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Abstract:Objective To study the effect of ghost red blood cells (GRBCs) on white blood cell (WBC)-mediated adhesion of tumor cells (TCs) on endothelial cells (ECs) in shear flow. Methods GRBCs with hematocrit (Hct) of 20% were added in the parallel plate flow chamber to observe changes in the number of tethered WBCs on ECs, the collision between TCs and adhesive WBCs, and the number of firmly adhered TCs at different shear rates of 62.5, 100, 200 s-1, respectively. Results GRBCs could increase the number of adhered WBCs on ECs and the collision between TCs and adhesive WBCs, and finally enhance the adhesion of TCs on ECs, especially at high shear rate (200 s-1). However, the adhesion efficiency of TCs was not significantly influenced by GRBCs. Conclusions GRBCs in shear flow can promote TC adhesion on ECs, and the research finding will provide a theoretical basis for cancer therapy.

Abstract:Objective To investigate the effects of triangle stents with different rotation angles on hemodynamics of cerebral aneurysms. Methods A non-uniform lattice Boltzmann method (LBM) was adopted to make local refinement on grids near the stent, and a scheme for the curved boundary conditions was used to numerically simulate the stented cerebral aneurysms. The stream plots of flows in the aneurysms, the velocity profiles at the aneurysm orifice and the velocity reduction were obtained and analyzed to evaluate the effects of stents with different rotation angles on treating cerebral aneurysms. Results With respect to velocity reduction, the best treatment effect was achieved in the triangle stent with rotation angle of 180°, while the triangle stent without any rotation caused the smallest velocity reduction. In addition，the dynamic differences were not obvious in triangle stents with different rotation angles at small porosities. Conclusions The non-uniform LBM combined with curved boundary conditions can be used to study hemodynamic characteristics of the cerebral aneurysm accurately, which provides reference for the design of such stent and also offers some guidance for intervention therapy in clinic.

Abstract:Objective To investigate the pattern of load transfer in cervical spine treated with Hybrid surgery using total disc replacement (TDR) and spinal fusion, so as to deepen the understanding of Hybrid surgery from the biomechanical view. Methods A finite element model of cervical spine C3-7 (INTACT model) was built to simulate three types of fusion surgeries at C4-6 degenerative segments: upper TDR combined with lower bone graft fusion (TDR45 model), upper fusion combined with lower TDR (TDR56 model), two-level fusion (Fusion456 model). Results In all surgical models, mobility of the fused levels was almost lost, while mobility of the TDR levels increased. Under the axial load of 160 N, the entire cervical motion was less than 4° in the INTACT model, while the motion in the TDR45 model and TDR56 model increased to 8.2° and 8.9°, respectively. In the TDR56 model, the force transferred through the C5 vertebra decreased by 20%, while the force transferred through the facet joint force was 3.8 times larger than that of the INTACT model. The facet contact force in the TDR45 model increased by 50%. The maximal stress in the INTACT model was 0.8 MPa, while the facet contact force in the TDR45 model and TDR56 model were almost 2 times as that in the INTACT model. Conclusions Due to the increased mobility at the TDR levels, the cervical curvature after Hybrid surgery changes greatly under the axial load. The alteration of spinal alignment will result in a decrease in anterior vertebral section force at the operative level, as well as an increase in facet joint force and facet cartilage stress.

