Fluid-Structure Interaction Simulation of Carotid Plaque / 医用生物力学

Objective To propose a two-way fluid-structure interaction (FSI) method based on real patients with carotid artery stenosis, and analyze the hemodynamic parameters of carotid plaques with different types at the lesion as well as deformation and stress changes of the plaque itself. Methods Three-dimensional ( 3D) modeling was performed based on computed tomography angiography ( CTA) data of patients with moderate carotid artery stenosis. The carotid artery wall model and plaque model were separated, and transient fluid structure coupling calculation was performed. The situation from early stage of carotid atherosclerosis to formation of the plaque was simulated. The plaque types were divided into thickened plaques, lipid plaques, mixed plaques and calcified plaques, among which thickened plaques were regarded as non-plaque conditions for representing the thickening of vascular intima-media. The stenotic carotid arteries with different plaque types were compared and analyzed. Results The plaques with different types had little effect on the overall blood flow, but the wall shear stress of lipid plaques at the lesion was lower than that of other plaques. With thickened plaques as a control, concurrence of the plaque would inhibit artery expansion, and lipid plaques were the most obvious. Calcified plaques had the highest average plaque structure stress, while lipid plaques had the lowest average plaque structure stress. Conclusions The method proposed in this study can analyze fluid area and solid area at the same time. The results can contribute to better understanding the influence of different plaque types on carotid artery diseases.

Risk Assessment of Carotid Atherosclerotic Plaque Rupture under Cervical Rotatory Manipulation Based on Fluid-Structure Interaction Finite Element Model / 医用生物力学

Objective To evaluate the rupture risk of carotid atherosclerotic plaque under cervical rotatory manipulation. Methods The fluid-structure interaction (FSI) model of carotid atherosclerotic plaque was established, and tensile deformation of the plaque and lumen under cervical rotatory manipulation was simulated.Mechanical parameters such as the maximum flow shear stress(FSS), the maximum wall shear stress (WSS), the maximum plaque wall stress (PWS), wall tensile stress (WTS) and wall pressure (WP) of the plaque and lumen were recorded. Results Under 16% carotid tensile deformation, the maximum WSS of the plaque was 40.54 Pa. The maximum PWS was 66.16 kPa, which was far smaller than the threshold of plaque rupture.The maximum WTS of fiber cap and the maximum strain were 156.75 kPa and 0.56, which were larger than the fracture strain range. The maximum WTS of the lumen was 1 040.30 kPa, which approached the threshold of medial membrane rupture and might cause vascular injury. Conclusions When the cervical spine rotates to the end range of motion, large carotid artery stretch may cause damage to epidermal tissues of the plaque, leading to abscission. Lesions, ulcers, bleeding and vascular damage may form inside the plaque, which will affect stability of the plaque. Cervical rotatory manipulation should be performed cautiously in patients with cervical diseases who also have carotid atherosclerotic plaques.The finite element assessment of plaques before manipulation may be an effective safety screening method.

Fluid-Structure Interaction Simulation of Multiple Overlapping Uncovered Stent Intervention in Aortic Dissection / 医用生物力学

Objective To propose a one-way fluid-structure interaction (FSI) method based on an idealized aortic dissection model, so as to analyze the hemodynamics and wall stress in the false lumen (FL) under the influence of multiple overlapping uncovered stents (MOUS). Methods Upon establishment of the numerical model, the models were divided into two categories according to whether the model involved FL perfused branch artery. The characteristics of hemodynamics and wall stress state in the post-operative scenarios were simulated under different surgical strategies. The wall stress state of the FL before and after thrombosis formation was also compared and analyzed. ResultsThe release process of the stents had little influence on wall stress of the FL. The high velocity and high wall shear stress (WSS) area in the FL could not be reduced by using the MOUS alone. If only the proximal entry tear was blocked with a covered stent-graft, the distal end would maintain a region of high flow rate and high WSS. The combination of covered stent-graft and MOUS would result in a region of low flow rate and low WSS, as well as reduced wall pressure and wall stress in the FL. Compared with the model with FL perfused branch arteries, the model without it was more likely to form a region of low flow rate and low WSS after surgery. However, blood pressure in the FL was relatively higher. The formation of thrombus in the FL could greatly reduce wall stress in the area covered by the thrombus. Conclusions The method proposed in this study can simultaneously investigate hemodynamics and wall stress characteristics of the FL, and provide support for studying mechanical mechanism of FL thrombolysis induced by MOUS and the post-operative aortic expansion.

