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Abstract:Objective To study dynamic characteristics of the ankle gait simulator, simulate plantar forces in the vertical, anterior-posterior, right-left direction during the stance phase, and validate such forces in the experimental setup. Methods The Adams virtual prototype and ankle model (including tendons, ligaments and soft tissues of foot) were established for dynamic simulation based on the self-developed 5 DOF gait simulator. The dynamic results from both the prototype and gait simulator were compared with the real plantar forces. Results The simulated plantar force could accurately fit the normal in vivo ankle position curves during a stance phase in three directions, and the tendons, ligaments and soft tissues had important influences on the correct gait. The simulated plantar force by the gait simulator could be repeatedly fit for the real stance plantar force. Conclusions The gait simulator was proved to simulate the human gait stance well and can provide a clinical research platform for those experiments which are incapable of in vivo measurement.

Abstract:Objective To study biomechanical effects of the lumbar spine under different traction conditions by using three-dimensional (3D) finite element method. Methods The CT images of lumbar segment L1-5 were input to the Mimics 10.01 for developing 3D geometrical model of L1-5. Then the mesh model of L1-5 was obtained using Geomagic Studio 12.0 and Hypermesh 11.0. The finite element simulation of the lumbar spine under different traction conditions was made by using Abaqus. Results Head-down titling angle was related to the nucleus pulposus stress. When the head-down tilting angle was smaller than 10°, the nucleus pulposus stress regularly changed with the swing cycle; while the head-down tilting angle exceeded 10°, the stress was decreased. In the swing mode, the annulus inner ring stress was increased to promote intervertebral retraction. Conclusions The traction mode helps to relieve the lumbar pain with the swing helping to coordinate the traction effect in each direction, which can better sort out and relieve the rear facet joint disorders. In addition, patients should be careful to select the appropriate traction force in the treatment to achieve good therapeutic effect.

Abstract:Objective To analyze the clinical feasibility of unilateral transforaminal lumbar interbody fusion (TLIF) for treating lumbar degenerative diseases by finite element method. Methods Based on CT scan data, three-dimensional (3D) finite element models of the normal L3-5 segments under physiological status (intact lumbar model), L4/5 with unilateral pedicle screw fixation plus interbody fusion (unilateral TLIF model) and L4/5 with bilateral pedicle screw fixation plus interbody fusion (bilateral TLIF model) were established by using Mimics, Pro/E, ANSYS software, respectively. Preload of 500 N and load of 10 N?m torque were applied on the superior surface of the L3 segment to simulate 5 physiological activities: body upright, flexion, extension, left lateral bending and right axial rotation. The deformation and stress distributions in vertebral body, vertebral discs, pedicle screw and cage under different loads were then recorded and analyzed to compare mechanical properties of the two fixation methods. Results The deformation of L3-5 segments fixed with unilateral TLIF or bilateral TLIF decreased as compared to the intact lumbar model; the stresses in cage reached the maximum in both unilateral TLIF model and bilateral TLIF model during back extension, meanwhile peak stresses on pedicle screws in unilateral TLIF were significantly higher than those on bilateral TILF model, with the peak stress of 463.39 MPa during back extension. ConclusionsUnilateral TLIF can be selected as a method for treating lumbar degenerative diseases; however, its stability was inferior to bilateral TLIF due to the higher peak stress. Therefore, less stretch exercises may be safe for patients during rehabilitation to avoid surgery failure or pedicle screw fracture.

Abstract:Objective To investigate the effects of different bypass grafting for treating DeBakey Ⅲ aortic dissection. Methods The patient-specific models of DeBakey Ⅲ aortic dissection based on CT images were reconstructed by using Mimics software, and two bridge models of bypassing between ascending aorta and abdominal aorta (AA), and between left subclavian artery and abdominal aorta (LA) were established by computer-aided method, respectively. Then numerical simulations were performed by using fluid-structure interaction (FSI) method to compare hemodynamic differences of these two models. Results After bypass surgery, the mass flow, mean and maximum velocities of the through lumen models were reduced to different degrees. Meanwhile, both the maximum blood pressures and displacements of the vessel walls of AA models were decreased, but those of LA models were increased. In contrast, all the above-mentioned hemodynamic parameters of the blind lumen models were decreased, especially for AA models. Conclusions The AA bypassing is a better treatment for DeBakey Ⅲ aortic dissection of through lumen and blind lumen. The therapeutic effects can be easily explained through simulation results, to ensure the scientific validity and clinical utility of bypassing.

Abstract:Objective To introduce the structure of the self-developed design for customized hip stem prothesis and decribe its standard cross-section shape. Methods The proximal femur model was reconstructed based on a patient’s CT image with DICOM format. The rectangle borders on cross-section of the matching area of the hip stem prosthesis were created, and the cross-section contour lines in rectangle borders were formed preliminarily by using simple lines. Based on the proximal femur model, the hip stem prosthesis was verified, and made modification to match the corresponding femoral cavity of the patient through adjusting design parameters. Results The cross-section of the customized hip stem prosthesis was of standard shapes, which was convenient for the quick design of this kind of individualized prosthesis with a simple design course. The parametric design program greatly reduced the workload when designing individualized hip stem prosthesis. Conclusions The design of customized hip stem prosthesis with standard cross-section shape could help to increase the success rate of artificial hip replacement surgeries, promote the application of customized hip stem prosthesis in clinic, and further improve the life quality of patients.