Abstract:Objective To discuss the feasibility of constructing a 3D finite element model of the temporomandibular joint (TMJ) including the musculoskeletal system based on imaging and anatomy, and to provide new ideas of modeling for TMJ biomechanical researches. Methods CT images of the skull, MRI images of masticatory muscles and bilateral TMJ from No.23 Chinese virtual human in the second generation were collected and imported in batches into Mimics in format of DICOM for 3D reconstruction. Then the model was integrated and optimized by Geomagic Studio, and the TMJ capsule and articular cartilage were also constructed. After the material properties of TMJ tissues were defined, a 3D finite element model of TMJ including the musculoskeletal system was finally constructed by ANSYS. Results The 3D finite element model of TMJ with the musculoskeletal system was constructed, including TMJ disc, articular cartilage, TMJ capsule, maxilla (including zygoma and nasal), mandible, sphenoid, temporal bones (including part of parietal), maxillary teeth, mandibular teeth, temporalis muscles, masseter muscles, medial/lateral pterygoid muscles, temporomandibular ligaments, sphenomandibular ligaments and sylomandibular ligaments. Conclusions Based on CT and MRI images and anatomy, the 3D finite element model of TMJ including the musculoskeletal system can be precisely and feasibly constructed by Mimics, Geomagic Studio and ANSYS. This model can restore the biomechanical environment of the TMJ, provide new ideas of modeling for biomechanical researches on the TMJ, and offer the simulation platform for visualization treatment of TMJ disease in clinic.

Abstract:Objective In order to fully reconstruct the accident by utilizing pedestrian injuries information gained from the car-pedestrian collision, a new method based on finite element simulation and genetic neural network to deduce the car-pedestrian collision parameters in reverse is proposed. Methods Crash simulations from different contact angles (back, left, front, right) at different impact speeds (25, 40, 55 km/h) were conducted by using Hyperworks and LS-DYNA, so as to obtain the head injury criterion (HIC) value and the maximum velocity of the thoracic wall. According to the criteria of injury biomechanics, the severities of the pedestrian head and thorax and corresponding injury locations were analyzed and set as predictors, and the predictive values of collision parameters were then acquired by using genetic neural network. Finally, this method was verified by two car-pedestrian accidents with the video and exact collision parameters. Results For both cases of the car-pedestrian accidents, the car speeds at the collision of pedestrian were 54 and 49 km/h, respectively, and the car-pedestrian contact angles were both 180°. While according to the pedestrian injuries information, the predictive values of the car speeds at the collision of pedestrian were 51 and 43 km/h, and the predictive values of the car-pedestrian contact angles were 184° and 169°, respectively. The reconstruction accuracies of two cases were 0.94 and 0.88. Conclusions The proposed method in the study can be used to predict car-pedestrian collision parameters efficiently and accurately by utilizing the pedestrian injuries information, which provides a new method for cause analysis and responsibility recognition, as well as theoretical references for the treatment and protection of head and thoracic injuries occurred in the car-pedestrian collision.

Abstract:Objective To investigate mechanical characteristics of the spirochete flagella with tight-fitting ribbon configuration in micro-periplasmic space. Methods The 2D model of two parallel plates was used to simplify the periplasmic space, and the effects of flagellum spacing and eccentricity on force and torque acted on the spirochete flagella, and wall shear stress acted on the spirochete protoplasmic cylinder were studied by using numerical simulation method. Results (1) The relationship between the flagellum horizontal force and eccentricity was presented as a parabolic curve, and the peak value of the flagellum horizontal force was mainly caused by the gradual increase of pressure difference at two sides of the cylinder and the resistance viscous force as well. Flagellum spacing had no significant influence on flagellum horizontal force. (2) The relationship between the flagellum torque and eccentricity was presented as an exponential curve, and smaller flagella spacing would cause bigger flagella torque. (3) Flagellum spacing had no significant effect on wall shear stress of the protoplasmic cylinder, but it would be increased with the number of flagella and the eccentricity increasing. Conclusions Numerical simulation results in this study can qualitatively reflect mechanical characteristics of the spirochete flagella, and also provide references for further understanding the morphology of spirochete as well as its kinematic mechanism and pathogenic characteristics.

