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Abstract:For implantable medical devices, traditional mechanical property testing is achieved by mechanical testing devices, while such method is lack of pertinence during sampling of series of products, and also time consuming during experimental testing. With the complete development of finite element analysis (FEA) techniques, introducing FEA to quality supervision and inspection will become a scientific method for saving resources and time, and also improve the pertinence. In this study, the creditability of FEA in application of highest risk sample selection, failure analysis of marketed products and auxiliary optimization of fatigue test testing was verified through case study and experimental testing. The feasibility of FEA during implants inspection was illustrated. In order to ensure the accuracy and reliability of FEA in the application of implants inspection, the essentials of establishing related finite element standards were proposed.

Abstract:Objective To study the role of abnormally changed migration of vascular smooth muscle cells (VSMCs) induced by low shear stress (LowSS) in vascular remodeling during atherosclerosis as well as the molecular mechanism involved in this process. Methods By using comparative proteomic analysis with two-dimensional electrophoresis combined with mass spectrometry, differential protein expression profiles of cultured vascular tissues under normal shear stress (NSS) (1.5 Pa) and LowSS (0.5 Pa) were studied. Using endothelial cells (ECs) and VSMCs co-cultured parallel plate flow chamber system, two levels of shear stress i.e. LowSS and NSS, were applied, respectively. Western blot was used to detect the protein expressions of Rab28 and phosphor-ERK. Transwell system was used to detect the migration ability of VSMCs. After using RNA interference and ERK inhibitor PD98059 to decrease the expressions of Rab28 and phosphor-ERK, respectively, the migration ability of VSMCs was observed again. Results The expression of Rab28 in the cultured rat aorta was significantly up-regulated by the LowSS (0.5 Pa) application in comparison with the NSS (1.5 Pa). The migration, expressions of Rab28, and phosphorylation of ERK in VSMCs were significantly increased by the LowSS application. Target RNA interference of Rab28 significantly decreased the migration of VSMCs, but had no specific effect on the phosphorylation of ERK. Target inhibitor of ERK, PD98059, significantly decreased both the migration and Rab28 expression in VSMCs. Conclusions The LowSS may increase the phosphorylation of ERK and then increase the expression of Rab28 in VSMCs, which subsequently modulate VSMC migration during vascular remodeling. The investigation on the role of Rab28 and its signal path in LowSS-regulated VSMCs as well as the molecular mechanism might provide a biomechanical reference for understanding the pathogenesis of vascular remodeling during atherosclerosis and finding the therapeutic target of new drugs.

Abstract:Objective To evaluate differences in genes expression of rat bone marrow stromal cells (rBMSCs) under continuous mechanical strain by gene microarray technology．Methods rBMSCs were isolated and cultured in vitro. Continuous stresses with amplitude of 10% and frequency of 1 Hz were applied on rBMSCs for 6 hours by Flexercell mechanical loading system to investigate rBMSC gene expression profiles, and quantitative PCR was used to verify gene expression changes related to osteoblastic differentiation. Results Compared with the control group, 1 244 differentially expressed genes were found in mechanical loading group, among which 793 genes were up-regulated, while 451 genes were down-regulated．GO (gene ontology) analysis suggested that differentially expressed genes were mainly involved in multicellular organismal development, cell differentiation, chemotaxis, cell adhesion and so on. Four signaling pathways as Notch, Wnt, FGF and IGF might participate in the regulation of stress-induced osteoblastic differentiation. PCR validation results were consistent with the gene chip results. Conclusions Mechanical stress could induce osteoblastic differentiation of the BMSCs, while several differentially expressed genes screened by gene microarray may attribute to this process.

Abstract:Objective To obtain distributions of normal displacement on different layers of articular cartilage under sliding loads and investigate effects of compressive strain, sliding rate and sliding numbers on depth-dependent normal displacement of articular cartilage. Methods The non-contact digital image correlation (DIC) technique was applied to investigate the normal displacement of different layers for fresh pig articular cartilage under sliding loads, respectively. ResultsThe largest normal displacement was found on the superficial layer, while that on the deep layer was the smallest, with the middle layer was in between under sliding loads. The normal displacement for cartilage at different normalized depth increased with compressive strain increasing and the largest increasing amplitude was in the superficial layer. The depth-dependent normal displacement for cartilage decreased with sliding rates increasing. The normal displacement for cartilage kept increasing with different sliding numbers within its sliding time. The most significant increasing amplitude of normal displacement was found between the first and second slide. Conclusions Under sliding loads, the normal displacement of cartilage usually changes along with its depth from surface to deep layer, and compressive strain, sliding rate and sliding numbers all play important roles in such normal displacement distributions on different layers. These results can provide the basis for clinical cartilage disease treatment and cartilage defect repair, and are also important for structure and construction of artificial cartilage as well as in mechanical function evaluation.

