• Volume 23,Issue 4,2008 Table of Contents
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    • Streaming potential in human dentin

      2008, 23(4):257-261. DOI: 10.3871/j.1004-7220.2008.4.261.

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      Abstract:Objective To reveal the streaming potential in human dentin and the related influencing factors. M ethod Fresh human third molars without visible evidence of caries were used in this investigation. A cell was designed and manufactured for facilitating the measurement of steaming potential in human dentin under a simulated physiological condition. A system including the cell, a mechanical testing machine, a scanner and a personal computer was established for cyclic loading and data acquisition. The streaming potential of the dentin specimens was evaluated under the loading frequency ranging from 0.05 to 0.2 Hz. Subsequently, a hole of 0.5 mm in diameter was drilled in each dentin specimen for simulating the effect of deep caries on the streaming potential in dentin, the streaming potential of these dentin specimens were reexamined. Results Human dentin revealed streaming potential under testing condition. The value of streaming potential increased with the increase of the frequency of cyclic loading. The phenomenon may result from the increasing difference of pressure between the opposite surfaces of the dentin specimen upon the increase of velocity of the fluid through tubules as a result of increasing loading frequency. Introducing small hole into dentin specimen resulted in the decrease of peak streaming potential. C onclusion Human dentin revealed steaming potential as loaded cyclically in a simulated physiological condition. Increase of loading frequency lead to the increase of streaming potential. Introducing small hole into dentin specimen resulted in the decrease of peak streaming potential.

    • In vitro pentraxin-3 expression in human alveolar epithelial cells induced cyclic stretch

      2008, 23(4):262-265. DOI: 10.3871/j.1004-7220.2008.4.265.

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      Abstract:Objective To study the effect of mechanical stretch on pentraxin-3 (PTX3) expression and release in human alveolar epithelial cells(A549). Methods The cells grown on collagen 1 BioFlex plates were exposed to square cyclic stretch at 0.3Hz using the Flexercell system with 20% elongation of cells. After stretching for 1,2,4,6 hours, conditioned media were collected and the levels of PTX3 protein were measured by Western blotting. Real-time PCR of PTX3 mRNA extracted from stretched cells was performed. Apoptosis? and viability of the cells following treatments were routinely monitored. Results The results of this study showed that: 1) cyclic stretch led to increase gene expression and release of PTX3 from alveolar epithelial cells ;2 ) stretch induced apoptosis? in alveolar epithelial cells; 3) PTX3 levels correlated with severity of apoptosis of alveolar epithelial cells.C onclusion The above results suggest that PTX3 may act as an important mediator for tissue damage and play an important role for ventilator-induced lung injury

    • Gradient shear stress induces vascular endothelial cells proliferation

      2008, 23(4):266-269. DOI: 10.3871/j.1004-7220.2008.4.269.

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      Abstract:Objective To explore the effect of shear stress on proliferation of vascular endothelial cells (ECs) around stent edge. Methods ECs were divided into static group (as control group), gradient shear stress group (ECs in parallel-plate flow chamber (PPFC) with gradient shear stress ) and steady shear stress group (ECs in rectangular PPFC). Two shear stress groups were subjected to 0.566-1.438 Pa and 1.137 Pa for 6h, respectively. The ECs cell cycle in each group was detected by flow cytometry (FCM). Results The amount of ECs entering cell cycle phases of S and G2+M in gradient shear stress group was much more than that in static group and steady shear stress group P( < 0.05), while the amount of ECs in steady shear stress group entering phases of S and 2G+M was significantly less than that in other two groups (P < 0.05).Conclusion Gradient shear stress induces ECs to enter phases of proliferation while the cell cycle phase is inhibited by the steady laminar shear stress. The result suggests that the gradient shear stress caused by planted stent can induce ECs proliferation, which may play an important role in initial hyperplasia in the restenosis process within the stent.

    • Biomechanics properties of small-diameter & microporous polyurethane vascular graft

      2008, 23(4):270-274. DOI: 10.3871/j.1004-7220.2008.04.274.

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      Abstract:Objective To analyse the microcosmic structure of small-diameter PU vascular graft and explore the influence by the wall thickness of vascular graft on its porous properties and tensile stress.M ethods The small- diameter vascular graft with microporous structure was prepared by casting polyurethane (PU) film onto the glass rod model. The microporous structure was charactered by SEM. According to ISO [7198], the testing equipment for such PU vascular graft was designed to test its porous property. The tensile stress was also investigated at INSTRON tensile strength tester (model: 5566). Results The inner surface, the outer surface and the crossing section of this small- diameter PU vascular graft all presented uniformly microporous structure, and the size of micro hole was under 100μ m. Additionally, the porous properties of this vascular graft would reduce with its wall thickness increased, while the tensile stress would increase first and then reduce. All the testing values gained were similar with the results of the same studies made in the world. Conclusions This kind of small-diameter vascular graft made with PU could basically satisfy the needs of implant vascular graft in biomechanics properties.

