## 2 Materials and Methods
### Background--Prosthesis Design and Patient Case Description  
The design was commenced with a project of an intelligent model of the upper limb prosthesis, which is characterized by a modular structure. The device represents a cohesive entity comprising multiple interconnected elements. The model is loaded with anthropometric and configuration data directly from an external Excel file [22], enabling both the generation of anatomically matched prosthesis components and the manipulation of its variants to create any combination of all parts. Therefore, the model allows for the quick and fully automated production of many configurations of individualized prostheses for  
Figure 1: Basic concept—low-cost 3D printed bicycle prosthesis made for child patients [21]. Figure 2: Research stages with basic technical information. the same or different patients. It is presented in Figure 3 and is its basic variant, containing a compressive-release socket (CRS [23]), a forearm with elbow joint, and C-shaped end effector with Cardan joint at the wrist. The prosthesis model was adapted to an adult patient. A case of 40-year-old male patient was selected for the studies. The patient was born without his right forearm (no functioning elbow joint). Both of the patient's upper limbs were 3D scanned (Figure 4), and the resulting data were automatically processed, using the AutoMedPrint system hardware and software capabilities (as described in earlier works [14; 22]). In the preliminary studies, the initial version of prosthesis was manufactured and tested by the patient. After minor corrections (for strength improvement), the prototype was tested in real conditions by the patient riding the bicycle (Figure 5). These tests were positively concluded, and the patient was given the prosthesis for longer use, to obtain feedback regarding further construction and use issues. Figure 4: 3D scanning of patient: (**a**) stump; (**b**) healthy arm; and (**c**) mesh data during processing. Figure 3: Basic variant of an intelligent CAD model created in Autodesk Inventor. In the course of numerous tests and subsequent design iterations (considering patient's comments and usage reports, as well as authors' observations), the following modifications have been introduced in the mechanical part of the prosthesis:  
1. The CRS socket was modified as a result of removing the movable connection in the elbow joint. It was connected to the forearm rigidly due to too much load in the case of an adult The mounting plane was moved away from the tip of the socket to a properly selected distance, mounting hardware was added to allow connection to the forearm (Figure 6a). 2. The forearm model was changed as a result of abandoning the movable joint in the elbow joint. It was a decision of the patient as he uses bicycle in one, stable position, the presence of elbow joint in the prosthesis (that he does not have in his stump) would not be ergonomic and could be potentially destabilizing the body position while riding. In other words, eliminating the elbow joint helped with safety and rigidity, while introducing no practical function impairment. The space of elbow was filled in with material for better strength. Five mounting holes and two access holes were added (Figure 6b). 3. The C-handle was modified by extending the jaws and narrowing the distance between them. These changes were introduced after patient's feedback as they increased the stability and comfort of cycling. In addition, the connection used in the wrist was abandoned as the lack of a joint resulted in an increase in stiffness with the simultaneous impossibility of rotation. This was possible after adjusting the angles for a given patient and his bicycle (Figure 6c). The improved prosthesis in its mechanical version was well proven in use. It must be emphasized that the patient was using the first version (as shown in Figure 5) for one full bicycle season and the second version (modified and visible in Figure 6) for another full season.