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Abstract:Objective To conduct the operation of capture and deformation in virtual three-dimensional (3D) environment with force feedback device and simulate the coronary artery bypass operation. Methods Based on data collected from real CT images of the patient with heart disease, digitized visual model of the heart was reconstructed. Then the bypass vessel was built and the vessel model was sculptured by force feedback device to simulate the bypass surgery from pulmonary artery to ventriculus dexter in Fontan operation. Results Space structure of the heart was shown in the virtual 3D reconstructed environment. Bypass vessel with any diameter and angle was transformed to simulate the coronary artery bypass operation. Heart patch with any size was built to repair the heart model. The satisfactory model and parameters of the postoperative model were finally achieved. Conclusions The application of force feedback device in virtual coronary artery bypass operation sets the stage for cardiovascular surgery planning system with mechanical characteristics to simulate multiple modalities of such operation.

Abstract:Objective To investigate the influence of different protrusion distance of stent strut into the subclavian artery on local hemodynamics of the vertebral artery (VA) ostium.Methods Five models of the VA were established. Model 1 was without stent implantation, Model 2 to 5 was with stent protruding into the subclavian artery for 0, 1, 2, 3 mm, respectively. Computational fluid dynamics analysis was performed to study the differences of hemodynamics in these models. Results After stent implantation, the wall shear stress and the blood flow velocity at the stent segment in the Model 2 was reduced by 85.33% and 35.36%, respectively. The phenomenon of swirling flow disappeared. For models with different protrusion distance, the maximum difference of wall shear stress of VA was 0.76%, and the maximum difference of blood flow velocity is 0.45%. ConclusionsStent implantation can improve the hemodynamics of vertebral artery ostium stenosis, while the protrusion distance of stent strut has no obvious influence on the blood flow velocity and wall shear stress.

Abstract:Objective To investigate the effects of different anteversion angles on stress distributions of the proximal femur after femoral neck fracture fixation by cannulated screw, and to provide biomechanical evidences for the importance of anatomical reduction in internal fixation in clinic. Methods Femoral neck fracture with Pauwells angle 70°was treated with cannulated screw internal fixation, and its three-dimensional finite element models with five different anteversion angles set at 0°，5°，10°，15°and 20°, respectively, were constructed based on normal human anatomical data from multi slice spiral CT as well as reverse engineering and CAD software. Loads were applied on each model to simulate normal walking status. Changes in stress distributions of the proximal femur in each model were observed. Results When the anteversion angle was 10°, the stress, displacement and equivalent strain of the femur was were the minimum, as the maximum stress of the proximal femur was 1.7 MPa, and the displacement was 1.1 mm. With the anteversion angle increasing or decreasing, the effective stress and displacement of the proximal femur was gradually increasing. When the anteversion angle was 20°, the stress of on the proximal femur and on the cannulated screw was became the maximum. When the anteversion angle was 0°, the displacement and equivalent strain of the femur also became the maximum. The stress concentration site of the femoral neck was gradually transferred from the inside rear to the outer top of the head and neck junction. The three cannulated screws there stood the higher stress than the surrounding bone tissues, and with the bottom screw stood the higher stress than the other top two screws. Conclusions Anatomic reduction is essential for femoral neck fracture fixation treated by cannulated screw. Changes in biomechanical factors after femoral neck fracture may play an important role in postoperative femoral head necrosis.

