###### Abstract  
This paper investigated the feasibility of using 3D printing processes, specifically material extrusion (MEX) and vat photopolymerization (DLP--Digital Light Processing), to produce customized wrist-hand orthoses. Design, printability, and usability aspects were addressed. It was found that minimizing printing time for orthoses with intricate shapes, ventilation pockets, and minimal thickness is difficult. The influence of build orientation and process parameters, such as infill density, pattern, layer thickness, and wall thickness, on printing time for ten parameter configurations of orthoses in both ready-to-use and flat thermorformed shapes was examined. The findings revealed that the optimized orientations suggested by Meshmixer and Cura (Auto-orient option) did not reliably yield reduced printing times for each analyzed orthoses. The shortest printing time was achieved with a horizontal orientation (for orthoses manufactured in their ready-to-use form, starting from 3D scanning upper limb data) at the expense of surface quality in contact with the hand. For tall and thin orthoses, 100% infill density is recommended to ensure mechanical stability and layer fill, with caution required when reducing the support volume. Flat and thermoformed orthoses had the shortest printing times and could be produced with lower infill densities without defects. For the same design, the shortest printing time for an orthosis 3D-printed in its ready-to-use form was 8 h and 24 min at 60% infill, while the same orthosis produced as flat took 4 h and 37 min for the MEX process and half of this time for DLP. Usability criteria, including perceived immobilization strength, aesthetics, comfort, and weight, were evaluated for seven orthoses. Two healthy users, with previous experience with traditional plaster splints, tested the orthoses and expressed satisfaction with the 3D-printed designs. While the Voronoi design of DLP orthoses was visually more appealing, it was perceived as less stiff compared to those produced by MEX. 3D printing; wrist-hand orthosis; material extrusion; direct light processing; process parameters; usability assessment; build orientation; design +
Footnote †: journal: Applied  
1 Faculty of Industrial Engineering and Robotics, National University of Science and Technology Politechnica Bucharest, 060042 Bucharest, Romania; [EMAIL_ADDRESS]  
2 Department of Orthopedics, Colletina Clinical Hospital, 202125 Bucharest, Romania; [EMAIL_ADDRESS]  
2024 14 6157 1  
known also as 3D Printing--3 DP) particularly advantageous in this context. Additionally, it offers the necessary design flexibility to enhance the comfort of these devices and promote patient adherence to wearing them. The proper fit of an orthosis to the limb is essential, as an ill-fitting one can cause discomfort, pain, and skin issues, leading the user to discontinue using the orthosis prematurely, even before completing the rehabilitation program. Therefore, static 3D-printed wrist-hand orthoses (3 DP-WHOs) are a modern alternative to the traditional immobilization methods that involve the use of plaster of Paris [4], fiberglass, or thermoplastic splints [5]. The significance of this research is emphasized by the high occurrence of hand trauma, a condition requiring medical attention despite its non-fatal nature. As an example, from January 2009 to December 2018, around 2.6 million cases were reported annually by USA emergency departments [6]. The most common wrist-hand injuries include sprains, strains, carpal tunnel syndrome, fractures, tendonitis, and ligament injuries. It is worth noting that even minor hand injuries can negatively impact daily life by making the ability to perform tasks a challenge. Moreover, the substantial costs associated with the disability resulting from painful or unstable wrist joints are a notable concern in hand injury care [7].