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Abstract:Hemodynamics is closely related with the initiation, development and treatment of neo-cardiovascular diseases. The studies on the hemodynamics in neo-cardiovascular system are the hotspots of biomechanics and biomedical engineering. The research topics, research method, research achievement and its medical application, which are issued in the articles in this special column, were remarked. Emphasis was paid to the review of the research driver, research progress and research tendency of hemodynamics. The application prospect of hemodynamics research on the clinical procedure and healthcare was demonstrated with respect to its multi level application in prevention, diagnosis and treatment.

Abstract:The aorta is the major blood vessel with spiral shaped geometry where the flow pattern is swirling in late systole. The swirling blood flow may have a positive physiological role in preventing cardiovascular diseases by reducing turbulent flow and enhancing mass transport. Several factors have shown to contribute to the formation of the swirling flow in the aorta such as the ventricular twisting, the 3D spiral shaped aorta, the pulsatile blood flow in the aorta and the motion of ascending aorta. Inspired by the above basic researches, the swirling flow mechanism has been applied to the vascular interventional therapies and the design of cardiovascular interventional devices. In the present review, the observation of swirling patterns in the aorta, its physiological significance, the factors contributing to its formation and its potential clinical application are summarized.

Abstract:Objective To predict the influence of connecting position between left superior vena cava (LSVC) and pulmonary artery on bilateral bidirectional Glenn (BBDG) shunt by numerical simulation. Methods Firstly, a 3D anatomical geometrical model was reconstructed by the medical images of a hypoplastic left heart syndrome (HLHS) patient with LSVC. Secondly, based on haptic deformations, several computational models were virtually generated, and computational fluid dynamics (CFD) numerical simulations were conducted using finite volume method. Finally, hemodynamic parameters were analyzed and evaluated. Results Flow recirculation was observed in the pulmonary artery between the LSVC and right superior vena cava (RSVC). The diameter of RSVC was defined as D. Varying the distance between LSVC and RSVC from 2D to 3.5D resulted in the least energy dissipation at 3D and the most at 2D. The blood flow rate ratios of left pulmonary artery to right pulmonary artery (LPA/RPA) ranged from 0.65-1.11. Conclusions Too close distance between LSVC and RSVC would bring out unfavorable hemodynamic distributions and consume more energy in the treatment of BBDG shunt. This study is of significance for surgeons to evaluate the optimal Fontan options in the treatment of HLHS accompanied by LSVC.

Abstract:Objective To compare the differences in the hemodynamic parameters of abdominal aortic aneurysm (AAA) between fluid-structure interaction model (FSIM) and fluid-only model (FM), so as to discuss their application in the research of AAA. MethodsAn idealized AAA model was created based on patient-specific AAA data. In FM, the flow, pressure and wall shear stress (WSS) were computed using finite volume method. In FSIM, an Arbitrary Lagrangian-Eulerian algorithm was used to solve the flow in a continuously deforming geometry. The hemodynamic parameters of both models were obtained for discussion. Results Under the same inlet velocity, there were only two symmetrical vortexes in the AAA dilation area for FSIM. In contrast, four recirculation areas existed in FM; two were main vortexes and the other two were secondary flow, which were located between the main recirculation area and the arterial wall. Six local pressure concentrations occurred in the distal end of AAA and the recirculation area for FM. However, there were only two local pressure concentrations in FSIM. The vortex center of the recirculation area in FSIM was much more close to the distal end of AAA and the area was much larger because of AAA expansion. Four extreme values of WSS existed at the proximal of AAA, the point of boundary layer separation, the point of flow reattachment and the distal end of AAA, respectively, in both FM and FSIM. The maximum wall stress and the largest wall deformation were both located at the proximal and distal end of AAA. Conclusions The number and center of the recirculation area for both models are different, while the change of vortex is closely associated with the AAA growth. The largest WSS of FSIM is 36% smaller than that of FM. Both the maximum wall stress and largest wall displacement shall increase with the outlet pressure increasing. FSIM needs to be considered for studying the relationship between AAA growth and shear stress.