Abstract:Objective To evaluate biomechanical properties of internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate in reconstructing stability of the upper cervical vertebra, and compare them with conventionally used anterior internal fixation after C2-3 intervertebral fusion and posterior internal fixation by C2 transpedicle screws. MethodsSix fresh human upper cervical vertebra specimens (including C2-4) were divided into five groups: the intact specimen group(control group), the incision of the C2-3 group (Hangman group), the posterior internal fixation by C2 transpedicle screw group (posterior fixation group), the anterior internal fixation after C2-3 intervertebral fusion with Zephir plate group (anterior fixation group), and the internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate group (C2-4 incision +internal fixation group). Range of motion (ROM) of the C2-3 and C3-4 segments was tested respectively under 0.5, 1.5 and 2.5 N?m moment by measurement system for three-dimensional spinal movement, and the statistical analysis was also conducted. Results(1) C2-3 segment: ROM of anterior fixation group and C2-4 incision +internal fixation group was significantly smaller than that of Hangman group and posterior fixation group in all six directions under various loading conditions (P<0.05); there was no significant difference between anterior fixation group and C2-4 incision +internal fixation group. ROM of posterior fixation group was larger than that of intact group in all six directions under various loading conditions (P<0.05); There was no significant difference in flexion and extension direction under all loading conditions between posterior fixation group and Hangman group, but significant difference was found in left/right and right/left axial rotation and under 2.5 N?m moment between posterior fixation group and Hangman group (P<0.05). (2) C3-4 segment: there was no significant difference in ROM in six directions under various loading conditions among all groups except for C2-4 incision +internal fixation group. ROM of C2-4 incision +internal fixation group was significantly smaller than that of other groups in all six direction (P<0.05). Although ROM of anterior fixation group was slightly larger than that of Hangman group and posterior fixation group, the difference was not statistically significant. Conclusions From the view of biomechanics, internal fixation after C3 corpectomy and C2-4 anterior fusion with Zephir plate is a better surgical option for stabilizing the fracture than that of posterior internal fixation by C2 transpedicle screws to treat type II Hangman fracture with C2-3 intervertebral disc injury.

Abstract:Objective To establish the operating force database of Chinese young males and provide basis information for the design of operating force in working place. Methods Anthropometric parameters of 843 Chinese young males from northeast, north, northwest, southwest, southeast, central and south China were collected, including the back force, hand twisting force, arm forces in four exerting directions and with various elbow angles. The data were statistically analyzed and compared with related researches in China and abroad. Results For arm forces in four exerting directions, the pushing force was greater than the pulling force, and the inward force was greater than the outward force. The pushing force was the largest and the outside outward force was the smallest. With the increase of the elbow angle, the pushing and pulling forces were increased significantly, while the inward and outward forces were decreased significantly. A significant correlation existed among the operating forces. There was significant correlation between the operating force and body weight, while weak correlation was found between the operating forces and anthropometric parameters. Operating forces of Chinese young males were relatively smaller than those of the Westerns. Conclusions By sampling on a national scale, the operating force database was established for Chinese young males. This study provides the basic data for the design of operating force in man-machine system and could be also used as reference for ergonomics researchers, occupational health workers and rehabilitation researchers.

Abstract:Objective To evaluate the role of simvastatin in preventing and curing osteoporosis vertebrae by examining the effect from simvastatin on osteogenesis of the lumbar vertebrae in aging rats. Methods Sixty 15-month-old male SD rats were divided into six groups: the control group (injected with normal saline for three month), the baseline group (executed upon the gastric irrigation), the simavastatin-treated group (gastric irrigation with simavastatin at the dose of 5, 10, 20 and 40 mg/kg/d, respectively, for three month). L4 vertebrae were checked by Dual-Energy X-ray Absorptionmetry (DXA), Peri-quantiy CT (pQCT) and mineral apposition rates test. L5 vertebrae were checked by mechanical compression test. Results The value of DXA, pQCT and mineral apposition rate of 10 mg simvastatin group were slightly higher than that of the control group, but no significant differences were found between the two groups. The bone material properties of 10 mg and 20 mg simvastatin group were better than those of the control group, with no significant differences. Conclusions Although 10 mg simvastatin group (equivalent to 12~24 mg/d for human) seemed to have better properties than the other simvastatin groups, but there were no significant differences among these simvastatin-treated group. It is indicated that simvastatin doesn't play a positive role in promoting osteogenesis of the lumbar vertebrae in aging rats, so it may have no preventing or curative effect for osteoporosis of the lumbar vertebrae.

Abstract:Objective To discuss the effects of elastic modulus on propagation characteristics of ultrasonic guided waves in long bones based on finite-difference time-domain (FDTD) method, so as to provide the theoretical references for evaluating bone fatigue damage at the early stage. Methods A cylinder was used to model the long bone, and FDTD method was used to simulate the long bone with different elastic modulus. Then, the propagation characteristics of different guided wave modes were calculated, including the phase velocity, the group velocity, the central frequency and the energy. Results The elastic modulus of long bones was closely related with the propagation characteristics of ultrasonic guided waves. The phase velocity, the group velocity, the central frequency and the energy were all reduced with the decrease in elastic modulus, and the variation tendency of L(0,5) mode was the most obvious. Conclusions The propagation of ultrasound guided waves can reflect the variation of elastic modulus of long bones, which provides a possible way to evaluate the fatigue damage at the early stage in long bones.

