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.

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