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Abstract:Objective To simulate clinical operation and investigate feasibility of Coflex dynamic device for fixing L5/S1 segment of lower lumbar degenerative diseases. Methods The lower lumbar-sacral digital model was extracted from platform of the second generation of Chinese Digitized Human “Male No.23” data set, and three finite element (FE) models (the model of normal lower lumbar sacrum, L4/5 and L5/S1 segment fixed with Coflex) were developed respectively using a series of CAX software. According to the spinal three-column loading theory and the lower lumbar physiological behaviors, FE model tests were analyzed, validated and compared under the physiological load of upright standing, anteflexion and extension. Results The FE models of normal lower lumbar sacrum (Healthy), Coflex fixed-L4/5 segment (L4/5), Coflex fixed-L5/S1 segment (L5/S1) were developed, respectively. Based on biomechanical indexes (stability and compatibility) of the controlled trial for the FE model, the two Coflex-fixed FE models showed similar biomechanical effects for fixing the lower lumbar. Conclusions The controlled trials of FE models provide biomechanical evidence for the fixation of lower lumbar L5/S1 segment by Coflex dynamic device, which is of significance for application of Coflex in fixing L5/S1 segment in clinic.

Abstract:Objective To make biomechanical evaluation on three prosthesis retention schemes for unilateral maxillary defects-clasp retention, one or two zygomatic implants and zygomatic implant and clasp united retention. Methods A three-dimensional (3D) finite element model of normal human skull was constructed based on CT scan data. The maxillary complex stress distributions on three reconstructed models were calculated and analyzed by 3D finite element method to make comprehensive comparison on stress level of the prosthesis, abutment, clasp, implants and zygoma. Results For single clasp retention, peak stress of the abutment was 130.7 MPa, and displacement of the prosthesis was 4.439 mm, while peak stress of the clap was 452.4 MPa, and stress of the contralateral orbital rim was 23.32 MPa. After one zygoma was implanted, the stress of the clap was reduced to 118.1 MPa, while peak stress of the abutment was 31.12 MPa, and stress of the contralateral orbital rim was only 5.387 MPa. For two zygomatic implant retention, zygomatic stress was decreased from 66.11 MPa to 48.12 MPa, and the maximum stress on the zygomatic implants was reduced from 500.2 MPa to 313.8 MPa. Conclusions For zygomatic implant and clasp united retention, the maxillofacial skeleton stress distributions were more consistent with the rules of bite force transduction. The research findings will provide important references for design and optimization of human unilateral maxillary defect reconstruction program.

Abstract:Objective To develop a shear force-induced intervertebral disc degeneration (IDD) in vivo animal model, and investigate the relationship between shear stress and IDD. Methods A total of 20 Japanese white rabbits were randomly divided into two groups. In loading group (n=10), shear force of 50 N was applied on the disc of L4/5 for 4 weeks by a custom-made external shear force loading device. In control group (n=10), the animals underwent a sham operation with the external loading device situated, but their discs remained unloaded. After 4 weeks, all the intervertebral discs of L4/5 were executed for the pathologic examination. Results The postoperative radiographic examination showed a perfect position of the loading device, and the operation process and implanted loading device had no effect on daily activities and diet of the experiment animals. The pathological examination showed an irregular arrangement of annulus fibrosus and a significant decrease of normal nucleus pulposus cells in loading group. Conclusions The new custom made device greatly reduced the wounds on animal vertebra and provided a reliable shear force. The development of in vivo animal model indicates that IDD can be induced by shear force, which is of significance to further study the relationship between loading and IDD.

Abstract:Objective To develop a measurement device and provide a platform for researching the characteristics of human upper respiratory tract flow field based on PIV (particle image velocimetry) technology with respect to the characteristics that human upper respiratory tract flow may form the vortex structure, flow shunt and secondary flow. Methods A transparent physical model of human upper respiratory tract was prepared based on the completely scanned medical images. By means of selecting appropriate air pressure system, combined with two-dimensional PIV system, a complete experimental apparatus was established. Based on the apparatus, preliminary experiment on air velocity in human upper respiratory tract flow field was conducted, and the experiment result was compared with the numerical simulation result. Results Under the steady breathing pattern at respiratory flow of 30 L/min, respiratory air flow measured by the experimental apparatus led to the formation of vortex structure in the front part of oral cavity. Air velocity was relatively higher both in the lower part of oral cavity near the upper tongue and in the middle part of oral cavity, while the velocity was relatively lower in the other parts of oral cavity. The results were in accordance with numerical simulation. Conclusions The experimental apparatus for human upper respiratory tract flow measurement based on PIV technology is practical and reliable, which can be applied in the measurement of airflow organization patterns and vorticity distributions in human upper respiratory tract, and realize the verification of numerical simulation results.

