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Abstract:Objective To investigate the wear mechanism of artificial hip joints and the criteria for wear life definition, analyze the causes of abnormal wear and the clinical manifestations of wear failure, establish the reasoning route of failure incidents. Methods The wear process and early factors on abnormal wear in artificial hip joints were studied through elastohydrodynamic lubrication computation and finite element analysis; the service life of artificial hip joints was determined through establishing criteria for wear life definition; the clinical manifestations of wear failure were introduced and classified through wear-osteolysis morphological matrix; the reasoning logic of failure incidents was established through clinical investigation. Results The minimal synovium thickness and contact stress between the femoral head and the acetabular cup were calculated, and the effect of relevant parameters was studied as theoretical references for wear analysis; the criteria on wear life definition of artificial hip joints were proposed, namely the mechanistic failure due to geometric change in artificial hip joints and the biological failure due to osteolysis; nine kinds of clinical manifestation for wear failure were found; the reasoning route for failure incidents was presented. Conclusions Primary wear process in artificial hip joints includes boundary and mixed friction, adhesive, ploughing and third-body wear; surface quality, fit clearance between the acetabular cup and the femoral head, and roundness have great impact on early abnormal wear; normal mechanistic life of metal-UHMWPE artificial hip joint can reach 40 years, but its maximum biological life is no more than 10-15 years, which is the constraint of prosthesis life today; the diversity of clinical manifestations for wear failure is the morphological Results of mechanical wear and osteolysis, which is helpful for the reasoning route of failure incidents.

Abstract:Objective To observe the electromyography (EMG) activities and kinematic characteristics of the back, abdomen and hip muscles under the static symmetric loading and unloading with the flexion and extension posture. Methods Six healthy male subjects stood on a specially designed testing platform, doing flexion/extension under symmetric loading and unloading, respectively. Each trial lasted 4 seconds and was repeated 3 times. The EMG activities of 10 muscles(rectus abdominis，obliquus externus abdominis，erector spinae，multifidus，gluteus Medius), the 3D angular movement, the plantar COP (center of pressure) were recorded during the trial.The normalized EMG, trunk angle and COP displacement were calculated, and statistical analyses of all data were made. Results Muscle activities of the back were greater (10.47~16.94) with flexion both under loading and unloading. Muscle activities of the abdomen were greater with extension under unloading, and those of the back (3.70~17.95) and hip (6.64~11.52) were increasing under loading, with muscle activities of the abdomen decreasing (10.66~4.18). The flashing trunk numbers was increased with the increase of loading, especially 1.55-time increase in the trunk angle. The COP displacement in anterior posterior direction was shifted greater than that in lateral direction, and this shift was more during flexion (14.60) than that during extension (7.65).Conclusions Extension increases the activities of back muscles, especially for multifidus, and it also increases the torso angular displacement and flashing trunk numbers, especially under loading.

Abstract:Objective To investigate the effect of mechanical properties of anterior cruciate ligament (ACL) on finite element simulation of knee joint. MethodsA three-dimensional finite element model of knee joint including all the main tissues was reconstructed based on medical images, and the transverse isotropic hyperelasticity of ligament was considered as well. Three groups of ACL material property parameters were acquired by fitting three different experimental stress strain curves based on the same ligament constitutive equation, to compare the influence of different ACL mechanical parameters on the kinematic and biomechanical properties of knee joint. Results Different ACL mechanical properties resulted in different displacements in knee joint. With the change of ACL mechanical properties, the stress and principal strain in ACL changed a lot, while the trend of their distributions were basically the same. Conclusions The selection of different ACL experimental stress-strain curves can influence the simulating result of the finite element analysis. More attention should be paid to the determination of ACL mechanical properties, the reconstruction and validation for the finite element model of knee joint.

Abstract:Objective To simulate the internal structure of proximal tibia in both normal and valgus knees. Methods The internal structure of proximal tibia under normal mechanical environment was simulated using quantitative bone remodeling theory combined with finite element method. Based on this structure as the initial model and the changing pattern of pressure distributions on tibial plateau in valgus knee, the internal structure of proximal tibia in valgus knee was simulated with the action point of resultant force on the lateral tibial plateau. Results The simulated distributions of bone mineral density (BMD) were compared with the real tibia, and found the simulated results highly consistent with the actual ones both under normal mechanical environment and in valgus cases. Conclusions The method and the load distributions adopted in this study can accurately simulate and predict the internal structure of proximal tibia, thus could be served as the basis for further study on periprosthetic bone remodeling behavior after the total knee arthroplasty.

