## 2 Materials and Methods
### Prototype Development
#### 2.1.4 Manufacturing of the Device
A key feature of these devices is the high availability of materials in the parts list. In compliance with this practice, the use of fishing line cable was considered. The brand of rigid cable used is Konger X8 Braider (Konger Machinery Co, Ningbo, China), which is a multifilament based on high-density microfiber polyethylene. In Figure 11, the palm structure is illustrated. It has special assembly zones for the fingers. A group of 4 assembly links are located frontal-lateral and 1 other is placed radially on the side. The structural role played by the palm led to the design decision of placing a square pattern of holes on the palmar side responsible for ventilation and reinforcement of the device itself. Figure 11: Three-dimensionally printed palm structure featuring the finger joints and major joint. Figure 10: Assembled 3D-printed fingers with tendons attached. The palm cover in Figure 12 houses a maze of channels that allows for the finger actuation in either mode, mechanical or electrical. It is located on the dorsal side of the palm, and it is assembled with M3 threaded screws in threaded inserts near the finger articulations and with M2 self-tapping screws laterally on the side of the palm. The actuation cable travels from the fingertips, through the palm channels up the gauntlet, and is tied to the motor shafts. The thumb has 2 phalanxes and 2 joints and is located laterally. The other 4 fingers have 3 phalanxes and 3 joints and are placed at different elevation levels to simulate the human hand's anatomy. The palm subassembly in Figure 13 also has a major joint that allows for assembly with the gauntlet. These joints house a ball bearing and have a side channel where a part of the locking system is situated. The thumb channel is the most complex. It makes the cable turn at a \(c_{a}=270^{\circ}\) angle to travel from the palm to the gauntlet area. The motor subassembly in Figure 14 has a housing and a cover that allows for it to be secured on the gauntlet. A spool is present on the output shaft of the motor's gearbox that allows for the cable to be spooled when trying to actuate the device. Figure 12: Three-dimensionally printed palm cover with assembly points. Figure 13: Assembled 3D-printed palm with cover and fingers. The locking system has a component on the major joint of the palm structure and another one on the gauntlet, as seen in Figure 15. The system is made up of 2 covers with a channel between them which houses a locking key with a spring. The assembly allows for the device to lock in the closed position. The gauntlet in Figure 16 is composed of 2 main parts: (1) the upper gauntlet, which has the motors and electronics mounted on it while also connecting to the palm, and (2) the lower gauntlet, which houses the battery. The 2 main parts are joined together by a metal pin that is inserted on the side in a hinge-like system on one side and a Vel  
Figure 14: Motor subassembly with housing and cover. Figure 7:0 Three-dimensionally printed locking system area with respect to the gauntlet. The full assembly of the device in Figure 17 has its finger distal made up of 2 parts that are assembled with a screw and threaded insert, and the method is similar throughout all the finger subassemblies. Two adjacent segments are assembled using a bolt and a nut that also supports the ball bearing and torsion spring. The finger subassembly has a channel through all the segments. A rigid cable travels through it and is used for actuation. In the distal part, the pretension system is located, which has a moving element that can either advance or return and with the help of a screw and a threaded insert can allow for fine cable tensioning adjustments. During assembly of generic designs for transitional prosthetics, a tendency to lose parts due to unfixed joints was noticed. As a solution to the problem, metal fasteners were proposed. Furthermore, a similar problem occurred with rotational joint jamming or snapping, to which the roller bearing solution was given.