Abstract:Objective To investigate the effect on aneurysmal pressure after stent intervention treatment for aneurysm accompanied by stenosis. Methods Computational fluid dynamics (CFD) analyses were carried out to make comparative study on aneurysm models with and without stenosis. Three models (M1, M2, M3) were constructed to compare the pressure variations. M1 was the aneurysm model with no stenosis and no stent, M2 was forming from M1 model with a preaneurysm stenosis, and M3 was the M2 model with stent implantation at the place of the aneurysm. Results For comparison between M2 and M1, pressure increase in the aneurismal sac caused by a mild stenosis (50%) was about 1.399 9 kPa(10.3 mmHg) with the peak systole, and the average pressure increase in a cardiac cycle was about 0.572 kPa(4.3 mmHg). For comparison between M2 and M3, pressure increase in the aneurismal sac was about 1.037 kPa(7.8 mmHg) at peak systole in a cardiac cycle, and the average pressure increase in the aneurismal sac in a cardiac cycle was about 0.399 kPa(3 mmHg). Conclusions A mild stenosis could not result in the sharp pressure increase with stent intervention applied to the treatment of aneurysm accompanied by stenosis harbored on a tortuous intracranial artery. The geometry of the parent vessel and its aneurysmal/stenotic diseases do have influence on the pressure variation at the place of aneurysm.

Abstract:Objective To propose an inverse method for determining nonlinear mechanical properties of the blood vessel based on the results of experimental data and numerical simulation.Methods Pressure loading was applied on the blood vessel to obtain the experimental data of in vitro holistic blood vessel by using the self-designed device. The finite element model of vessel inflation was established by supposing that material characteristics of the blood vessel were in corresponding with the hyperelastic Ogden model. Mechanical properties of the blood vessel were then computed by the reverse method based on these experimental data and simulated results .Results The first-order and second-order Ogden material parameters of the rabbit abdominal aorta were identified, in which α=10.86±1.98 for the first-order Ogden material model. The mechanical properties of the rabbit abdominal aorta could be characterized as the hyperelastic material. Conclusions The inverse method based on the experimental measurement and numerical simulation can be used to identify the nonlinear mechanical properties of the blood vessel.

Abstract:Objective To study the effect from drug diffusion coefficient of atherosclerotic plaque on drug diffusion within the arterial wall, so as to truly reflect the drug distributions. Methods Using computational fluid dynamics (CFD) method, five plaque models with different diffusion coefficients were employed to numerically investigate the distributions of drug concentration both within the arterial wall and the plaque. Results The drug concentration in the arterial wall was increased gradually with the diffusion coefficient of the plaque increased; however, the increment would become gentle. Conclusions When the diffusion coefficient in the plaque was smaller than the tissue, the plaque inhibited the drug diffusion within the arterial wall, or conversely, it would promote the diffusion. Especially when the diffusion coefficient in the plaque was much larger than the tissue, it no longer affected the drug diffusion within the arterial wall. It is necessary to consider the impact of plaque in further research, which is beneficial to the optimization design of drug-eluting stents.

Abstract:Objective To study a quantitative indicator for measuring the similarity between blood pressure waveforms and its application in the analysis on the simulated blood pressure waveform for pulsatile flow simulation system.Methods Based on the past similarity measurement algorithm and the known feature of blood pressure waveforms, the weighted average algorithm was presented in this paper, which possessed advantages of both global matching and partial matching by integrating the correlation coefficient with the characteristic parameter algorithm, and calculating similarity degrees through overall and partial waveform.Results The weighted average algorithm was proved to be more suitable for the analysis on the blood pressure waveform similarity compared with the angle cosine method, average absolute deviation method, and numeric similarity coefficient method.Conclusions The weighted average algorithm showed excellent ability in calculating the similarity degree between different waveforms, or in comparing the performance with different pulsatile flow simulation systems, and it could be applied to other physiological waveforms with further improvement.

