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Abstract:Objective To investigate the role of rho-associated coiled-coil containing protein kinase 1 (ROCK1) and the relative signal molecules in sensing the mechanical stimulation from tensile strain and regulating the proliferation of vascular smooth muscle cells (VSMCs). Methods Physiological cyclic strain with magnitude of 10% and at frequency of 1.25 Hz was applied to VSMCs in vitro by using strain loading system. The proliferation level of VSMCs was analyzed by BrdU ELISA; the expression level of ROCK1, phosphorylations of protein kinase C (PKC) α/β II, protein kinase D (PKD) and extracellular regulated protein kinase (ERK) in VSMCs modulated by cyclic strain were detected with Western blotting; the expression of ROCK1 was specifically repressed by using RNA interference (RNAi). Results Compared with the static control, 10% cyclic strain significantly decreased the expression of ROCK1 and phosphorylations of PKD and ERK. The phosphorylation of PKCα/βII was decreased significantly under 10% cyclic strain for 12 h, but returned to normal level after 24 h-loading. Repressed expression of ROCK1 with RNAi significantly down-regulated VSMC proliferation, suppressed phosphorylations of PKCα/βII and PKD, but no obvious change was found in phosphorylation of ERK. Conclusions Physiological cyclic strain with magnitude of 10% may repress the phosphorylation of PKCα/βII and PKD via inhibiting the expression of ROCK1, which subsequently affect VSMC proliferation and maintain vascular hemostasis. The investigation on intracellular mechanotransduction network of VSMCs under mechanical stimulation of cyclic strain may contribute to the physiological and pathological mechanisms of cardiovascular diseases.

Abstract:Objective To develop the finite element model of six-year-old child occupant lower extremity with higher biofidelity and validate the model of knee joints, as well as analyze the biomechanical responses of growth plate under frontal impact load and injury mechanisms of the knee joint by using this model. Methods The six-year-old child occupant lower extremity with growth plate was modeled based on children’s anatomy and CT images, and corresponding material properties of the lower extremity model were assigned．The model was validated according to biomechanical experiments by Kerrigan et al. and Haut et al. and then was used to analyze the injury results of growth plate with different material properties. Results The model validation was qualified by comparing the curves from the experimental and simulation results．The growth plates at knee regions could change injury patterns of the child occupant lower extremity fracture. The material properties of growth plate could affect threshold of axial damage of the femur as well as relative position of the fracture． Conclusions The validated model can be used for related study and application on biomechanical responses and injury mechanisms of six-year-old child occupant lower extremities．

Abstract:Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery, so as to provide references for selection of interbody cage. Methods The finite element model of normal cervical spine (C2-7) was built and validated, and the cages with different height (5, 6, 7, 8 mm) were implanted into C5-6 disc (cage5, 6, 7, 8 model). All the models were loaded with pure moment of 1.5 N?m to produce flexion, extension, blending and axial torsion motions on the cervical spine, and the effects of cage height on range of motion (ROM), facet joint stress, intervertebral pressure in cervical spine were investigated. Results The intervertebral angle at the fusion segment increased by 0.68°with per 1 mm-increase of height. The ROM at C5-6 after cage implantation was less than 0.44°. The influence of cage height on ROM in C4-5 was greater than that in C6-7, and the changes of ROM in non-fusion segments were less than 7.3%. The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure. The stresses in the capsular ligament, cage and screw-plate system increased gradually with the increase of cage height, and these stresses in the cage6, 7, 8 models were much higher than those in the cage5 model. Conclusions For patients who need implanting fusion cage, the cage height should be 0-1 mm greater than the original intervertebral space height.

Abstract:Objective To establish the three-dimensional finite element model of human lower cervical spine C3-7 motion segments after anterior cervical corpectomy and fusion (ACCF) surgery with titanium mesh and bone graft, and to analyze the stability of cervical spine and stress distribution of internal fixation devices after ACCF surgery. Methods The finite element model of cervical spine C3-7 segments after ACCF of C5 segment with titanium mesh, bone graft, plate and screw fixation was established，and C3-7 segment intact model of cervical vertebra was also constructed. The torque moment of 0.5, 1.0, 1.5, 2.0 N﹒m was applied to the ACCF surgery model. The ROM, maximum stress in facet joint and stress distributions on internal fixation devices under flexion, extension, lateral bending and torsion movement were analyzed. Results ROM of reconstructed C5 segment increased with the torque moment increasing after ACCF surgery. In the case of 1.0 N﹒m torque moment and 50 N preload, the ROM of reconstructed C5, C3-4, C6-7 and C3-7 segment was reduced by 81%, 62%, 58% and 80% compared with the intact model. The maximum stress in facet joint of reconstructed C5 segment reduced and the stress in adjacent segments significantly increased. The stress of titanium mesh was mainly distributed on the compression side of movement, and high stress was located in the roots of screws. Conclusions ACCF surgery can promote the stability of cervical spine, decrease the stress in facet joint of operation segment, and has better treatment effect on easing compression from spinal cord caused by cervical spondylotic myelopathy. The research results will provide some theoretical basis for clinical application of ACCF.

