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Modifications Could Render 3-D Printed Prostheses More Functional, Comfortable

ORLANDO, Fla. — Researchers at Florida Atlantic University have developed an open-source device for variable ulnar eminence that could increase patient comfort, dexterity and ability to perform activities of daily living.

Chad Coarsey, master’s degree student in biomedical engineering at the university and researcher of the study, presented at the American Academy of Orthotists and Prosthetists (AAOP) Annual Meeting and Scientific Symposium.

Coarsey, who has a congenital amputation of the left hand and variations in ulnar head prominence, acted as the study’s sole participant. C. Perry Weinthal, master’s degree student in electrical engineering at the university, was the lead researcher of the study.

Methods and results

Using computer-assisted design (CAD) software packages and open-source models, Coarsey and Weinthal built a modified version of the Raptor II, a 3-D printed prosthetic hand design provided by e-NABLE. Measurements for ulnar variance were taken in zero rotation to adjust the scale in the CAD program. Total print time was 12 hours.

Chad Coarsey
Chad Coarsey

“[The advantage of] 3-D printing is that we can create devices, layer by layer, and make them customizable to any user,” Coarsey said. “With CAD, we have the ability to isolate and modify certain portions of the device on a microscale [and] replicate it many times.”

The team performed various stress tests and a preliminary series of contractions by flexing palm muscles. After a 3-month to 6-month period, they performed the same tests and measured the amount of time that the muscles took to fatigue.

Results showed that after 3 months to 6 months of wear, there was a longer period of time until muscle fatigue, indicating conditioning to some extent, Coarsey said.

Findings also showed limited ambidexterity in the study participant, whose anatomy was hindered by the prosthesis design, as well as muscle discomfort as a result of extensive use.

Modifications

Following further observation, researchers opted to remove material from the ulnar prominence of the device. Additional padding and cushioning including moleskin, wool packing and adhesive blue foam padding applied to self-grip straps were included and led to an increase in comfort while preventing skin breaks and frictional damage. Recessed modifications were designed using CAD software.

“Using the specific measurements of my anatomy, we were able to go back to the CAD and make such modifications to optimize the process,” Coarsey said. “[We] recessed the material and within 20 minutes were able to start the print again and get a new hand out.”

Using the adjusted device, Coarsey was able to lift objects of up to 30 lbs. Subsequently, he showed greater dexterity and was more comfortable with the additional scale and material recess. He also showed greater ability to complete routine tasks such as steering wheel control and bicycle riding. In addition, he began running his basic lab experiments with assistance provided by the device.

Future leanings

The researchers believe with additional padding and design modifications, they can further decrease discomfort and lower the risk of skin breaks and ulceration.

Patient growth or changes in medical conditions often present a challenge when fitting prostheses, but Coarsey said this design can easily be modified, replaced or updated as needed by the user. He said the personalization and input by the user also could assist in compliance.

“The idea is that we are able to print these devices that are custom-made for the user from an open-source [design] and then put them together,” he said.

He added, “If the user is growing in size, we are able to go to the CAD model, take the same design that is already fit for them and scale it up to a size that would fit. Need another copy in a different color? Reprint it.”

This allows for immediate, customized repair, Coarsey said, and “it gives a personal touch for the patient because they are a part of the process and feel that this is something they created.”

The team is looking for ways to continue to build and refine the device. Coarsey sees it becoming simpler and more affordable, closing the gap between the availability of personal adaptive devices and those in need of them.

Coarsey and Weinthal are interested in working with prosthetists and clinicians to ensure that patient safety is incorporated, Coarsey said. They hope their work will become another practical option for management of hand amputations. – by Shawn M. Carter

Disclosure: Coarsey reports the research was supported by funding from Florida Atlantic University and the Quantum Foundation of Palm Beach County.

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