Abstract:Objective To investigate the mechanical mechanism of bypass graft for the treatment of DeBakey III aortic dissection and explore the valid surgical planning. Methods Patient-specific models of DeBakey III aortic dissection, including the models of through lumen and blind lumen, before and after bypassing between ascending aorta and abdominal aorta, between left subclavian artery and abdominal aorta, were constructed, and then numerical simulations were performed using computational fluid dynamics (CFD) method under physiological flow conditions based on fluid-structure interaction (FSI). Results Blood flow velocity, pressure, vessel wall displacement of the false lumen after bypass graft were reduced by 38.86%, 15.347 kPa and 39.46% on average, respectively. Conclusions Bypass graft is an effective surgical method for the treatment of DeBakey III aortic dissection under specific conditions with good prospects in clinical application.

Abstract:Objective To compare the mechanical environment of chondrocytes between superficial zone and deep zone by multiscale computation. Methods The chondrocyte biphasic model was set up and made the results of the articular cartilage (AC) biphasic model mapped to the corresponding borders of the chondrocyte model as the boundary condition. The chondrocyte model was computed to obtain the results of the mechanical environment of chondrocytes and analyzed. Results The results showed that the stress of chondrocytes at deep zone was half of that at superficial zone, but both were much smaller than those outside chondrocytes. The pericellular matrix (PCM) sustained the high stress outside chondrocytes and remarkably reduced the stress inside chondrocytes. Interstitial flow directions adjacent to two chondrocytes were totally the opposite.Conclusions The bearing property of AC reduced the stress near chondrocytes at deep zone prominently and protected the chondrocytes at deep zone and subchondral bone. PCM sustained the high stress outside chondrocytes to provide lower stress environment for chondrocytes living. The opposite interstitial flow direction of two chondrocytes supported the theory that synovia seepage from cartilage surface and nutrient pumped out from subchondral bone constitute the bidirectional nutrient supply in AC.

Abstract:Objective To investigate the effect of a novel hip flexor training machine on muscle activation and range of motion (ROM) in lower limb under the condition of different resistances. Methods Six volunteers performed consecutive rightly hip flexion and extension for 30 times under light or heavy resistance randomly on the training machine, and the muscle activity and ROM in lower limb during the movement were measured at the same time. Results The muscle activation of rectus abdominal, hip flexor muscles, gluteus maximum, rectus femoris and biceps femoris under heavy resistance was significantly higher than that under light resistance (P<0.05); the muscle activation of rectus abdominis, hip flexor muscles and rectus femoris at during the last 3 times were significantly higher than that at of the first 3 times under heavy resistance (P<0.05); under light resistance, only the muscle activation of erector spinae and rectus femoris during the last 3 times were significantly higher than that of the first 3 times. The ROM and angle of hip extension under heavy resistance were significantly smaller than those under light resistance. Conclusions Under the rational ROM of hip joint, this new hip flexor training machine can stimulate the hip flexion and extension muscles and other co-contraction muscles to accomplish the movement, especially under the condition of heavy resistance.

Abstract:Objective A blood assist index (BAI), defined as ratio of the output power of LVAD (left ventricular assist device) to the total input power of circulatory system, was proposed in this paper to regulate the energy distribution between LVAD and natural heart. Methods A control strategy based on model free adaptive control (MFAC) algorithm was designed by using BAI as the control variable. The algorithm could track the desired BAI by regulating the pump speed to maintain the measured BAI. A mathematic model of cardiovascular system was used to verify the feasibility of the controller in presence of heart failure, slight physical active and recovery of cardiac function. Results The simulating results demonstrated that the proposed controller could automatically regulate the pump to respond to the reduced peripheral resistance (5 500 r/min vs. 6 000 r/min). When Emax increased from 80 to 240 Pa/mL to simulate the heart recovery, the blood flow rate could increase accordingly from 5 to 8 L/min.Conclusions The proposed control strategy can provide an adjustable and accurate energy distribution between LVAD and native heart by regulating the pump speed, which would be of benefit to promoting left ventricle reverse remodeling.

Abstract:Objective To establish a model of respiratory mechanics with consideration of gas exchange and directly correlate with the gas content in blood during mechanical ventilation with the mechanics of respiratory system. Methods By coupling the physiological parameters of respiratory system and blood circulation system, including the molecular numbers of oxygen and carbon dioxide in alveoli and clinically monitored physiological parameters such as gas content, hemoglobin content, heart rate and cardiac output, a mechanical model was constructed to predict those dynamic parameters of gas content, pressure and flow rate in airway and alveoli in continuous breathing cycles. Results The gas content in different locations of a respiratory system was estimated by the model and the sensitivity of gas content in expiration to the undetermined parameters was evaluated. Conclusions The model of respiratory mechanics developed in the study is a preliminary attempt to predict the regulation roles of physiological parameters clinically monitored during mechanical ventilation, which will provide a theoretical support for the design and development of novel respirators in the follow-up experiment.

