I must make, is that radiopaque 3D printing is not totally new. Many papers have made anatomical models with FDM printers (that use thermoplastic filament) that have regions of varying radiopacity. However, the resolution for this technology is much less than that of resin-based 3D printers. Smallest features can be as large as 1mm compared to 0.1mm for some resin-based printers. And since resin-based 3D printers have higher resolution, they generally come with more limitations than FDM printers, making high-quality radiopaque multi-material 3D printing difficult. Some research groups are adding radiopaque material to PolyJet 3D printed parts after printing, however, the quality does not compare to printing with radiopaque resin.

For this project, we used a Connex 500 multi-material 3D printer (I have described this in an earlier blog post here) so that radiopaque material could be printed within non-radiopaque materials. This “multi-material” feature was perfect to demonstrate the new material. The base material for this project was MED610, a clear, biocompatible material. The second was TangoBlackPlus, which is a black, rubber-like material. We added radiopaque powder to MED610 in order to create the radiopaque ink.

MaterialDescription
MED610Clear, biocompatible material Rigid when cured
TangoBlackPlusSoft, black material Rubber-like when cured
Radiopaque materialWhite, rigid material when cured. Visible under X-ray.

Proof of concept

As a proof of concept experiment for this radiopaque ink, we 3D printed a hand with radiopaque bone. We could have selected any feature for this, but our Connex 3D printer came with a hand/bone demo model so we decided to make use of this. TangoBlackPlus was used for the soft tissue and the radiopaque material represented bone. These 3D printers are not made for custom material so we had to trick the 3D printer that it was actually printing commercially available material (which could actually invalidate the 3D printer warranty). Since TangoBlackPlus is visually opaque, the bones could only be seen under X-ray, forming an ideal proof-of-concept experiment:

Above: X-ray of the two hands, one with radiopaque bone and the other with MED610 bone.
Below: Photograph of the two hands. The hands are completely indistinguishable in the photograph but clearly different under X-ray.

Limitations

This project was overall successful in 3D printing radiopaque material but there were also some limitations. The temperature of the print head accelerates the powder settling out of suspension. The hand took four hours to print and so settling was not a major issue. As well as settling, the powder did block up the print heads slightly which caused some uneven layers. We developed a cleaning method to restore it after each ‘experimental print’ . Overall, this proof-of-concept experiment was successful and the material now needs to be further developed to reduce these limitations.

Applications

A radiopaque 3D printable material has potential applications in a wide variety of industries, including med-tech, aerospace, automotive and general manufacturing. Since our research group focuses on medical devices, I will go into greater detail on the medical applications for this material.

  1. Anatomical models: More realistic anatomical models can be produced, which would be very similar to the patient’s original body part under X-ray. This can be used to practice procedures on a patient-specific model or even teach medical students how to perform procedures under X-ray imaging such as fluoroscopy.
  2. Calibration for medical imaging: Any medical imaging technique that makes use of X-rays also causes potentially harmful radiation to interact with the patient’s body. New imaging equipment, for example a CT machine, could make use of anatomically-accurate phantoms for calibration, as well as testing new machine features. This would prevent any unnecessary radiation exposure to patients. A 3D printed limb or torso with controlled radiopacity could be used for daily calibration on existing machines.
  3. Medical training: Rare cases, such as complex injuries, could be 3D printed and used for diagnostic and therapeutic exercises for medical students. Standardised phantoms could be used to train radiologists to make diagnoses from X-ray or CT imaging.
  4. Better visibility of plastic-based devices within the body: Currently, instruments/implants that do not show up under X-ray have marker bands added so they are visible. Polymer/plastic-based medical devices, such as catheters, could be 3D printed in a single pieces including a radiopaque marker band which could allow easier manufacturing of these devices since the part is made in a single step.

Visuals

I have linked two YouTube videos here that are useful for better visualising this exciting technology.

The first is a full-scale CT reconstruction of the hand and the control hand (with MED610 bones).

The second video shows a microCT reconstruction of the experimental hand only. This video has a smaller field of view and so the thumb did not fit within the area being scanned. The microCT shows greater details such as the streaky layers that have already been mentioned as part of the limitations.

