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Contribution of co-contraction to arm impedance in the free planar movement

Journal of Medical Biomechanics.2009;24(6):427-433.

Objective Impedance control plays an important role in stability.This paper intends to explore such mechanism through modeling human reaching movement.Method Implemented with revised model,we ap-ply optimal control theory to neuro-muscle-skeleton model to calculate the stiffness ellipses.Result Com-pared with the original model and experimental figures,the model we proposed could overcome the shortage of monotonous changing of the original one and fit the data better.Conclusions So that this paper concludes that co-contraction contributes to impedance control even during free upper limb planar movement.

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Advances of mechanical conditions in engineering cartilage tissue

Chunqiu ZHANG ; Minlin SUN ; Jiang LI ; Jinduo YE ; Haiying LIU

Journal of Medical Biomechanics.2009;24(6):462-467.

There are many physical factors affecting the development of cartilage tissue,the mechanical con-dition is the main important one that particularly act.The mechanical conditions used in engineering cartilage tissue,such as compressive and shear force,fluid flow,hydrostatic pressure and tissue deformation or with some of them combined,were reviewed.From the standpoint of bionics,the mechanical environments ap-plied on tissue engineering should work in three aspects:providing adequately mechanical stimuli to the cells seeded in 3-D scaffold;ensuring the efficient mass-transport of the nutrients and waste products in the cells:promoting the development of functionally extracellular matrix in 3-D scaffold.The mechanical environments currently used only represented the part of mechanical conditions of in vive articular cartilage will be reviewed.In our view that rolling depression load may achieve the fit mechanical environment for cultivation of functional cartilage constructs in vitro.

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Fatigue life analysis of coronary stent by finite element analysis

Jianjun LI ; Qiyi LUO ; Zhiyong XIE ; Yu LI

Journal of Medical Biomechanics.2010;25(1):68-73.

Objective After the implantation,coronary stent is expected at least to keep its integrity and maintain the predicated function for over 10 years or 4e8 cycles under the pulsatile loading conditions,so the fatigue property of the stent should be evaluated.Method The finite method was used to analyze the stress distribution of different phases and evaluate the fatigue life according to Goodman criteria,meanwhile,the accelerated fatigue experiment was also performed.Results It can be concluded that the dangerous points are all but located in the lateral inner surface of stent curvature.Conclusions The results prove that the fatigue property can be simulated through the finite element analysis,which can provide the theoretical guidance for the stent design.

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Numerical analysis of the effect of capillary geometry on oxygen transport in the microcirculation by MATLAB

Kai ZHU ; Ying HE

Journal of Medical Biomechanics.2009;24(4):263-269.

Objective Delivery of oxygen in tissues is limited in the space where oxygen must diffuse between the vascular and the surrounding tissues. Normal capillaries are relatively straight and well spaced, in contrast, the tumor vascular networks usually display more irregularity and the vessel wall shows higher permeability and less elasticity. The purpose of this study was to investigate the effect of capillary elasticity and tortuosity on the oxygen distribution and make further investigation on the mechanism of the formation of hypoxic regions in tumor. Method One-dimensional capillary model was coupled with the oxygen diffusion model. Oxygen transport was investigated in a Krogh and tortuous tissue model. The capillarygeometrywas obtained bythe one-dimensional model and transferred to the tissue model. Finite element method was employed in the analysis. Result The capillary radii along the flow direction under pressures were obtained for different initial radii and the oxygen distribution in the Krogh cylinder tissue model and the model with a tortuous capillary were computed. Conclusions when the capillary radius is small, the effect of vessel elasticity may have not significant effect on the oxygen distribution. However, with the capillary radius increasing, the effect on the oxygen transport becomes obvious. Moreover, with the tortuosity of the capillary increasing, the oxygen distribution becomes more heterogeneous, which is in agreement with the result in available reference. This work will be helpful to the investigation of oxygen transport within tumor.

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Establishment and validation of a dynamic finite element model of human head-neck

Ying-Fu GUO ; Hong-Xi HE ; Wen-Xin NIU ; Zhi-Hua CAI

Journal of Medical Biomechanics.2017;32(5):393-400. doi:10.16156/j.1004-7220.2017.05.001

Objective To construct a three-dimensional (3D) dynamic head-neck finite element model which ac cords with the anatomical structure,and study its dynamic responses under the extemal force.Methods By using the neck CT images of a Chinese adult male volunteer and obtaining the 3D cervical point cloud data,the finite element model of cervical spine was established using ICEM-CFD and HyperMesh software.This model,including vertebrae,intervertebral discs,facet joints,ligaments and cartilage tissues,and combining with the es tablished and verified head finite element model,was assembled as human head-neck finite element model with detailed anatomical structures.Results The model was validated by data of head-neck axial impact experiments reported in previously published literature.The simulation results showed that the neck deformation,head acceleration,head force and injury positions were preferably consistent with the experimental data.Conclusions The established 3D dynamic finite element model can be used to study head-neck dynamic responses and damage mechanism in the fields of traffic safety and impact injuries.

