ABSTRACT
Objective To study the process of single stent and double-stent thrombectomy at the Y-shaped bifurcation of the ideal internal carotid artery by finite element simulation, analyze the stent-thrombus-vessel interaction during the thrombectomy process based on the simulation results, and provide guidance for improving the effect of stent thrombectomy at the bifurcation. Methods The CAD software was used to build the model and the finite element analysis software was used to simulate the process of single stent and double-stent thrombectomy. Results Thrombectomy was unsuccessful in single stent model and successful in double-stent model, and the maximum stress of thrombus during embolus retrieval was twice that of single stent, the maximum strain was 1.12 times that of single stent, and the maximum contact pressure on the surface of vessel was approximately twice that of single stent. Conclusions Double Solitaire stents can effectively prevent thrombus displacement at the bifurcation and successfully retrieve the thrombus, but there is a risk of fracture due to the high stress level in the middle section of the thrombus. The contact pressure of the vessel on the anterior artery side is higher during thrombectomy, and the risk of vessel damage is greater. Therefore, it is necessary to optimize the design of the stent-retriever to improve its flexibility.
ABSTRACT
The patient-specific aortic silicone model was established based on CTA data. The digital particle image velocimetry (DPIV) test method in the modified ViVitro pulsatile flow system was used to investigate the aortic hemodynamic performance and flow field characteristics before and after transcatheter aortic valve replacement (TAVR). The results showed that the hemodynamic parameters were consistent with the clinical data, which verified the accuracy of the model. From the comparative study of preoperative and postoperative effective orifice area (0.33 cm2 and 1.78 cm2), mean pressure difference (58 mmHg and 9 mmHg), percentage of regurgitation (52% and 8%), peak flow velocity (4.60 m/s and 1.81 m/s) and flow field distribution (eccentric jet and uniform jet), the immediate efficacy after TAVR is good. From the perspective of viscous shear stress and Reynolds shear stress, the risk of hemolysis and thrombotic problems was low in preoperative and postoperative patient-specific models. This study provides a set of reliable DPIV testing methods for aortic flow field, and provides biomechanical basis for the immediate and long-term effectiveness of TAVR from the perspective of hemodynamics and flow field characteristics. It has important application value in clinical diagnosis, surgical treatment and long-term evaluation.
Subject(s)
Humans , Transcatheter Aortic Valve Replacement/methods , Aortic Valve/surgery , Heart Valve Prosthesis , Hemodynamics , Aortic Valve Stenosis/diagnosis , Treatment OutcomeABSTRACT
The radial force of the degradable esophageal stent before and after degradation is one of the important indicators for effective treatment of esophageal stricture. Based on a combination of in vitro experiments and finite element analysis, this paper studies and verifies the biomechanical properties of a new type of degradable esophageal stent under different esophageal stricture conditions. Under radial extrusion conditions, the maximum stress at the port of the stent is 65.25 MPa, and the maximum strain is 1.98%; The peak values of stress and strain under local extrusion and plane extrusion conditions both appear in the extrusion area and the compression expansion area at both ends, which are respectively 48.68 MPa, 46.40 MPa, 0.49%, 1.13%. The maximum radial force of the undegraded stent was 11.22 N, and 97% and 51% of the maximum radial force were maintained after 3 months and 6 months of degradation, respectively. The research results verify the safety and effectiveness of the radial force of the new degradable esophageal stent, and provide a theoretical basis for the clinical treatment of esophageal stricture.
Subject(s)
Humans , Esophageal Stenosis/surgery , Finite Element Analysis , Mechanical Phenomena , StentsABSTRACT
Objective:To study the effects of FcγRIIb gene modified dendritic cells on liver function and rejection after orthotopic liver transplantation in rats.Methods:The recombinant lentivirus expression vector TRE-FcγRIIb containing Lewis rat FcγRIIb gene was constructed by gene cloning technique. TRE-FcγRIIb expression virus and TET-on regulatory virus were packaged and co-infected with immature dendritic cells derived from DA rat bone marrow. The expression of FcγRIIb was detected. Donor rats DA and recipient Lewis were paired according to body weight and then randomly divided into three groups. The control group (group A) did not receive any pretreatment. The Lewis rats in group B were treated with cyclosporin A on the 2nd day after liver TX. Immature dendritic cells derived from bone marrow of DA rats were injected intravenously one day before liver TX in FcγRIIb gene modified immature dendritic cells (1×10 6 cells)group (group C). Blood and liver tissue were biopsied 7 days after operation to detect liver function and pathological changes. Results:The abnormal liver function in FcγRIIb gene modified immature dendritic cells group (group C) was significantly lower than that of control group 7 days after operation ( P<0.05), and the liver pathological rejection of FcγRIIb gene modified immature dendritic cells group (group C) was significantly lower than that of control group 7 days after operation ( P<0.05). The average survival days of rats in the control group was 12.8 days; the average survival days of rats in the cyclosporin A group was 65.3 days; the average survival days of rats in the FcγRIIb gene-modified immature dendritic cell group was 58.5 days. Conclusion:FcγRIIb gene modified immature dendritic cells can ameliorate liver dysfunction and acute liver rejection after orthotopic liver transplantation.
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Biodegradable vascular stent, also known as the third generation stent, has recently been widely studied. Finite element models of three stents with the same structure and different specifications were developed. The mechanical behavior under crimping, expanding and fatigue testing were assessed by von Mises yield and Goodman convergence. The maximum stress during crimping, expanding and fatigue testing were all observed in the stent with the largest size. The results indicated that the largest stent had the highest risk of failure and also provided theoretical evidence for the worst case scenario in the fatigue testing.
Subject(s)
Finite Element Analysis , Polyesters , Stents , Stress, MechanicalABSTRACT
In the present study, a finite element model of L4-5 lumbar motion segment was established based on the CT images and a combination with image processing software, and the analysis of lumbar biomechanical characteristics was conducted on the proposed model according to different cases of flexion, extension, lateral bending and axial rotation. Firstly, the CT images of lumbar segment L4 to L5 from a healthy volunteer were selected for a three dimensional model establishment which was consisted of cortical bone, cancellous bone, posterior structure, annulus, nucleus pulposus, cartilage endplate, ligament and facet joint. The biomechanical analysis was then conducted according to different cases of flexion, extension, lateral bending and axial rotation. The results showed that the established finite element model of L4-5 lumbar segment was realistic and effective. The axial displacement of the proposed model was 0.23, 0.47, 0.76 and 1.02 mm, respectively under the pressure of 500, 1 000, 1 500 and 2 000 N, which was similar to the previous studies in vitro experiments and finite element analysis of other people under the same condition. The stress distribution of the lumbar spine and intervertebral disc accorded with the biomechanical properties of the lumbar spine under various conditions. The established finite element model has been proved to be effective in simulating the biomechanical properties of lumbar spine, and therefore laid a good foundation for the research of the implants of biomechanical properties of lumbar spine.