September Blog: My busiest month since starting my PhD

Writing these blogs is a catch-22. The more time I have to write the blogs, the less I have to write about. When I have loads of updates and events to write blogs on, I barely get a chance to sit at my desk to write them. This was definitely the case during the month of September as I have been so busy and am only getting around to writing the September blog now.

Since my last blog at the end of August, I have started studying a new module, teaching tutorials/labs as a teaching assistant, attended a 3D printing workshop, travelled to a manufacture exhibition, I did a school visit and set up an Instagram page for our 3D printer. September has definitely been my busiest month since starting the PhD!

I will start with the college-related updates. As I am doing a structured PhD I am required to study and pass exams for two taught modules (at least two, and more if I want to). This semester I am taking ‘General Microbiology’. I haven’t studied biology since the Leaving Cert and at that, we only spent one week studying microbiology. I am actually enjoying the module more than I anticipated. The lecturer does his best to make the classes interesting (which I imagine is difficult with 200+ students in the lecture) and the labs seem easy so far with a focus on understanding core concepts. I think this is important as many students (including myself during my undergrad) don’t understand ‘the basics’ of modules they take in college, even though they can pass the exam.

As part of my contract, I can teach up to six hours a week. This semester I am assisting with the materials half of a product design module. I sit in on the classes and give thoughts on student’s assignments that were assigned the previous week. As part of this I am delivering two lectures; one on ‘environmentally-friendly alternatives to plastics’ and a second on ‘Additive manufacturing/3D Printing’. I have been preparing the presentations for these and my lectures will be delivered in the next two weeks. I have been collecting samples from different 3D printing technologies this month to pass around the class as I talk through the different types.

Tensile samples printed on an Ultimaker FDM 3D printer

I really feel that I have been away from the office for the majority of September. I attended a ‘Point Of Care 3D printing’ in St. Thomas’ Hospital London. This event was sponsored by Materialise. I flew from Shannon to London the night before, stayed in a hotel and flew home again straight after the conference. I met some very interesting people at this event, some were in early stages of their career, like me. It was nice to chat to people in the same boat as me at a conference as I have felt much younger/much more inexperienced than others that I have chatted to at conferences in the past.

A few months ago, a science/physics teacher that I am friends with asked me to visit her school and talk to some of the students about 3D printing and what I do. I feel that the visit went really well, with loads of interesting questions from the class. I was actually surprised at the level the questions were at – it showed that they had understood majority of what I had been talking about and were genuinely interested in the technology. I hope they enjoyed the visit as much as I did.

Last week I attended the TCT show 2019 (Design-to-Manufacture Innovation). This exhibition was not just for 3D printing but Majority of people there were demonstrating their 3D printers, new 3D printing materials as well as launching brand new 3D printers. For this event, I travelled over to Birmingham and back in the same day. This is really only possible because the event is in the NEC, which is a two minute train from Birmingham airport. I flew back to Dublin and stayed in Dublin as I had three training days in the National Children’s Research Centre (NCRC, Crumlin) directly after this trip.

The NCRC part-fund my PhD, along with the Irish Research Council. My PhD mentor is the Research and Operational manager for the NCRC. She organised these training days for me and the other students that receive funding from the NCRC. As part of the training we covered grant writing, GDPR, health research regulations (HRRs), lay abstract writing, biosample storage, media training and good clinical practice training. I have mentioned this in previous blogs, but I really think now is the best time to get these training sessions done as I am just beginning my research project and these skills will be so important. I got to meet the other students who all had completely different PhD projects to mine. This was a great networking opportunity as well as being able to compare what is different in each of our universities. The others were from UCD, Trinity, NUIG and RCSI.

As well as everything else, this month I have also set up an Instagram account for our 3D printer/ my PhD project. We decided to name the printer Grey, so the Instagram account is simply named ‘Greys3DPrinting‘. I find the best way to explain the technologies are with time-lapses of parts being printed. As well, 3D printed models are so easy to understand when you can hold them and look at them from a range of angles. For this exact reason, I think it is worth setting up an Instagram account to upload relevant photos and videos of my project to. I will document interesting prints here (as well as trips to conferences and events) in real time but I will continue to write a blog once every month or so.