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Abstract:Objective To explore the influence of child head injury under different impact angles by applying the finite element model of six-year-old child pedestrian as specified in the European New Car Assessment Programme (Euro NCAP). Methods Based on the finite element model of 6-year-old pedestrian with detailed anatomical structure as specified by the Euro NCAP (TB024), four groups of simulation experiments were set up to explore the mechanism of head injury in children under different impact angles. The initial position for head mass center was on the longitudinal center line of the car. The initial speed of the car was 40 km/h. The car contacted with the model from the direction of the right (0°), the front (90°), the left (180°) and the back (270°). The kinematics differences and head impact responses were compared, and injuries of the facial bone and skull were analyzed. Results Through the analysis of head contact force, acceleration of head mass center, resultant velocity of head mass center with the vehicle, head injury criterion (HIC15), facial bone fracture and skull stress distribution, it was found that the risk of head fracture and brain contusion under back impact and front impact was higher than that under side impact. The risk of head fracture and brain contusion was highest under back impact, while the lowest under side impact. Conclusions Child pedestrian head injury was the largest under back impact. The results have important application values for the assessment and development of car-pedestrian collision protection device.

Abstract:Objective To evaluate biomechanical properties of the personalized titanium alloy short femoral prosthesis by finite element analysis. Methods Based on the validated femoral finite element model, the base of the femoral neck was simulated, and by inserting different short femoral prostheses, four total hip replacement (THR) models, namely, the SMF stem model (Model A), BE1 stem model (Model B), MINI stem model (Model C) and personalized stem model (Model D) were established, respectively. The same loads and constraints were applied to four groups of models, and the von Mises stress distribution and deformation were calculated and analyzed, so as to compare mechanical stability of each model. Results The deformation of all THR models was smaller than that of the femur model under physiological state. The deformation of Model B was close to that of Model C, and the deformation of Model A was close to that of Model D. The peak stress of Model C was higher than that of the other 3 models, reaching 9555 MPa. The overall stress trend was Model C > Model B > Model D> Model A > Model under physiological state. Conclusions The peak stress, stress distribution of personalized short femoral stem were similar to that of SMF stem, with reasonable stress distribution, small stress shielding of the proximal femur, minimum overall deformation and shear stress of the prosthesis, and its effectiveness and stability could meet the requirements of human biomechanics, which could provide references for joint surgeons and prosthesis researchers.

Abstract:Objective To quantitatively judge the degree of tibial bone healing using the finite element wall thickness analysis method, so as to provide an intuitive diagnostic basis for clinical judgment of tibial union and delayed bone healing. Methods After three-dimensional (3D) modeling for the affected and healthy limb side of 48 patients, the maximum wall thickness (MWT) was calculated, and the ratio (B value) was used as a quantitative index of bone healing. When both BMWT2 and BMWT1 were greater than 0.9, bone healing could be judged. When BMWT2 was between 0.9 and 0.7, bone union was judged to be poor, and there was no significant increase in this value after regular reexamination. When BMWT3 was above 0.9 while both BMWT1 and BMWT2 were smaller than 0.7, it could be judged as internal fixation failure, which should be replaced during the second operation. The clinical diagnosis was revised twice, and the final clinical healing results were observed. Results Clinical diagnosis analysis and finite element wall thickness analysis were carried out in 48 patients during each review period, and 21 cases of delayed bone healing and 27 cases of bone nonunion were judged clinically. Among them, 2 cases were judged to be ineffective, and bone grafting intervention was adopted to replace the internal fixation, 12 cases were judged to be still effective, and all cases were finally healed by surgical intervention of bone grafting alone. By Bowker test, P=0.094 was obtained, indicating that the wall thickness analysis method was consistent with the clinical diagnosis. Conclusions The wall thickness analysis method can be used to quantitatively analyze the degree of bone healing at fracture end and realize the rapid calculation of bone healing degree. The case results in this study show that the finite element wall thickness analysis method is superior to the simple clinical diagnosis method, and has better differential diagnostic significance for early diagnosis of poor bone healing.

