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Abstract:Objective To study the effect of bone mineral density (BMD) change on response of human spine to landing impact by numerical simulation. Methods The three-dimensional material point model of human head skull, cervical vertebrae, thoracic, lumbar vertebra, pelvis, ligament and disc was constructed from the computed tomography (CT) scanned images, and they were attached together as a human spine model and placed on the backrest of the chair, which was constructed by the MPM3D program. The acceleration loading was applied on the back rest of the chair to simulate the landing impact loading when the human spine model was laid on the back of the chair. The different responses of human spine to landing impact were simulated by changing the BMD and the corresponding elastic modulus. Results The general risk of injury γ value of normal BMD was 1.589 3, and when the BMD was reduced by 2%, 4%, 6%, 8%, 10%, respectively, γ values were 1.608 6, 1.634 7, 1.641 0, 1.662 5, 1.680 5, correspondingly. Conclusions Under the same landing impact loading, the smaller the bone mineral density, the larger the response of human spine to landing impact loading, and human body is more vulnerable to injuries.

Abstract:Objective To design a novel high performance stent with preferable axial flexibility by using smaller strut thickness and less metal coverage which would not compromise its radial strength, so as to reduce the in-stent restenosis. Methods Based on researches about deformation properties of both the symmetric and asymmetric cell structures, the new stent structure was designed and analyzed through numerical simulation. The radial strength and bending stiffness tests were performed to evaluate the stent made by the new design. Results The proposed design possessed a higher radial strength, smaller metal coverage and good flexibility, which would be beneficial for the reduction of in-stent restenosis. Conclusions The asymmetric structure-based stent design method is effective, by which a high performance stent design can be obtained.

Abstract:Objective To investigate a method determining the number of preconditioning cycles in uniaxial tensile test on soft tissues by calculating the decay rate of strain energy. Methods The abdominal skin of healthy New Zealand rabbits was selected as study object, from which strip specimens were obtained in directions parallel to linea alba (0°)and perpendicular to linea alba(90°). Then the uniaxial preconditioning tests with 15% preconditioning strain were performed on these specimens. Load displacement preconditioning data were obtained, and transformed into the stress strain data correspondingly. The preconditioning cycles (n values), at the decay rate of strain energy being 5% and 10%, respectively, were then calculated by MATLAB programme when n values satisfy the inequality η=Wn－Wn－1Wn－1×100%≤5% or≤10%（Wn signifies the strain energy loss in the nth preconditioning cycle）. Results When the decay rate of strain energy was 5%, the number of preconditioning cycles in 0° and 90° direction was 11.11 and 13.67, respectively. When the decay rate of strain energy was 10%, the number of preconditioning cycles in 0° and 90° direction was 6.67 and 7.78, respectively. Conclusions By calculating the decay rate of strain energy, the number of preconditioning cycles in uniaxial tensile on soft tissues can be quantified, which could help provide the research basis for standardization of biomechanical testing on soft tissues.

Abstract:Objective To develop a novel computer method for identifying the critical amino acid residues in the receptor-ligand interactions. Methods GPIbα/vWF-A1 crystal structure was taken from Protein Data Bank (PDB code 1SQ0). Free molecular dynamics simulations were performed to observe the formation and evolution of hydrogen bonding and salt bridge on the binding sites of GPIbα and vWF-A1 by VMD. A residue interaction index, which was scored with the survival ratios of salt bridges and/or hydrogen bonds involved in interaction of a residue to other(s), was used as a criterion of the residue’s role in interaction between the receptor and ligand. Results In the interface, 21 residues in GPIbα and 21 residues in vWF-A1 were significantly identified to participate in the interaction between GPIbα and vWF-A1; 20 of these 42 key residues were verified by previous mutagenesis experiments. Conclusions This novel approach is useful for computationally identifying the key residues involved in GPIbα-vWF interaction, and has potential in developing new strategy for the traditional mutagenesis experiments and the antithrombotic mAbs drug design.