Abstract:Objective To evaluate the fatigue life of coronary stent under the effect of blood flow and thus optimize the stent design.MethodsA simplified model of the stent, blood, plaque and artery was established using Pro/Engineering, and the periodic blood flow impact on the vascular stent was simulated by finite element method via ANSYS. The result on hemodynamics from such stent was then used to evaluate its fatigue life. The geometric parameters of the stent were chosen as design variables for optimization. By using Latin Hypercubic sampling and ANSYS program, responses of the sample points could be obtained and the Kriging surrogate model was then constructed to optimize the fatigue life of the coronary stent.Results Goodman’s method showed that the optimized stent was safe. The cumulative damage method indicated that the largest damage occurred at the second cross-section of the bridge struts. The fatigue life of the optimized stent could be enhanced by 30.55%. Conclusions The finite element method can be used to evaluate the fatigue life of the coronary stent, and the optimization of stent by establishing Kriging model can effectively enhance the fatigue life of the stent.

Abstract:Objective To numerically simulate the propagation of pulse wave in human arterial tree by proposing a novel calculation method which combines a transmission line model and a recursive algorithm of input impedance, and to study the effects of individual differences and arterial tree parameters on pulse wave so as to provide references for the analysis on physiologic and pathologic characteristics of human arterial tree. MethodsThe transmission line model of human arterial tree was constructed, which consisted of 55-segment large and medium sized arteries. The recursive algorithm was applied to compute the input impedance of arterial tree at each point. The blood pressures and flows of 55 arteries were calculated and showed in the distribution graphs. Based on this method, the effects of height, heart rate, stroke volume, internal radius and wall thickness on pulse wave propagation and blood pressure distribution were compared. Results The simulation results were in good agreement with the general rules of pulse wave propagation. The propagation of pulse wave in arterial tree showed significantly different characteristics for different parameters. Conclusions The proposed method can effectively simulate the propagation of pulse wave in arterial tree and accurately reflect the effects of individual differences and hemodynamics parameters on pulse wave propagation, and it is an important assistant means for the pathophysiologic analysis and diagnosis of human arterial tree.

Abstract:Objective Due to the limitation of manufacturing techniques, possible design optimization selecting and influence of its wearing in clinical application, the bearing surface of hip joint replacements is presented as non-spherical geometry, and the finite element method can be used to study the contact mechanics behavior in such kind of non-spherical hip joint replacement. MethodsThe reconstructing of non-spherical articular surface based on spherical-grid-data model (SGDM) was developed to investigate the effect of contact mechanics of an ellipsoidal head against a spherical cup in a typical metal-on-metal hip joint replacement. Results The maximum contact pressure of the non-spherical bearing was decreased effectively, and meanwhile the contact area was increased when curvature radius of the ellipsoidal head around the centre of the contact zone was increased, while the effects of the cup inclination angle on the maximum contact pressure and contact area of the non spherical bearing under the same load showed relatively small, but the contact pressure distributions were different. Conclusions A well-controlled non-sphericity can improve the magnitude and distribution of contact pressures on metal-on-metal hip joint replacements. In addition, the developed model and evaluation method in this paper can be used for simulation of dynamic contact and wear prediction of non-spherical hip joint replacements.

Abstract:Objective To investigate and analyze the risk of dislocation failure after total hip arthroplasty (THA). Methods The optical motion capture system was used to obtain the kinematic data of the lower limbs during actions of daily living (ADLs) from normal people. The visual hip prosthesis motion analysis software was designed and developed to measure the maximum safe motion space of the hip prosthesis with different design parameters and judge the safety of the hip prosthesis by analyzing the relative motion relation between the cup and prosthetic stem. Results Based on the measured kinematics data, the motion analysis software could compare the range of motion of the natural joints and that after THA. Thus, the relationship between the dislocation of hip prosthesis and ADLs was obtained and the dislocation risk after THA was investigated. Conclusions There is a high risk when activities that require a high flexion motion are performed, especially for the kneeling and squatting activity.