Abstract:Objective To study correlation between the deformation and displacement trend of the lumbosacral vertebra (L1-S1) for two typical scoliosis spine under vertical load, so as to provide the mechanical basis of treatment and prevention of scoliosis in clinic. Methods The X-ray computed tomography (CT) imaging of two typical scoliosis spine (Lenke-4AN type and Lenke- 5CN type) were converted into 3D models，and their finite element models were then established and verified. The internal stress distribution and displacement variation of the models were calculated by the finite element software; the correlation between the lumbosacral vertebral structure and displacement of the spine was analyzed. Results Under the same boundary conditions and load cases, the stress and displacement for two kinds of lumbosacral vertebral models showed different trends. Due to its left-leaning and forward convex bending deformation as well as relatively large lordosis angle(60°) and smaller left-leaning angle (17.37°), the Lenke-4AN type lumbosacral spine produced slightly small forward convex displacement(8.18 mm) and relatively large left-leaning displacement (0.97 mm). The Lenke- 5CN type lumbosacral spine showed left-leaning and forward convex bending deformation as well, with relatively large lordosis angle (59°) and left-leaning angle (26.97°), so it produced more severe left-leaning (20.65 mm) and forward deformation (9.22 mm). Conclusions The deformation trend of lumbosacral vertebra is closely related to its structural characteristics, and different scoliosis lumbosacral vertebral structures will cause corresponding deformation trend. The research findings are important for the prevention and treatment of scoliosis.

Abstract:Objective To investigate the optimal scheme about the external loading of resetting tensile stress for clavicular fractures, so as to provide some mechanical references for optimal design of external fixators for clavicular fractures. Methods The shoulder CT scanning data from a volunteer were used to establish the three-dimensional model of human left shoulder by Mimics software. In order to better simulate the actual human shoulder, the ligament tissues were added in the model and the constraints of muscles were considered, and the experimental model for simulation analysis on resetting tensile stress was established. By 3 simulation experiments, the impacts from directions of resetting tensile stress, positions of action points and value ranges were simulated and analyzed, respectively. The resetting tensile stresses obtained from clavicle of the shoulder model under various external loading cases were simulated by orthogonal test methods. Results When the (angle between the horizontal plane projection of shoulder force which was loaded by external fixator and the coronal axis ) was greater than 45°, clavicle could obtain the resetting tensile stress, which became greater with the angle increasing. When (angle between the sagittal plane projection of shoulder force which was loaded by external fixator and the sagittal axis) was 30°-45°, the resetting tensile stress of clavicle was the maximum. The farther the position on which the loads from external fixator was exerted from the horizontal position of clavicle, the larger the resetting tensile stress of clavicle was. Conclusions The results of orthogonal test show that the optimal resetting tensile stress is produced with parameter combination of θ=65°, η=50°, acting on the center of humerus head of the shoulder

Abstract:Objective To study mechanical properties of the bone scaffold with different structure and its internal flow field distributions, so as to provide a direct comparison and judgment on model structure and offer an effective guidance for bone scaffold structure design. Methods Bone scaffold with natural, woven and spherical pore structure were reconstructed respectively by using Pro/Engineer and Mimics. The effective elastic modulus for three kinds of scaffolds, as well as their stress distributions and internal flow field distributions under threedimensional perfusion culture system were analyzed with the finite element method. Results The bone scaffold with natural structure showed smaller effective elastic modulus, smaller peak stress and more uniform stress distributions under the same pressure. With the same initial velocity and fluid viscosity, the bone scaffold with natural structure showed smaller internal velocity, wall shear stress and wall pressure. Conclusions The bone scaffold with natural structure has better biomechanical properties, which corresponds to the design criteria of bone scaffold in bone tissue engineering.

