The hydrodynamic behavior of the perfusion process (cleaning) of the liver endovascular before the operation was studied to provide a theoretical guidance to the relative operations. A straight and a curved first-class vascular entity model with foreign matter and the control equations of turbulence liquid in vessel was established. With the physical parameters of a medical infusion liquid measured, an estimation method of perfusion parameters as an example, the perfusion velocity was proposed. The simulation was performed by changing technical parameters of the perfusion. Based on the control equations of turbulent liquid in vessel and the preliminarily calculated results using the vessel model, the results fitted the values of the real operation. The simulation results showed clearly the fluid dynamics behavior around the foreign matter, for example the swirling flow. The results also showed the distribution of velocity of the fluid and the wall pressure of the vessels. With the increasing velocity of the entrance perfusion, the pressure and the velocity field were increased in the two types of the vessel model. The negative wall pressure and recirculation region appeared and located in the foreign matter. Because of influence of the shape, the fluid dynamics behavior in the curved vessel model was more complicated than that in the straight vessel model. The swirling flow and the phenomenon of stagnation of the perfusion fluid were more likely to appear in the curved vessel than in the straight vessel. The most important conclusion of this paper is that the appropriate perfusion velocity can be esti-mated using the methods proposed in this paper.
Fluid shear stress (FSS) caused by interstitial fluid flow within trabecular bone cavities under mechanical loading is the key factor of stimulating biological response of bone cells. Therefore, to investigate the FSS distribution within cancellous bone is important for understanding the transduction process of mechanical forces within alveolar bone and the regulatory mechanism at cell level during tooth development and orthodontics. In the present study, the orthodontic tooth movement experiment on rats was first performed. Finite element model of tooth-periodontal ligament-alveolar bone based on micro computed tomography (micro-CT) images was established and the strain field in alveolar bone was analyzed. An ideal model was constructed mimicking the porous structure of actual rat alveolar bone. Fluid flow in bone was predicted by using fluid-solid coupling numerical simulation. Dynamic occlusal loading with orthodontic tension loading or compression loading was applied on the ideal model. The results showed that FSS on the surface of the trabeculae along occlusal direction was higher than that along perpendicular to occlusal direction, and orthodontic force has little effect on FSS within alveolar bone. This study suggests that the orientation of occlusal loading can be changed clinically by adjusting the shape of occlusal surface, then FSS with different level could be produced on trabecular surface, which further activates the biological response of bone cells and finally regulates the remodeling of alveolar bone.