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Abstract:Bone defects have always been an important cause of threat to human health, and artificial biomimetic bone repair replacement materials are currently one of the most effective and feasible solution approaches to treat bone damage. To develop artificial bone biomimetic materials, an in vitro biomimetic mineralization system must be constructed first to study in vitro biomimetic mineralization mechanism of natural bone matrix. Collagen is a template for mineralization, and its properties such as crosslinking degree, diameter, osmotic pressure, and surface charge can all directly affect mineralization progress. The biochemical and mechanical environments in which mineralization occurs are also quite distinct in their effects on mineralization process, particularly noncollagenous proteins and fluid shear stress (FSS). FSS is considered to be the main mechanical stimulation of bone tissues in micro-environment, which is of great significance to bone growth, repair and health maintenance. FSS at different levels and loading regimes has significant effects on transformation of amorphous calcium phosphate to bone apatite, self-assembly and directional alignment of collagen fibrils, and formation of hierarchical intrafibrillar mineralization. In this paper, the factors affecting collagen mineralization and their mechanism were summarized, with focus on regulation of FSS on collagen mineralization, and development direction in future was also prospected.

Abstract:Tissue has a complex three-dimensional (3D) dynamic structure, and is affected by various forms of forces. Cells sense mechanical forces from extracellular matrix (ECM), and the mechanical micro-environment constructed by ECM regulates different biological functions of cells. To prepare biomaterials which can simulate the ECM mechanical micro-environment of tissues is one of the research hot spots and difficulties in biomechanical field. Different physical and chemical properties of biomaterials endow materials with specific mechanical properties, which further affect the behavior and function of cells. Based on the latest literature of biomechanics of materials in the year 2021, this study mainly focused on the role of novel mechanical biomaterials in regulating cell biological behavior and application in tissue engineering. The future development direction in the field of biomechanics of materials was also discussed.

Abstract:Objective To study the effect of irrigation mechanical stimulation on scaffold degradation by numerical simulation, so as to predict its degradation degree. MethodsBased on perfusion experimental data, the fluid-solid coupling model was established by Comsol. The finite element model of scaffold was established by ABAQUS. Based on the models, the degradation performance of scaffold was simulated and predicted. Results The fluid-solid coupling simulation showed that the initial pressure at the speed of 15.79 mL/min was two-fold of that at 7.89 mL/min. Along the thickness of scaffold from the surface to the bottom, the pressures between the two velocities were decreased and gradually close to each other. The degradation of scaffold structure could be simulated dynamically by combining the degradation constitutive model with the finite element model. The obtained degradation data were consistent with the experimental data, and the residual molecular weight reached 0.643 on the 56th day. Compared with the experimental data, the simulation accuracy was higher than 98%. Conclusions The larger the perfusion velocity is, the greater the pressure on scaffold will be. Under the same perfusion velocity, the maximum force occurs on the surface of scaffold. The degradation pattern of scaffold can be predicted by applying the degradation constitutive model and the finite element model.

Abstract:Objective To study the effect of storage duration on compressive mechanical properties of rabbit patellar, so as to provide references for in vitro ligament storage.Methods The compressive mechanical properties of rabbit patellar ligament storaged at -20 ℃ at different storage durations (in 36 d) were tested with the universal tensile test machine. The microscopic morphology of collagen fibers was observed under the scanning electron microscopy (SEM). The enthalpy and denaturation temperature of collagen fibers were measured with differential scanning calorimetry (DSC).Results With the increase of storage duration, the compressive stress of the patellar ligament at 40% strain increased from 19 kPa to 112 kPa and then decreased to 57 kPa. SEM observation showed that the cross-linking of collagen fibers was initially strengthened and then weakened. DSC results showed that the enthalpy increased from 59.47 J/g to 67.10 J/g and then decreased to 54.43 J/g. The denaturation temperature increased from 67.62 ℃ to 77.28 ℃ and then decreased to 64.10 ℃.Conclusions When rabbit patellar ligament is stored at -20 ℃, with the increase of storage duration, the compressive stress of rabbit patellar ligament at 40% strain increases at first and then decreases. This change may be due to the variation of cross-linking level of collagen fibers. The stronger the cross-linking of collagen fibers, the stronger the compressive mechanical properties will be.

