Abstract:There are two important recent advances in cardiovascular biomechanics. One is cardiovascular mechanobiology, which illustrates how mechanical factors can generate biological effects resulting in vascular remodeling. By studying signal transduction pathway in the cardiovascular system and means of mechanical control, cardiovascular mechanobiology aims to investigate the nature of cardiovascular disease at cellular and molecular level. The other is cardiovascular numerical simulation and individual design of surgery operation on the basis of clinical images. Based on fluid mechanics, clinical images as well as advanced measuring and testing methods of flow field, cardiovascular numerical simulation and quantitative analysis can be conducted. New in vivo techniques for studying cardiovascular function and the design of individual surgery system can provide biomechanical solutions for the diagnosis, therapy and prewarning of cardiovascular disease. In this special issue, seven papers on cardiovascular biomechanics are published, covering vascular cell mechanobiology and cardiovascular numerical simulation connected with the clinical problems tightly. These papers show us some recent advances in cardiovascular biomechanics in China.

Abstract:Objective To investigate the effects of shear stress and vascular smooth muscle cells (VSMCs) on the proliferation of endothelial cells (ECs) and the molecular mechanism involved in. Method Using parallel-plate flow chamber system, normal shear stress of 15 dyn/cm2(1 dyn=10-5 N) was applied to ECs cultured singly and cocultured with VSMCs respectively. Then, the expression of PCNA, a molecule representing cell proliferation ability, and phosphorylation of Akt were analyzed by Western blotting in order to investigate the roles of shear stress and VSMCs in EC proliferation. Under the static condition, the expressions of PCNA and p-Akt were analyzed in ECs co-cultured with VSMCs with and without physical contact. And then TGFβ1 neutralizing antibody was employed to demonstrate the contribution of TGFβ1 in VSMCs induced EC proliferation. Results Normal shear stress decreased EC proliferation and Akt phosphorylation. VSMCs increased EC proliferation and Akt phosphorylation in both co-culture conditions with and without physical contact. Normal shear stress partly reversed the increase of proliferation and Akt phosphorylation in ECs with physical contact to VSMCs, and TGFβ1 neutralizing antibody exerted the similar effects in ECs without physical contact to VSMCs. Conclusions Normal shear stress is a protective factor with its inhibitory effect on EC proliferation. VSMCs induced EC proliferation via TGFβ1 and pAkt pathways by paracrine model.

Abstract:Objective To elucidate the mechanical chemical interaction and its mechanobiological mechanism on the migration of endothelial cells. Method RTPCR, Western blot and immunofluorescence were applied to detect the expression of CXCR1 and CXCR2 and their distributions under three levels of shear stress; anti-IL8RA and anti-IL8RB were used to inhibit CXCR1 and CXCR2 to evaluate endothelial cell migration under shear stress; ECs were transfected to obtain the wild type Rac1(Rac1WT) or RhoA (RhoAWT), the constitutively active forms of Rac1(Rac1Q61L) or RhoA (RhoA63L), and the dominant negative forms of Rac1(Rac1T17N) or RhoA (RhoA188A) respectively, with lipofectamine 2000 reagent. ECs transfected with three plasmids of Rac1 were exposed to three levels of shear stress and IL-8, respectively; ECs transfected with three plasmids of RhoA were stimulated by IL-8. Results CXCR1 and CXCR2 are novel mechano sensors mediating laminar shear stress induced endothelial cell migration. High expression of Rac1 and RhoA can promote EC migration, while their low expression inhibits EC migration. Conclusions CXCR1, CXCR2, Rac1 and RhoA are critical signaling molecules in mechanical chemical interaction of EC migration.