Abstract:Objective To analyze the load-bearing mechanism and stress relaxation properties of the articular cartilage (AC) through finite element simulation and experimental validation. Methods By comprehensively considering the solid phase of the matrix, the liquid phase of the pore and the reinforced phase of the collagen fibrils in AC, as well as the dilatation dependent permeability of AC, a fibril reinforced poroelastic (FRPE) model was built including changes of void ratio with subsurface depth of the AC. Based on the proposed model, and by utilizing ABAQUS software and FORTRAN language, the finite element analysis (FEA) on unconfined ramp compression of AC was conducted. The equilibrium modulus of porcine cartilage tissues under unconfined compression was measured by a self-designed biomechanical property measuring system, and the results between the FEA and the unconfined ramp compression test of the AC were compared. Results The liquid pore pressurization could last about 80 seconds and contributed up to 90 % of the total stress at the middle point of the test specimen when it was compressed at a strain rate of 0.45%/s. Conclusions The FEA on the unconfined ramp compression of AC based on the FRPE model can quantitatively evaluate the load bearing capacity of the solid and liquid phase, respectively, changed with different strain and loading time. Simulation analysis combined with the unconfined ramp compression test results facilitates the evaluation on mechanics properties of the cartilage with more accuracy.

Abstract:Objective To measure the shear modulus of biological tissues by using Zener model so as to overcome the limitation of Voigt model-based ultrasound vibrometry, and to provide effective approaches of tissue characterization. Methods The mechanical constitutive relation-based shear wave propagation velocity formula was utilized to estimate the shear modulus in terms of the velocities at multiple frequencies via mathematical methods. To obtain shear wave velocities in different objects, experiments were conducted by using different consistencies-based gelatin models and thermally damaged porcine livers as subjects, in which shear waves were induced by ultrasound radio forces. Results Voigt and Zener models were utilized to fit the velocities respectively. The Zener model exhibited higher fitting accuracy than the Voigt model, and the shear modulus could well distinguish gelatin models with different consistencies or porcine livers of different damage degrees. Conclusions The method in this paper provides a potential means of measuring the shear modulus of biological tissues non invasively, which is very promising for tissue characterization and disease diagnosis in medicine.

Abstract:Objective To analyze the dynamic response and strain of the major muscles in head-neck complex of pilot with or without wearing the helmet during carrier aircraft arrested deck landing. Methods Ten-rigid body dynamic model of human head-neck complex was created including head, seven cervical vertebrae and two thoracic vertebrae; mechanical properties of the ligaments, intervertebral discs and other surrounding soft tissues were described by lumped parameter method; mechanical properties of the 15 pairs of muscles in this human head-neck complex were represented by non-linear stress-strain relationship. The model was validated by using experimental data of dynamic responses from the human head-neck complex in a set of different types of automobile crashes. Results The overload curve and strain of this 15 pairs of muscles in head-neck complex of the pilot during arrested deck landing were obtained. The results showed that the extension of splenius cervicis was the largest. The strain of splenius cervicis could reach 50% when the pilot wore the helmet, and it could reach as high as 56% if the helmet’s weight was 2.7 kg. Conclusions Wearing helmet would extend the stretch of neck muscles, and the simulation result could be used for further evaluation on head/neck injury of the pilot.

Abstract:Objective To detect the recruitment pattern of motor unit in human flexor digitorum superficialis (FDS) at different force levels produced by the index finger. Methods Eight subjects were recruited to produce a certain force level with the index finger to match the ordered force level (20%, 40%, 60% maximum voluntary contraction). During the force tracking task, the multi-channel surface electromyography (sEMG) signals were recorded on FDS using 8×1 (row×column) electrode-array. The motor unit action potential (MUAP) information was extracted by Fast Independent Component Analysis (FastICA), and then the correlation between MUAP pattern and force level was analyzed. Results Four different types of MUAP were extracted successfully by FastICA from original sEMG signals and the total number of MUAP showed an increasing trend with the force level increasing. At different force levels, the proportion of different types of MUAP was different, showing different trends with change of the force level. Conclusions At different levels of the finger force, the recruitment pattern of motor unit in FDS will be changed so as to produce the force accordingly.

