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Abstract:Objective To investigate the regulating effect and mechanism of microRNA-21 (miR-21) on extracellular matrix (ECM) of vascular smooth muscle cells (VSMCs) by vascular remodeling of hypertension. Methods By narrowing the abdominal aorta in rats, the hypertension models were established and divided into 2-week hypertension group and 4-week hypertension group, and sham-operated group was also established as control. VSMCs from the rat aorta were subjected to 0% (static), 5% (normal) and 15%（hypertensive）elongation strain at a constant frequency of 1.25 Hz and duration of 12 hours, respectively. The expressions of Smad 7 and ECM were detected by Western blotting, and the expression of miR-21 was examined by Real-time RT-PCR. Finally, miR-21 siRNA was used to study the role of miR-21 in the mechanical strain-induced expression of ECM, miR-21 and Smad 7. Results Compared with the sham-operated group, ECM and miR-21 in thoracic aorta of 2-week hypertension group were significantly elevated. Collagen I, collagen III and miR-21 in thoracic aorta of 4-week hypertension group were significantly elevated. Compared with the static and 5% strain groups, the protein expression of collagen I in VSMCs did not show significant change, but the protein expression of collagen III was significantly elevated and Smad 7 expression was significantly decreased in 15% strain group. The cyclic strain also enhanced miR-21 expression in VSMCs. miR-21 inhibitor effectively decreased the expression of miR-21 in VSMCs and protein level of collagen III, while enhanced Smad 7 expression under the static and 15% strain. Conclusions The vascular remodeling of hypertension causes the high expressions of ECM and miR-21. The cyclic strain induces the high expression of miR-21, which via Smad 7 results in enhancing the expression of ECM, collagen III especially, in VSMCs under vascular remodeling of hypertension.

Abstract:Objective To investigate the effects of unevenly-distributed backpack loads on human physiological parameters as compared to the traditional centrally-placed load at the backpack bottom. Methods For the unevenly-distributed load mode, the backpack was divided into four spaces including top right, top left, bottom right and bottom left. The loads were divided into two parts proportionally (1/2∶1/2, 1/4∶3/4 and 3/4∶1/4) and placed at the bottom left and top right of the backpack, respectively. The remaining two spaces were filled with the plastic foam. Ten healthy volunteers performed 30-min walking trials on the treadmill at the speed of 1.1 m/s with the backpack load equal to 10% body weight (BW). The changes of subjects’ body posture, muscle fatigue, heart rate, blood pressure before and after the trial, as well as the electromyography (EMG) changes at 0, 5, 10, 15 min after the trial were measured by the Bortec AMT-8 and the NDI Optotrak Certus. Results The muscle fatigue of right upper trapezius and forward-leaning angle increased as the loads at top right of the backpack increased. However, the muscle fatigue in the new mode of backpack load distribution showed no significant differences as compared to the traditional mode under the same backpack loads. The new mode with the load ratio of 3/4∶1/4 had no significant effects on posture. The new mode with the load ratio of 1/2∶1/2 could contribute to the decrease of heart rate and blood pressure as compared to the traditional mode. Conclusions Adopting a new and more reasonable load distribution mode can guarantee the body posture unaffected by the backpack loads, and decrease heart rate and blood pressure. Therefore, the cross and evenly distributed load mode is recommended for the backpack design.

Abstract:Objective To reveal the mechanical regulation mechanism for activation of lymphocyte function-associated antigen 1 (LFA-1). Methods The LFA-1 expressed on Jurkat cell surface was pre-activated by Mg2+ from quiescent-to intermediate-affinity state, and the tether events of Jurkat cells under different wall shear stresses (4.5-10 mPa) were observed and analyzed by flow chamber experiment. Meanwhile, a probabilistic model of integrin affinity jumping was established. Results The affinity jumping model was well fitted with the data obtained from flow chamber experiment. Under flowing loads, LFA-1 from intermediate to high-affinity state was observed, with prolonging of the adhesion bonds. The probability of tether event was 15%-26%. LFA-1 at high-affinity state contributed a significant fraction (about 26%-40%) of the bond lifetime. The off-rate of LFA-1 at high-affinity state was slower by 19%-65% as compared to that at intermediate-affinity state. Dissociating of ICAM-1 from LFA-1 was force-dependent and governed either by slip-bond at intermediate-affinity state or by catch-slip bond at high-affinity state. Conclusions The force-induced activation of LFA-1 mediates the slower rolling and firm adhesion of the cells. This research finding will further the understanding of inflammatory response events of circulating leukocytes, and contribute to the discovery of new antibody drug targets for the associated diseases.