Abstract:Objective The effect of different flow shear stress gradient on the changes of arrangement and shape of endothelial cells was evaluated in order to investigate the effect of shear stress gradient on ECs morphology and function. Method A flow chamber system with gradient shear stress was established, in which the range of shear stress is from 15 dyn/cm2 to 6.6 dyn/cm2(1 dyn=10-5 N), and the shear stress gradient is 1.5 dyn/cm2 and 3 dyn/cm2 respectively. After ECs were subjected to the gradient shear stress for 6 hours, cell angle, cell width length ratio, as well as cell shape index of ECs under the different shear stress gradient were examined. Results The cell angles of ECs were straggling under both 1.5 dyn/cm2 and 3 dyn/cm2 shear stress gradient. The cell width length ratio and cell shape index of ECs were decreased under 1.5 dyn/cm2 shear stress gradient compared with that of 3 dyn/cm2shear stress gradient. Conclusions The ECs show random orientation under the different shear stress gradient. The ECs are trending to stretch and elongate shape under smaller shear stress gradient, and to approach cycloid under larger shear stress gradient.

Abstract:Objective To apply the swirling flow mechanism to the design of arterial prostheses with small diameters and the arterial bypass surgery to resolve the acute thrombus in small diameter prostheses after implantation, and lessen the restenosis of bypassed arteries due to the formation of internal hyperplasia. Method The computational fluid dynamics (CFD) method was used to investigate the flow field and wall shear stress distribution of a new graft, an Stype bypass and an axis deviated arterial bypass, which all had the swirling flow. In addition, the platelet adhesion under swirling flow and internal hyperplasia in S-type bypass were measured. Results The swirling flow can apparently enhance the wall shear stress (WSS) and suppress the platelet adhesion and internal hyperplasia. Conclusions The swirling flow can significantly improve the flow field in arterial graft and bypass to inhibit the acute thrombus in small diameter prostheses and internal hyperplasia after bypass surgery.

Abstract:Objective To investigate the influence from the left pulmonary artery (LPA) with different stenosises (50%,20%,0%) after complete repair of tetralogy of fallot (TOF) on the hemodynamic features using computational fluid dynamics(CFD). Method The 3D models were reconstructed by the computer tomography (CT) images. CFD simulations were performed on these three models to describe the flow characteristics of the main pulmonary artery and the bifurcations such as average speed in LPA and right pulmonary artery(RPA), flow patterns, static pressure and wall shear stress. Results In the unsteady state simulation, different regurgitation and flow velocity distribution can be easily found in the start of LPA due to the stenosis rate of LPA, while the flow velocity distribution is uniform in the RPA. The flow velocity distribution, static pressure, pressure drop and wall shear stress are also different in these three models. Conclusions It is important to expand the branch pulmonary arteries during the TOF operation. LPA stenosis may be an early and important cause of pulmonary artery regurgitation. The use of CFD simulation can provide the early reference information for the effect after TOF operation.

Abstract:Objective To investigate effects of endovascular stents with different structures and wire cross section shapes on the treatment of internal carotid aneurysm and its influence on hemodynamics and flexibility. Method Based on the same model of internal carotid aneurysm, five models with different stent intervention treatment were constructed, which had different stent structions or wire cross section shapes while their porosity rates were approximately the same. Numerical simulations were performed using finite volume method to get quantitative information of biomechanics. Results Among the five models, the mean flow rate in aneurismal cavity decreased maximally in the model with stent of rectangular cross section. Wall shear stress in aneurismal dome and aneurismal neck were found to decrease much more in models with circular cross section and rectangular spiral stent. The flexibility of mesh stent was far better than that of the spiral stent. Conclusions Mesh stent with rectangular cross section has better biomechanical influence on the treatment of internal carotid aneurysm. These findings may help clinicians to select a proper stent when treating arterial aneurysm.

Abstract:Objective To study the flow field of a new vascular bioreactor with small diameter at different operating conditions. Method To investigate the flow field of a new vascular bioreactor with small diameter under three operating conditions by numerical simulation: outerbox rotating, innerbox rotating and both innerbox and outerbox rotating. A comparison of parameters such as flow velocity and shear stress was made. Results The culture medium in the bioreactor rotated with the innerbox and outerbox, and the velocity was uniformly distributed; the bioreactor could therefore provide a low shear stress environment that is nondestructive for the cells in the medium; the shear stress in bioreactor had a quadratic function relation with the rotation rate. Conclusions This bioreactor could provide a good culture environment for vascular tissue regeneration, and this study provided theoretical basis for the experimental research of bioreactors.