Abstract:Objective To investigate effects of F-actin cytoskeleton on differentiation of endothelial progenitor cells (EPCs) under laminar shear stress. MethodsEPCs isolated from rat bone marrow were treated with laminar shear stress (1.2 Pa). Then the gene and protein expressions of the endothelial cell differentiation markers, such as vWF and CD31, were assayed with real time RT-PCR and Flow Cytometry. The effects of laminar shear stress on F-actin cytoskeleton and Ras activity were investigated by immunofluorescence technique and Pull-down assay. Results Compared with the untreated group, the expressions of vWF and CD31 were obviously increased in the group treated with laminar shear stress (P<0.05). Moreover, exposure of EPCs to laminar shear stress led to the reorganization of cytoskeleton and enhanced the activity of Ras in EPCs. The treatment to EPCs with either F-actin stabilizer jasplakinolide or depolymerizers cytochalasin D inhibited the cytoskeleton reorganization induced with laminar shear stress, the activity of Ras and the up-regulation of the vWF and CD31 genes. However, over-expression of Ras augmented the up-regulation of the vWF and CD31 genes induced by laminar shear stress in EPCs.Conclusions The mechanism that laminar shear stress accelerates the differentiation of EPCs may be related with the laminar shear stress-induced cytoskeleton rearrangement and Ras activation. This study is of significance in revealing the mechanism of vascular endothelial repair which could be useful for the prevention and treatment of atherosclerosis.

Abstract:Objective To establish the model of dentulous mandible and straight wire appliance and investigate the stress and displacement distributions of the roots and periodontal tissues under en masse space closure with sliding mechanics. Methods The three-dimensional finite element model of mandible and teeth was developed from CT images, which consisted of the dentin, enamel, dental pulp, PDL (periodontal ligament), cortical and cancellous bone. The models of Roth straight wire brackets with actual data were also constructed. The dental adhesives were used to stick the brackets on the corresponding teeth. Contact elements were used to simulate the interaction between the stainless steel arch wire and the brackets. Moreover, spring elements were used to connect the brackets and the arch wire. The load with the value of 1 N was applied on the model to close the space. Results The lingual tipping of lateral and central incisors was found, corresponding with the clinical observation of en masse space closure with sliding mechanics. High stress in the teeth and periodontal tissue appeared at the incisors and the distal roots of the first molars. The maximum von Mises stresses in PDL of the central incisors and the distal roots of the first molars were 3.97 kPa and 5.75 kPa, respectively. Conclusions In order to avoid root resorption of incisors, the torque of the brackets could be increased. Less orthodontic forces or orthodontic implant could be used to avoid distal roots of first molars.

Abstract:Objective To evaluate the influence from deformation history of arch-wires on its orthodontic force. MethodsA finite element model including brackets and arch-wires in free status was built, and the position of brackets under clinical condition was obtained through laser scanning on the plaster dental model. Based on the finite element method, the brackets were moved to the clinical position through two different movement pathways, using a thermal-mechanical shape-memory-alloy model of arch-wires. The orthodontic force obtained from the two pathways were then compared and analyzed. Results The relative differences in the orthodontic force obtained from the two pathways were significant, with a range from 0.3 to 8.0. The influence of deformation pathway on the orthodontic force was reduced if the arch-wire was first overloaded and then unloaded to the clinical condition，but reduction of the orthodontic force varied at different positions of arch-wires, and the relative differences might increase at certain positions. Conclusions The deformation history of arch-wires has some direct relation with the orthodontic force produced on the NiTi shape-memory-alloy, and the evaluation on the orthodontic force should trace its deformation history.

Abstract:Objective To develop a registration method for 3D human atlas models by using geometric information of the vertices so as to lay a foundation for statistical modeling of atlas. Methods Based on CT images of the normal human, thirty 3D models of human atlases were created and marked by the manual selected points, including 1 standard module, 20 training sets and 9 testing samples. The training sets were first registered with the standard module, including calculation on geometric information of the individual vertex and optimization process of weight coefficients in the registration models. By minimizing the energy function defined with the Euclidean distances between the automatic registered points and the manual selected points in training sets, the optimized weight coefficients could be obtained. The testing samples were then registered with the standard module to calculate the Euclidean distances between the automatic registered points and the manual selected points. The results were then compared with the training sets to evaluate the stability of the registration method. Results The registration function and the corresponding optimized weight coefficients were obtained, and the average errors for the training sets and testing samples were 1.983 mm and 2.045 mm, respectively. Further statistical analysis showed that there were no obvious differences in the error distributions among the training sets and testing samples. Conclusions The accuracy and stability of the proposed registration method meet the requirement in medical applications, and it can provide automatic registration of points of interest on human atlas models and be used for element classification in statistical modeling.