Abstract:Objective To investigate the changes of morphological structures and biomechanical properties of scleral tissues in rabbits at different month ages. Methods The eyeballs of 1, 2 and 3 month-old New Zealand white rabbits were obtained for measuring the diameter and axial length, and the thickness of scleral tissues. Part of the scleral tissues was used to observe scleral structures with HE staining, some other part was used to observe collagen fibrils by electron microscope, and the left part were cut into strips and used to test the elastic modulus of the sclera on Instron 5544 system. Results The diameter, axial length of eyeballs and the thickness of the sclera were increased with month age. The elastic modulus of scleral tissues was also increased with month age. The numbers of scleral fibroblasts were decreased and the numbers of fiber bundles were increased with month age. The diameters of collagen fibrils were increased with month age. Conclusions In the post-embryonic stages, the structures of eyeball and sclera are changed continually, with growing numbers of thicker collagen fibers, and the biomechanical properties of scleral tissues are improved correspondingly. The mechanism of post-embryonic development in sclera is further explained in the study, which can provide theoretical guidance for prevention of sclera-related diseases.

Abstract:Objective To establish the finite element model of knee joint and investigate changes of stress and strain in normal and cartilage sclerosis cases, so as to provide reference for clinical treatment of the knee osteoarthritis. Methods CT scanning images of normal knee joint were used to establish the 3D finite model using Mimics and ANSYS software. Loadings of 350 N pressures were applied on the model of normal knee joint and knee joint with cartilage sclerosis, respectively. The related material parameters of cartilage before and after sclerosis were set, and the Von Mises stress and strain changes of the knee joint were then analyzed. Results In case of cartilage sclerosis, the function of shock absorption and load transfer in articular cartilage basically disappeared. The stress and strain on the femur changed with uneven distribution, showing more obviously than those on the inner and outer condyle, and the overall stresses were increased obviously. The largest stress and strain occurred on the meniscus. Conclusions The long-term cartilage destruction will affect nutrient metabolism of articular cartilage and cause the deterioration of osteoarthritis diseases. This study can preferably explain the pathogenic mechanism of osteoarthritis, and also provide relevant data for establishing parametric study system.

Abstract:Objective To analyze the badminton athletes’dynamic responses in their lower limbs under impact loads. Methods A human musculoskeletal model was established based on AnyBody Modeling System software and verified by measuring surface electromyography (EMG). The muscle force, joint force, joint torque of lower limbs during right Front-Court Lunge Step in badminton were studied by inverse dynamic simulation and analysis through Vicon motion capture system and force platform. Results The musculoskeletal model was validated to be effective by EMG. During right Front-Court Lunge Step in badminton，the force peak of the hip and ankle joint in Z direction was larger than that in X and Y direction, and the force peak of the knee joint in X direction was larger than that in Y and Z direction. During buffer period, the hip joint in X, Y, Z direction showed adduction, extension and internal rotation torque, respectively, the knee joint in X, Y, Z direction showed abduction, flexion and external rotation torque, respectively, and the ankle joint in X, Y direction showed varus and plantar flexion torque, respectively. The peak torque of the hip, knee and ankle joint in X direction was significantly larger than that in Y and Z direction. Vastus lateralis, biceps femoris, anterior tibial and medial gastrocnemius played a larger role against the ground reaction, while rectus femoris, semitendinosus, soleus played a relatively smaller role against the ground reaction. Conclusions The established musculoskeletal model in the study can provide a technical platform to analyze athletes’biomechanical properties of lower limbs under impact loads. To avoid sport injuries, more attention should be paid to the effect from ground reaction force load at touchdown instant on hip, knee and ankle joints in anteroposterior and mediolateral direction during footwork similar to Front-Court Lunge Step in badminton, and at the same time, the strength training of vastus lateralis, biceps femoris, anterior tibial and medial gastrocnemius of badminton players should not be ignored during specialized training.

Abstract:Objective To investigate the differences in rotation trends of maxillary complex through planting mini-implants in different maxillary positions for the protraction of craniofacial suture, so as to provide reference and basis for the appropriate implantation location in clinical orthodontics. Methods The 3D finite element model of the maxillary complex with mini-implant assisted maxillary protraction was established, and the mini-implants were planted in maxillary infrazygomatic crest and the anterior region (6 mm above the root of bilateral incisors and canine), respectively. Traction force of 500 g was applied to analyze the differences in rotation trend of the maxillary complex at different maxillary positions and in different directions. Results When protracted in maxillary infrazygomatic crest region, the maxilla mainly showed counterclockwise rotation trend. When protracted in anterior region, the maxilla mainly showed clockwise rotation trend. Conclusions Protraction at infrazygomatic crest is more suitable for treating patients with hypodivergent crossbite, while protraction in maxillary anterior region is more suitable for treating patients with hyperdivergent crossbite.