Abstract:Objective To compare the differences in biomechanical properties of embalmed and PMMA femurs under axial loads, so as to provide a more reliable and unified femoral model for replacement. Methods Ten embalmed femurs and ten PMMA femurs were selected, and each femur was instrumented with 49 strain gauges totally on the medial and lateral side. The axial load was applied dynamically up to a maximum of 1.2 kN, and the strain of each strain gauge and load displacement curve were recorded. Results The strain distributions on two types of femur were similar, and the load displacement presented a linear relationship, but the vertical displacements under different loads were significantly different (P<0.05). The axial stiffness value of PMMA femur and embalmed femur were (259.84±24.63) and (600.40±78.56) N/mm, respectively, showing significant difference (P<0.01). The strain concentration parts at the proximal part of two femurs were the same, but the average strain value of the PMMA femur was significantly different from that of the embalmed femur (strain gauge No. 1~5: PMMA femur (-3 420.63±373.31) με, embalmed femur (-1 289.42±417.89) με; strain gauge No. 26~27: PMMA femur (1 748.67±193.98) με, embalmed femur (673.42±104.49) με; strain gauge No. 7~10: PMMA femur (-4 028.25±267.27) με, embalmed femurs (-1 139.01±288.83) με; strain gauge No. 30~36: PMMA femur (1 599.02±194.68) με, embalmed femurs (590.52±153.18) με, P<0.01). The strain concentration parts at the distal part of the two femurs were different. The medial and lateral parts of strain transformation between positive and negative of PMMA femurs were similar to embalmed femurs. The strain-load curves of strain gauge No. 2, 26, 6, 29, 8 and 33 indicated a linear relationship, but the strain value of the two femurs had significant differences (P<0.05). Conclusions The PMMA femur can replace the embalmed femur to a certain degree in biomechanical experiments on the upper part of femur. Due to the difficulty of obtaining fresh femurs, the PMMA femurs provide a more reliable and unified femoral model for replacement.

Abstract:Objective To study the vortex structure and vortex evolution induced by jets in mouth-pharynx area, so as to deepen the understanding of jet motion characteristics and disease prevention in mouth-pharynx area. Methods CT scanning and 3D reconstruction were used to construct 3D model of realistic human mouth-throat model, and the method of large eddy numerical simulation was used to accurately simulate the process of vortex evolution in the model. ResultsIn the phase of inhalation, several vortex tubes were formed in mouth, and a turbulence jet appeared in the glottal region. In the phase of exhalation, the intense jet in the glottal region caused complex vortex structures in throat. Conclusions During inhalation, transition occurrs in the pharynx, and the “horseshoe vortexes” which are similar to the shape of horseshoe appeared on the anterior wall of the trachea. During exhalation, “arch vortex” are formed on the posterior wall of throat with the barrier of epiglottis.

Abstract:Objective To develop an automatic segmentation and mesh generation technique for abdominal aortic aneurysm (AAA) and to build a 2D numerical analysis model that can be used for finite element analysis (FEA). Methods A method that totally based on morphology processing was developed to segment all the components of the AAA. For each closed curve that obtained, its signed distance function was then calculated. According to the set relationships between each curve, the final signed distance function was calculated. Under the control of this function and an equilibrium relationship, iterated Delaunay algorithms were used until the equilibrium relationship was satisfied or the set conditions were reached. Then the program ended and the finite element model was generated. Results Automatic segmentation of the lumen as well as semiautomatic segmentation of the wall and calcification were achieved. Different parts of the AAA were meshed, and the type and density of the mesh could be controlled. Two finite element models were established for stress analysis: one was the coupling mesh of the thrombus and the wall, and the other was the coupling mesh of the thrombus, the wall and the calcifications. Conclusions An automatic segmentation and mesh generation algorithm with high accuracy has been developed, without any complicated computation or initial curve. The mesh generation algorithm tends to produce high quality meshes and the generation is easy to be controlled by only two parameters. The generated mesh has been verified to be useful in FEA simulation.