Abstract:Objective To investigate biomechanical properties of the complete mandibular subperiosteal implant under four different bite loads, and provide some references for the personalized implant design in clinical cases. Methods Based on the three-dimensional model of human mandible, two kinds of matching complete mandibular subperiosteal implants, meshy base (implant 1) and zonary base (implant 2), were established, respectively. Stress distributions of both the two implants under four different bite loads were calculated and compared. Results The maximum stress of implant 1 was 230.42 MPa under the load Ⅳ and that of implant 2 was 311.11 MPa under the load Ⅰ. The stress distributions and maximum stress showed that the implant with meshy base had better resistance to the vertical loads, while the implant with zonary base had better resistance to the horizontal loads. Conclusions Rational arrangement for the number of posts and the distance between posts can effectively control the stress of implants. Posts should be placed in a vertical direction with the alveolar bone to avoid amplifying the horizontal component. In addition, posts should be well bounded to the bases, so that the stress on the bottom of posts won’t be at a high level. The complete denture should be guaranteed to contact at several spots during centric, protrusive and lateral bites to keep occlusion balance and decrease the maximum tensile stress on the contact surface.

Abstract:Objective To explore the synergistic effects of substrate stiffness and cytokine TGF-β1 on phenotypic transformation of hepatocytes by establishing an in vitro culture model with the substrate stiffness that is relevant to hepatic cells physiologically and pathologically. Methods Immunofluorescence and Western blotting were adopted to observe the morphological adjustment, motion characteristics, cytoskeleton arrangement of hepatocytes on polyacrylamide substrates with different stiffness, as well as the changes in expression of integrin and phenotypic markers E-cadherin, albumin and alpha-smooth muscle actin (α-SMA). Image analysis software was also used for quantitative study on the obtained data. Results On the 3.6 kPa substrates, the scattered single cells were actively deformed and relocated, but the bulk cell population had little change in polarization and microfilament organization. Muscle actin was assembled as cortical ring in cell periphery. There was more abundant expression of E-cadherin and albumin, but less expression of integrin and α-SMA in TGF-β1 treated group as compared to the control group. On the 30 kPa substrates, the motion and deformation of cells were not so active, and expression of both E-cadherin and albumin in TGF-β1 treated group was decreased, while that of α-SMA was increased as compared to the control group. For 30 kPa and 3.6 kPa control groups and 30 kPa and 3.6 kPa TGF-β1 treated groups, expression of both E-cadherin and albumin was reduced (P<0.05), but that of alpha-SMA was increased (P<0.05), while no significant differences were found in both 10 kPa control group and TGF-β1 treated group, as well as in 30 kPa and 3.6 kPa control groups and TGF-β1 treated groups. Conclusions The increase of substrate stiffness can induce transformation of hepatocyte phenotype and promote the influence of TGF-beta 1 on behavior of hepatocyte metabolism.

Abstract:Objective To evaluate the viscoelastic properties of porcine acellular dermal matrix (PADM) by comparison and analysis on physical parameters of the skin. Methods Full-thickness skin defects were performed on the back of white rabbits as wound models, and randomly divided these wounds into 3 groups according to different methods of skin grafting: PADM group (autogenous skin and PADM were grafted to the surface of the wound), TS group (autogenous skin was grafted in situ), NS group (normal skin as the control). Experiments on the stress-strain relationship of the implanted skin in the three groups were conducted. Results The curves of stress relaxation, creep, and stress-strain relationship showed that under a given stress, PADM group had the lowest strain, NS group had the highest strain, while the strain of TS group was in between the PADM and NS group. Conclusions The skin viscoelasticity mechanical model is a four-parameter solid model. When the skin wounds are grafted by using PADM which may have poor elasticity, its recovery capacity after deformation is also poor, and this is in agreement with the clinical results.

Abstract:Objective To analyze the relationship between compression deformation and mechanical bearing characteristics of articular cartilage. Methods Indentation test was used to measure the compression displacement of bovine knee articular cartilage with different indenter diameters and under different loads. The fluid flow and bearing characteristics of the articular cartilage were simulated by the finite element model. Results The maximum relative error between simulated maximum compression displacement and experimental result was 1.73%. The elastic modulus and permeability coefficient of cartilage increased with indenter diameter increasing under the same load, while decreased with indentation load increasing at the same indenter diameter. Fluid flow was mainly in the internal cartilage when the load was exerted on cartilage. With the load sustaining, fluid flow was gradually moved to outside of the cartilage. Pore pressure, axial stress and radial stress on the cartilage surface then presented a nonlinear change due to the fluid flow. Conclusions Fluid flow, pore pressure and stress distribution on the cartilage surface have a great impact on its bearing characteristics, which varies greatly with different indenters and under different loads.