Abstract:Objective To analyze the pressure-driven streaming potential in a cancellous bone meso-mechanical model with numerical simulation, so as to understand characteristics of streaming potential distributions in cancellous bone. Methods Based on the control equations of electric field and fluid, the finite element method was used to calculate the streaming potential in the cancellous bone model when subjected to pressure. Results The streaming potential near the solid surface of the model was relatively large (about 43.4 μV), while the streaming potential away from the solid surface was smaller (about 19.7 μV). Pressure and Zeta potential had a significant impact on the streaming potential of the model, presenting a linear relationship with the streaming potential. The streaming potential was greatly affected when the ion concentration was low, whereas the effect on the streaming potential was small when the ion concentration was high. Conclusions This research finding provides a theoretical reference for prevention and treatment by stimulation methods of electric current and electromagnetic fields in clinical fractures, senile osteoporosis and other bone diseases.

Abstract:Objective To investigate biomechanical properties of the femur during slow walking and stair climbing before and after total hip replacement (THA), so as to provide theoretical basis for optimal design and manufacturing of the prosthetic hip. Methods The 3D finite element model of hip femur was established and validated first, and the stress distributions and stress shielding rates during slow walking and stair climbing before and after THA were calculated. Results During slow walking, the stress increased gradually from the proximal femur to the distal femur, reaching the maximum 90.6 MPa at the lower part of the femur before THA. A stress shielding phenomenon occurred on the femur after THA, but the stress amplitude decreased, with the maximum stress reaching 82.5 MPa. The maximum shielding rate appeared near the greater trochanter of the proximal femoral prosthesis and the total stress shielding rate reached 14.9%-99.0%. In addition, excessive stress concentration occurred at the prosthetic neck. Meanwhile, the stress distribution during stair climbing had a similar regular pattern as that appeared during slow waling, but with a more obvious stress shielding effect. Conclusions The greater stress shielding of the proximal femur and the excessive stress concentration on the prosthetic hip during stair climbing will both influence the THA surgery quality, so patients should minimize the movement involving large joint angle after THA.

Abstract:Objective To investigate effects of 3D co-culture of human keratinocytes (HKC) and human fibroblasts (HFB) under pressure on cell proliferation and collagen synthesis. Methods The HKC and HFB were planted on chitosan-gelatin scaffolds, respectively, for 2 d. The HKC-chitosan-gelatin complex (3D HKC) was cultured at air-liquid interface for 1 d to induce differentiation, and then co-cultured with the HFB-chitosan-gelatin complex (3D HFB) for 12 h. 3.4 kPa pressure was applied on the co-culture group for 24 h. The group of single culture with pressure, the group of single culture without pressure and the group of co-culture without pressure were used as control. HE staining was used to observe distribution and growth of HKC and HFB on chitosan-gelatin scaffolds. MTT method was used to test proliferation of HKC and HFB. Hydroxyproline kit was used to observe collagen concentration of the supernatant fluids. Results HE staining showed that HKC and HFB could grow confluently on chitosan-gelatin scaffolds；3.4 kPa pressure or co-culture both could promote the HKC proliferation and collagen synthesis, while restrain the HFB proliferation and collagen synthesis. Conclusions Pressure and co-culture play an important role in HKC and HFB proliferation and collagen synthesis. This research finding provides some reference for exploring the therapeutic mechanism of hyperplastic scar from clinical operation of resecting scar by transplanting tissue-engineered skin to the wound and then combined with pressure treatment.