Abstract:Objective To establish four finite element models for repairing root canals of the maxillary central incisors, study the influences from different post and core materials as well as root canal rehabilitations on stress distributions of the maxillary central incisors, so as to provide theoretical references for clinical application. Methods Four finite element models of repairing system were established by CBCT scanning, Mimics software, Rapidform.xor3, Solidworks and Ansys Workbench software. The occlusal loads were simulated and Von Mises stresses on the roots were calculated. Results Four precise 3D finite element models for repairing maxillary central incisors were established, including dentin, all ceramic crow, coping crown, post and core, gutta percha point, periodontal ligament, glue and alveolar bone. The analysis found out that different post and core materials as well as glues had different influences on Von Mises stress of the dentins as the greater elastic modulus of the post was, the smaller Von Mises stresses of the dentin would be. The Von Mises stress on the post and core made of cobalt-chromium alloy was 23.15 MPa, which was the smallest. Conclusions Stress distributions on repairing systems of the maxillary central incisors with different post and core materials can be predicted by establishing such different finite element models and provides a basis for the clinical application of maxillary central incisors repair systems.

Abstract:Objective To study the basic regular patterns of stress distributions inside and outside periacetabular districts during normal gait cycle of healthy adults, so as to provide clinical guidance for acetabular reconstruction of total hip arthroplasty (THA). Methods Based on CT scans of a male and a female healthy adult volunteer, The three-dimensional model including pelvis and proximal femur was reconstructed. By using an inhomogeneous material distribution scheme which was based on CT data to calculate elastic modulus and convergence analysis, each element was given a corresponding material attribute. The dynamic change of hip contact force during a normal gait cycle was used as the load condition to the model. Von Mises stress of the nodes inside and outside the model was considered as the criterion to assess the results. Results During normal gait, the stress on the hip surface of two volunteers was mainly transmitted from postersuperior part of acetabulum to auricular surface along posterolateral of iliac wing, and the maximum stress was at the district near greater sciatic. As for the superior, middle and inferior section of two volunteers' acetabulum, the stress was distributed both on cortical and cancellous bone of postersuperior part. However, in terms of acetabular anterior and posterior column, the stress distribution was mainly found on cortical bone. Conclusions According to the observed acetabular stress distribution pattern of health adults during normal gait cycle, choosing acetabular component with more suitable size and controlling the placement of acetabular component with more accuracy could obtain some acetabular reconstruction plan better in accordance with stress distributions during normal gait.

Abstract:Objective To study the contact performance of hip joint replacements with different material combinations typically used in clinic. Methods The finite element model of spherical conformal contact of hip joint replacements was developed to analyze the different contact mechanics performance of hip joint replacements with different material combinations by simulation test under a vertical constant load within one normal walking gait. The corresponding wear prediction was also evaluated. Results The contact mechanics performances of hip joint replacements with the material combination of metal-on-metal (MOM), metal-on-ceramic (MOC), ceramic-on-ceramic (COC), metal-on-polyethylene (MOP) and ceramic-on-polythene (COP) were analyzed. The results obtained from the simulations showed that contact stress was decreased in the order of COC＞MOC＞MOM＞COP＞MOP, while contact area was decreased in the order of MOP＞COP＞MOM＞MOC＞COC. Conclusions Hip joint replacement with the material combination of high elastic modulus and low Poisson’s ratio has smaller deformation, but could induce larger local stress, while flexible material polythene of low elastic modulus and high Poisson’s ratio might have smaller concentrated contact stress, but cause larger deformation and edge contact phenomenon on the acetabulum cup of hip joint replacements. In addition, hip joint replacements with MOC and MOM material combination may have lower contact bearing performance, which provides references for material choices of typical artificial hip joints in clinic.

