## 2 Materials and Methods
### Design of the System  
The proposed passive continuous distraction osteogenesis device consists of different mechanical parts that can generate a continuous pushing force with controlled parameters, including DR and time, without the need for an active power supply of the pushing force. The device has a hydraulic and spring-mediated mechanism with a flow rate control for continuous force generation. The required energy is stored in the pressurized spring, which can supply the required force to generate continuous distraction of the bone. A miniature double-action hydraulic cylinder integrated with a spring and a microfluidic component with a flow rate control mechanism is used to enable continuous force generation with predetermined factors that commence at the start of the activation phase during the reconstruction process. Figure 3 illustrates a 3D model of the proposed device and the components used in the system's design.  
As shown in Figure 3, the passive distractor is a purely mechanical device, devoid of any electronic components in its design. Consequently, an active power supply is unnecessary during the reconstruction process. Within the system, a spring (5) is housed within a double-action cylinder (4), facilitating the pushing force by pushing the piston (9) continuously. Adjacent to the cylinder, a hydraulic chamber (6) is positioned and connected to the cylinder via two miniature channels (3) forming two lines for fluid transition. A threaded screw (1) and hole (2) are utilized to fill hydraulic fluid within both the hydraulic cylinder and chamber. Additionally, another set of threaded flow control components (FCCs) and holes (7) enables the activation mechanism to be controlled. The FCC incorporates a microchannel capable of regulating the flow of hydraulic fluid. By adjusting the specifications of the microchannel, the flow rate can be set to the desired level, ensuring that the predetermined DR is achieved during the device's activation.  
Before the surgical operation and installation of the device in the surgical zone, the moving part of the distractor (13) needs to be pushed to pressurize the spring and store the necessary energy. Once the spring is pressurized and the moving part of the distractor is in the initial position, the FCC is locked to maintain a zero-flow rate. During the surgical procedure, following the osteotomy of the affected bone, the device is installed in the surgical reconstruction area. Mechanical fixtures (8) are employed to secure the device onto the bone, while additional mechanical fixtures (14) fix the moving part of the device to the BS. The guide rail (12) ensures the distraction vector is stabilized, enabling a precise movement of the BS towards its final position.  
Figure 3: _Cont._Following the latency phase, the FCC is unlocked when the activation phase begins. Subsequently, the spring starts to expand gradually and smoothly while the FCC controls the flow rate to achieve the desired DR of the BS. This controlled expansion ensures that the pushing force is transmitted to the bone part through the piston rod (12) and the fixed moving segment of the distractor in a continuous distraction manner.  
Figure 4 illustrates the distractor's initial and final positions during the activation phase of the reconstruction process. The proposed distractor is versatile and suitable for addressing various mandibular defects, including mandibular retrognathia.  
Figure 4: _Cont._  
Figure 3: Threaded part/screw, 2. Threaded hole, 3. Micro channel, 4. Double-action hydraulic cylinder, 5. Spring, 6. Hydraulic chamber, 7. Threaded FCC, 8. Mechanical fixture, 9. Piston, 10. Rod seals, 11. Piston rod, 12. Guide rail, 13. Moving segment, 14. Mechanical fixture.