    • Numerical analysis of pathologic tympanic membrane of human ear

      2008, 23(4):275-278. DOI: 10.3871/j.1004-7220.2008.4.278.

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      Abstract:Objective To study the effects of thickness and stiffness of tympanic membrane on sound transmission of human ear. Methods A healthy living volunteer is scanned using spiral CT to obtain the whole temporal bone showing. The images are digitized by Matlab program along the outlines of the ear structures. The digitized outlines are then imported into ANSYS to construct a three-dimensional finite element model of the human ear.R esults The uniform pressure of 105 dB is applied on the entrance of the ear canal, and the harmonic analysis is calculated on the model within the frequency range of 200-8000 Hz. The model is set to analyze the displacement change of tympanic membrane and stapes footplate of the pathologic tympanic membrane.C onclusion The principle of sound transmission was explained based on the numerical method. The results may provide the useful mechanical reference for tympanic membrane reconstruction.

    • Three-dimensional numerical simulation of hemodynamics in human aortic arch

      2008, 23(4):279-283. DOI: 10.3871/j.1004-7220.2008.4.283.

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      Abstract:Objective The key techniques for geometry reconstruction based on Magnetic Resonance Images (MRIs) was elaborated. The three-dimensional numerical simulation of blood flow in human aortic arch was performed to provide fundamentals in genesis of aortic dissection and arteriosclerosis.M ethods Digital geometry reconstruction based on the clinical Magnetic Resonance Images (MRIs) was made by using image analysis. Pulsating flow rate were imposed on the CFD model as boundary conditions and three-dimensional blood flow field in the aortic arch was numerically modeled. Results Distributions of blood velocity, pressure, wall shear stress (WSS) in the human aortic arch at different point during one cardiac circle were determined by calculation.C onclusion The key techniques used in geometry reconstruction is helpful to carry out the further more research in bio-fluid mechanics. Numerical simulation of the blood flow in the present study could play an essential role in clinic diagnosis and treatment of aortic dissection and arteriosclerosis.

    • Study on biomechanical characteristics of artificial heart prostheses

      2008, 23(4):284-287. DOI: 10.3871/j.1004-7220.2008.4.287.

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      Abstract:Objective To determine the biomechanical properties of two kinds of artificial heart prostheses (made in France (InterGard) and made in Suzhou, respectively) and provide theoretic reference for its manufacture and clinical use. Method Tensile strength, stress-strain relationship, stress relaxation and creep of these specimens were tested by using a material testing machine and analyzed the results.R esult The specimens made in France are superior in its properties compared with that of the specimens made in Suzhou.C onclusion Biomechanical properties of artificial heart prostheses mainly depend on the the material it is made of and the factures such as its stuff, structure, etc.

    • 3D reconstruction finite element model of cerebral aneurysm based on CT data

      2008, 23(4):288-290. DOI: 10.3871/j.1004-7220.2008.4.290.

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      Abstract:Objective To establish the finite element model of 3D reconstruction for cerebral aneurysm to provide the basic analysis with hemodynamic mechanism in rupture of cerebral aneurysm.M ethod According to clinical CT scanning data, 3D cerebral aneurysm is reconstructed with integrating MIMICS 8.1 digital medical image management software and the result document was transferred to ANSYS software to computerize the hemodynamic parameter.s Results Finite element model of cerebral aneurysm, which can be applied to simulate hemodynamics in cerebral aneurysm, is presented. Conclusions This model has not only digital but also individual properties, and can be used to calculate the hemodynamic property in cerebral aneurysm and help to analyze its rupture mechanism.

    • Effect of drug dosing regiments on drug delivery in solid tumor by lumped parameter modeling and animal experiments

      2008, 23(4):291-295. DOI: 10.3871/j.1004-7220.2008.4.295.

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      Abstract:Objective To investigate effects of dosing regiment on drug delivery in solid tumor via Lumped parameter modeling, and to validate them with experiment on rats. Methods Lumped parameter Models of pharmacokinetic and of drug delivery in tumor were developed, to simulate time courses of average drug concentration (tC) in tumor interstitium with two types of injection-methods (single-shot and trio-shot). The same performance was also made in rats experiment with two groups by given HCPT. Result It showed by lumped parameter modeling that trio-shot method is more efficacious than single-shot method and also validated by the experimental data from the rats test.C onclusion Trio- shot injection is more effective than single-shot injection. The present lumped-parameter model is quantitatively competent for the effect of different drug delivery on solid tumor.

    • Patient-specific FE modeling of whole pelvis and simulation of sacroiliac joint fracture

      2008, 23(4):296-300. DOI: 10.3871/j.1004-7220.2008.4.300.