Abstract:Objective To study the flow characteristics of the upper airway and force dynamics of the soft palate and uvula in a representative male OSAHS (obstructive sleep apnea hypopnea syndrome) patient during normal respiration. Methods A CT image-based reliable geometry model of the upper airway was established. Numerical simulation boundary conditions were determined by clinical data of sleep monitoring, and the low-Reynolds number turbulence model was adopted to calculate the flow movement during a complete respiration period. Results The flow characteristics of the upper airway were obviously different in the breathing process of OSAHS patient. During inspiration, the maximum velocity of airflow in the upper airway reached 9.808 m/s, and the maximum negative pressure of airflow reached -78.856 Pa. Backflow districts were found at top of the nasal cavity. The maximum pressure on the soft palate was -10.884 Pa, and that on the uvula was -51.946 Pa. The maximum shear stress on the soft palate and uvula was 78 and 311 mPa, respectively. During expiration, the maximum velocity of airflow in the upper airway was 10.330 m/s, and the maximum negative pressure was -51.921 Pa. Backflow was observed to appear both at the oropharynx and top of the nasal cavity. Specifically, clockwise backflow was remarkable at the oropharynx. The maximum pressure on the soft palate was 2.603 Pa, and that on the uvula was -18.222 Pa. The maximum shear stress on the soft palate and uvula was 51 and 508 mPa, respectively. Conclusions Oropharynx is most likely to collapse in the upper airway. Numerical simulation on the respiratory cycle can capture the salient backflow features of the flow field in the upper airway. The backflow in the upper airway directly affects the forces on the soft palate and uvula and the breathing fluency of OSAHS patients.

Abstract:Objective To study the hemodynamics of central shunt (CS) by numerical simulation and investigate the effects of the elastic and rigid vessel wall on distributions of hemodynamic parameters in the vessel. Methods Two idealized CS models were constructed, one with a rigid wall (the rigid model) and the other with an elastic wall (the elastic model). Numerical calculation was conducted by the finite element method, and the elastic model adopted the fluid structure interaction. Results The distribution of flow velocity and pressure in both models were generally the same. About 68.9% of the aortic blood was directed into the pulmonary artery for the rigid model, as compared to 70% for the elastic model. The pressure drops within the shunt for the elastic model and rigid model were about 7.668 8 kPa and 7.222 3 kPa, respectively. The maximum variation in the average cross sections along the shunt was about 2.2% for the elastic model, appearing at the proximal end to side (ETS) anastomosis. The maximum difference of wall shear stress (WSS) between the two models at five key regions of each was about 16.1%. Conclusions Generally, the global flow structure in both the CS models remains unchanged; the elasticity of the vessel wall slightly influenced the flow distributions and pressure drop of the shunt; the effect from elasticity of the vessel wall on average cross sections along the shunt was higher at the proximal ETS anastomosis than that at the distal ETS anastomosis; the hypothesis that the vessel wall is rigid is acceptable in CS numerical simulations for the treatment of tetralogy of Fallot (TOF). However, the coupling of flow dynamics and wall mechanics may lead to a more reliable simulation result in the CS.

Abstract:Objective To investigate the effect of vascular endothelial growth factor (VEGF) expression level and sources on tumor-induced angiogenesis by numerical simulation. Methods A two-dimensional discrete mathematical model of tumor-induced angiogenesis was developed to simulate the growth of microvascular networks inside and outside of the tumor, focusing on endothelial cell proliferation, degradation, random motility, chemotaxis, haptotaxis and stromal-derived VEGF and tumor-derived VEGF. The relationship between VEGF derived by each compartment and tumor microvessel density was discussed. Results The high VEGF region was consistent with proliferating cell and tumor periphery regions in which microvascular density was also high. The simulation demonstrated that an enlargement of proliferating cell region could lead to higher VEGF expression level and higher microvascular density. However, for different types of tumors, the correlations between different VEGF expression sources and microcascular density were not significant. Conclusions The effect of VEGF expression level and source on VEGF-mediated angiogenesis can be investigated by the proposed model. Particularly, taking VEGF expression from different sources into consideration could be a useful modeling tool for anti-VEGF targeted therapies.

Abstract:Objective To compare the stability of greater tuberosity fractures of humerus treated by three different fixation techniques (screws, tension band, locking plate, respectively) through biomechanical testing, so as to provide the biomechanics basis for choosing a better fixation in the clinical treatment for greater tuberosity fractures of humerus. Methods Standardized fracture models of the greater tuberosity from 18 fresh-frozen proximal humeri with intact rotator cuffs were created. The specimens were randomly assigned to 3 groups and treated by screws, tension band and locking plates, respectively. An increasing force was applied to the supraspinatus tendon. The force displacement curve and two parameters: LtYP(Load to 5 mm yield point) and Ltf(load to failure) were recorded. Results LtYP from the screw group, tension band group and locking plate group was (377±86), (499±90), (793±52) N, respectively, with significant differences among the three groups (P<0.01). Significant differences were also found between the groups as locking plate group (only 3 cases in locking plate group reached to 5 mm displacement before LtF in this study ) and screw group, locking plate group and tension band group, tension band group and screw group (P<0.01). LtF of screw group, tension band group and locking plate group was (744±112), (908±93), (979±143) N, respectively, showing significant differences among them, and which were also found between locking plate group and screw group, tension band group and screw group (P<0.01), but no significant differences were found between locking plate group and tension band group (P>0.05). Conclusions Locking plates show more obvious biomechanical stability than screws and tension band, which provides a new and better choice for treatment of isolated greater tuberosity fractures of humerus.