Abstract:Objective To analyze the neck muscle activity during head flexion and explore the cause of muscle fatigue in human head and neck. Methods A musculoskeletal model of head neck complex was established based on AnyBody software platform, and the muscle strengths during head flexion were simulated according to the input data measured by Vicon motion capture system, which were validated with the literature data. Results The neck muscles played a major role during head flexion. The force assignment mode among muscles was different during 45% and 75% flexion process. The integral of muscle strengths on flexion angle WM could reflect the muscle fatigue to some extent. Since the largest WM was found in the semispinalis cervicis and multifidus muscles during head flexion, it may indicate that those muscles have the easy tendency to be fatigue. Conclusions The musculoskeletal model established in this paper can provide a technical support for the exploration of neck fatigue mechanism.

Abstract:Objective To investigate the effect of different perfusion flow rates on proliferation and osteoblastic differentiation of human mesenchymal stem cells (hMSCs) in large scale β-TCP (tricalcium phosphate) scaffold at perfusion bioreactor. Methods hMSCs isolated from iliac bone marrow aspiration were loaded into large scale β-TCP scaffold and cultured in perfusion bioreactor at the perfusion flow rate of 3, 6 or 9 mL/min for 15 days. The culture media were collected for D-glucose consumption assay every 3 days. After perfusion culture for 15 days, the cell-scaffold composites were harvested for assessment of cell viability by MTT colorimetric method, SEM observation and osteogenic gene expression by real-time PCR. Results The proliferation of hMSCs assayed by daily glucose consumption showed that at early stage of culture, cells proliferated faster at flow rate of 9 mL/min than at 3 or 6 mL/min (P<0.001); while at late stage of culture, cells proliferated faster at flow rate of 6 mL/min (P<0.05). The cell viability indicated that the cell-scaffold composites at flow rate of 6 mL/min exhibited the most viable cells (P<0.001). SEM indicated that all the macropores of the scaffold at different flow rates were filled with cellular layers. All cellular layers at flow rate of 3 mL/min were incompact, but that at 9 mL/min were compact; at flow rate of 6 mL/min, the cellular layers were either compact or incompact. Real-time PCR revealed that after perfusion culture for 15 days, the mRNA expression of osteobalstic genes including ALP and OP, were enhanced significantly at flow rate of 6 and 9 mL/min as compared to that at 3 mL/min (P<0.01); however, the 9 mL/min group presented the higher OC expression than 3 and 6 mL/min group (P<0.001). Conclusions At early stage of perfusion culture, the proliferation of hMSCs was promoted at flow rate of 9 mL/min, while at late stage, there was more viable cells in scaffolds at flow rate of 6 mL/min. The osteoblastic differentiation of hMSCs was facilitated with the increase of perfusion flow rate, which was attributed to the increased flow shear stress.

Abstract:Objective To investigate the biomechanical properties of transverse fractured femurs when fixed by TiNi shapememory alloy embracing plate (TiNi SMA), limitedcontact dynamic compression plate (LCDCP) and static interlocking intramedullary nail (SIiN), respectively, so as to provide the theoretical evidence for orthopedic surgeons in clinical application. Methods Eight pairs of cadaveric femurs were used with one side randomly fixed by TiNi SMA and SIiN and the other side fixed by LC-DCP. Then the axial compression test, threepoint bending test, and torsion test were conducted. Results For axial compression test, the strains of TiNi SMA group were greater than those of LC-DCP group and SIiN group (P<0.05), while no significant differences were found between LC-DCP group and SIiN group (P>0.05). The displacements of TiNi SMA group were greater than those of LC-DCP group and SIiN group (P<0.05) under the load of 200~600 N, and there were no significant differences between LC-DCP group and SIiN group (P>0.05). For three-point bending test, the displacements of TiNi SMA group were greater than those of LC-DCP group and SIiN group (P<0.05), while no significant differences were found between LC-DCP group and SIiN group (P>0.05). For torsion test, the torsion angels of TiNi SMA group were similar to those of SIiN group (P>0.05), but the torsion angles of LC-DCP group were smaller than those of TiNi SMA group（≥3 N?m）and SIiN group (P<0.05). Conclusions When the fractured femurs are fixed by three internal fixation devices, the stability of TiNi SMA group is weakest, SIiN group being better, and LCDCP group being best. The axial micromotion in TiNi SMA group can promote the healing of fracture.