Abstract:Objective To test the validity for mechanical equation of the TC4 self-tapping bone screw and analyze the influence of bone screw parameters on its mechanical properties. Methods In order to derive the equation of self-tapping and pull-out for bone screw, the physical model of bone screw-polyurethane foam block was built. By reference of ASTMF543-07 standard specification and test method for metallic medical bone screw, the mechanical verification tests of selected conical head shallow thread locking bone screw (HAZ) and conical head deep thread locking bone screw (HBZ) with different diameters were performed on Instron E3000 mechanical testing machine, and the data of self-tapping force, self-tapping torque and pull-out force from 5 groups of bone screws were tested respectively. Results The calculated and measured values were basically the same, except for a few points with large individual errors. The average error of the two values was 11.02%, so the theoretical calculation formula was highly credible. The bone screw with a larger diameter or a higher tooth height would require greater self-tapping force and pull-out force. Conclusions The research results provide the calculation basis for mechanical properties of bone screw and the research direction for optimization and improvement of bone screw in future.

Abstract:Objective In order to simulate different angles of acetabular blocks that need to be adjusted during operation, the optimal angle was determined through analyzing the contact stress and contact area of cartilage around the hip joint, so as to provide an individual scheme for acetabular osteotomy. Methods The finite element models for development dysplasia of hip (DDH) and normal pelvis were established to investigate morphological characteristics of the acetabulum and the causes of stress concentration. To simulate osteotomy for the DDH model, a total of 20 postoperative osteotomy models were obtained through the combination of different angles for anterior rotation and lateral rotation of acetabular blocks, and the differences in optimal results of the models during simulated one legged-standing were compared and analyzed. Results The maximum contact pressure of acetabular cartilage in normal model was 7.85 MPa. The maximum contact pressure of acetabular cartilage in DDH model was 13.42 MPa. The optimal contact pressure after simulated osteotomy decreased to 8.49 MPa, and the contact distribution was improved more significantly. Conclusions Changing the anterior rotation angle can significantly improve the contact pressure distribution and size, as well as stay away from the preoperative lesion area, which has a positive impact on postoperative outcomes. Personalized osteotomy plan based on actual situation of each patient before the operation is crucial for the surgical effect.

Abstract:Objective In order to avoid early restenosis after drug-eluting stent (DES) implantation, the retrievable structure of the NiTi alloy stent and its biomechanical analysis were studied. Methods The geometric models of the retrievable vascular stent and the retrieval system were established. The retrieval part of the stent consisted of four symmetrically distributed tendons, which were designed as circular meshes. The distribution of the maximum strain during stent compression and its uniformity during compression and self-expansion were analyzed, and the simulation experiments of the retrieval process were also performed. Results The maximum strain of the stent was 3.7% and the index of non-uniformity (INU) was 0.62% when the stent was compressed to the minimum size. While the IBU was 1.31% after the self-expansion process completed. The maximum strain was 1.2% when half of the stent was retrieved into the outer sheath. Conclusions The stent could be safely and successfully retrieved into the outer sheath as the strain was within the bearable range of the material and the compression and self-expansion process was relatively uniform. The research findings provide important references for structural design, biomechanical analysis and potential clinical applications of the novel retrievable vascular stent.

Abstract:Objective To investigate the hemodynamic effects of morphological parameters on renal artery stenosis （RAS）, so as to provide theoretical references for clinical practice. Methods The idealized models of RAS were established, then the hemodynamic effects from morphological parameters of stenosis including its area, symmetry, length and shape on renal artery was explored using computational fluid dynamics （CFD） method. Results The renal perfusion, pressure drop and wall shear stress (WSS) distributions in renal artery were significantly correlated with area stenosis (AS). When the stenosis area increased from 50% to 70%, all hemodynamic parameters changed significantly. In addition, an asymmetrical stenosis resulted in a significant increase of abnormally high WSS and length of recirculation flow in renal artery, but the change of stenosis length or shape only led to marginal changes in hemodynamics. Conclusions Although AS is still the most significant factor to influence hemodynamics in RAS, other morphological parameters, especially asymmetric stenosis, cannot be neglected. Therefore, it is suggested that clinical treatment plans should be a comprehensive evaluation based on these morphological parameters.