Abstract:Objective To study the effect of continuous tensile stress on expression of Forkhead box protein O1 (FoxO1) in MC3T3-E1 cells in vitro during osteogenic differentiation, and explore the role of FoxO1 in the mechanism of continuous tensile stress induced-osteogenic differentiation. Methods MC3T3-E1 cells were seeded and applied with tensile stress at the frequency of 1 Hz and amplitude of 10% by FX-4000TTM mechanical loading system. MC3T3-E1 cells were divided into control, 1 h, 4 h, 6 h, 12 h, 24 h, 48 h, 72 h group, respectively, according to the time subjected to the tensile stress. Alkaline phosphatase (ALP) staining, real-time PCR, Western blotting and immunofluorescence were applied to detect the effects of continuous tensile stress on osteogenesis ability of MC3T3-E1 cells, mRNA and protein expression of FoxO1, and allocation of FoxO1 in MC3T3-E1 cells. Results (1) Continuous tensile stress could promote the osteogenic differentiation of MC3T3-E1 cells. Compared with the control group, the mRNA expression of ALP increased significantly at 24 h, 48 h, and the mRNA expression level of osteocalcin (OCN) reached the peak value at 72 h, which was significantly higher than that in the control group. The mRNA expression of runt-related transcription factor-2 (Runx2) significantly increased at 4 h as compared to the control group, and Runx2 protein level changed accordingly. The ALP staining results of the stress group and control group were significantly different. (2) Continuous tensile stress could increase mRNA and protein expression of FoxO1. The mRNA expression of FoxO1 markedly increased at 24 h, and its protein expression significantly elevated at 12 h. (3) FoxO1 was expressed in the nucleus and cytoplasm at 6 h, and then significantly increased in the cytoplasmat at 24 h. Conclusions 10% continuous tensile stress can stimulate the osteogenic differentiation of MC3T3-E1 cells, up-regulate the mRNA and protein expression of FoxO1 and change the allocation of FoxO1 in MC3T3-E1 cells. The investigation on the change rules of FoxO1 expression and allocation under mechanical stimulation will provide the experimental basis for studying the role of FoxO1 in mechanical stimulation.

Abstract:Objective To explore the influence of footwear and barefoot on movement coordination of the lower extremities and metatarsophalangeal (MP) joints during push off phase in typical lunge footwork of badminton, so as to provide theoretical basis for scientific training of badminton, as well as choice and development of badminton shoes. Methods Male badminton elites were recruited and required to perform the typical push-off footwork in playing badminton under two shod conditions (commercial badminton footwear and a prototype) and the barefoot condition. A Vicon motion capture system and a high-speed video camera were simultaneously employed to collect the kinematics and coordination characteristics of the hip, knee, ankle and MP joints during the push-off stage of the lunge step. Results (1) No substantial difference was found in joint kinematics of the lower extremities during push-off stage for wearing two types of badminton shoes adopted in this study. Compared with barefoot, wearing badminton shoes could increase the angular velocity of ankle and MP joints to some extent and significantly decrease the time of peak angular velocity occurrence in each joint; (2) With respect to characteristics of movement coordination, the hip, knee, ankle and MP joints were accelerating successively in a proximal-to-distal way during push-off under three foot-shoe conditions. Conclusions Footwear can provide the dynamic source during push-off, and contribute to improve the velocity and effects of push off in order to enhance performance. The movement coordination of the lower extremities during push off in the lunge step is more inclined to be a rational combination of sequence and synchronization. Consequently, more attention should be paid to the speed/strength training of the ankle and MP joints.

Abstract:Objective To investigate a reasonable and effective internal fixation method for posterolateral fracture of the tibial plateau. Methods Specimens of the tibial plateau with posterolateral fracture made from 12 adult male cadavers were randomly and evenly divided into 3 groups, and fixed by anterior 6.5 mm lag screw, lateral 4.5 mm L-shape plate, posterior 3.5 mm T-shape plate, respectively. All the specimens were loaded in turn by stress of 250, 500, 750, 1 000 N, and the corresponding axial displacement and stress were measured. Results Under the same stress, the Y-axial displacement of the anterior lag screw group was the smallest, showing a significant difference with the lateral plate group and the posterior plate group, while there was no significant difference between the lateral plate group and the posterior plate group in the Y-axial displacement. The stresses on marked points in the anterior lag screw group were evenly distributed. Conclusions For fixation of isolated posterolateral fractures of the tibial plateau, the anterior 6.5 mm lag screw can effectively increase the axial stability and balance the stress distribution around the fracture block, indicating it is an effective method for mechanical fixation. The lateral plate has certain advantage in lateral stability control, while the posterior plate has certain value to reduction of the posterior tibia plateau fracture.