Abstract:Objective To construct a variable-parameter nonlinear model for the research on stress relaxation properties of human intervertebral disc under the cyclic strain. Methods The variable-parameter nonlinear model combined with experimental data on stress relaxation and creep response of the intervertebral disc were used to study stress relaxation properties under the cyclic strain and compare the differences of linear and nonlinear model in viscoelastic properties of the intervertebral disc. Results The cycle modulus and relaxation coefficient obtained by the variable-parameter nonlinear model under the of frequency 0.01 Hz was very close to the experimental data, and the cyclic modulus under the frequency of 0.1 and 1 Hz were also close to the experimental data, but the relaxation coefficient obtained in 0.1 and 1 Hz had serious distortion. Conclusions The intervertebral disc experiences a nonlinear stress behavior under the compression strain, so the variable-parameter nonlinear model is more suitable for studying the stress relaxation response of the intervertebral disc under the cyclic strain.

Abstract:Objective To investigate stress distributions on temporomandibular joint (TMJ) with different disc displacements through numerical simulation. Methods A three-dimensional finite element model of normal TMJ including the mandible, teeth, discs and articular cartilage was established according to CT images of a volunteer with asymptomatic joints. Base on the model, four corresponding models with the anterior, posterior, lateral and medial displacement of the disc were developed. Contact elements were considered to simulate the interaction between the discs and articular cartilages of the condyle and the temporal bone. Cable elements were used to simulate the ligaments and attachments of the disc. The muscle forces and boundary conditions corresponding to the centric occlusions were applied on the models. Results The maximum compressive stress occurred at the intermediate zone due to the anterior displacement of the disc, which was as high as 3.23 MPa. The stresses in the model with the posterior, lateral and medial displacements of the disc were higher than the model with the anterior displacement of the disc and healthy TMJ model. The stresses at the back of the articular eminences in four models with disc displacements were much higher than those in healthy TMJ model. However, the effects of disc displacements on the stresses of the condyles were not obvious. Conclusions Disc displacements could cause higher stresses in the discs and at the back of the articular eminences, especially in the model with the posterior, lateral and medial displacements of the disc, which was likely to cause damage to TMJ structure and function.

Abstract:Objective To develop a method for measuring the piezoelectric effect in wet bone. Methods A piezoelectric voltage measurement system of wet bone was designed, which employed platinum/iridium electrodes to detect the piezo-voltages and an ultra-high input impedance bio-amplifier to amplify the piezo-voltage signals, respectively. Because there was nearly no electric current in the buffer solution, even the electrodes that did not contact the bone sample could detect the piezoelectric voltages at the side of two bone samples. Results Voltage-time curves were obtained under the trapezoidal loading, and the results were confirmed to be piezoelectric voltages produced from bone by experiment. A total of 6 samples were tested. The measurement results showed that the piezo-voltages of wet bone were induced during the dynamic loading process, which was consistent with dry bone. Conclusions Measurement of the piezo-voltages in wet bone was developed by employing platinum/iridium electrodes for detecting the piezo-voltages and an ultra-high input impedance bio-amplifier for amplifying the piezo-voltage signals, and the validity of the test system was confirmed via experiments. The peak value of piezo-voltage was between -0.75 mV and -1.69 mV under the loading peak value 9 N. The results are helpful to investigate the relationship between bone growth and electric signals, which provides the theoretical references for researches on bone healing in clinic.

Abstract:Objective To explore the mechanical testing technique suitable for biological materials under water environment. Methods Based on digital image correlation (DIC) method, the unique lens sleeves which can avoid the distortion caused by underwater photography was designed, and this technique was applied to determining mechanical properties of the fish scales. Results The experiment on translation of the water sink indicated that the use of the designed lens sleeves could effectively reduce errors for underwater measurement with high precision; the mechanical testing on fish scales showed that different regions of the fish scales had obviously different mechanical properties, but the differences induced by regions of the dehydrated fish scales were significantly reduced. Conclusions The designed lens sleeves in this study can be applied to image acquisition effectively, and determination of mechanical properties of the biological materials under water environment was achieved using DIC method.