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      Abstract:Objective To create a geometrical and mechanical accurate patient-specific 3D FE model of whole pelvis, and based on which simulate a common case of sacroiliac joint fracture.M ethods The individual geometry of the sacral and hip bones were well reproduced by CT data and then an ad hoc biomechanical semi-automatic mesh generator, which could take the advantage of pairs of frame curves capturing the bone shape feature, was employed to generate regular FE mesh of the pevis model. The sacroiliac joint related end plates, cartilages, and contact surfaces, as well as several important ligaments and the interpubic disc were finally reconstucted to consummate the whole model.R esults A realistic individual FE model of whole pelvis was constructed, including the cortical and trabecular bone of the sacral and hip bones, all anatomical features of sacroiliac joint: end plates, cartilages, and contact surfaces having friction, as well as interosseous sacroiliac ligament, anterior sacroiliac ligament, posterior sacroiliac ligament, sacrospinous ligament, sacrotuberous ligament, superior pubic ligament, arcuate pubic ligament, and the interpubic disc. The simulation results from this normal whole model undering loading as well as the case of sacroiliac joint fracture were closely correlated with published results of experimental biomechanics.C onclusion By a specifically designed biomechanical modeling tool, an accurate individual FE model of whole pelvis including almost all complex anatomical features was generated, which could be used as the foundation for biomechanical analysis of the whole pelvis structure.

    • Space closure using preajusted appliance and sliding mechanics: the 3D nonlinear finite element modeling and numerical analysis

      2008, 23(4):301-305. DOI: 10.3871/j.1004-7220.2008.4.305.

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      Abstract:Objective To construct a 3D nonlinear finite element model and analyze the biomechanics of the space closure by using preajusted直丝弓?? appliance with sliding mechanics. Method With the whole digital model including denture, periodontal tissue, wire and appliance直丝弓? set up by using laser scanning, 3D reconstruction and computer aid design technology, a finite element model was constructed. To make the nonlinear calculation by setting up the contacts between teeth and contacts between wire and brackets as contact relationship.R esults The distribution of stress in periodontal is lower and well-distributed. There existed only 1 contact point and 1.4N contact normal force at the first molar. The initial displacement of anterior teeth is more than that of posterior teeth. All this has made the wire more easier to sliding. Conclusions The results from the model are basically corresponded to the results from the clinic study, which proved the validity of the model and could be the groundwork for the further sudy on some more biomechanical problems about continuous wire.

    • Biomechanical study on strengthening pedicle screw fixation through partial solidification of track

      2008, 23(4):306-310. DOI: 10.3871/j.1004-7220.2008.4.310.

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      Abstract:Objective To evaluate the effect by partial solidification of track on strengthening pedicle screw fixation in vitro. Methods 30 fresh adult goat lumbar vertebrae were harvested. Usual fixation of pedicle screw was given to one side of each lumbar vertebrae (blank group),and partial solidification of track before fixation of pedicle screw was given to the other side (experiment group). 10 lumbar vertebrae were selected randomly followed by axial pullout test and periodical bending resistance test was performed on the other 20 lumbar vertebrae in 24 hours after the fixation.R esults: The maximum axial pullout strength is (637.60±109.95) N in blank group and (816.50±134.88) N in experiment group; energy absorption value is (1.268±0.252) J in blank group and (1.631±0.269) J in experiment group. There is significant difference between two groups (P<0.05). The screws in experiment group can resist more loading or reduce fewer shifts under the same loadings compared with screws in blank group in periodical bending resistance test. Conclusions: Partial solidification of track can significantly strengthen the stability of pedicle screw fixation and provide a novel clinical method to solve loosing of screws. It has a favorable perspective in clinical application.

    • Biomechanical study of vertebroplasty in treatment of thoracolumbar compression fracture

      2008, 23(4):311-316. DOI: 10.3871/j.1004-7220.2008.4.316.