Abstract:Objective To establish a three-dimensional (3D) visualization model for the vessel system of rabbit eyes using X-ray phase contrast imaging（XPCI）technique, and observe the morphological characteristics of iris vessels of the rabbit eyes. Methods Angiography on vessels of the New Zealand rabbit eyes was conducted using Barium sulfate as the contrast medium. The projected images of in vitro rabbit eye samples with high precision were obtained by XPCI technique, and then converted to tomography images by filter back projection. The 3D reconstruction of the rabbit eyes was completed by commercial visualization software Amira 5.2.2. Results The main blood vessels of the rabbit eyes were clear and coherent in the projection images, and the distribution and trend of some small vessels could be observed, with the smallest distinguishable blood vessel diameter being about 10 μm. The 3D model for vessel network of the rabbit eyes was built after 3D reconstruction of CT scan images. The major arterial circle of the iris could be observed at level 4 branch structure of vessels in the fundus, and the minimum diameter of vessels that could be identified was 40 μm. Conclusions The vessels of the rabbit eyes can be clearly observed and 3D visualization of vessel network can be constructed by using XPCI technique, which would provide basis for the analysis on hemodynamics of blood vessels in the eye and reference for the clinical study of glaucoma.

Abstract:Objective To establish a numerical model of human mitral valve and simulate its closing process, so as to analyze stress distributions on the valve apparatuses, study the interaction between leaflets of mitral valve and chordae tendineae, and explore the relationship between the force of chordae tendineae and their thickness. Methods A geometric model of human mitral valve was constructed. On the basis of the geometric model, the finite element model was established by defining the element type, material attributes, contacts, loads and constraints. Parameters such as stress, velocity and displacement were calculated after solving the model. Results The stress distribution on the valve was non-uniform. The clefts between the scallops in the posterior leaflet were always under the highest load. When no chordae tendineae were attached, the leaflets turned over to the side of the atrium. When chordea tendineae were attached, the anterior and posterior leaflet could close up successfully. Different chordae tendineae applied different forces to the valve. The strut chorea tendineae attached to the anterior leaflet applied highest force among all the chordea tendineae. The correlation coefficient between the thickness of chordae tendineae and their force was 0.954. Conclusions The two zones with higher stresses, namely the center of the leaflet and the clefts between the three scallops in the posterior leaflet, are also the positions of mitral valve cleft in clinic. Chordea tendineae can apply the pulling force on the leaflets while the mitral valve is under load, thus the leaflets won’t turn over to the side of atrium and the valve can close up in time. Chordea tendineae with thicker anatomic structure always apply a higher force on the leaflets.

Abstract:Objective To investigate the effects of shear stress on late endothelial progenitor cells (EPCs) functions in vitro and in vivo. Methods Density gradient centrifugation-isolated rat bone marrow mononuclear cells were cultured in EGM-2MV and induced into EPCs. The 3rd~4th generation of EPCs, namely late EPCs, were treated with shear stress (1.2 Pa). Then cell biological functions, such as proliferation, adhesion, migration and ability of tube formation, were assayed with EdU incorporation assay, adhesion testing, Boyden chamber assay and Matrigel, respectively. The gene expression of VEFG was analyzed by real time RT-PCR. The apoptosis and aging situation of late EPCs were assayed by FACS and senescence-associated β-galactosidase (SA-β-gal) staining. The reendothelialization capacity of late EPCs treated by shear stress was evaluated by establishing models of freshly balloon-injured carotid arteries of rats and cell transplantation in situ. Results Shear stress could increase proliferation, adhesion, migration and tube formation of late EPCs (P＜0.05), upregulate the gene expression of VEGF, inhibit EPC apoptosis and delayed EPC aging (P＜0.05). Transplantation of late EPCs treated by shear stress facilitated in vivo reendothelialization in the injured arterial segment and inhibited neointima formation. Conclusions Shear stress within the physiological range can improve the functions of late EPCs and enhance their therapeutic ability of repairing vascular endothelial injury, which provides experimental basis for the clinic application of EPCs and shear stress-mediated cell therapy.