Abstract:Objective To study mechanical properties of the anisotropy for pig trachea and main bronchi, and determine the constitutive model of trachea deformation by finite element numerical simulation. Methods The pig tracheas were collected and cut through in their axial directions and expanded into two-dimensional planes. Then, by setting the length direction of the trachea aortas as 0°, each planar trachea was anticlockwisely cut into 6 samples with orientation of 30°,60°,90°,120°,150° and 180°, respectively. Uniaxial tensile tests were applied on the specimen in 6 angular directions by using the electronic universal test machine, to obtain stress and strain of the specimen in different directions. Nonlinear fitting to the experimental data was performed by using the Mooney-Rivilin hyperelastic model, in order to obtain the material characteristic parameters. Finite element models of the trachea and the main bronchi were established, and tensile numerical simulation was carried out.Results Samples at different angles showed different stress-strain curves. In the trachea, the stresses of samples with angle of 30°, 120° and 150° were in the range of 1.0-1.5 MPa, the stresses of samples with angle of 60° and 90° were in the range of 0.5-1.0 MPa, and the stresses of samples with angle of 180° were in the range of 2.5-3.0 MPa. In the main bronchi, the stresses of samples with angle of 30°, 120° and 150° were in the range of 0.8-1.0 MPa, the stresses of samples with angle of 90° and 180° were in the range of 1.4-1.8 MPa, and the stresses of samples with angle of 120° were in the range of 0.4-0.6 MPa. There was an obvious difference between the trachea and the main bronchi. The finite element simulation verified that the Mooney-Rivilin constitutive model was suitable for describing small deformation behavior of the trachea. Conclusions The pig trachea exhibits strong anisotropy. Meanwhile, the Mooney-Rivilin model can characterize small tracheal deformations. The results provide theoretical references for tracheal resection and reconstruction in clinical treatment and intervention with surgical instruments such as bronchoscopy.

Abstract:Objective To study dynamic compression performance of adipose tissues, so as to further reveal the damage mechanism, and provide references for medical treatment.Methods Based on the improved split Hopkinson pressure bar (SHPB) experimental device, the adipose tissue dynamic compression experiment was conducted. The stress-strain curves of adipose tissues at different strain rates were obtained. Then the numerical model of SHPB was established, and the experimental process was simulated and analyzed. The numerical simulation for penetration process of 32 mm diameter rubber non-lethal projectile into the simulated target in human abdomen was carried out.Results Adipose tissues had a noticeable strain rate effect. The stress-strain curves at two high strain rates were approximately straight lines. The slope was similar, and the elastic modulus was 3.25 MPa, which was about 6 times of that under a quasi-static state. The simulation curves of fat SHPB were consistent with the experimental curves, which verified correctness of the constitutive model. In the process of non-lethal projectile penetrating human abdomen, an annular convex area similar to water wave appeared on skin surface, and the fat layer absorbed about 67% of the impact kinetic energy.Conclusions The experimental data of adipose tissues are very accurate. Numerical simulation can reproduce the penetration process well, and provide references for studying the damaging effect of non-lethal weapons on human body.

Abstract:Objective To investigate the influence from natural and constrained modal of the hip joint on internal fixation after implantation of hollow screws and locking plates for treating femoral neck fractures. Methods CT image data of a patient with femoral neck fracture were analyzed, boundary of the hip joint was extracted to generate a three-dimensional (3D) model of the hip joint, and the assembly of common internal fixation models and hip joint models was established. Finite element simulation was then conducted, with focus on vibration characteristics. Results Vibration had a certain effect on internal fixation stability of hollow screws and locking plates. The occurrence of torsion would destroy the fixation environment of hollow screws and locking plates, resulting in a small displacement at the fracture end. In a constrained state, the modal frequency range was lower. Deformation of the vibration shape mostly occurred at proximal end of the femoral head, leading to the loosening phenomenon of internal fixation and prosthesis. A method for judging the stability of internal fixation was proposed from the perspective of vibration characteristics, and it was found that the stability of internal fixation with hollow screws was better than that of proximal locking plates. Conclusions For choosing internal fixation, influences from natural frequency of the screw and plate should be considered, so as to avoid natural frequency of the femur, which may cause resonance. The results can be used as a guidance for the selection of internal fixation materials and the design of structure and configuration.