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      Abstract:Objective To assess the biomechanical effects and morphologic transformation in treating thoracolumbar traumatic compression fracture by precutaneous vertebralplasty (PVP) combined with reduction.M ethod L1 traumatic compression fracture was created with six fresh calf spines (T12-L3) and the destabilized specimens were augmented using PVP combined with reduction procedure. Each specimen was tested in four states: intact state as the control, L1 flexion-compression fracture state, PVP combined with reduction state, 3000 cycles of fatigue state, respectively. Biomechanical and morphologic analyses were made to test the mechanical stability of the fractured spine.R esults PVP combined with reduction can restore the L1 prevertebral height、strain and the spinal stability to intact states immediately after operation (P>0.05). 3000 fatigue cycles had no effect on the L1 prevertebral height and strain P(>0.05). In physiological loading, the specimens were associated with a significant decrease in rigidity from the intact state with flexio、nleft/right lateral bending (P<0.05) except axial compression and extension(P>0.05)after the fatigue. In left/right axial rotation, PVP was able to stabilize the spine after fatigue but not to the same extent as the intact state. Fatigue had no effect on ROM of T12- T13、L2-L3 at 4Nm moment (P>0.05). In T13-L1, no difference was encountered between the fatigue and intact state in extension、left/right axial rotation (P>0.05), PVP was able to stabilize the spine after fatigue but not to the same extent as the intact state in flexion ,ROM of left/right lateral bending after fatigue was the same as that of fracturedP (>0.05). In L1-L2, no difference was encountered between the fatigue and intact state in extensio、nleft/right axial rotation (P>0.05), PVP was able to stabilize the spine but not to the same extent as the intact state in left/right bending, ROM of flexion after fatigue was the same as that of fractured(P>0.05). No significant difference was found between intact and augmented vertebra for the failure strength after fatigue. Radiographs and cross-sectional observations indicated a good cement-bone bonding and fracture fill. Conclusion PVP combined with reduction can restore the stability of traumatic compression fracture immediately after operation, but the spinal stability decreased in some extent after 3000 cycles fatigue.

    • Stability evaluation of a new semirigid pedicle screw device

      2008, 23(4):317-320. DOI: 10.3871/j.1004-7220.2008.4.320.

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      Abstract:Objectives To evaluate the biomechanical stability of an new semirigid pedicle screw fixation device. Methods A model of destabilized spine was produced on six specimens of fresh calf cadaver spine from T11 to L1. Three fixation devices, (NRD、NSRD and RD) were ordinal applied in the specimens to strengthen the destabilized level. Ranges of three dimensional movements were measured in intact, destabilized and stabilized specimens, respectively. Results Three fixation devices all could provide significant stability for destabilized segment in flexion-extension, lateral bending and axial rotation. The range of motion (ROM) of the spine fixed with RD at T11-T12 was also significantly increased in comparison with the intact spine under flexion, extension and right axial rotation P(<0.05). The ROM of the stabilized spine with NSRD or NRD approximated the ROM of the intact spine at each motion of T11-T12 level.C onclusion The semirigid device could make the offer to a design that may not affect the ROM of adjacent segments while maintaining stability similar to that of rigid systems.

    • Progress of human mathematical model to study ship shock injury by underwater explosion

      2008, 23(4):321-326. DOI: 10.3871/j.1004-7220.2008.4.326.

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      Abstract:Underwater explosion can produce enormous shock acceleration in a very short duration, which could result in severe human injuries and degrade battle effectiveness seriously. Lumped parameter model, multi-body model and finite element model are commonly introduced to study the biodynamic response of shipboard personnel under vertical shock motion induced by underwater explosion. Each of the models has its advantages and limitations. Multi-body modeling method can supply possible useful information, provided it based on the most accurate human response data. Finite element modeling and its simulation provides a viable, cost effective alternative to live fire shock trials. Lumped parameter models emphasize larger scale information about human dynamic response. A model of hybrid form can be obtained by combining the finite element model and lumped parameter model. It has the potential not only to improve the analysis accuracy and spatial resolution but also to save the required computation time. Such hybrid form combining rigid body and FE techniques into one model can make full use of the advantages and offset the limitations of the each.

    • Advance in construction of three-dimensional finite element models after sacrectomy and reconstructing lumbosacral spine

      2008, 23(4):327-331. DOI: 10.3871/j.1004-7220.2008.4.331.

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      Abstract:Total sacrectomy is a useful method to treat the tumors which involve the first sacral vertebra. After operation, the destruction of pelvic ring often result in the separation between lumbar and pelvis, which need to be reconstructed clinically. But the loosening and fracturing after reconstruction could often occur. In order to evaluate the clinic work for reconstruction and to solve the stress concentration after reconstruction, finite element methods are commonly used to offer reliable basis for clinic study. The author reviews the recent advance in constructions for intact pelvis model, the defect model after sacrectomy, and the model after reconstructing lumbosacral spine to give a general summarization.

    • Influence of acetabular position on stress and wear of acetabular component after THA

      2008, 23(4):332-336. DOI: 10.3871/j.1004-7220.2008.4.336.

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      Abstract:Improperly placed acetabular component in THA could lead to dislocation, abnormal stress concentration and increased wear of the lining. For patients with acetabulum bone defect, medially and inferior placed acetabular component could broaden the contact area between bone and prosthesis so that decreased contact stress and better clinical outcome can be expected. Orientation of placed acetabular also influences its stress distribution and wear markedlyM.o st researchers recommend that the acetabular component should be placed at 40 45 for abduction and 5 20 for anteversion.

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