Abstract:Objective To construct an individualized fluid-solid coupling model, calculate and analyze the influence of different blood characteristics on hemodynamics in the aneurysm cavity, and further explore the influence on rupture of the cerebral aneurysm. Methods First, three-dimensional (3D) digital silhouette images were collected to construct an aneurysm model, and the influence of different blood flow characteristics on dynamic parameters of the carotid aneurysm was analyzed by computational fluid dynamic (CFD) method under the same boundary conditions. Finally, particle image velocimetry (PIV) experiment was performed on the simplified carotid aneurysm experimental model to verify reliability of the blood flow calculation method. Results For the fluid-structure coupling model with different blood flow characteristics, within a cardiac cycle, at the same time, obvious differences were found in the low velocity area of tumor cavity, the streamline distributions of tumor cavity, the wall shear stress (WSS) and deformation of the aneurysm wall. Through PIV experiments, it was found that the vortex position in tumor cavity changed with the velocity, which was consistent with flow trend of the simulation analysis results. Conclusions The two kinds of blood characteristics have small differences, but the non-Newtonian fluid is closer to true state of the blood, and the numerical results will be closer to true flow state.

Abstract:Objective To explore the influence of hook deflection angle and inclination angle on mechanical properties of the soft tissue suture passer hook. Methods Taking the end face far away from the tip of the needle (end face 1) as the study object, a mathematical model was established with the moment as dependent variable and the hook deflection angle and inclination angle as the independent variable. The moment was solved by the mathematical model with the deflection angle and inclination angle of 0°, 10°, 20° and 30°. Based on the finite element analysis method, 16 three-dimensional geometric hook models with deflection angle and inclination angle of 0°, 10°, 20° and 30° were established by SolidWorks. The stress analysis was carried out by ANSYS Workbench. Under the same puncture force, the maximum von Mises stress of each hook and the reaction moment of end face far away from the tip of the needle were calculated. Results The results from theoretical analysis and numerical simulation showed that the reaction moment of end face 1 increased with the increase of deflection angle, and increased with the decrease of inclination angle. The hook with deflection angle of 0° and inclination angle of 30° had the minimum reaction moment. The finite element analysis results showed that with the deflection angle of 0°, the maximum von Mises stress of the hook was the smallest and did not change with the inclination angle of the hook changing. Conclusions The established mathematical model can accurately explain the relationship between the moment at the end face of the hook and the deflection angle and inclination angle of the hook. This study provides the theoretical basis for designing hook geometry of the soft tissue suture passer, and improves the safety of the soft tissue suture passer in operation process.

Abstract:Objective To investigate the effects of athlete’s posture (including bending angle of upper body and angle between body and skis) on aerodynamic characteristics during flight in ski jumping. Methods The athlete and skis were regarded as a multi-body system. By using partially averaged Navier-Stokes (PANS) turbulence model and numerical simulation of computational fluid dynamics (CFD), the aerodynamic characteristics during flight under different postures were predicted. The calculation conditions for bending angle of upper body were 10°, 14°, 18°, 22° and 26°, and the calculation conditions of angle between body and skis were 8°, 12°, 16°, 20° and 24°. Results As the bending angle of upper body increased, the lift force and drag force of the multi-body system, the athlete and skis, and the pitch moment of skis all showed a monotonously decreasing trend, but the ratio of total lift force to total drag force increased first and then decreased. Meanwhile, the pitch moment of the multi-body system decreased first and then increased, and the pitch moment of athlete increased slightly and then decreased. As the angle between body and skis increased, the lift force and drag force of the multi-body system and skis increased first, then decreased and then increased, but the ratio of total lift force to total drag force decreased first, then increased and then decreased. Meanwhile, the lift force, drag force and pitch moment of the athlete increased monotonously, and the pitch moment of the multi-body system and the skis increased first and then decreased. The effect of bending angle of upper body on aerodynamic characteristics during flight in ski jumping was generally significantly larger than that of angle between body and skis. Conclusions The optimal range for bending angle of upper body is 14°-18°, and the optimal range of angle between body and skis is 16°-20°. The influence mechanism for bending angle of upper body and angle between body and skis on aerodynamic characteristics during flight in ski jumping can provide effective auxiliary support for on-the-spot prediction and decisionmaking,