Abstract:Objective To study the micro-pore architecture and mechanical properties of porous titanium scaffolds with diamond molecule structure produced by 3D print technology, so as to guide the development of 3D-prinited porous titanium orthopedic implants. Methods Selective laser melting (SLM) and electron beam melting (EBM) were used to fabricate porous Ti6Al4V scaffolds with diamond molecule structure. The micro-pore architectures of those scaffolds were observed using optical microscope and scanning electron microscope (SEM), and universal material testing machine was used to conduct compressive test on the scaffolds. Results Both SLM and EBM techniques had machining error and half-melted metal particles were found on the strut surface. The relative error of strut size produced by SLM and EMB was 20.9%-35.8% and －9.1%-46.8%, respectively. The scaffold with strut width of 0.2 mm could not be produced by EBM. The compressive strength and elastic modulus of the scaffold fabricated by SLM was 99.7-192.6 MPa and 2.43-4.23 GPa, respectively. The compressive strength and elastic modulus of the scaffold fabricated by SLM was 39.5-96.9 MPa and 1.44-2.83 GPa, respectively. Conclusions The manufacturing precision of SLM is higher than that of EBM. Porosity is the main factor that affects the compressive strength and elastic modulus of the scaffolds. In the same process, with the increase of porosity, both the compressive strength and elastic modulus decrease. When the porosities are similar, the scaffolds fabricated by SLM possess higher compressive strength and elastic modulus than those by SLM.

Abstract:Objective To investigate filtration efficiency of convertible vena cava filters on treating pulmonary embolism under the condition of different thrombus diameter and content. Methods Three kinds of convertible vena cava filter models with different filtering unit structures (L-style, S-style, W-style) were constructed to numerically simulate hemodynamics based on computational fluid dynamic (CFD) methods, and their filtration efficiency were comparatively analyzed under the condition of different thrombus diameter (5, 10, 15 mm) and content (10%, 15%, 20%). Results With the increasing of thrombus diameter and content, the volume fraction of thrombus distributed on the filter bars increased and filtration efficiency of the filter became better. When the thrombus diameter was 5 mm, the S-style filter’s filtration efficiency was the best as compared with the other two styles of filters. When the thrombus diameter was 10 mm, the W-style filter showed the best filtration efficiency. When the thrombus diameter was 15 mm, the S-style and W-style filter showed the same filtration efficiency, which was better than the L-style filter. Conclusions The implantation of vena cava filters will cause hemodynamic changes, and its filtration efficiency is not only related to filtering unit structures, but also closely related to the diameter and content of thrombus. These results provide a theoretical reference basis for the design and clinical choice of the novel convertible vena cava filter.

Abstract:Objective To explore the effect of cervical rotatory manipulation on tensile mechanical properties of carotid artery with atherosclerotic plaque. Methods Thirty healthy male New Zealand rabbits were selected and randomly divided into experimental group, model control group and blank control group. Carotid atherosclerosis model were made in the experimental group and model control group. The experimental group received the intervention of cervical rotatory manipulation, but the model control group did not. The blank control group did not receive any intervention. After 3 groups received different interventions, the differences in tensile mechanical properties of rabbit carotid artery in three groups were observed. Results The ultimate strain, ultimate load and physiological elastic modulus of rabbit carotid arteries in 3 groups were statistically significant (P<0.05); The ultimate strain in the experimental group was 24.87% and 52.09% smaller than that in the model control group and blank control group, respectively; The ultimate load in the experimental group was 2.21 and 3.47 times of the model control group and blank control group, respectively; The physiological elastic modulus in the experimental group was 1.60 and 1.89 times of the model control group and blank control group, respectively. Conclusions Compared with normal carotid artery, the presence of carotid atherosclerotic plaque will reduce tensile mechanical properties of the carotid artery, and cervical rotatory manipulation will further reduce tensile mechanical properties of the carotid artery with carotid atherosclerotic plaque. Therefore, for patients with carotid atherosclerotic plaque, it is better to avoid cervical manipulation.