Abstract:Objective To investigate the influences of loading time and loading angle on the stress, displacement of human periodontal ligament in dynamic jaw. Methods The three-dimensional assembly model of the mandible front teeth, periodontal ligament and alveolar bone was reconstructed by using the reverse engineering technology. The thickness of periodontal membranes was 0.2 mm. The stress, displacement at different positions of the periodontal ligaments during different jaw cycles were analyzed under dynamic load in the direction from bucca to tongue side with 0°, 15°, 30°, 45°, 60°, 75°, 90° angle to the long axis of the tooth. Results During one jaw cycle, the ratio of the maximum to minimum value of the maximum residual stress due to different loading angles was 5.5, and the ratio of the maximum to minimum value of the maximum displacement was 8.1. The ratio of the maximum to minimum value of the maximum displacement which was caused by five jaw cycles was increased in the range from 1.02 to 1.35 with the increase of loading angles. The ratio of the maximum to minimum value of the maximum residual stress which was caused by different loading angles was increased in the range from 1.86 to 3.00 with the increase of jaw cycles. The location of the maximum stress was at the tongue side of the cervical margin at different loading angles, and the location of the maximum residual stress was distributed at different positions of the cervical margin. Most stress was accumulated at the root of the periodontal ligament under the 0° dynamic load. Conclusions The situation of the accumulated residual stresses and the uncertainties in the distribution of the maximum residual stresses should be observed in the clinical choice of mandible incisors fixed by bridge abutments; large angle force applied to the tooth was harmful to the periodontal ligament and rapid succession of chewing hard food should be avoided as much as possible during the clinical treatment.

Abstract:Objective To simulate the pressure field for extracorporeal shock wave lithotripsy (ESWL) by attaching additional reflector with different angles at the side of the ellipsoidal reflector edge in the Dornier HM3 lithotripter. Methods Based on axisymmetric Euler equations and hybrid grid improved CE/SE numerical scheme, the pressure field of shock wave changed by the additional reflector in ESWL was simulated. Results Pressures of the additional reflector with different angles near the focus were compared. There were significant 50% increases of both the positive and negative pressure peaks in the pressure field as compared to ESWL without additional reflector. The peak pressures were gradually decreased with the reflector angle increasing. The peak pressure of 45° reflector angle was about 25% less than that 0° reflector angle. Conclusions At the initial stage of stone comminution, stones were broken into smaller pieces due to the more concentrated energy produced by the additional reflector, which could reduce the firing frequency to achieve the same or higher stone comminution efficiency. The numerical simulation results provide a reliable numerical calculation result and useful reference for the improvement and clinical application of ESWL lithotripter.

Abstract:Objective To observe and compare the effects of intraocular pressure (IOP) drop when the aqueous humor was drained to limbus, ambitus and posterior segment of rabbit eye by implanting medical silicone tube. Methods Forty-five healthy New Zealand white rabbits were chosen for the experimental group, each with the medical silicone tube implanted in one eye. According to different implanting ways, the rabbits were divided into the limbus group, ambitus group and posterior segment group respectively, with 15 rabbits in each group. Results According to statistical comparison of preoperative and postoperative IOP values among the 3 groups within 4 weeks, the IOP of the posterior segment group was decreased most by 26.6%, and that of the ambitus group and limbal group was decreased by 16.2% and 1.2%, respectively. The differences between the preoperative and postoperative IOP in first, second and fourth week were statistically significant (P<0.01) for all three groups. The IOP of the posterior segment group after 4 weeks was decreased most, and there were significant differences in IOP values among three groups (P<0.01). Conclusions The greatest IOP drop occurred when the aqueous humor was drained to the posterior segment of the rabbit eye, and this result could provide some reference for the clinical surgery.

Abstract:Objective To prepare a bilayer spider silk protein vascular scaffold using electrospinning, observe microstructure of the vascular scaffold and study its biomechanical properties and cell compatibility. Methods Spinning solution was electrospun to prepare (pNSR16/PCL/CS)/(pNSR16/PCL/Gt) bilayer spider silk protein vascular scaffold using rotating receiving rod as the collection device. The effects of mass fraction and wall thickness on the porosity, bursting strength, tensile properties, suture retention strength and water permeability of the vascular scaffold were investigated, and cytotoxicity and cell adhesion property of the vascular scaffold were tested. Results The vascular scaffold presented three-dimensional porous microstructure with randomly distributed fibers. The bursting strength, tensile strength and suture retention strength were directly proportional to mass fraction and wall thickness, but the porosity, water permeability and elongation at break were inversely proportional to mass fraction and wall thickness. The bursting strength range of vascular scaffold was 43~183 kPa, which was higher than the physiological blood pressure; the suture strength was above 0.19 N, which was consistent with the transplantation requirement in vivo; the tensile strength was higher than that of human radial artery, which met the transplantation requirement in vivo; the range of water permeability was 0.3~0.6 mL?min-1?cm-2. The vascular scaffold had no cytotoxicity and facilitated the adhesion and proliferation of endothelial cells. Conclusions It is feasible to prepare the bilayer spider silk protein vascular scaffold through electrospinning. The superior biomechanical properties and biocompatibility properties show that the bilayer spider silk protein vascular can be used for construction of the tissue engineered blood vessels in vitro, with prospect for further vascular graft study, which lays a foundation for its clinical application.