Abstract:Objective Based on time-coupled multiscale coupling algorithm, to simulate the hemodynamics after systemic-pulmonary shunt procedure on single ventricular patient so as to obtain the local three-dimensional (3D) fluid field and global hemodynamic information before and after surgery. MethodsFirstly, the 0D-3D coupled multiscale hemodynamic model of systemic-pulmonary shunt procedure was established based on the lumped parameter model (0D) before surgery and the shunt model (3D), then the 0D-3D interface coupling condition and the time coupling algorithm were discussed. Secondly, the multiscale simulation of 3D CFD (computational fluid dynamics) model coupled with 0D lumped parameter model was realized based on lattice Boltzmann method. Finally, the multiscale simulation results were compared with patient’s 0D simulation results to study the hemodynamic changes before and after surgery. Results The global hemodynamic change and local 3D flow pattern were obtained by this multiscale simulation. The pulmonary blood flow distribution ratio was increased from 32.21% to 57.8%. Conclusions The systemic-pulmonary shunt procedure can effectively increase the blood supply of pulmonary circulation by implanting the shunt between the systematic circulation and pulmonary circulation. The geometrical multiscale method can effectively simulate both the coarse global and detailed local cardiovascular hemodynamic changes, which is of great significance in pre-operation planning of cardiovascular surgery.

Abstract:Objective To establish a set of digital robot-aided surgery system to represent the real surgery process, and realize robot control and force feedback in virtual environment by digital human tissue simulation combined with outer force feedback instrument. Methods The digital robot aided-surgery system design includes human tissue biomechanical modeling, biomechanical model calculation, force feedback instrument design, control algorithm, digital robot-aided surgery system based on biomechanical information. Results After local area network was successfully connected between haptic device control system and virtual environment, the system completed closed-loop information transfer process. Conclusions The robot-aided surgery system can realize the master-slave control, visual feedback and force feedback in virtual environment, which will contribute to the development of digital surgery simulation technology and gain advantages in the aspects of improving surgery success rate and training new doctors.

Abstract:Objective To analyze the mechanical effect of invisible appliances with different material hardness and provide theoretical basis for selecting the suitable material for invisible appliance and its clinical application. Methods Three different three-dimensional (3D) finite element models of invisible appliance were established, of which the elastic modulus was chosen as 415.6, 816.308 and 2 400 MPa, respectively. In these models, the upper central incisors were all designed to move 0.3 mm mesially. Then 3D nonlinear finite element method was used to analyze the stress-distribution in invisible appliance, teeth and periodontal ligament and the instant displacement of every tooth. The comparative study was made among three invisible appliances with different hardness． Results Under experimental condition, the most instant stress and displacement of teeth was the upper central incisor, with initial displacement greater in crown section than that in apical section and the greatest displacement was 0.17 mm. The tendency of central incisor movement was tipping in all situations. The movement of lateral incisor had the second greatest distance (the greatest displacement was 0.10 mm) and the tendency of its movement was in the opposite directions of aimed teeth. When elastic modulus of material decreased, the stress on the invisible appliance increased. The stress in periodontal ligament and the displacement of aimed teeth were also increased. Conclusions If the hardness of invisible appliance increases, the displacement of the designed tooth and treatment efficacy increases, but the appliance with more hardness couldn’t provide better ability in controlling of orthodontic tooth movement. The study suggested clinicians should use attachments or cooperate with fixed appliance to help move teeth bodily.

Abstract:Objective To study the characteristics of stress distributions on a customized lingual self-locking orthodontic appliance under transient occlusal force and optimize its structure. Methods A whole 3D model including denture, appliances and wire was established by CT scanning, reverse engineering method and CAD technology; transient nonlinear dynamic analysis on this model during occluding and its structural optimization were conducted, and the optimized lingual appliance was made based on rapid prototyping technology to verify reliability of the finite element model. Results The equivalent stress on the bracket bottom was larger than that on other parts of the bracket; the maximum equivalent stress on the bracket cover was decreased by 60.9% after installing a reinforcing rib on it, which could effectively prevent stress concentration caused by the contact between the arch wire and bracket cover. The simulation results fundamentally agreed with the loading experiment on the bracket cover. Conclusions For lingual orthodontic treatment in clinic, the relative position between interaction points of the occlusal force and brackets should be concerned so as to avoid impairing the self-locking function; through optimizing the appliance design, the elastic potential energy of arch wire can be transferred more effectively to the teeth and reduce losses of the orthodontic force.

