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South Korea: 3D Printed Myolectric Hand Orthotics Improve Hand Function for Spinal Cord Injury Patients

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In the recently published ‘Development of 3D-printed myoelectric hand orthosis for patients with spinal cord injury,’ South Korean researchers propose the design for an innovative new wearable medical device meant to assist spinal cord injury patients in achieving greater hand function.

While researchers and manufacturers around the world have engineered numerous orthotics and prosthetics—from those meant for the ankle and feet to the hands and arms—the researchers point out the motivation behind their study as so few upper extremity orthoses have been created for successful functionality in patients. Previous research has focused on materials and strength but not actual affordability and ease in ease for patients.

The orthosis created for this study functions via customized electromyography (EMG) signals which send input to the controller, all of which can intuitively understand user intention for patients with cervical SCI. The team designed the parts in SolidWorks, and then they were 3D printed on a Moment2, using PLA. The device costs around $230 to make, and that is supposed to decrease further in the future.

The orthosis is made up of the forearm cuff, hand, and finger ring parts. The cuff is also comprised of a dorsal and volar forearm splint, featuring a linear motor controlling the wrist extension.

Schematic design of the hand orthosis. a Ring part. A total of 8 ring parts were printed for each phalange of the thumb, index, and middle finger. b Hand part. c Dorsal forearm splint. d Volar forearm splint. Note that cable guide structures were designed to the volar side of each finger ring part and hand part to guide the nylon thread.

“When the wrist is extended by the linear motor, the nylon thread tightens, which strengthens the tenodesis grip. Thus, wrist extension leads to the simultaneous flexion of the interphalangeal and metacarpophalangeal joints of each finger including thumb,” state the researchers.

Users can grasp objects when the motor is activated—emphasizing one of the main features that sets this device apart as more people can use the device—especially patients with more severe SCI and lack of wrist control.

Each motion of the 3D-printed orthosis. a When the linear motor is activated by sEMG signals, the wrist is extended, which causes the tenodesis grip. Also, the nylon thread connected to the tip of each finger ring part is tightened as the wrist extended, which enhances grip strength. b When the motor goes back into the place, the extended wrist and tension of the nylon thread are released, and the hand becomes in a neutral position. c-e A subject is using the orthosis to pick up a pop can, dice, and wooden block, which were used in TRI-HFT. f Top view of the orthosis. g Bottom view of the orthosis. The arrows indicate nylon thread that connects each finger ring and volar forearm splint.

The researchers employed an Arduino microcontroller board with a small control unit meant for portability at 10 cm × 5.3 cm × 1.7 cm and 81 g.

Overview of the control scheme. sEMG signals recorded from the surface electrodes were processed through some acquisition steps such as amplification and band pass filtering in order to improve the signal quality. Then, RMS values of the processed sEMG signals were compared with the customized threshold. The Arduino board classified whether to operate the orthosis according to the magnitude of the RMS value.

Ten patients with chronic cervical SCI—nine men and one woman all in the 31- to 65-year-old range—participated in the study from March 27th, 2019 to April 31st, 2019.

Overall, as the researchers worked with the participants, they found that the orthosis was able to ‘significantly improve’ hand function for people for cervical SCI, and they received good feedback regarding usability of the device. The researchers also expect even better results as the individuals participating continue to adapt to the system.

“Furthermore, if we optimize the orthosis in terms of volume and adjustments, it can be used in the clinic soon and extended to other neurologically injured people, such as stroke or brachial plexus injury patients,” concluded the researchers, following the study.

“It is still an early stage of research, and some areas need to be improved. However, this 3D-printed myoelectric hand orthosis seems to be cost-effective and promising to utilize as an alternative to conventional devices. We hope that this study will be the cornerstone of research on assistive devices using 3D printing technology.”

[Source / Images: ‘Development of 3D-printed myoelectric hand orthosis for patients with spinal cord injury’]

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