Abstract:Objective To reveal the shear stress regulation mechanism on vWF-A1A2A3-mediated rolling of platelets in flows. Methods Platelets were perfused with various flow rates over 200 μg/mL vWF A1A2A3 in parallel-plate flow chamber. The rolling events of platelets near the bottom of chamber were observed and analyzed to obtain the rolling characteristics. Results The mean rolling velocity and time, stop frequency and fractional stop time of platelets were all found to be biphasic dependent on wall shear stress, with all the threshold/inflection points occurring under the fluid stress of 0.8 Pa. Increasing shear stress below the threshold would slow and stabilize cell rolling in flows. Conclusions Wall shear stress regulates velocity of A1A2A3-mediated cell rolling by adjusting the cell stop time, suggesting that a catch-to slip-bond transition serves as a mechanical regulation mechanism for platelet rolling through A1A2A3 GPIbα interaction in flows.

Abstract:Objective To develop a biological canulated screw and evaluate its mechanical properties, so as to provide theoretical basis for the bio therapy of fracture with enrichment technique of bone marrow stem cells, which could be diffused through the canula, particularly for promoting bone union of femoral neck fracture and preventing avascular necrosis of femoral head. Methods TC4 titanium alloyed canulated cancellous screw (7.3 mm in diameter) commonly used for internal fixation of femoral neck fracture was improved by designing an end sealing plug and side holes in a 900 mm-long canulated screw. The side holes were arranged along the axis of screw, and the first side hole was 20 mm away from the screw tip. The distance between each side hole was 10 mm, and the number of side holes ranged from 0 to 6. The screws without holes were tested as control, and the rest were divided into two groups, i.e., group A: force direction parallel to the side hole, group B: force direction perpendicular to the side hole. Three point bending test on the screw was conducted by using Instron material testing machine, so as to study the relationship between the mechanical strength of the screw and the number of side holes, and the loading direction. Results (1) When the force direction was parallel to the side hole, which was confined within 0, 1 or 2, the bending deformation of the screw reached 3 mm, and no differences were found in the maximum loads and elastic modulus of the screw. However, when the number of side holes was increased to 3 or more, a significant reduction in the maximum load and elastic modulus of the screw was found (P＜0.05). (2) When the force direction was perpendicular to the side hole, which was confined within 0,1 or 2, and the bending deformation of the screw reached 3 mm, no significant differences were found in the maximum loads of the screw. While no significant difference was found in the elastic modulus of the screw when the side hole was 0, 1, 2 and 3. With an increase in the number of side holes, the maximum loads (≧ 3 side holes) and elastic modulus (≧ 4 side holes) were significantly reduced (P＜0.05). (3) When the force direction was perpendicular to the side hole and the number of side holes was 3 or more, the maximum loads and elastic modulus of the screw were all significantly higher than the screw with the same number of side hole under force direction parallel to the side hole. Conclusions (1) For achieving better mechanical properties of the screw, the number of side holes in titanium alloyed canulated cancellous screw (7.3 mm in diameter) should be within 2; (2) If the number of side holes was equal or over 3, screws under force direction perpendicular to the side hole could provide better mechanical properties than screws under force direction parallel to the side hole. This study may provide some theoretical evidence and support for future clinical development and practice of the biological canulated screw.

Abstract:Bone tissues constantly receive the mechanical stimulation and maintain the dynamic balance of bone formation and resorption. Currently, the mechanism of how bone tissues sense the mechanical stimulation is still unknown. An increasing number of studies have shown that primary cilium may be the mechanical sensor of bone tissues. The primary cilium maybe transfer the extracellular mechanical signals into intracellular biochemical message through them, and the mechanical stimulation received by bone tissues can regulate bone remodeling finally. This article reviews the current researches on primary cilium, predicts the research tendency and tries to lay some foundation for the use of primary cilium to prevent and treat osteoporosis.

Abstract:This article reviews the application of finite element method in spine biomechanics during the last three years. Major progress in both finite element model improvement of detailed microstructure, personalized vertebrae parameter weights, new accurate calibration method, automated modeling approach and spine biomechanics-related applications including implant design assessment, inter-vertebral disc biomechanics, biomechanics of abnormal spinal structure, dynamic simulation are classified and summarized. Future development of finite element method being applied in trauma mechanism, surgery simulation and drug evaluation is also discussed.