Layer by layer

Creating a prosthesis with 3D printing

Brittany Ballinger’s connection to MSOE isn’t obvious. She isn’t a student or alumna; in fact, the 28-year-old Appleton-native has never stepped foot on campus and she currently lives in San Francisco. But being unable to tell what role MSOE has played in Ballinger’s life is exactly the point.

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The RPC prototype next to Brittany Ballinger’s finished silicone prosthesis.

Ballinger was born with microtia, a congenital condition where the external ear is underdeveloped. As a result, she has been wearing a prosthetic ear since she was 10 years old. The prosthesis she is currently wearing was created by way of additive manufacturing technology through a partnership between MSOE’s Rapid Prototyping Center (RPC) and Medical Art Resources—a Milwaukee-based prosthesis fabricator.

The main business of Medical Art Resources, established in 1988, is in designing custom facial, digital and breast prosthetic devices. “All of the prostheses are made by hand,” said business founder Julie Jordan Brown, a certified anaplastologist. Anaplastology is an allied health profession dedicated to the art and science of restoring a malformed or absent part of the human body through artificial means.

“Our ear prosthesis are individually designed to restore aesthetic balance and symmetry to the face, providing support for eye glasses and hearing devices,” said Megan Spindel Thomas, a certified clinical anaplastologist. “When the ear canal is present, the prosthesis can also improve hearing by directing sound toward the ear opening.”

Though very durable, over time prostheses undergo a certain amount of wear and tear and eventually need to be replaced. An ear prosthesis has a typical life span of two to three years. During the course of her life, Ballinger has had 11 different ear prostheses.

“Creating a prosthetic ear from scratch typically takes three weeks, with the client coming in once a week,” Brown said. For clients who move out of state and return to have a new prosthesis fabricated, as Ballinger does, the process is compressed into four labor-intensive days. Brown’s search for improved efficiency led her to the RPC.

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Daniel Pulipati, a mechanical engineering graduate student who works in the Rapid Prototyping Center, scans the positive reproduction.

For 25 years, the RPC has provided expertise about and access to equipment and emerging technology that would otherwise be cost prohibitive for most companies to have internally. “We understand the how, when, where, and why, to implement emerging technologies,” said Vince Anewenter, RPC manager of operations. One of these technologies is additive manufacturing, or 3D printing – a process by which digital 3D design data is used to build a component up in layers. Read more about the RPC.

RPC Project Manager Jordon Weston, ’10, ’15 worked with Medical Art Resources to determine whether there was a place for this type of technology in prosthesis design and fabrication. “Julie explained their process to me and I looked for ways we might be able to help.”

The first step in the process of creating a prosthetic ear is taking an impression of the in-tact ear. The mold is then used to create a cast, or a positive reproduction. Anaplastologists use the positive reproduction to hand-sculpt a mirrored wax prototype of the absent ear—a time consuming and meticulous process that captures not only the ear’s shape but also its texture.

Instead of hand-sculpting the mirrored image of Ballinger’s intact ear, the positive reproduction was sent to the RPC, where graduate student and RPC research assistant Daniel Pulipati scanned the model into Computer Assisted Design (CAD) software. “The Creaform Handy SCAN 3D™ collects millions of data points off the surface of the object, which are then used to reconstruct an exact digital copy of the physical object,” Weston said. The digital copy is then mirrored. The data is transferred to an appropriate printer – in this case the 3D Systems ProJet® 660Pro, which selectively jets a binding agent into thin layers of a fine plaster powder to create an exact physical model.

“The additive manufacturing saved us from a four-plus hour sculpting session and it offers improved accuracy,” Brown said. “Although we do our best when we sculpt by hand, it’s difficult to capture the unique, organic form of each person’s ear completely accurately. The 3D print guarantees that details, dimension and anatomical relationships are perfectly replicated in our wax sculpture.”

The process continues

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Jessalynn Smith, a biomedical engineering major and employee of the RPC, uses the Projet®660Pro 3D printer to make the prototype.

After the prototype arrives at Medical Art Resources, it is cast to create an exact copy in wax. Because human faces are not perfectly symmetrical – especially when impacted by congenital malformation or cancer surgery – the wax reproduction will still need to be altered and adapted before a final prosthesis made from silicone can be fabricated.

“After I am fitted, they ask me to yawn and they watch me while I eat to see how it moves with my face,” Ballinger said.

All told, Brown and Thomas devote dozens of hours to studying the details of Ballinger’s intact ear and the colors and contours of her face. This information is used to achieve not only the perfect fit, but the most natural appearance for the prosthesis. Health-grade silicone in as many as eight different color tints are used to create the prosthesis so it blends with Ballinger’s skin tone.

“There is definitively an art to it,” Ballinger said. “It’s functional art.”

The finished wax sculpture is used to make a mold into which the pigmented silicone is painted in layers to produce the finished prosthesis. The silicone is cured and carefully trimmed before the prosthesis is fitted to Ballinger’s cranial implants and magnetically attached.

“We see 3D printing of the model ears as just a starting point – or launching point for other ways to incorporate that technology into our practice,” Brown said. “There is so much potential to improve our processes and ultimately the outcomes for our patients.”

3D technology also offers the advantage of increase throughput. The time needed to scan and print three models for three different patients is only marginally longer than scanning and printing just one. The RPC has created 15 prosthetic models for Medical Art Resources so far.

“It’s exciting to be a part of it,” Weston said. “Being able to utilize 3D printing to improve someone’s quality of life is very rewarding.”

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