Abstract:Objective To compare the biomechanical characteristics of lower limbs of young people with different body mass index (BMI) before and after the intervention of Baduanjin exercise, so as to provide references for scientific exercise and sport prescription for young Baduanjin practitioners with different BMIs. Methods Young volunteers with different BMI were divided into standard group, overweight group and obesity group. The BTS SMART 3D infrared motion capture system was used to capture the motion parameters and electromyography (EMG) parameters, the KISTLER dynamometer was used to collect the dynamic parameters, the AnyBody simulation software was used to calculate the kinematic parameters and dynamic parameters, and BTS SMART Analyzer was used to compare the different integral electromyography values. Results There was no significant difference in each parameter before the intervention of Baduanjin. After the intervention, the angle and angular velocity of the knee joint during extension and flexion in standard group, overweight group and obesity group, and the angular acceleration of the knee joint during extension and flexion in standard group significantly increased. Baduanjin significantly increased the knee flexion force and moment in standard group, overweight group and obesity group, and increased the hip flexion force and moment as well as ankle metatarsal flexion force and moment in standard group. Compared with obesity group, the knee flexion force and moment in standard group were significantly different. The knee joint force and moment were positively correlated with BMI. Baduanjin significantly increased muscle strength of iliopsoas, gluteus medius, piriformis, gluteus maximus, rectus femoris, sartorius, tibialis anterior, biceps femoris longhead, flexor digitorum longus, flexor pollicis longus, musculus peroneus longus and musculus peroneus brevis. Baduanjin significantly increased the integrated electromyogram (iEMG） of rectus femoris, tibialis anterior, biceps femoris. Conclusions Baduanjin can improve muscle strength and neuromuscular control ability of young people. The larger the BMI, the greater the flexion force and moment of the knee joint.

Abstract:Objective Based on the multi-camera digital image correlation (DIC) method, the dynamic deformation characteristics of human hand during grasping were studied. Methods A continuous four-camera DIC system was established to measure surface strain of the skin on the back of the hand during grasping process, and then through the connection between skin, joints, bones and muscles, the regular pattern of muscle deformation could be known indirectly. Results Four grasping postures (medium cylinder, lateral pinch, index finger extension, power sphere) were measured. It was found that the increases of strain magnitude were different at different positions on back surface of the hand under different grasping postures, and the maximum principal strains were between 0.1 and 0.3. The movement characteristics for each muscle group of the hand under different grasping postures were obtained through analysis. Conclusions This method has the characteristics of non-contact, full field, intuitive results, which provides a new way for in vivo measurement of dynamic deformation during grasping.

Abstract:Objective To analyze the statistical behavior of plantar pressure distribution, extract the characteristics of foot movement, and provide references for application of gait recognition in medical clinical diagnosis, rehabilitation training and public health. Methods The collected foot pressure data were prepossessed, statistical analysis on the data was performed, the footprint reconstruction was realized, and the pressure distribution rates of the footprints, segmented regions and each region were compared and analyzed, so as to decompose the foot motion characteristics. Results Based on the cross point of pressure peak curve in different regions, the plantar region was divided into toe region, metatarsal region, arch region and heel region, which could accurately extract the foot movement characteristics. Conclusions The peak plantar pressure is used to extract the characteristics of foot movement, which is divided into landing stage, whole foot contact stage, heel tiptoe stage and ground off stage.