Abstract:Objective By comparing biomechanical properties of two-screw rod and three-screw rod for fixing pelvic fracture, the difference in mechanical effects of different screw rod fixation positions in pelvic minimally invasive surgery was studied.Methods The mechanical models of pelvis fixed by two-screw rod and three-screw rod were established, and biomechanical characteristics of the pelvis during standing on both legs, during single-legged standing on healthy side or affected side, as well as in sitting posture were compared and analyzed by finite element simulation, and the fixation effect of three-screw rod was verified by clinical experiments.Results Both fixation methods could restore mechanical transmission of the pelvis. But for three-screw rod fixation, the stress on both sides of the pelvis was more balanced, and the displacement of the whole body and fracture surface was also lower during single-legged standing.Conclusions The three-screw rod fixation has an excellent effect in stability, which is more beneficial for fracture recovery.

Abstract:Objective To study mechanical properties of the novel micro-movement elastic implant of distal tibiofibular syndesmosis in dorsiflexion position.Methods A combination of simulation and experiment was used. The normal ankle dorsiflexion model, the bone nail repaired model and the micro-movement elastic implant repaired model were established by using Mimics and CT data. Besides, ANSYS Workbench was used for finite element analysis. Mechanical experiments on lower limb specimens were conducted on Instron E10000 mechanical test instrument, and five sets of experimental data were measured and analyzed.Results Mechanical properties of the micro-movement elastic implant repaired model were closer to those of the normal ankle dorsiflexion model, but stress of the micro-movement elastic implant repaired mode was greater than that of the bone nail repaired model. The results of two-sample heteroscedasticity t test indicated that there was no significant difference in resistance torque between the micro-movement elastic implant repaired model and the normal ankle dorsiflexion model.Conclusions For dorsiflexion position, repairing mechanical properties of the novel micro-movement elastic implant are much better than those of the bone nail, and there is still room for optimizing the micro-movement elastic implant.

Abstract:Objective To simulate dynamic response of cervical spine of the pilot during typical maneuver flight movements using finite element method, as well as make analysis and prediction on damage failure of the pilot neck during flight by impact injury and fatigue injury model of biological tissues.Methods A geometrically accurate finite element model of the neck was constructed, and validity of the model was verified by relevant examples. Then, the acceleration curves of centrifugal trainer under different modes were loaded for numerical simulation, and impact injury and fatigue injury of tissues were predicted by using the universal cervical injury criterion and the fatigue damage model of biological tissues.Results The maximum stress of the vertebrae and intervertebral disc caused by overload impact was 66.53 MPa and 58.63 MPa respectively during typical maneuver flight. According to the Nij injury criteria, the maximum Nij was 0.096, which was lower than the injury tolerance threshold of 1, and would not cause direct acute injury to cervical tissues. Based on fatigue damage model of biological tissues, it was found that cancellous bone suffered fatigue failure under the condition of uninterrupted repeated loading for more than 40 000 times. Considering the limited flight career of the pilot, the vertebral tissues would not be fractured due to the accumulation of fatigue damage.Conclusions To a certain extent, the results can contribute to formulating pilot training and flight plans, and also provide data support for the development of its protective equipment.

Abstract:Objective To make classification and segment measurement for the cases with tibiofibular and ankle fractures in parachuting landing, and investigate main classification types of parachuting fractures and fracture segments of high risk.Methods A total of 56 fracture cases in parachuting landing were collected, and the tibiofibula and ankle fractures were classified according to AO-OTA or Lauge-Hansen classification standards respectively based on their digital X-ray images. The medium plane between talus and tibia joint planes in ankle joint was defined as the reference plane. The highest and lowest injury points of tibia and fibula were marked respectively, and the fracture segment was defined between the highest and lowest point for statistical analysis.Results For tibiofibular and ankle fracture cases in parachuting landing, fracture at both tibia and fibula accounted for 80.4%. The major classification of tibiofibula fracture was 42-D/5.2 (45.8%) and 42-D/5.1 (16.7%). The major classification for ankle fracture was pronation-external rotation (PER, 59.4%) and supination-external rotation (SER, 37.5%). When tibiofibular and ankle fracture cases in parachuting landing occurred, the fracture segment of the tibia was mainly from 57 to 143 mm above the reference plane and from 6 mm below the reference plane to 24 mm above the reference plane, while the fracture segment of the fibula was 4-45 mm and 74-83 mm above the reference plane. Injury risks of all above segments were higher than 50%.Conclusions For protection of lower limbs in parachuting landing, the fracture at both tibia and fibula should be highly noticed. The ankle motion of PER and SER should be especially restricted in parachuting ankle protection.