Abstract:Objective To study mechanical responses from mesenchymal stem cells (MSCs) under different mechanical stimulus duration, by measuring its elastic modulus and characterizing its stress fibers. Methods High resolution images of MSCs cytoskeleton in vitro were acquired by using atomic force microscope (AFM) and laser scanning confocal microscope (LSCM). AFM cantilever with micro-bead attached probe was used to perform force-distance curve experiment on MSCs at the approaching time of 0.1，0.5, 1, 5,10 s, respectively. The elastic modulus of MSCs at 300 nm indentation depth were measured and compared. Results The rat MSCs cytoskeleton presented an intensely organized network structure. The elastic modulus of rat MSCs varied obviously for different mechanical stimulus duration. The median and quartile (QR) of MSCs elastic modulus were 10.02 (QR=9.66),1.94 (QR=7.71),3.63 (QR=19.33),17.15(QR=35.13), 23.52 kPa(QR=34.87), with probe approaching time at 0.1，0.5, 1, 5,10 s, respectively. The MSCs elastic modulus showed the tendency of increasing with stimulus duration increasing, except for the extremely short stimulus (0.1 s). Conclusions Unlike inorganic elastomer, rat MSCs possess complete and flexible mechanical load-bearing structure and can respond actively to a relatively longer mechanical stimulation, with an increase of elastic modulus. These results may provide basic data for further tissue engineering researches on mechanical regulation of MSCs behavior.

Abstract:Objective To establish a 3D finite element model of an anti-shearing force Ni-Ti memory shape alloy patella claw for fixing patellar fracture, and analyze its mechanical performance. Methods The internal fixation model of transverse patellar fracture by patella claw was established by Pro/E 5.0, and then imported it into ABAQUS 10.1 for finite element analysis on its mechanical properties. The mechanical performance and deformation of the patella claw under two different patella femoral joint forces FQ at the knee flexion angle of 30°, 60°, 90° were analyzed, respectively. Results Under the same boundary condition, with the respective FQ as 367.5 N and 3 675 N, the maximum displacements of deformation were different at different flexion angles. As compared to fixation by tension band, using patella claw was preferable, with stronger resistance to tension and more stable anti-shearing force. Conclusions Deformation and displacement of the patella claw are in accordance with the biomechanical results needed in clinic, and its stability can satisfy clinical requirements for functional exercise as early as possible.

Abstract:Objective To establish a 3D finite element model of cervicothoracic spinal segments C5-T2 based on CT images and test its validity and effectiveness. Methods By using the Mimics, Geomagic and Hypermesh software, the 3D model of cervicothoracic spinal segments C5-T2 was reconstructed, repaired and pre-processed. Moment of ±0.5, 1, 1.5, 2 N?m were applied on top of the model to simulate loads produced during the flexion and extension movement of human body. The range of motion (ROM) of the segments C5-T2 during flexion and extension was calculated by ANSYS, and the reliability of the model was verified by comparing the experimental results in the previous literature with the finite element analysis results obtained in this study. Results Under the moment of 1 N?m, the ROMs of C5-6, C6-7, C7-T1 and T1-2 during flexion were 4.30°,3.21°,1.66° and 1.41°, and those during extension were 3.47°, 2.86°, 0.96° and 0.92°, respectively. The maximum stress during flexion appeared on the front of the vertebral body, while that during extension appeared on the back of the vertebral body. The trends of ROM and stress distributions were consistent with results reported in the previous literature. Conclusions The 3D model established in this study is accurate and realistic, and conforms to biomechanical properties of the cervicothoracic spine. The simulation results can be further used to explore clinical pathology of the spine and provide theoretical references for evaluation on cervicothoracic spine surgery.