Abstract:Objective To improve the clinical application of body weight support treadmill training (BWSTT) robot and develop a practical way for promoting the rehabilitation robot, this paper proposes a design plan of lower limb robot with flexible structure, simple operation, and strong practicality in allusion to the weak clinical applicability of traditional BWSTT robot. Methods Based on methods of modular design and intensive design, the whole body of the robot was divided into several functional modules including wearable exoskeleton, weight loss training device, adaptive treadmill and suspension vest from the view of ergonomics, rehabilitation medicine, and mechanical design and so on. Meanwhile, an optimization analysis design was made for key parts of the robot through theoretical calculation and SolidWorks simulation. Results After the concrete manufacturing and clinical experiments, the feasibility and scientificity of the BWSTT robot design was validated. Conclusions This clinical application design can improve the practical application of BWSTT robot and also provide a reference for the wider use of the lower limb rehabilitation robot.

Abstract:Objective To numerically simulate the specific deformation and calculate the critical pressure of red blood cells in the osmosis experiment. MethodsThe shell model of red blood cells was established. Based on the constitutive hyperelastic model of the form Neo-hookean strain-energy potential and the experimental data for shear modulus of cell membrane provided by references, the red blood cell osmosis model was calculated in finite element software ABAQUS. Results The whole phases of red blood cell deformation when subjected to osmotic pressure were obtained. It was found that cell membrane rapidly changed from biconcave shape to oval shape when osmotic pressure was increased to 50-60 mPa, with the value of critical pressure falling in the scope provided by references. Meanwhile, the Mises stress distributions of cell membrane in different phases were also obtained. Conclusions The critical pressure for red blood cells changing from biconcave shape to oval shape is 50-60 mPa. The shell model and the constitutive hyperelastic model of the form Neo-hookean strain-energy potential can be used in the simulation of the osmosis experiment to provide a clear and reasonable phase of red blood cell deformation.

Abstract:Objective To investigate the effects from cyclic mechanical stretch on proliferation of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs). Methods In the experimental groups, cyclic mechanical stretch, with frequency of 1.0 Hz and magnitude of 3%, 6% and 9%, respectively, was applied to RA-FLSs for 2 h, 6 h, and 12 h. The control group remained in the same culture condition as the experimental groups, but without any mechanical stretch. After mechanical loading, the cell viability was analyzed by MTS, and its proliferation was assayed by flow cytometry. RT-PCR was used to measure the gene expression of the cell cycle regulatory factors, including CDK2, cyclinD1, cyclinE1, and P27. Results Cyclic mechanical stretch with magnitude of 6% and 9% for 6 h or 12 h significantly decreased the cell proliferation and viability in RA-FLSs (P<0.05). Meanwhile, both CDK2 and cyclinE1 gene expressions were significantly decreased, but P27 gene expression was increased (P<0.05). The cyclic mechanical stretch had relatively small influence on expression of cyclinD1 (P>0.05). Conclusions The effects from cyclic mechanical stretch on proliferation of RA-FLSs depend on the stretch magnitude and duration. Mechanical stretch with magnitude of 6% and 9% can inhibit RA-FLSs proliferation, which may be achieved by regulating the expression of Cyclin E1, CDK2 and P27. This study provides references for investigating the role of mechanical stimulation in pathogenesis of rheumatoid arthritis, as well as its prevention and treatment.

Abstract:Stent intervention has become one of the most effective ways in treating cardiac and cerebral vascular stenosis. However, postoperative in-stent restenosis remains a major unsettled issue. The occurrence of in-stent restenosis is related not only to the mismatch between stent and artery, as well as the stress induced by mechanical support of the stent struts on arterial wall, but also to the intimal hyperplasia induced by the hemodynamic change. Recent literatures on biomechanics of the stented artery were reviewed in this paper. In particular, from the view of solid mechanics and hemodynamics, the research progress of stented artery in biomechanical simulation was given detailed discussion; moreover, the biomechanical factors associated with in-stent restenosis were analyzed and summarized. Numerical simulation is a good method for investigating the relationship between stent intervention and in-stent restenosis, and it also provides a scientific guideline for the design of stent structure and clinical procedure of stent intervention.