Todd Pietila May 27, 2016

A talented team of engineers at Michigan Technological University has developed a method for creating a patient-specific 3D-printed cast to treat bone fractures of the forearm and wrist. The project leverages Materialise's Lightweight Structures Module which was used to create the high porosity lattice structure of the casts. These were then 3D printed at Materialise’s production facilities for human testing.

patient-specific, lightweight 3D-printed cast

Orthopaedic casts are used for the treatment of fractured wrists as they stabilize and restrict the motion of the broken bones. Current casting methods are rudimentary and use a soft inner cotton layer together with a hard outer plaster or fiberglass layer. These casts have many issues as they are bulky and uncomfortable; if moisture enters the cast, they can become extremely itchy and can cause skin irritation to occur. Because of the prevalence of wrist fractures, there is a need for a more effective and convenient treatment of these fractures.

The engineers started by taking a 3D surface scan of the patient’s arm, which yielded the subject-specific geometry. The scanning method needed to be cost-effective and without radiation, which eliminated imaging procedures such as magnetic resonance imaging and computed tomography (CT) scanning. Bearing these requirements in mind, an open-air photogrammetric scanner was used. The photogrammetric scanner consisted of a sensing element, and an XBOX 360 Kinect, which was spun in a 360 degree arc around the subject’s arm to generate a 3D image of the patient’s geometry.

3D-printed cast: scan of the subject's surface geometry
Scan of the subject’s surface geometry obtained via the open air photogrammetric scanner

After acquiring the 3D model of the patient’s arm, the digital file was imported into 3-matic, part of the Materialise Mimics Innovation Suite. In 3-matic, the structure of the cast was designed to fit the patient’s anatomy. In addition, the Lightweight Structures module in 3-matic enabled a porous structure to be incorporated into the design. This allowed for a strong reduction in weight while preserving the necessary structural requirements of the cast. The final cast designs were printed from PA 2201 via laser sintering at a Materialise production facility.

Designing a lightweight 3D-printed cast in 3-matic
Lightweight cast design in 3-matic 10.0

Using both mechanical benchtop testing and Finite Element Analysis, the final 3D-printed cast prototype was verified to ensure that it would provide the appropriate stiffness and protection for the fractured arm. Four patients volunteered to further test the cast and collect user feedback on the experience.

Dr. Jingfeng Jiang from Michigan Technological University commented:

“The Lightweight Structures Module enabled us to rapidly design and create prototypes of these orthopedic casts given any patient-specific wrist geometry. Furthermore, the software allowed us to export the virtual design directly to ANSYS for FEA analysis, so that we could make sure the model was strong enough to withstand different loading conditions.”

Michigan Tech team presenting their 3D-printed cast research

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