Abstract:Objective To explore the effect of attachment wear on tooth movement in clear Aligner treatment, and to provide references for improving the efficiency of orthodontic treatment. Methods The tooth cone bean computed tomography (CBCT) scanning data were obtained, and the tooth model was established and assembled with the worn and complete attachment, respectively. When the appliance applied 2° distal torsion, 0.25 mm distal displacement, 0.1 mm depression displacement and 0.1 mm elongation displacement to the teeth, the changes of tooth displacement, periodontal ligament stress and root equivalent stress in the worn and complete attachment groups were compared. Results When the clear Aligner was used to apply distal torsion and elongation displacement to the teeth, the maximum tooth displacement decreased significantly, and the worn attachment caused the teeth to move obliquely when the distal translation and elongation displacement occurred. When the tooth was subjected to distal torsion, distal translation, depression and elongation, the maximum principal stress of periodontal ligament and the equivalent stress of tooth root decreased when the worn attachment caused the tooth to be subjected to distal torsion, distal translation, depression and elongation. Conclusions Attachment wear will affect the efficiency of tooth rotation and elongation.When the attachments are obviously worn, they should be replaced in time to ensure normal function of the attachments.

Abstract:Objective To compare the stress distributions in temporomandibular joint (TMJ) for patients with bilateral anterior disc displacement with reduction (ADDwR) after wearing stabilization splints with two different thicknesses during prolonged clenching by using three-dimensional (3D) finite element methods. Methods The 3D TMJ finite element models were constructed based on CT and MRI image data when the patient was biting in maximum intercuspation (working condition 1), on 3 mm thickness splint (working condition 2) and on 5 mm thickness splint (working condition 3), respectively. The von Mises stresses in the articular cartilages ,the TMJ disc and bilaminar zone under 3 working conditions were evaluated after the maximum jaw-closing forces were applied to the mandible for 60 s. Results The von Mises stress of left TMJ was bigger than that of right TMJ under each working condition. After wearing the 3 mm thickness splint, the disc was not recaptured, the stress was concentrated at the posterior band and bilaminar zone of the disc, and the stress on bilateral TMJ was significantly increased. After wearing the 5 mm thickness splint, the right disc was recaptured, the maximum stress was located at intermediate zone of the disc, and the von Mises stresses of articular cartilages and bilaminar zone were decreased by about 40%. However, the left disc was not recaptured, and the von Mises stresses of glenoid fossa cartilage and bilaminar zone were only slightly decreased by about 6%. Conclusions Different thicknesses of occlusal splints lead to different stresses and stress distribution patterns in TMJ of patients with ADDwR. The 5 mm thickness stabilization splint can reduce the stress of glenoid fossa cartilage and bilaminar zone in ADDwR patients. Disc recapture is helpful for ADDwR patients to relieve TMJ stress. When using stabilization splints for the treatment of ADDwR patients, on the premise of comfort wearing, a thicker splint can achieve more favorable stress distributions.

Abstract:Objective To fabricate a foldable microplate for single cell culture and establish finite element model of the folding microplate, so as to calculate traction force of single cells during contraction in three-dimensional (3D) state.Methods The folding angle of the microplate casued by cell traction force was calculated. Then the relation between bending moment and folding angle as well as the relation between traction force and bending moment were derived by using finite element simulation, so as to realize the characterization of traction force for singel cell in 3D state.Results The folding angles of the microplate with HSF and MC3T3-E1 cells in 3D state were 73°-173° and 49°-138°, respectively. The single cell traction forces of HSF and MC3T3-E1 cells were 55-210 nN and 52-161 nN, respectively.Conclusions The proposed method for measuring traction force of single cells in 3D state by fabricating the foldable microplate for single cell culture will provide some references for further development of calculating traction forces in 3D cell adhesion, spreading and migration.

Abstract:Objective To establish a mathematical model of tumor growth and invasion under radiotherapy, so as to numerically simulate the effect of radiotherapy on tumor growth and make sensitivity analysis.Methods The mathematical model of tumor growth and invasion with time evolution before and after radiotherapy was established. The model included four key variables in the process of tumor invasion: tumor cells, extracellular matrix （ECM）, matrix-degradative enzymes （MDEs） and oxygen. The linear quadratic (LQ) model was used to simulate the survival probability of tumor cells after radiotherapy, and the effects of different radiotherapy schemes and radiotherapy coefficients on the treatment effect were discussed. Traditional radiotherapy and intraoperative targeted radiotherapy were compared.Results Under the premise of constant total dose, the results of radiotherapy were directly proportional to the radiotherapy coefficient, but not related to the radiotherapy frequency; the therapeutic effect of intraoperative targeted radiotherapy was better than that of standard treatment.Conclusions Simulation results are basically consistent with clinical experimental results. As a more efficient treatment method, intraoperative targeted radiotherapy can provide new ideas for clinical tumor treatment.