Abstract:Objective To investigate the effect from helmet mass and deviation of mass center on neck muscle activity in military pilots. Methods Based on AnyBody software platform, a musculoskeletal model of head neck complex was established including C0, C1-C7, T1 and 136 muscles. Concentrated loads were applied to simulate the role of helmet. Strength from seven main muscle groups under different helmet mass, mass center and +Gz acceleration loads were simulated and calculated.Results When mass center of the helmet and the head coincided with each other, the muscle groups (such as semispinalis, levator scapulae, splenius capitis and cervicis) which took charge of extension were activated. Muscle strength increased with helmet mass linearly and +Gz acceleration loads would make this increase multiplied. Flexion muscle began to work when mass center of the helmet moved backward, so did the lateral bending muscles when mass center of helmet moved in the right-and-left direction. Conclusions Helmet mass and its center have an obvious influence on neck muscle activity in military pilots. The musculoskeletal model established in this paper can be used to calculate the change in muscle strength under different situations and conduct a quantitative analysis for helmet design and validation.

Abstract:Objective To analyze the distribution characteristics of blood flow and wall shear stress with the consideration of elasticity of the artery wall and to investigate the biomechanical factors inducing aneurismal rupture. Methods The three-dimensional patient-specific internal carotid artery aneurysm model was constructed based on two-dimensional medical scan images. The artery wall model was created based on the statistical data of human body. According to the condition of the pulsatile blood flow in human body, hemodynamics in internal carotid aneurysm with fluid structure interaction was simulated using finite volume method and finite element method. Results An obvious vortex flow in aneurismal cavity was found with the direction unchanged during a cardiac cycle. There was a region at the aneurismal neck and aneurismal dome where the value of wall shear stress was relatively high. It also found two regions in the aneurismal neck and the aneurismal dome where the value of Von Mises Stress reached the maximum locally. In view of the material strength, it should be easy to have aneurismal rupture in these areas. Conclusions The distribution characteristics of vascular wall stress can be obtained by the calculation of fluid structure interaction to further predict the possible position of aneurismal rupture.

Abstract:Objective To design a kind of bionic drag reduction needle and investigate its mechanism of painless injection. Methods Based on the analysis of mosquito's mouthpart structure, two types of bionic drag reduction injector needles, sawtooth needle and stripe needle, were designed with the painless feature as mosquito's blood-sucking action. The injection processes of normal smooth needle and two bionic drag reduction injector needles were simulated by using explicit kinetic software LS-DYNA, and analyzed the pain-relief mechanism of bionic drag reduction needles. Results Through contrast and analysis on the stress contour, internal energy curves and resistance curves of both the smooth needle and bionic needles during the puncturing process in soft tissue, the bionic needle was found to have obvious drag reduction effects. The drag reduction rate of the saw-tooth needle and stripe needle was 23.48% and 31.57%, respectively. Conclusions The bionic needles can minimize the friction resistance to achieve the painless injection by drag reduction, and its effect is determined by the structure and shape of the bionic needle.

Abstract:Objective In order to improve the local hemodynamics of coronary artery bypass graft and reduce the incidence of restenosis, a double-bypass-graft design was proposed to alleviate artery stenosis. Methods Based on finite element method, the hemodynamics of the conventional bypass graft model and the double-bypass-graft model was adopted for numerical simulation. The distributions of hemodynamics such as flow field and wall shear stress in the vicinity of anastomosis were calculated. Results This new design provided better hemodynamics near the main anastomosis region, eliminated the vortex and flow stagnation, and increased the wall shear stress at the artery floor. The axial length of vortex near the assistant bypass graft by this new design was only 3 mm, which was shorter than that of 4.5 mm in the conventional design. Nearly 36% of the total blood was directed into the assistant bypass graft. Conclusions The new design could help to reduce the incidence of intimal hyperplasia.

Abstract:Objective The present biomechanical model built for extravehicular activities (EVA) of astronaut is lack of human anatomy features, and still there isn’t a reasonable verification method. This study is aimed at solving the problems above and providing references for the further application of EVA simulation. Methods Based on a typical extravehicular activity, an inverse kinematical and dynamical upper limb model with muscle forces was built to conduct simulation calculation. Both the kinematical and dynamical results were verified through OpenGL animation sequence driven by kinematical calculation results and verification experiment with a real model, respectively. Results The animation built for kinematical verification proved that the calculation results were correct. The relative error of two muscle forces between dynamic verification and simulation was 14.54% and 0.91%, respectively. Conclusions A reasonable upper limb model of astronaut is established in this study. The simulation results are credible and the verification Results showed that this feasible method could supports the further research on EVA simulation and verification.