Abstract:Objective On the basis of explicit dynamics calculation theory, a numerical model for calculating active and passive properties of muscles with high strain rate was proposed. Methods In the process of calculating the motion equation of muscle element with high strain rate, Hill’s three-factor muscle model with high strain rate was introduced into the noda force formula to modify the node force in each time step. Results As Hill’s three-factor muscle model was introduced in numerical calculation, the muscle element had the passive characteristics of the general structural constitutive model and its proprietary active characteristics. Conclusions The research findings will contribute to numerical calculation for dynamic response and damage of muscles with high strain rate.

Abstract:Objective To study bone remodeling behavior under different damage conditions. Methods A bone remodeling model under fatigue mechanism was proposed. By establishing a three-dimensional (3D) finite element model of the proximal femur and combining with the finite element method, the bone remodeling under three loading conditions was simulated, and the mechanical properties and density changes of the proximal femur were analyzed. Results The damage increased with the number of loading cycles increasing. Under different damage conditions, bone showed different remodeling behaviors. As a kind of repair mechanism, bone remodeling could make up for the loss of bone mass due to fatigue damage within a certain range. Conclusions The damage adaptive remodeling model proposed in this study can simulate the bone remodeling behavior under different damage conditions, and the overload absorption caused by excessive loading cycles. The study on the behavior of bone remodeling under fatigue damage can provide references for fracture prevention and postoperative rehabilitation treatment.

Abstract:Objective To study the effect of three kinds of commonly used liquid culture media for in vitro cell experiments on elastic modulus of breast cancer cells, so as to provide references for developing novel diagnosis and treatment approach of tumour based on mechanics principles. Methods The elastic modulus and adhesion force of breast cancer cells MCF7 to atomic force microscopy (AFM) probes in phosphate buffered solution(PBS), Dulbecco’s modified eagle media (DMEM) and DMEM+10% fetal bovine serum (FBS) were measured using AFM technology. Results The elastic moduli of breast cancer cells in PBS, DMEM and DMEM+10% FBS were 2.59, 2.11 and 1.59 kPa, respectively. The cell adhesion forces in the above three kinds of liquid medium environment were 63.81, 66.09 and 121.97 pN, respectively. Cell adhesion force in DMEM+10%FBS was significantly different from that of the other two kinds of liquid media. Conclusions There are significant differences in elastic modulus of breast cancer cells in three kinds of liquid media. The difference between DMEM and DMEM+10%FBS might be caused by the different adhesion force caused by serum proteins in the media, and the difference between DMEM and PBS might be attributed to the difference in pH of the media.

Abstract:Objective To investigate the effect of whole body vibration training on biomechanics and Wnt3a protein expression of the femur. Methods Forty-eight female SD rats were randomly divided into sham operation group, osteoporosis group and whole body vibration group, 16 in each group. The bone morphometric parameters were measured by Micro-CT, mechanical parameters of bone structure and materials were measured by three-point bending test, protein expression of Wnt3a and β-catenin was measured by Western blotting, and gene expression of Wnt3a, β-catenin, cyclin D1 and tcf1 was detected by qRT-PCR. ResultsCompared with sham operation group, bone mineral density (BMD), bone volume fraction (BVF), trabecular number, trabecular thickness and cortical bone thickness in osteoporosis group were decreased, and trabecular space was increased; compared with osteoporosis group, BMD, BVF, trabecular number, trabecular thickness and cortical bone thickness in whole body vibration group were increased, and trabecular space was decreased. Compared with sham operation group, the maximum load, elastic load and deflection of osteoporosis group were significantly reduced; compared with osteoporosis group, the maximum load, elastic load and deflection of whole body vibration group were significantly increased. Compared with sham operation group, the maximum stress, elastic stress, maximum strain and elastic modulus in osteoporosis group decreased significantly; compared with the osteoporosis group, the elastic stress, maximum strain and elastic modulus in whole body vibration group increased significantly. Compared with sham operation group, Wnt3a, β-catenin protein and gene expression decreased, cyclin D1, tcf1 gene expression also decreased; compared with osteoporosis group, Wnt3a, β-catenin protein and gene expression increased, cyclin D1, tcf1 gene expression increased as well. Conclusions Whole body vibration training can improve biomechanical properties of the femur and expression of Wnt3a protein in osteoporotic rats. The research findings provide laboratory reference data for the prevention and treatment of osteoporosis by whole body vibration training.