Abstract:Objective To obtain the ratcheting strain of articular cartilage under different loading conditions, and construct the theoretical model so as to predict the ratcheting strain of cartilage. Methods The fresh articular cartilage obtained from the trochlear of distal femur was used as experimental subject. The ratcheting strain of articular cartilage was tested under cyclic compressive loads by applying the non-contact digital image correlation technique. The theoretical model was constructed to predict the ratcheting strain of articular cartilage with different stress amplitudes and stress rates. The results from predictions were compared with the experimental results. Results The ratcheting strain of cartilage increased rapidly at initial stage and then showed the slower increase with cycles increasing. The ratcheting strain increased with stress amplitude increasing when the stress rate was constant. However, the ratcheting strain decreased with stress rate increasing when the stress amplitude was constant. When the stress rate increased, the ratcheting stain decreased. The prediction results of the established theoretical model were in good agreement with experimental results. Conclusions The ratcheting strain of articular cartilage is proportional to the stress amplitude, and inversely proportional to the stress rate. The established theoretical model can predict the ratcheting strain of articular cartilage and provide guidance for the construction of tissue engineered artificial cartilage.

Abstract:Objective To design a device for studying the effects of shear stress on the activity of blue-green algae. Methods The device was optimized in terms of the weakness of current shear stress devices, such as small volume, unstability, inability for quantitative analysis and short working period. The effective volume of the new device was 400-700 mL, and the error was less than 13.8%. Moreover, this device could produce a quantitative and uniform shear stress field and be continued to follow observation for more than 96 hours. Results By experiment on growth of microcystis aeruginosa, the device was proved to generate shear stress that could significantly affect the activity of microcystis aeruginosa cells. Conclusions This experimental device is an effective equipment for investigating the effects of shear stress on the activity of blue-green algae.

Abstract:Objective To study the anatomic and biomechanical characteristics of the dorsal radial ligament and anterior oblique ligament in carpometacarpal (CPC) joints of the thumb, so as to provide references for ligament repair. Methods Forty fresh hand specimens of adult male cadavers were dissected to make specimen of trapezium bone- ligament-the first metacarpal bone, of which 20 cases retained the dorsal radial ligament and 20 cases retained the anterior oblique ligament, respectively. The ligaments were tested on the biomechanical testing machine, and their length, width, thickness, the maximum load, elastic modulus and elongation rate were measured and calculated. Results For the dorsal radial ligament and anterior oblique ligament, their maximum load was (213.5±72.4) and (168.7±35.2) N, their elastic modulus was (17.2±6.7) and (9.3±2.5) N/mm2, their elongation rate was (116.2±21.3)% and (92.7±22.4)%, respectively. The maximum load, elastic modulus and elongation of the dorsal radial ligament were larger than that of the anterior oblique ligament. Conclusions In the capsular ligament in CPC joints of the thumb, the dorsal radial ligament has a higher stiffness and stronger toughness, which plays an important role in maintaining the stability of the joint. The stiffness of the anterior oblique ligament is smaller, the toughness is poor, which is easy to be damaged. The anterior oblique ligament is suggested to be reconstructed firstly to treat arthritis of CMC joints, and material whose elastic modulus and elongation rate is similar with the dorsal radial ligament should be selected.

Abstract:Objective To provide references for human gait analysis and its application in clinical medicine and rehabilitation through research on practical application of piezoelectric gait analysis system in plantar pressure monitoring. Methods Piezoelectric gait analysis system was designed to collect pressure signals of six acquisition points in insole. The signals were transferred by bluetooth, and then analyzed and handled by APP and MATLAB. Results The plantar pressure cloud chart, center of pressure (COP) butterfly diagram were obtained by interpolation and color mapping in MATLAB, the walk cycle was calculated by measuring swing phase of both feet, and real time pressure monitoring was realized by mobile APP to give an accidental fall alarm. Conclusions The system can achieve monitoring of standing posture, state of equilibrium, walk cycle and accidental fall, and the experimental results are coincident with clinical research conclusions. Meanwhile, the wearable structure is more suitable in real walking scene.

Abstract:The spinal manipulation in traditional Chinese medicine (TCM) has a prominent clinical advantage in the treatment of chronic lumbar pain, such as low back pain, but the insufficient basic research on manipulation is a serious obstacle to its development. Using finite element analysis (FEA) can preferably simulate the mechanics under various kinds of spinal manipulation, analyze its action mechanism, test the hypothesis, standardize the operating practices, make quantitative, qualitative and optimal treatment plans, so as to provide an effective method for the basic research on manipulation therapy. This paper reviews the FEA studies of spinal manipulation in recent years, discusses the influence of different spinal manipulation on intervertebral disc, lumbar accessory structures, spinal loads and mechanical stability of the vertebral body. The results show that current FEA studies on spinal manipulation need to make the simulation method standardized and precise. Meanwhile, the research ideas of finite element method should be developed to guide the clinical application of spinal manipulation.