Abstract:Objective To study the effect of reasonable jogging speed on body shape and walking gait to make people acquire graceful posture through jogging. Method Five jogging speeds were selected according to related measurements. Kinematical data of subjects (15 young women volunteers) in jogging were measured by the motion capture system, while the EMG signals of 8 major muscles in lower limb were collected simultaneously. The mean angles of hip, knee and ankle joints in sagittal plane at different speeds were calculated. The subject whose data was closest to the mean value was chosen as the research subject and analyze the kinematical data. Results The angles of the subject's hip, knee and ankle joints in sagittal plane at different speeds in a gait cycle were presented, and activation curves of her 8 major muscles were obtained during lower limb movements. Relationships between the jogging speed, jogging stage, muscle activation and joint angle were described by the scoring method. Conclusions The range of joint angle and maximum of muscle activation don't change with jogging speed monotonously. The study provides a reference for young women to choose their own jogging speed.

Abstract:Objective To investigate the effects of gender and body mass index(BMI) on dynamic plantar pressure among children by comparing the plantar pressure parameters of obese boys and girls, as well as normal boys and girls when walking at preferred speed on flat ground and reviewing the relativity of children’s BMI and these parameters. Method 79 children were enrolled in this research to make gait test when walking naturally, using a 0.5m footscan plate system (RSscan International, Belgium). The results were statistically processed and analyzed by SPSS16.0. Results(1) There is no significant difference in mostly dynamic plantar pressure parameters between genders for both obese and normal children; (2) There is significant difference in the impulse percentage in mid foot and ground, and appearing time of pressure peak values of several areas including M5, MF and HL for normal children; (3) There is no significant correlation between BMI and foot support duration, impulse percentage between mid foot and ground, pressure peak value of T25, appearing time of pressure peak value of HM and HL; (4) BMI and the other plantar pressure distribution indicators are well correlated. Conclusions(1) There is no significant difference on dynamic plantar pressure distribution between genders for obese children, but there are effects of genders on partial dynamic plantar pressure distribution parameters for normal children; (2) Children with larger BMI are of worse walking stability and lower efficiency; (3) Children with larger BMI tend to feel fatigue in walking and get injured in ankle joints and other parts of the body more easily.

Abstract:Objective To evaluate the static viscoelastic properties of the porous gradient UHMWPE material by the creep, stress relaxation and creep recovery tests. Method The porous gradient UHMWPE material was prepared by the template leaching (T-L) method. The porous structure was characterized by scanning electron microscopy(SEM) and the porosity and pore distribution of porous layer were measured by a pressure mercury analyzer. The creep, stress relaxation and creep recovery properties were tested by the experimental determination of flat indentation. Results The porous layer of T-L UHMWPE was well bonded with the substrate material. With the increase of NaCl content, the porosity and pore size distribution scope improved clearly. Creep deformation and modulus presented a nonlinear increase with time and the stress and modulus of stress relaxation showed a nonlinear decrease with time. The buffering capacity for impact loads of porous gradient UHMWPE was significantly higher than the compact UHMWPE. Experimental results showed that the creep recovery properties of the reasonable porosity of U50 and U60 samples were almost similar to the compact UHMWPE material. But the higher porosity caused the increase of the plastic deformation. Conclusions The porous structure of UHMWPE effectively increased the elastic property and strain response sensitivity, which may be beneficial to improve the lubrication of frictional contact surfaces and reduce the wear of artificial joints.