Influence of Dimple Depth on Lubricant Thickness in Elastohydrodynamic Lubrication for Metallic Hip Implants Using Fluid Structure Interaction (FSI) Approach

@#Introduction: The lubricant thickness in clearance between bearing surfaces for metallic hip implants are currently incapable of accommodating the motion experienced (high load and low entraining motion) in hip walking cycle. Thus, micro-dimpled surfaces were introduced onto surfaces of metallic acetabular cups to improve lubricant thickness. Micro-dimpled surface is a method of advanced surface improvement to increase the lubricant thickness in various tribological applications, such as hip implants. However, the application of micro-dimpled surfaces in hip implants has not yet been explored adequately. Therefore, this study aims to identify the influence of micro-dimpled depth on lubricant thickness elastohydrodynamically for metallic hip implants using Fluid-Structure Interaction (FSI) approach. Methods: Fluid-Structure Interaction (FSI) approach is an alternative method for analysing characteristics of lubrication in hip implant. Dimples of radius 0.25 mm and various depths of 5μm, 45μm and 100μm were applied on the cup surfaces. The vertical load in z-direction and rotation velocity around y-axes representing the average load and flexion-extension (FE) velocity of hip joint in normal walking were applied on Elastohydrodynamic lubrication (EHL) model. Results: The metallic hip implants with micro-dimpled surfaces provided enhanced lubricant thickness, namely by 6%, compared to non-dimpled surfaces. Furthermore, it was suggested that the shallow depth of micro-dimpled surfaces contributed to the enhancement of lubricant thickness. Conclusion: Micro-dimpled surfaces application was effective to improve tribological performances, especially in increasing lubricant thickness for metallic hip implants.

FSI simulation of patient-specific aortic dissection and its bypass grafting / 医用生物力学

Objective To investigate the effects of different bypass grafting for treating DeBakey Ⅲ aortic dissection. Methods The patient-specific models of DeBakey Ⅲ aortic dissection based on CT images were reconstructed by using Mimics software, and two bridge models of bypassing between ascending aorta and abdominal aorta (AA), and between left subclavian artery and abdominal aorta (LA) were established by computer-aided method, respectively. Then numerical simulations were performed by using fluid-structure interaction (FSI) method to compare hemodynamic differences of these two models. Results After bypass surgery, the mass flow, mean and maximum velocities of the through lumen models were reduced to different degrees. Meanwhile, both the maximum blood pressures and displacements of the vessel walls of AA models were decreased, but those of LA models were increased. In contrast, all the above-mentioned hemodynamic parameters of the blind lumen models were decreased, especially for AA models. Conclusions The AA bypassing is a better treatment for DeBakey Ⅲ aortic dissection of through lumen and blind lumen. The therapeutic effects can be easily explained through simulation results, to ensure the scientific validity and clinical utility of bypassing.

Fluid-structure interaction analysis on lubrication system of artificial hip joint / 医用生物力学

Objective To compare the method based on computational fluid dynamics (CFD) and fluid structure interaction (FSI) with the traditional Reynolds equation method in the study of an artificial hip joint lubrication system. Methods Using business software Adina as a computing platform, the metal-on-metal total hip replacement (MOM THR) model was developed as the subject to establish the rigid and elastic CFD model, respectively. Results The film- thickness curve obtained by the CFD&FSI method had a significant depression in the center, which was more reasonable than that obtained by the traditional Reynolds equation method. The model with elastic surface under the given load showed a significant deformation at the FSI surface of the acetabular cup femoral head, and the deformation was consistent with the pressure and film thickness distribution in fluid field. Conclusions The CFD&FSI method used here was more reasonable than the traditional method when computing the elasto-hydrodynamic lubrication of an artificial hip joint system.