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Postmortem interval estimation by time-dependent changes of morphology and biomechanical properties in brain tissues

Chang TANG ; Chao LIU ; Rui-Bing SU ; Jun-Yao L(U) ; Shan-Qing CAI ; Xiao-Hu XU ; Xiao-Jun YU

Journal of Medical Biomechanics.2017;32(5):401-406. doi:10.16156/j.1004-7220.2017.05.002

Objective To explore the regularity of time-dependent changes in morphology and biomechanical properties of brain tissues in pigs,and value the feasibility of deducing the postmortem interval (PMI).Methods Brain tissues were taken from 42 pigs and kept in an artificial climate chamber with the temperature of 25 ℃ and humidity of 75％.The samples were collected from telencephalon at sequential time intervals (0,12,24,36,48,60 h;n =6) according to the principle of predefined time,position,direction,ratio,quantity and shape.The samples fixed with formaldehyde were then immediately tested by mechanical testing machine to obtain their biomechanical parameters and the histological sections were prepared.Results With the extension of PMI (0-60 h),brain tissues gradually became discolored,weak,mudding and liquefied under the influence of autolysis and putrefaction.Both clearance area of the white matter and its integrated optical density (IOD) significantly increased during 0-48 h.Biomechanical properties of brain tissues including the limit load,average force,elastic modulus and fracture energy all presented a declining tendency at the interval of 12-60 h.The limit load was considered highly statistically significant,and statistical differences were found in average force,elastic modulus and fracture energy.Conclusions There exists a significantly negative structure-activity relationship between the morphology of brain tissues and biomechanical properties.The limit load of postmortem brain tissues in 60 h is the optimum in the window period,which can be used as a new method for estimating PMI.

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Design and biomechanical study of a novel double-leaf proximal humeral locking plate

Lang-Qing ZENG ; Lu-Lu ZENG ; Yun-Feng CHEN ; Yan-Jie LIU ; Hui YANG ; Zhi-Rong LIN ; Wen ZHANG ; Hai-Feng WEI

Journal of Medical Biomechanics.2017;32(5):407-414. doi:10.16156/j.1004-7220.2017.05.003

Objective To design a novel double-leaf proximal humeral locking plate for fixing greater and lesser tuberosities in complex proximal humeral fractures,and evaluate its fixing stability by biomechanical tests.Methods Twelve fresh-frozen humerus specimens with intact rotator cuff were randomly divided into two groups (Group A and Group B) to establish the same greater and lesser tuberosities fracture models.Specimens in Group A were fixed with the double-leaf proximal humeral locking plate,while specimens in Group B were fixed with the proximal humeral internal locking system (PHILOS) and tension band suture,and a 3.5-mm cannulated screw was added to stabilize the lesser tuberosity.The tensile test on subscapularis,infraspinatus and teres,supraspi natus as well as the load-to-failure test on greater and lesser tuberosities were performed on specimens in two groups.Results For subscapularis tensile tests,displacements under 150 N tensile stretch and after fatigue test in Group A were both significantly smaller than those in Group B (P ＜ 0.05).For infraspinatus and teres tensile tests,there were no statistical differences between Group A and B in displacements under 150 N tensile stretch and after fatigue test (P ＞ 0.05).For supraspinatus tensile tests,there were no statistical differences between Group A and B in displacements under 90 N tensile stretch and after fatigue test (P ＞ 0.05).For load-to-failure tests on lesser tuberosity,the failure load in Group A was significantly greater than that in Group B (P ＜ 0.05),and the failure displacement in Group A was significantly smaller than that in Group B (P ＜ 0.05).For load-to-failure tests on greater tuberosity,there were no statistical differences between Group A and B in both the failure load and failure displacement (P ＞ 0.05).Conclusions Compared with the ordinary tension band suture plus cannulated screw for fixing lesser tuberosity,the novel double-leaf proximal humeral locking plate shows more obvious biomechanical stability,with the advantage of simultaneously fixing greater and lesser tuberosities.The research findings provide a new choice for the clinical treatment of complex proximal humeral fractures.

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Finite element analysis on the optimal unilateral pedicle screw-implanted angle and cage position for TLIF surgery

Wei-Bo YU ; Jian WANG ; De LIANG ; Xiao-Bing JIANG ; Lin-Qiang YE ; Xue-Cheng HUANG

Journal of Medical Biomechanics.2017;32(5):415-421. doi:10.16156/j.1004-7220.2017.05.004