Abstract:Objective By a thorough analysis of the baseball batting to provide a theoretical instruction for baseball players with a simple and efficient dynamic model. Method Based on the moment of impulse theory, the closed form linear equations were derived by the dynamic analysis of the hinged multi-rigid body model. The numerical results would be obtained after solving the equations. Results (1) The batting speeds have been obtained by the numerical calculation under various conditions of different initial speeds of the baseball and bat; (2) The knockout speeds of wood bats are much smaller than the aluminum ones; (3) The coefficient of restitution has the significant effect on the batting speeds, and has no effects on sweet spot and center of position. Conclusions The numerical results are consistent with the data of experiments in reference. The calculating procedure is easy for baseball coaches and players to understand and can be applied in the training of baseball batting directly.

Abstract:Objective To identify whether the calf or porcine cervical spine is a suitable substitute specimen for vitro spine study by comparing the biomechanical characteristics of porcin, calf and human cervical segments. Method Twelve fresh (age: 1 year; average weight: 60-80 kg) porcine cervical spines (C0-T1) and twelve fresh (age: 1 week; average weight： 40-50 kg) calf cervical spines (C0T1) were taken. The twelve specimens were divided into two groups. One group of six was divided into C2-C3, C4-C5, C6-C7; the other group was divided into C3-C4, C5-C6. The muscle and soft tissue of each functional segment (C2-C3, C3-C4, C4-C5, C5-C6, C6-C7) were removed, preserving the full ligament, and then each functional segment was tested respectively. The flexion/extension, axial left/right rotation, and right/left lateral bending were applied continuously on the range of motion(ROM) and neutral zone(NZ). The findings in the study were compared with the published data of human cervical spine. Results In rotating and extension/flexion of NZ, the calf and human cervical spines were relatively similar, but they were far greater than that of the porcine cervical spine. In the lateral bending, the NZ of porcine C2-C3 was 69.7% of human, the NZ of porcine C6-C7 was 60.4% of human, and other segments were far smaller than human; the calf cervical spines were different from human, except the C2-C3. In bending and extension flexion of ROM, the porcine and human cervical spines were very similar. But they were far less than the calf, approximately 50% of calf; in the rotation, C2-C3 of porcin was about 69% of human, and other segments were less than the human. The calf cervical spine was much larger than human, and the smallest gap was in C4-C5 of 3.5 °. Conclusions The C2-C3 and C6-C7 of porcin can replace the human cervical spine in nearly all biomechanical experiments on spines. The ROM of calf is bigger than human cervical, but the C2-C3 and C3-C4 of calf are similar to human in biomechanics.

Abstract:Objective To explore the influence of positioning of the femoral tunnel for medial patellofemoral ligamentre (MPFL)construction on the isometric characteristics of grafts.Method Knee specimens from ten fresh frozen cadavers were used. The attachment of medial patellofemoral ligament was observed. The distance between points from the adductor tubercle, the medial femoral epicondyle, and proximal, distal and central point of the MPFL’s femoral attachment site respectively to the middle point of its patellar attachment site were measured. Changes in length were recorded while the knee was measured by angles of knee flexion (0°, 30°, 60°, 90°, and 120°). Results The length changes in every point were compared. All of the maximal length changes of its adductor tubercle: proximal points were not greater than 3 mm. There was no significant difference between the length changes of adductor tubercle and proximal points（P>0.05）. Conclusions The position of the femoral turnel for MPFL reconstruction should be located as follows: MPFL should be at the middle point of upper edge of femoral attachment site (proximal point), and the point can appropriately be shifted to adductor tubercle.

Abstract:Recently, twoimplantsupported single crown has been applied more and more in molar restoration with the advantages of antirotation, antibend, distributing stress, reducing bone resorption and increasing the success rate of molar restoration. The biomechanical study of two-implant can solve the problems of clinical application such as the stress concentration and the degree of bone resorption around implants, and it could contribute to the development of twoimplant restoration standard of a natural twofurcation simulation and regulate the two implant restoration technique, which is important for its extensive clinical application. Therefore, in this paper, the clinical application, biomechanical and biological characteristics and advantages of two implant will be reviewed.