How to create low-cost, multicolor 3D-printed models

By Abraham Kim, staff writer

December 14, 2017 -- 3D printing multicolor models of organs, vessels, and bones can be much more affordable than it has been with traditional methods by using a new technique presented at the recent RSNA 2017 meeting in Chicago.

Using a relatively inexpensive desktop stereolithography (STL) printer and paint, researchers from the University of Pittsburgh and Yale New Haven Hospital created a multicolor 3D-printed kidney at roughly 1% of the cost of conventional approaches. They subsequently produced a diverse collection of models with this technique to help physicians prepare for various surgical procedures.

"At such a low cost, there's no reason not to use this [technique] for every similar case," Dr. Anish Ghodadra told attendees. "The take-home message here is that you can mimic the extensive capabilities of expensive PolyJet printers for a fraction of the cost."

Cutting printing costs

3D printing is rising in popularity for use in planning procedures and improving surgical precision. Creating customized, multicolor models is especially valuable because it allows physicians to visualize internal structures relative to overall anatomy. However, the high cost of more sophisticated 3D printers and lack of reimbursement continues to be a major barrier hindering their use in clinical settings.

Dr. Anish Ghodadra
Dr. Anish Ghodadra from Yale New Haven Hospital.

Printing multicolor models with clear components traditionally requires the use of a PolyJet 3D printer that tends to exceed $150,000 in price, as well as the use of raw materials that can soak up hundreds to thousands of dollars in charges per model, according to Ghodadra. One alternative to a PolyJet 3D printer is a low-cost ($3,500) STL printer, but such a machine can only print one color and use a single material at a time.

Seeking to boost the viability of 3D printing for preoperative planning, Ghodadra and colleagues identified a simple method they call "print and fill" to reduce the cost of creating multicolor 3D-printed models.

"The basic idea is that prior to this, if you wanted to create a model that had clear and colored components, e.g., a model of the kidney containing a tumor, you had to use expensive PolyJet 3D printers," Ghodadra told "With our print-and-fill technique, we model the components we want in color as hollow cavities and then create them with low-cost stereolithography printers."

As a test, the researchers produced 3D-printed models of kidneys from six different patients with renal cell carcinoma. First, they performed CT urography to obtain images of the kidneys. Next, they used open-source 3D modeling software for 3D slicing and segmentation; they left the kidney itself solid, while they digitally designed the other components -- including the collecting duct system of the kidney and the renal tumor -- to be hollow, with a small hole for access to the cavity.

After adjusting the scans, the group merged them together, sent the unified scan to a desktop STL printer, and 3D printed the kidney models. Finally, they used a syringe to fill the hollow areas with an acrylic water-based paint to give each part a distinct color, added a dollop of resin near the opening, and cured the additional resin with a handheld UV laser.

3D kidney model made from low-cost desktop stereolithography printer
A 3D kidney model made from a low-cost desktop stereolithography printer. The model comprises multiple components: a kidney (clear), a renal collecting system (yellow), and a tumor (blue). Image courtesy of Dr. Anish Ghodadra.

Reaching more patients

"Using this technique, you can create very nice kidney models that show the collecting system and the tumor for a much lower overall cost," Ghodadra said.

On average, generating the 3D-printed kidneys cost the team around $25 -- a hefty drop from the approximately $600 needed to make a similar model with a PolyJet 3D printer. The technique also took much less time, at a mean of 1.6 hours; processing with a PolyJet printer would have taken an estimated 10 to 20 hours.

"We're not limited to simple models like this, where we have one block with one color and another with a separate color -- relatively simple anatomy," he said. "You can actually create multicolor models that have very complex anatomy."

The researchers have already printed patient-specific 3D models of the ulnar nerve in baseball pitchers, as well as models of the liver for diverse procedures such as transjugular intrahepatic portosystemic shunt (TIPS) insertion and liver transplantation. They have received a growing number of requests from various departments in the hospital for models.

"We now use this technique to create low-cost models for many different specialties including interventional radiology, otorhinolaryngology, orthopedics, transplant surgery, and urology," Ghodadra said. "Because we can use this technique to create these complex models at 1% of the cost of traditional methods, we can reach many more patients."

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