Abstract:Objective To compare the effects of different support method on eccentric control angle and muscle strength of knee joints in 10-week Nordic hamstring exercise.Methods Twenty-eight college male football players were randomly divided into hand support group (HS group, n=14) and non-hand support group (NHS group, n=14) for 10 weeks. The eccentric control angle and eccentric muscle strength of knee joints were tested before and after the intervention.Results After 10 weeks of Nordic hamstring training， the eccentric control flexion angle of knee joint in HS group and NHS group was significantly decreased by 8° and 10°, and the knee joint angle in NHS group was 12° lower than that in HS group (P＜0.05); the peak torque of hamstring and quadriceps femoris in both HS group and NHS group was significantly increased, and the peak torque of hamstring centrifugal motion at 60°/s and 120°/s in NHS group was 16 and 13 N·m higher than that in HS group, respectively (P＜0.05).Conclusions NHS group is better than HS group in improving knee flexion angle and centrifugal muscle force. It is suggested that Nordic hamstring training should be taken as one of the daily training tasks for football players to prevent hamstring injury.

Abstract:Objective To propose a human-machine coupling dynamics modeling method based on virtual muscles, so as to quantitatively analyze the characteristics of human-computer interaction force and muscle activation of the musculoskeletal system. Methods First, in the gait experiment of wearing exoskeleton, the human motion capture system and self-developed mechanical monitoring device were used to obtain the wearer’s walking dynamics, electromyography (EMG) signals, exoskeleton drive status and local human-computer interaction information. The human-machine coupling model was established in modeling environment of the bone system, and the gait experiment data and the exoskeleton joint torques were used as driving information of the coupling model to perform inverse mechanical calculations. Finally, by adjusting strength and stiffness parameters of the virtual muscles, the real data of the model was compared with the experimental test result, to quantitatively evaluate effectiveness of the human-machine coupling model of the lower extremity exoskeleton. Results The normal interaction force calculated by inverse dynamics of the coupled model and the activation of lower limb muscles had a good consistency in response curve trend compared with measurement results of the gait experiment, and the interaction force results had a high degree of correlation (r=0.931, P<0.01), the root mean square error was small, and the peak error of lower limb muscle activation was lower than 5%. Conclusions The human-machine coupling model proposed in this study can effectively calculate the interaction force between human and exoskeleton. The establishment of the coupling model provides a theoretical basis for verification and iteration of the exoskeleton structure optimization and control algorithm, as well as performance evaluation on mobility assistance effects of the exoskeleton.

Abstract:Objective By establishing finite element model of the proximal femur, the injury risk of proximal femur under the conditions of self-selected speed rise and rapid rise at initial stage of standing during sit-to-stand (STS) transition was analyzed.Methods CT images of proximal femur in the elderly were processed with three-dimensional (3D) reconstruction and reverse modeling, so as to complete the solid model. The finite element model was established through material assignment and meshing. Based on the finite element analysis software ANSYS, the boundary conditions were constrained, and 1.733 kN and 1.837 kN loads were applied to obtain stress distributions and strain of proximal femur at different rising speeds. Results The stress concentrated at medial edge of the greater trochanter and the femoral neck. The peak stress and micro-strain appeared on inner edge of the larger rotor. The peak stress was 30.16 MPa and peak micro-strain was 2 553.5 at rapid rising speed. The peak stress and peak micro-strain at self-selected rising speed were 28.69 MPa and 2 430.4, respectively, which were relatively lower. For stress concentration area of femoral neck, the stress ranges at rapid rising speed and self-selected rising speed were 13.42-23.46 MPa and 12.76-25.51 MPa, respectively.Conclusions Frequent STS transition may increase the risk of fatigue fractures for proximal femur in the elderly. Rapid STS transition has a higher injury risk for proximal femur than STS transition at self-selected speed.