Abstract:Objective To observe and compare the effects of intraocular pressure (IOP) drop on using two kinds of aqueous drainage device implantation. Methods Forty healthy New Zealand white rabbits were chosen for the experiments. According to different implant devices, they were divided into NADI (new aqueous drainage implant) group and Ahmed group respectively, with 20 rabbits in each. Results Neither group appeared shallow anterior chamber after operation. At 8th week after operation, the postoperative IOP of NADI group and Ahmed group was decreased by 19.4% and 15.7%, respectively, as compared to the preoperative IOP. Statistical comparison showed that there were significant differences in IOP between two groups within 8 weeks (P＜0.05), and the IOP of NADI group was decreased more significantly than that of Ahmed group. Conclusions The IOP in NADI group was reduced more than that in Ahmed group, and such IOP drop was maintained for a longer period in NADI group, which means that NADI has an obvious IOP drop effect and good prospect in clinical application.

Abstract:Objective To study the biomechanical effect from different prosthetic materials used on unilateral maxillary defect repair by three dimensional finite element (FE) analysis method. Methods The maxillary unilateral defect model was reconstructed by medical image processing software MIMICS. The prosthesis was generated by mirroring technology. After processing, the FE unilateral maxillary defect model and healthy maxillary model were established to simulate stress distributions on the maxilla during occlusion. Results The maximum stress on maxilla using different repair materials was always found concentrated on the edge of maxilla connected with zygoma (the positions attaching zygolabialis and levator anguli oris). The minimum stress of from the maxilla edge on the repair side was 8.471 MPa by using tricalcium phosphate (TCP) composite. The maximum stress from the maxilla edge on the repair side was 17.55 MPa by using hydroxyapatite (HA) material. Conclusions Different repair materials had no significant effect on natural side of the maxilla after restoration, while a greater impact of force status on the repair side was found. The elastic modulus of different repair materials can be used as a basis for maxilla restoration in clinic.

Abstract:Objective To conduct a comprehensive study on pulsatile blood flow in arteries by proposing a convenient theoretical research system for hemodynamics. Methods Based on Womersley algorithm for fully developed pulsatile flow, numerical algorithm was introduced to establish the solving and analytical system of hemodynamics based on flow rate in arteries during one cardiac cycle. The flow rate of carotid artery in pig was measured under three blood flow states: the ideal state with a sinusoidal inflow waveform, the normal physiological state and the enhanced external counterpulsation (EECP) state for comprehensive hemodynamic research. Results Important hemodynamic parameters such as the axial speed vector, the wall shear stress (WSS), and the oscillatory shear index (OSI) during one cardiac cycle under the mentioned three flow states were solved respectively. The waveform of flow rate had a certain effect on WSS distributions and OSI level; the EECP performance obviously resulted in a significant increase in the level of WSS (WSS peak in particular) and OSI. Conclusions The solving system developed in this paper can be used for hemodynamics study conveniently and effectively. One of the most important hemodynamic mechanisms that lead to EECP’s good clinical effect may lie in its promotion to WSS level under physiological state, but the effect of OSI on endothelial function of the artery might much smaller than WSS itself; therefore, OSI may not be an ideal hemodynamic index for predicting the lesion of atherosclerosis.

Abstract:Brain injury has become the most severe injury in traffic accident due to its high incidence and high fatality rate. The brain injury model plays a critical role in researches on brain injury. The constitutive model and the material properties used in the model are key factors in determining the accuracy of injury prediction. The present paper aims to review the application of constitutive models and material properties in brain simulation so as to better understand biomechanical properties of brain and provide references for finite element researches on brain injury.

Abstract:Axillary crutch is one of the common mobility aids, with extensive usage in the given crowd. Due to the lack of adequate theoretical support, the past design of crutches often leads to occurrence of the secondary damage, such as axillary nerve injury, wrist injury and so on. Thus, it is necessary to carry out biomechanical study on axillary crutches. In this paper, the problems related with biomechanics in axillary crutches were reviewed by inquiring and analyzing the relevant references, and discussed from the aspects of human biomechanics, ergonomics, and industrial design. Also in this paper, through man machine interface research, the mechanical analysis on crutches usage, gait analysis and ergonomics design were made to lay a solid foundation for the design and correct use of axillary crutches so as to provide some reference for the option, adaptation and assessment of axillary crutches, which would have great clinical significance.