Abstract:Objective To explore postural stabilization of visual feedback to human body and its mechanisms. Methods Displacement of the center of pressure (COP) of 12 healthy young adult volunteers were investigated under upright posture with and without visual feedback conditions. The Brownian motion model was employed to compare the differences in diffusion coefficients, Hurst exponents, and critical points of the COP trajectories under the above two conditions, and one way repeated measures ANOVA was utilized to test the significance of these differences. ResultsUnder the visual feedback condition, in long-term time intervals, diffusion coefficients were reduced by about two thirds and Hurst exponents reduced by half; in short-term time intervals, no significant differences were found in diffusion coefficients in the medial-lateral (ML) direction and in Hurst exponents; in addition, the coordinates of the critical points presented no statistically significant differences in the time intervals except for the mean square displacement in the anterior posterior (AP) direction. ConclusionsVisual feedback enhances the closed-loop control mechanism of postural control, while it does not have great impact on the open-loop control mechanism and transitional characteristics of the two mechanisms; moreover, the effect of visual feedback on postural control in AP direction is more obvious than that in ML direction.

Abstract:Objective To investigate effects from the protrusion height of drug-eluting stent (DES) on kinetics of drug release and hemodynamics, so as to provide references for the optimization of DES design. Methods Based on computational fluid dynamics (CFD), coupling analysis on kinetics of drug release and hemodynamics was conducted by studying three stent models with different protrusion height to numerically investigate the distribution of drug concentration and wall shear stress. Results The increase in protrusion height of the stent was beneficial to the drug deposition; however, it could also increase the length in the low shear stress area. Comparatively, the increase percentage of drug concentration with the increasing protrusion height was remarkably less than that of the increasing length in low shear stress area. Conclusions By comprehensive consideration of both the drug concentration and wall shear stress, lower protrusion height is recommended for DES so as to effectively reduce the risk of restenosis.

Abstract:Objective To make a quantitative research on the vertical force homogeneity of Yizhichan manipulation and look for the quantitative index and reference value which can describe the force homogeneity of Yizhichan manipulation effectively. Methods After the force homogeneity was described mathematically, the vertical force signals from Yizhichan manipulation operated by 5 experts, 5 skilled doctors and 5 beginners were measured and analyzed, respectively. Results The period homogeneities and the waveform homogeneities were obtained. No significant differences were found in the period homogeneities among the three groups, but significant differences appeared in waveform homogeneities between the beginner and expert group or the beginner and skilled doctor group. Conclusions The waveform homogeneities are more suitable for evaluating the vertical force homogeneity of Yizhichan manipulation by different operators, and 0.927 can be used as a reference value to evaluate the vertical force homogeneity of the operator.

Abstract:Objective To validate the significance of forced oscillation technique (FOT) for diagnosis of asthma by using it to measure respiratory resistance of adult asthma patients and healthy subjects. Methods Respiratory resistance was measured by a hand-held FOT device for 5 adult asthma patients and 5 adult healthy subjects, respectively. The variation of respiratory resistance with time was also compared by statistical analysis. Results The respiratory resistance measured by FOT varied periodically with time in all cases, with the respiratory resistance for asthma patients was (294.98±86.24) and for the healthy subjects was (151.9±39.20) Pa?s/L, respectively, showing significant differences in two groups. Conclusions FOT measurement results showed that asthma patients exhibited a greater magnitude and variability of respiratory resistance as compared to their healthy counterparts, which was in agreement with the conventional diagnosis. FOT can provide a novel method for detecting mechanical parameters of the respiratory system in clinic, and as an important reference particularly for the accurate diagnosis of lung dysfunction, such as asthma.

Abstract:Research on biomechanical testing of the spine in vitro is crucial to advance understanding about the function of spine, spine injury, spinal degeneration, and the influence of implants on spinal disorders. Spinal biomechanics is mainly composed of two parts: loading methods for the spine and measurement for the spinal movement. The loading method has gone through a process from gradual loading to continuous loading. In this paper, current literatures on spinal biomechanics were studied and up-to-date loading methods for the spinal movement in vitro were summarized to provide some references and help for the future research on loading methods of spinal movement.

Abstract:Despite the significant progress in the fields of electrocardiology and cardiac biomechanics, theoretic limitations still exist and many problems on mechanism underlying the electrical changes of the heart still remain to be solved. Based on the fact that experimental studies deeply rely on the microscopic and quantitative information, and the electrical changes and mechanical activities of the heart have long been treated as two individual processes, dynamic forces generated in the whole spring-loading system during the cardiac contraction and relaxation were discussed first from a macroscopic view. Next, the temporal co-relationship between the electrical and mechanical processes after “excitation-contraction coupling” was particularly identified, which indicated that the intertwined electrical and mechanical activities, in their nature, are integrated parts of a same process. Finally, once all the electrical and mechanical “gating” mechanisms were taken into consideration, the electrical changes of the heart could be classified into three different phases: the preceding excitation formation and conduction, the myogenic changes during ventricular contraction, and the complete restoration of the heart both mechanically and electrically during active relaxation.