Abstract:Objective To investigate the differences in biomechanical properties of 3 internal fixation patterns(the lateral plate and screw group, the rear plate and screw group, and the front and rear lag screw group) for treating posterolateral tibial plateau fracture under different axial loads. Methods Based on CT data of the tibial plateau, the entity model of 1/2 and 1/4 posterolateral tibial plateau fracture with 3 internal fixations were established and meshed to analyze force status of the fracture models with 3 internal fixations under different axial loads. ResultsUnder the axial load of 1 kN, for the 1/2 posterolateral tibial plateau fracture model, the displacements of the fracture fragments in the lateral plate and screw group, the rear plate and screw group, and the front and rear lag screw were 552.082, 67.964, 54.085 μm, respectively, and the stresses on the fixation device were 306.745, 231.844, 73.047 MPa, respectively. For the 1/4 posterolateral tibial plateau fracture model, the displacements in the three groups above were 416.072, 302.107, 150.639 μm, respectively, and the stresses on the fixation device were 306.673, 208.467, 73.607 MPa, respectively. Both the displacements of the fracture fragments and the stresses on the fixation device increased correspondingly under the axial load of 1.5 kN, and the trend of the data was similar to that under the axial load of 1 kN. Conclusions The results from the fracture models with 3 internal fixation patterns show that the front and rear lag screw group has a superior biomechanical stability under two different axial loads, and the similar mechanical properties can be achieved in the rear plate and screw group. Therefore, the front and rear lag screws will be preferred to treat posterolateral tibial plateau fracture with less obvious displacement in clinic.

Abstract:Objective To quantify the stress and strain of trabecular bone with microdamage/microfracture by using micro-CT and micro-finite element (μFE) analysis, so as to investigate the effects of osteoporosis on relationship between trabecular stress and microdamage/microfracture. Methods Two cylindrical specimens of healthy and osteoporotic acetabular trabecular bones were scanned by micro-CT to build 3D μFE analysis models. The uniaxial compression on two specimens was simulated under frictionless displacement boundary condition. The trabecular stress, trabecular strain, microdamage and microfracture under different apparent strains were calculated through nonlinear μFE analysis. Results For both the healthy and osteoporotic trabeculae under apparent strain of 0.05%-0.50%, the undamaged trabecular stress was under 50 MPa, while the damaged trabecular stress was above 110 MPa. Compared with the osteoporotic trabeculae, the mean stress of the healthy trabeculae was relatively higher, but the maximum stress of the osteoporotic trabeculae was higher. Trabecular damage occurred in both the healthy and osteoporotic trabeculae, while the healthy trabeculae showed more microdamage, and microfracture occurred in the osteoporotic trabeculae. Conclusions Within the scope of apparent strain, the healthy trabeculae can withstand a higher stress with more trabecular microdamage, and microfractures might occur in the osteoporotic trabeculae under the high stress.

Abstract:Objective To investigate the effect of 1,25-(OH)2-vitamin D3 (VD3)

Abstract:Bone marrow-derived mesenchymal stem cells (MSCs) are a kind of multi-functional stem cells with self-renewal and multi-lineage differentiation potentials, which play an important role in repair and regeneration of damaged tissues. The MSCs mobilization from bone marrow and migration through peripheral circulation into injured tissues are a key function of MSCs for tissues repairing. It has been proved in resent years’studies that various mechanical and chemical factors play a significant part in regulating the directed migration of MSCs to the damaged tissue. In this paper, the effects of mechanical and chemical factors on migration of MSCs through peripheral blood circulation to the damaged tissue are reviewed, and the possibly involved molecule mechanisms are discussed, trying to further understand the mechanochemical coupling in this process, and to provide the theoretical guidance for making mechanochemistry induced efficient migration of MSCs in tissue repair in clinic.

Abstract:Total knee arthroplasty (TKA) is the most common surgery for treating late-stage knee osteoarthritis. Previous studies have shown that after unilateral TKA, the load-carrying on lower limbs is asymmetrical and the contralateral knee have to bear even greater loads. Therefore, the osteoarthritis side is susceptible to become even worse and under the risk of subsequent replacement. In this review, factors affecting asymmetrical loading on lower limbs, including changes in alignment, pain, muscle weakness, loss of proprioception, and psychological factors are reviewed. The overall effects of these affecting factors on human body,

Abstract:Each of the syndesmotic ligaments has different biomechanical effects. Minimal movement occurs in the syndesmosis during the motion of the ankle joint, and the syndesmotic injury is associated with the ankle position and the patterns of external forces. Controversy still exists with respect to the optimal fixation of the syndesmosis. Malreduction of the syndesmosis would lead to abnormal pressure distribution on the ankle joint. Therefore, the flexible fixation might more accord with the physical movement of the syndesmosis. In this article, the biomechanical studies on syndesmosis are reviewed to provide the reference for proper treatment method for syndesmotic injury.