Abstract:Objective To investigate relative translations of the glenohumeral joint during abduction, scaption and forward flexion in normal Chinese, so as to provide references for diagnosis, treatment and follow-up of glenohumeral joint instability and subacromial impingement syndrome.Methods The biplanar fluoroscopy system combined with model-image registration technique were used to measure the humeral translation relative to the scapular in 13 healthy volunteers during abduction, scaption and forward flexion.Results The anterior-inferior glenohumeral translation during abduction, scaption and forward flexion was (4.0±1.3), (4.1±1.5),(4.8±1.9) mm, respectively. The superior-inferior glenohumeral translation was (3.0±1.0), (3.1±1.1), (3.3±1.5) mm, respectively. During the whole motion, there was a significant difference in superior-inferior translation at different arm elevation angles, while other significant differences were not found.Conclusions For normal Chinese, the humeral head was positioned posteriorly and superiorly on the glenoid. During forward flexion, the anterior-inferior and superior-inferior glenohumeral translation was the maxium. Therefore, in the process of clinical diagnosis, treatment and follow-up, patients performing the forward flexion may obtain a better evaluation effect.

Abstract:Objective Based on hemodynamic analysis, to investigate the cause of distal re-entry tear in Stanford type B aortic dissection after thoracic endovascular aortic repair (TEVAR).Methods A patient with type B aortic dissection was reexamined regularly with computed tomography angiography (CTA) at 1st month, 6th month, 12th month and 24th month after TEVAR. Based on the CTA images in each period, three-dimensional （3D） aorta models were reconstructed to perform morphological analysis and hemodynamic simulation.Results Compared with the diameter at 1st month after TEVAR, the diameter of true lumen at 12 months after TEVAR increased by 1.8 times and the global distortion of aorta increased by 16.67%. At postoperative 1st, 6th and 12th month, the maximum blood velocities at the new entry tear in systole were 69.6%, 33.7% and 92.1% higher than the average ones at distal landing zone, and the maximum wall shear stresses (WSSs) were 2.52, 2.32 and 3.52 times of the average WSSs respectively. In addition, the maximum time-averaged WSS (TAWSS) at 1st, 6th and 12th month after TEVAR were 1.88, 2.53 and 3.62 times of the mean TAWSS respectively.ConclusionsThe morphology of the aorta remodeled after TEVAR, and a sudden change in the diameter of true lumen occurred at distal anchoring zone and continued to increase. As a result, the blood flow velocity in this area accelerated, and the intima was continuously exposed to high WSS, leading to the redissection.

Abstract:Objective To study the mock circulation system (MCS) which can accurately reproduce the human hemodynamic environment for in vitro test in the development of artificial organs such as ventricular assist devices (VAD) and artificial heart-lung machine.Methods A double-heart MCS including the systemic and pulmonary circulation was established, which basically covered the main physiological characteristics and functions of the cardiovascular system. The simulation of valves and arteries were proposed with a new way made of silicone material. The MCS could simulate a variety of physiological environments such as normal human body, heart failure, valvular diseases, arteriosclerosis and peripheral obstruction changes by adjusting the control system parameters or structural parameters.The sensor and control system were used to realize the real-time display, control and data preservation of pressure and flow.Results The MCS could simulate the hemodynamic environment of normal human body and a variety of diseases, which were basically consistent with the actual human condition. The new valve and artery model reduced pressure fluctuations in a much better way. The HeartCon VAD of RocketHeart was connected to the experimental platform under simulated state of heart failure, and the hemodynamic environment (aortic pressure, left atrial pressure, cardiac output, etc.) could all be recovered to the normal range.Conclusions The MCS can accurately reproduce the hemodynamic environment of body and pulmonary circulation under a variety of physiological states, and provide an effective experimental platform for the performance test and control strategy design of artificial organs such as VAD. At the same time, the simulation method of making valves and arteries with silicone material can also be further improved in MCS.

Abstract:Objective To explore the role of adenosine monophosphate-activated protein kinase (AMPK), a key regulator of cellular energy metabolism, in vascular smooth muscle cell (VSMC) migration in response to physiological cyclic stretch. Methods The Flexcell-5000T mechanical loading system was applied with a physiological cyclic stretch at 10% amplitude and 1.25 Hz frequency to primary rat VSMCs, to simulate mechanical stimulation of VSMCs in vivo. The protein expression of p-AMPK in VSMCs was detected by Western blotting, and VSMC migration was detected by wound healing test. Results Compared with the static group, physiological cyclic stretch loading for 24 h significantly decreased the area of wound healing, indicating that physiological cyclic stretch inhibited VSMC migration. The protein expression of p-AMPK in VSMCs was increased significantly after physiological cyclic stretch loading for 3 h, and was decreased significantly after 24 h. Under physiological cyclic stretch loading conditions, incubating AMPK inhibitor could significantly reduce the protein expression of p-AMPK after 3 h, and promote VSMC migration after 24 h; incubating AMPK activator AICAR under static conditions significantly increased the protein expression of p-AMPK after 3 h, and weakened VSMC migration after 24 h. Conclusions Physiological cyclic stretch inhibits VSMC migration by increasing the protein expression of p-AMPK, indicating that VSMC migration regulated by physiological cyclic stretch is of great significance for maintaining vascular homeostasis.

