## 2 Materials and Methods  
The current study included patients admitted to the rehabilitation medicine department due to tetraplegia caused by cervical SCI from June 2019 to November 2019. The inclusion criteria were as follows: patients with normal cognitive functions who had severe hand dysfunction and who cannot perform normal ADL, and those without communication issues. Patients with tetraplegia caused by traumatic brain injury or stroke were excluded. To develop the special assistive device, the patient's hand was initially positioned for specific functions and was scanned with a 3D scanner. The scanned 3D image was converted into STL files, which were loaded or designed using Autodesk Fusion 360 (San Rafael, CA, USA). Then, 3D printing was performed using RAISE3D Pro2 Plus (Tesla, Irvine, CA, USA) with the fused deposition modeling method (FDM), which involved stacking up melted flexible thermoplastic elastomer filaments layer by layer. FDM is one of the most widely used manufacturing techniques in 3D printing. Moreover, it has several advantages: it can print products rapidly and is cost-effective [8]. Polylactic acid (PLA), which is the same thermoplastic material used in manufacturing conventional orthosis, is the plastic monofilament used in the hand device. We manufactured and applied various types of 3D-printed assistive devices. We used this 3D printer technology to design a customized orthosis for the size of the patient's hand. At the beginning of the study, we designed a prototype made of PLA material and applied it to the patients. Figure 1 summarizes the design evolution of various device prototypes for the recruited patients. First, is an assistive device made of PLA material wherein the patients place their finger (Figure 1A,B). However, patients found it difficult to maintain pronation and were unable to continuously use the assistive device. As such, a device that can be used in the neutral position and allow writing and typing was needed. The second device designed allowed for typing and writing even in a neutral position but had the disadvantage of having to change the device, which was cumbersome depending on the situation. Another disadvantage was that the pen fell out when writing (Figure 1C). Accordingly, each function was separately produced using a design that allows for simultaneous typing and writing. Moreover, unlike the second design, one fixing screw was added (Figure 1D). However, one disadvantage of this design was problems in both the typing device and the integrated device used by inserting the patients' fingers. In other words, several patients with spinal cord injury, especially those with cervical injuries, exhibited hand muscle atrophy, which made it difficult to utilize the device given the difference in the individual's hand size or hand function. In summary, plastic-type typing and writing assisted devices could not be applied because the hand grasp power of patients with cervical SCI is extremely weak. Further, plastic-type devices were extremely hard and difficult to carry. Thus, we switched to making and applying band-type assistive devices using silicon. A frame was designed for band-shaped devices (Figure 2B). Then, it was printed using RAISE3D Pro2 Plus (Tesla, Irvine, CA, USA) with FDM (Figure 2C). Liquid silicone of different hardness was poured into the 3D-printed frame (Figure 2E,F). The liquid silicon comprised materials A and B. The materials were mixed at room temperature in a 1:1 ratio (A, which is the main material, and B, which is the hardener material and is cured for 16 h). The sizing scheme was based on the hand measurements of each patient (Figure 2D). Thus, we created a device that was pulled out with a 3D-printed frame of different sizes that was suitable for each patient and that can improve function (Figure 2E). The time required for typing and writing before and after wearing the device was evaluated by an occupational therapist.