Abstract:Objective To determine key muscles during muscle strength training of patients with knee osteoarthritis (KOA) by studying the correlation of KOA symptoms and disease stages with knee extensor/flexor strength. Methods Ninety-nine community volunteers were recruited and stratified into healthy group, single KOA group, and bilateral KOA group. The relationship between isokinetic extensor/flexor strength and KOA symptom, full-body aerobic exercise capacity, joint function were analyzed by knee isokinetic muscle strength test, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), 6-minute walk test, and CS-30 test. ResultsKnee isokinetic extensor peak torque of the symptomatic leg was significantly lower than that of the asymptomatic leg in single KOA group. There were significant differences in knee isokinetic extensor/flexor peak torque of both the severe and mild symptomatic leg in bilateral KOA group. Knee isokinetic extensor peak torque in bilateral KOA group was significantly lower than that in healthy group. Knee isokinetic extensor/flexor peak torque of KOA patients was positively related to 6-minute walk test, CS-30 test, while negatively related to age. Knee isokinetic extensor peak torque was negatively related to pain score and physical function score of WOMAC. Conclusions Both knee extensor and flexor strength are related to KOA. Therefore, during KOA rehabilitation therapies, muscle training for knee extensors (particularly quadriceps femoris muscles) and knee flexors (hamstring muscles, gastrocnemius muscles) need to be valued.

Abstract:Objective To make a quantitative analysis on the main bibliometric indices of Journal of Medical Biomechanics during 2010-2013, so as to evaluate the journal’s academic level and influence and provide some references for the authors, readers and the journal’s future development. Methods The data of bibliometric indices were searched from Chinese S&T Journal Citation Reports by Institute of Scientific and Technical Information of China (ISTIC) and China National Knowledge Infrastructure (CNKI) database, and bibliometric analysis was then conducted. ResultsDuring 2010-2013, the journal’s total citations, impact factors, immediacy index, number of source papers, average citations, affiliations, ratio of funded papers, citing half-life were steadily increased, while the non-self-cited rate, cited half-life, ratio of overseas papers were declined in totality. No obvious change was found in the number of citing journals, average authors and regions, and the papers showed an intensely regional distribution. Conclusions During 4 years, the journal has established a steady and high-level group of core authors and editorial members, with a wide range of subject distributions in published papers. The journal’s publication quality and academic influence have been improving steadily, but the academic impact of the journal still needs to be expanded due to its strong cross-discipliniary characteristics.

Abstract:Endothelial cells (ECs) and smooth muscle cells (SMCs) are the most crucial components of the vascular wall, and the interactions between them are essential for the maintenance of normal vascular physiology, as well as the initiation and development of cardiovascular diseases. Various typical co-culture models have been developed to simulate the location and growth situation of ECs and SMCs in vivo. In this review, the co-culture systems combined with the device applying fluid shear stress were introduced with discussion on the strengths and limitations of each system. The influences of ECs-SMCs interaction on the phenotype and alignment of ECs and SMCs, growth and migration of SMCs, and adhesion molecules expression of ECs under shear stress were briefly reviewed. The established evidence indicates that nitric oxide (NO), cytokines and microRNA are the most important signal molecules mediating the interactions between ECs and SMCs.

Abstract:atigue is a common phenomenon in many medical and neurologic diseases. Understanding the origins of fatigue in these diseases is of great guiding significance in developing targeted interventions for muscle fatigue. In this review, the central origin (including all the supraspinal and spinal physiological phenomena capable of inducing a decrease in motoneuron excitation) and the peripheral origin (including neuromuscular transmission, propagation of action potentials in muscle, excitation-contraction coupling) of muscle fatigue were summarized. The methods of assessing the central or peripheral origin of muscle fatigue were discussed, including the direct measurement (maximal voluntary contraction force, twitch force) and the indirect tests (twitch interpolation, electromyography, motor cortical stimulation).