Abstract:Objective Under noninvasive positive pressure ventilation, in view of inconvenient operations in human airway, and avoiding the interference of spontaneous breathing and the necessary leakage flow, the method for dynamic online monitoring of the respiratory resistance (R) and compliance (C) was studied.Methods At the end of expiration, when the exhaled flow was 0, relative to the expiration positive airway pressure (EPAP), a step-dropped pressure was produced with the amplitude Δp and hold time Δt. Under this dropped pressure, a short-time discharged flow was generated from the lung, and the discharged flow was applied to calculate the R and C. In addition, a respiratory model was developed in MATLAB to simulate the breaths of normal adult, acute respiratory distress syndrome (ARDS) patient and chronic obstructive pulmonary disease (COPD) patient. A serial of simulation experiments were carried out for obtaining data and verification.Results The calculated R and C from simulation for normal adult, ARDS patient, COPD patient, deviated from the actual value by 1.60% and -1.60%, 1.21% and -1.19%, -12.53% and 14.32%, respectively.Conclusions The proposed algorithm is practicable and feasible for calculating the R and C. The simulation results are beneficial for studying and realizing the intelligent ventilation and proportional assist ventilation in respirator.

Abstract:Objective To analyze the similarities and differences between four-point hand-knee position and hand-foot kneeling positions in trunk muscle activation and co-contraction, explore the possibility of hand-foot kneeling position as core stabilization exercises, so as to provide suggestions for actual training.Methods Nineteen healthy volunteers randomly performed exercises of four-point hand-knee position (4 motions) and hand-foot kneeling position (3 motions), while surface electromyography (sEMG) signals were collected from bilateral rectus abdominis, external oblique, erector spine, and multifidus muscles. The average sEMG and muscle co-contraction index (CCI) based on the sEMG signals were analyzed and compared.Results Significant differences were found in the sEMG and CCI within and between the two positions. Under four-point hand-knee position with the right hand and left leg lifting, the activation of all muscles was higher than that in the starting position. In four-point hand-knee position with the left leg lifting, the activation of ipsilateral multifidus muscle was significantly higher than that in hand-foot kneeling position. The activation degree of external oblique muscle and rectus abdominis was higher in hand-foot kneeling position with right hand lifting. A total of 28 muscle matching methods were obtained by pair-to-pair matching of 8 muscles. The starting posture in four-point hand-knee position fluctuated the least, indicating that the spine was the most stable, while the index of other exercises fluctuated in a larger range.Conclusions The possibility of hand-foot kneeling position as core stabilization exercises was proved from two aspects, namely, muscle activation and CCI. The hand-foot kneeling position and four-point hand-knee position can be used for strengthening abdominal muscles and back muscles, respectively. The four-point hand-knee position with contralateral upper and lower limbs lift is a more advanced exercise for trunk muscles, but sports injuries should be avoided.

Abstract:Objective To explore the proprioception characteristics of knee joints for knee osteoarthritis (KOA) patients before unicondylar knee arthroplasty (UKA) and total knee arthroplasty (TKA). Methods Twenty-nine single-compartment KOA patients were selected. Fifteen patients were treated with UKA (UKA group) and fourteen patients were treated with TKA (TKA group). The test was performed 1 to 3 days before the operation.The keen society scores (KSS) of KOA patients in UKA group and TKA group were compared, and their joint position sense and kinesthesia were compared with control group. Results Significant differences in KSS were found in TKA group and UKA group, and the knee joint position sense and kinesthesia showed no significant differences between TKA group and UKA group.There were no significant differences in the knee joint position sense and kinesthesia between the operated leg and unoperated leg in TKA group and UKA group, and between the left leg and right leg in control group. Compared with control group, there were significant differences between UKA group and TKA group in 60° position sense of the operated leg and unoperated leg.The kinesthesia of the operated leg and unoperated leg in UKA group and TKA group were also significantly different from that in control group. Conclusions Compared with control group, the proprioception of the knee joint in KOA patients was significantly reduced before the surgery, but the characteristics of proprioception in UKA group and TKA group were similar.