Objective To compare biomechanical properties of pedicle screw with different axial angles and interbody cage with different positions for unilateral transforaminal lumbar interbody fusion (TLIF) surgery.Methods The normal L3-5 finite element (FE) model was established and validated.Then one bilateral TILF reconstruction FE model and four unilateral TILF reconstruction FE models with different pedicle screw-cage combination types at L4-5 level were constructed,respectively.Namely,Model A (a small axial angle-implanted screw and an ipsilaterally-placed cage),Model B (a small axial angle-implanted screw and a contralaterally-placed cage),Model C (a large axial angle-implanted screw and an ipsilaterally-placed cage),Model D (a large axial angle-implanted screw and a contralaterally-placed cage).The range of motion (ROM) of 4 reconstruction models under various physiological stresses as well as the maximum Von Mises stresses on pedicle screw,cage-L4 inferior endplate were compared.Results The ROMs at fusion segment (L4-5) in 4 unilateral TLIF reconstruction models were significantly decreased compared with the normal model,but they were still larger than bilateral TLIF reconstruc-tion model.For 4 unilateral TLIF reconstruction models,Model C showed the largest decrease in stability,and the ROM of Model C was 50.7％,89.9％,90.3％ of the normal model in flexion-extension,lateral bending,axial rotation,respectively.When comparing the maximum Von Mises stress of posterior pedicle screw and cage-L4 inferior endplate in 4 unilateral TLIF reconstruction models,Model C could bear relatively smaller stress under most loading modes,except in ipsilateral lateral bending and axial rotation.Conclusions The unilateral TLIF reconstruction model with a large axial angle-implanted screw and an ipsilaterally placed-cage can achieve the optimal stability.By narrowing the difference in stability with the bilateral TILF model,the unilateral TLIF reconstruction model can reduce the risk of screw failure and cage subsidence,which is worth of clinical application.

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The effects of cervical spinous process fracture with posterior ligamentous complex injury on stability of the goat cervical spine

Rong WU ; Ji-Kang MIN ; Shu-Feng HUANG ; Jian-Xiang ZHU ; Qiang LI ; Chao-Yang WANG ; Yan SHEN ; Wen ZHANG ; Hui-Lin YANG

Journal of Medical Biomechanics.2017;32(5):422-426. doi:10.16156/j.1004-7220.2017.05.005

Objective To investigate the effect of cervical spinous process fracture with posterior ligamentous complex (PLC) injury on biomechanical stability of the goat cervical spine specimen in vitro,and evaluate the role of posterior structure in maintaining the stability of cervical spine.Methods Twenty-four fresh goat cervical spine C3-6 specimens were randomly and evenly divided into 3 groups:control group (group A),simple cervical spinous process fracture group (group B) and cervical spinous process fracture with PLC injury group (group C).Under loading of 1.5 N · m torque,the range of motion (ROM) in each group was respectively measured under 6 working conditions:flexion,extension,lateral bending and axial rotation,and the ROM differences among 3 groups were compared by using one-way ANOVA analysis.Results Simple cervical spinous process fracture had little effect on the stability of cervical spine and there was no significant difference in ROM between group B and control group (P ＞ 0.05) under all working conditions.Compared with control group,the ROM in flexion,extension and axial rotation significantly increased in group C (P ＜ 0.05),and no significant ROM difference was found in lateral bending between control group and group C (P ＞ 0.05).Conclusions Simple cervical spinous process fracture does not affect the overall stability of cervical spine.Cervical spinous process fracture with PLC injury is more likely to cause cervical instability than simple cervical spinous process fracture,and surgical intervention is required in cervical spinous process fracture with PLC injury.

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Effects of two fatigue protocols on lower extremity kinematics and time/frequency-domain characteristics of impact forces during drop landing

Rui XIA ; Xi-Ni ZHANG ; Wei-Jie FU

Journal of Medical Biomechanics.2017;32(5):427-435. doi:10.16156/j.1004-7220.2017.05.006

Objective To compare the influence of two fatigue protocols on kinematics of lower extremities as well as time/frequency-domain characteristics of impact force during human landing.Methods A total of 15 trained male athletes (sprint/jumping events) were selected and their kinematics in sagittal/frontal plane and time/frequency-domain characteristics of ground reaction force (GRF) under pre-and post-fatigue conditions with two fatigue protocols (constant speed running,shuttle running + vertical jumping) were collected by the Vicon motion capture system and Kistler 3 D force plates.Results (1) Both fatigue protocols showed a significant decrease in the angle of hip and knee joints on the sagittal plane,and an increase in the flexion range of motion (ROM).The running + jumping fatigue protocol showed a significant increase in the flexion ROM of ankle joint,the maximum flexion angular velocity of knee joint (P＜0.05),the abduction ROM of hip joint and the maximum abduction an gular velocity of hip and knee joints (P ＜ 0.05).(2) No significant differences were found in time/frequency-domain characteristics of impact force between pre-and post-tests for both fatigue protocols.The running and running + jumping fatigue protocols showed lower amplitude spectra of the GRF in the frequency domain at 3.51,8.20 Hz and 1.17,3.51,7.03 Hz,respectively (P＜0.05).Conclusions Both fatigue protocols can induce a more flexed landing posture of lower extremities under the impact of landing,and the running + jumping fatigue protocol shows a better effect with shorter intervention time,which indicates such fatigue protocol has more ad vantages from the perspective of experimental methodology.The research findings can provide further references for studying force characteristics after fatigue.

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