Abstract:Objective To investigate the effect of bilateral knee osteoarthritis (KOA) ondynamic balance ability of ankle strategy in aged women. Methods The dynamic balance ability tester was used to test the balance score, the rotation speed, the maximum rotation speed, and the percentage of the target ball's residence time in each area of KOA patients (KOA group)and the general elderly (control group), and a comparative analysis between groups was conducted. Results The balance score of KOA group was lower than that of control group; the dynamic balance control ability of KOA group in the horizontal direction was basically the same as that of control group, but the dynamic balance control ability of KOA group in the vertical direction was weaker than that of control group.Bilateral KOA reduced dynamic balance ability of ankle strategy in the aged women.It could not affect the left-right symmetric balance ability of the aged women, but it would reduce its forward-backward symmetrical balance ability. Conclusions Bilateral KOA aged women may be more likely to fall forward or backward, while not easy to fall laterally. For elderly female patients with bilateral KOA, methods such as strengthening ankle joint strength, proprioception and responsiveness can be used to prevent falls that may be caused by reduced dynamic balance ability, especially falls in the forward and backward directions.

Abstract:Prosthetic loosening and periprosthetic inflammation, as serious complications after joint replacement surgery, often require the secondary surgery for repair, which is easy to adversely affect the physical/mental health and economic status of patients.Studies have shown that the functional phenotype expressed by macrophages by different stimuli, namely macrophage polarization state, prolonged M1 polarization can lead to the continuation of long-term inflammation, while timely and effective M2 macrophage phenotype will lead to enhanced osteogenesis and tissue remodeling cytokine secretion and subsequent osseointegration, which play a crucial role in the development and outcome of prosthetic loosening and periprosthetic inflammation.The local micro-environment of extracellular matrix (ECM) is an important factor in the activation, migration, proliferation and fusion of macrophages. Researchers have deeply understood it mainly through the crosstalk between surface properties of biomaterials and macrophages. As an effector cell, macro-phages can perform complex spatiotemporal cellular functional responses by sensing the physical and chemical environment (surface topography, wettability, chemical composition, biological proteins) represented by surface properties of biomaterials.This paper summarizes the recent findings on macrophage polarization and material surface properties.

Abstract:With extraordinary mechanical properties, articular cartilage is one of the most critical factors in human movement and load transmission. With the increase of sports participation and population aging, more and more patients suffer from cartilage injury and related diseases. Accurate acquisition of mechanical properties for articular cartilage is the key process of cartilage injury and functional evaluation. In this paper, the research progress of indirect estimation for mechanical properties of articular cartilage was summarized. Furthermore, some new perspectives were prospected on mechanical characterization of articular cartilage.

Abstract:Due to damage to the hemi-advanced central nervous system of stroke hemiplegic patients, their ability of sit-to-stand transfer is impaired, and they are prone to fall during the sit-to-stand transfer. This article describes the characteristics of sit-to-stand transfer for hemiplegic patients at different foot placement from a biomechanical perspective, discusses the correlation between different features, analyzes the reasons for their fall, and describes the application of sit-to-stand transfer training in postoperative rehabilitation of hemiplegic patients， so as to provide references for postoperative rehabilitation of hemiplegic patients.

Abstract:Abnormal mechanical loading is the main risk factor for the development of osteoarthritis (OA), and it can lead to collagen degradation, glycosaminoglycan loss and chondrocyte apoptosis, as well as damage to articular cartilage and subchondral bone. However, due to the lack of understanding in chondrocytes mechanotransduction pathway and invalid method of cartilage repair and regeneration, there is an urgent need for understanding chondrocytes mechanotransduction pathway and mechanism of cartilage damage induced by mechanical loading. In this review, how chondrocytes sense and transmit mechanical signals from cell membrane to cecullar mechanosensors is introduced in detail, and the role of chondrocytes mechanotransduction in OA development is discussed with emphasis.