Abstract:Objective To examine the effects of ankle brace on biomechanics of the lower extremity during landing, so as to provide a theoretic support to choose ankle brace for people with different sports levels. Methods The key words (ankle brace OR ankle braces OR ankle bracing OR ankle support) AND (landing OR land OR jump OR hopped OR hopping) AND (biomechanics OR kinematics OR kinetics OR electromyography OR neuromuscular) in Chinese and English were searched from different electronic databases (CNKI, Web of Science, EBSCO, PubMed and other databases), for a period of Jan. 2000 to Dec. 2020. Cochrane was used to evaluate the quality of eligible studies. For meta analysis, subgroup analysis was used to assess the impact of ankle braces on ankle biomechanics.Results Thirteen studies with a total of 222 participants were included for mata analysis in this study. The semi-rigid ankle brace reduced the peak of ankle inversion by 25.8% compared with the elastic ankle brace (SMD=-0.562, P＜0.001). Moreover, the elastic ankle brace reduced ankle plant flexion during landing among athletes (SMD=-3.42, P=-0.021). As for collagiate students, both elastic ankle and semi-rigid ankle decreased the ankle inversion (elastic ankle brace: 35.4%, SMD=-1.000, P=-0.013; semi-rigid ankle brace: 31.11%, SMD=-0.881, P＜0.001) and ankle plant flexion (elastic ankle brace：23.30%, SMD=-1.381, P＜0.001；semi-rigid ankle brace: 36.33%, SMD=-1.605, P＜0.001).Conclusions Both ankle braces can prevent ankle sprain for athletes (basketball, volleyball, running) who experience training more than 5 years. The elastic ankle brace can limit the inversion and plantar flexion, while the semi-rigid ankle brace can merely decrease the ankle inversion. Therefore, athletes are more suitable for the elastic ankle brace. As for collegiate students without training history, both ankle brace can decrease the ankle inversion and plantar flexion. The elastic ankle brace has greater restriction on inversion, while the semi-rigid ankle brace has more restriction on plantar flexion. Therefore, the elastic ankle brace should be utilized if collegiate students have calcaneofibular ligament injury, while the semi-rigid ankle brace is more suitable for collegiate students who have a history of anterior talofibular ligament injury.

Abstract:Exosomes are extracellular vesicles secreted by cells with a variety of molecular components, which can play the role of substance transport and signal communication between cells through autocrine and paracrine. Exosomes exist widely in vivo and participate in many physiological and pathological processes, including force-related periodontal inflammation. There are stress receptor cells in the periodontium, which can sense force loading on the tooth. An appropriate amount of mechanical loading can maintain health of the periodontium, while excessive mechanical loading may cause destruction and absorption of the periodontium, leading to periodontal inflammation. This article reviews the role of exosomes in force-related inflammation response, especially in periodontal inflammation response.

Abstract:There is a tight regulatory network between the skeletal muscle system and the immune system, and they are jointly involved in functional regulation and response of the skeletal muscle system and the immune system. Cytokines are important signaling molecules that constitute this regulatory network. The cytokines produced by skeletal muscle atrophy and the cytokines produced by mechanical stimulation of skeletal muscle have different compositions and biological effects. The normal immune system and abnormal immune function can also affect skeletal muscle through the synergistic effect of different cytokines. According to this, a complex regulatory network between the two major systems is formed. The cytokine-mediated regulatory network between the skeletal muscle system and the immune system was reviewed in order to provide the theoretical basis for prevention and treatment of the skeletal muscle atrophy and mechanical intervention of the body immune function.

Abstract:Tympanic membrane perforation is one of the common diseases in otolaryngology. The main causes of tympanic membrane perforation are otitis，trauma and etc. With the rapid development of finite element analysis method, this method is applied to clinical evaluation of tympanic membrane perforation and repair materials. By establishing the finite element model of the middle ear, the characteristics of tympanic membrane perforation and tympanic membrane repair materials were analyzed from the biomechanical aspect, with combination of clinical application results. In this review, the finite element analysis and clinic research progress of tympanic menbrane perforation and tympanic membrane repair materials were summarized.