The making of a 3D printed rehabilitation orthosis

There’s still a lot of untapped potential for helping the patients with cases of mild and partial paresis who need lighter and more comfortable 3D printed rehabilitation orthosis which won’t harm their existing but weak extremities.

Eliza Wrobel faced this problem during her Biomedical Engineering studies under Bogdan Dybala, PhD. Eng. at the Faculty of Mechanical Engineering of Wroclaw University of Technology. She was asked for help by a 33 years old man suffering from tetraplegia (the limb paresis) after being in an accident a few years back. He needed a light, yet durable orthosis that could help him grab objects during the rehabilitation and other physical activities as he couldn’t hold even the lightest dumbbells. In order to play his favorite table tennis, someone had to tie a paddle to his hand which wasn’t too comfortable.

The 3D printed rehabilitation orthosis had to answer the patient’s needs which meant that Eliza have had to reverse engineer it. She started with making a plaster cast of the patient’s hand which was later filled with liquid ceramic mass and supported by a metal bar inside, so the model itself was easier to hold. After 24 hours, the hand’s model was grinded and then 3D scanned using the ATOS II machine available at Wroclaw University of Technology.

With a 3D model of the patient’s right hand ready, the actual designing of the orthosis have started. In CAD software Eliza tried different mechanical solutions for the rehabilitation device. The biggest challenge was to bring together both the device and the flesh. Solutions used in prosthetics could harm the man’s tissues while standard orthosis used for broken bones would keep his hand in only one setting – open or clenched.

Answer was found somewhere in between. The husk of the orthosis had to be closely fitted to the wrist, while the fingers were supported by smaller parts imitating their joint-structure – 2 joints for the thumb and 3 joints in every other finger. To connect these parts into a working device, Eliza added a series of lever mechanisms controlled by one big lever at the top of the husk. Pressing the main lever accelerated the hand grip while pulling it away returned the fingers to their rest state.

The design of the rehabilitation orthosis consisted of over 70 different parts. They were all exported as an STL files, checked for any shortcomings in Netfabb Basic and then imported to the Voxelizer software in order to prepare them for 3D printing. The parts for the orthosis were later 3D printed on ZMorph 2.0 S hybrid 3D printer with single head extruder 1.75mm using ABS filaments of different colours.

ZMorph’s precision and the quality of the prints allowed Eliza to minimise the number of non-printed parts in her device. Small 3D printed pins were used to connect the smaller leverages and finger casings to each other while the main lever was connected with the husk with a 3D-printed latches. Velctro strap was added later in order to fasten the orthosis around patient’s hand.

With the help of ZMorph 2.0 S hybrid 3D printer, Eliza was able to quickly fabricate, improve and finalise a working prototype of her design. Desktop machine proved to be a quick, reliable and inexpensive alternative to outsourcing prototyping services based on industrial 3D printers. Thanks to the durability of ABS-based 3D parts printed on the ZMorph, the prototype can be used in a limited capacity by the patient during his physical activities.

Further works on this student’s idea could soon result in a wide production of custom-made 3D printed rehabilitation orthosis for patients with a hand paresis and thus significantly improve their everyday life.