Abstract:Objective To analyze the dynamics of vault springboard designated to using in formal competitions by the Federation International de Gymnastique (FIG), and find a new method measuring the reaction force of the springboard, so as to provide scientific supports for diagnosis of its take-off technique. Methods The stiffness values of GYMNOVA soft and hard springboards were derived by method of material mechanics, then the springboards were then tested with static, dynamic experiments and computer simulations. In the static experiment, two video cameras with the sample frequency of 600 Hz were placed at a 90° angle to capture the deformation of the springboards under the loads of 160, 180, 210 and 230 kg, respectively. In the dynamic experiment, a volunteer performed drop jump (DJ) from a 1.25 m high platform onto the hard and soft springboards, respectively, while a camera was employed to capture the deformation at the sample frequency of 300 Hz. All the three cameras were calibrated using a 2-dimensional framework, and the changes of the board height, velocity under different loads and acceleration of center of mass (COM) of the human body in DJ experiment were all obtained by digitizing the videos using SIMI MOTION software. Finally, modeling and computer simulation were performed to simulate the DJ in the dynamic experiment. Results The equation F=kx+c describing force-displacement of both the springboard was obtained. The depressing displacements of the board under different loads in the static experiment were close to those calculated by the equation. The vertical reaction force curve in DJ calculated by the equation was highly correlated to that obtained by acceleration of COM. The coefficient of multiple correlation was all greater than 0.86. Conclusions The study developed a new method for measuring the vertical reaction force of the springboard based on board depressing displacement and velocity with the help of high-speed camera. This method, which can be employed with convenience to rapidly monitor the board reaction force during take-off, provides scientific supports for enhancement of vaulting techniques and plays an active role in prevention of vaulting injuries.

Abstract:The mechanism of balance controlling and maintaining during human motion is quite complex, and many physiological and non-physiological factors such as aging, apoplexy and limb disability can lead to balance dysfunctions.Thus, the functional tests and evaluation on balance plays a vital role in the diagnosis and evaluation of many diseases. The common equipment and methods for investigating balance funciton of human body, as well as their limitations were summarized, and the design and method of serveral light-weight, low-cost, novel systems such as wearable motion capture systems based on microelectronic sensors and human balance measuring and training systems based on somatosensory games were also proposed in this paper.

Abstract:The study of hemodynamics, which refers to dynamics inside the blood circulation, mainly includes the flow rate, flow resistance, pressure, shear stress, disturbed flow, as well as their associations in between. Therefore, with its important significance in the clinical treatments of vessel curvature, arterial stenosis or occlusion, pathological artery branches and aneurism, study about hemodynamics is essential to human health. Currently, extensive researches on hemodynamics have been conducted with respect to artery bypass, coronary arterial stenosis, abdominal aortic aneurysm, atherosclerosis, cerebral aneurysm and swirling flow. With the development of such research on hemodynamics, surgical planning and interventional therapy have improved rapidly. The influence mechanism of hemodynamic parameters, including pressure, flow resistance, flow rate, wall shear stress, blood viscosity, flow separation, turbulent flow, vortex on the post-operation complications could be deeply explored with the help of more and more clinical apparatus and have gained some achievements.

Abstract:It is known that rigid pedicle screw fixation may cause abnormal stress concentration on the posterior part of the spine, which may lead to stress concentration on the fixation device; meanwhile, due to the motion limitation to the fixed segment, the excessive motion at the adjacent segment may further fortify the disc degeneration. To solve these issues, the dynamic fixation is used in clinic, and many studies have investigated the biomechanical mechanism and clinical outcome of the dynamic fixation. The ideal dynamic fixation should meet the following conditions: offering enough stabilization for the fixed segment; reducing the load on the fixation device through enhancing the strain on the anterior vertebral bodies; preventing the degeneration at the adjacent segment; controlling the horizontal shear force at the fixed segment. In this article, the biomechanical properties and clinical application of the posterior dynamic fixation were reviewed and the biomechanical mechanisms of different dynamic fixations were compared.

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