Abstract:Objective To study the effects of oscillatory flow, as well as pore size and porosity of the 3D scaffold on distributions of flow rate and shear stress in perfusion bioreactor, and to propose optimization methods for preparing the 3D decellularized bone scaffold and perfusion bioreactor based on theoretical results. Methods Based on the previously established 3D decelluarized scaffold and perfusion bioreactor for bone tissue engineering in the laboratory, the decelluarized scaffold was simplified as an isotropic porous media. The velocity and shear stress distributions in the bioreactor were further simulated theoretically. Results Under the oscillatory flow, the Darcy shear stress and velocity in the 3D porous scaffold presented a consistently regular pattern. Compared with the unidirectional flow, the difference of velocity and Darcy shear stress decreased at different radius, which could contribute to the homogeneous 3D culture of seed cells in bone tissue engineering. Increasing the inlet perfusion velocity could improve the average Darcy shear stress. Increasing the pore diameter or porosity of the scaffold had no obvious effects on the peak value of velocity, but sharply reduced the average Darcy shear stress. Increasing inlet oscillation frequency could decrease the peak value of velocity and obviously decrease the difference of velocity at different radius. Conclusions Appropriate oscillatory flow was beneficial for generating required shear stress for stem cells in bone tissue engineering. The research findings in this study are expected to provide theoretical guidance to optimize the 3D culture method of seed cells for bone tissue engineering.

Abstract:Objective To study the effect of myocardial bridge oppression on blood flow, positive pressure, circumferential stress and shear stress of the coronary artery. Methods The original myocardial bridge simulative device was greatly improved to be able to measure multi-hemodynamic parameters, such as normal stress, circumferential stress and shear stress, so as to exactly simulate real blood dynamics environment with the common effect of several stresses, and comprehensively investigate the relationship between hemodynamics and atherosclerosis of mural coronary artery under the combined effects of several stresses. Results The results from the myocardial bridge simulative device indicated that the hemodynamic abnormalities were mainly located in the proximal end of mural coronary artery, and the mean and oscillation values of normal stress at the proximal end were increased by 27.8% and 139%, respectively, showing a significant increase with the intensification of myocardial bridge oppression. Conclusions It is myocardial oppression that causes the hemodynamic abnormity of proximal coronary artery, which is quite important for understanding the hemodynamic mechanism of coronary atherosclerotic diseases and valuable for studying pathological effects and treatments of the myocardial bridge in clinic.

Abstract:Objective To investigate the role of pathologically increased-cyclic stretch in proliferation of vascular smooth muscle cells (VSMCs) during hypertension, and the effect of Forkhead box protein O1 (FOXO1) during this process. Methods Coarctation of abdominal aorta above kidney artery of rat was used as hypertensive animal model, and sham-operated animal as control. FX-4000 cyclic stretch loading system was used to apply 5% physiologically cyclic stretch and 15% pathologically cyclic stretch during hypertension on VSMCs in vitro. Western blot was used to reveal the expressions of FOXO1 and phosphor-FOXO1 in VSMCs, and BrdU kit to detect the proliferation of VSMCs in vitro. By using RNA interference in static, the role of FOXO1 on cell proliferation was further detected. Results After abdominal aorta coarctation for 2 and 4 weeks, respectively, the blood pressure was significantly increased compared with the sham operated rats. The proliferation of vascular cells in aorta of hypertensive rat was significantly increased, and so did the expressions of FOXO1 and phosphor-FOXO1. In vitro experiment revealed that 15% cyclic stretch remarkably increased the proliferation and expressions of FOXO1 and phospho FOXO1 in VSMCs. Target siRNA transfection in static decreased the expression of FOXO1 and phosphor-FOXO1, as well as the proliferation of VSMCs. Conclusions Pathologically increased-cyclic stretch may increase the expression and phosphorylation of FOXO1, subsequently modulate VSMC proliferation during hypertension. Based on animal models, this study intends to reveal the role of FOXO1 in vascular reconstruction of hypertension and the involved biomechanical mechanism, so as to make the mechanobiological mechanism of hypertension explicit and discover new target in the prevention and treatment of vascular remodeling.

Abstract:Objective To explore the combined effects of mechanical stretch and interleukin-1β (IL-1β) on gene expression of extracellular matrix in rabbit corneal fibroblasts. Methods Isolated rabbit corneal fibroblasts were subjected to 15% equibiaxial stretch at frequency of 0.1 Hz for 12 h, 24 h and 36 h, respectively, in presence of IL-1β. The gene expressions of matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinases 1 (TIMP-1) and collagen type I alpha 1 (Collagen Iα1) were detected by real-time quantitative PCR. Results The mRNA levels of MMP-1, MMP-3 and MMP-9 could be up-regulated by IL-1β alone. However, MMP-1 and MMP-3 mRNA levels decreased with time, while MMP-9, TIMP-1 and collagen Iα1 increased with time. Compared with corresponding IL-1β treatment with mechanical stretch groups, the mRNA levels of MMP-1, MMP-3 and MMP-9 were increased and the mRNA levels of TIMP-1 and collagen Iα1 were decreased in a time-dependent manner. The mRNA level of Collagen Iα1 was decreased by loading mechanical stretch alone, and would further decrease time-dependently in combination with IL-1β treatment. Conclusions Mechanical stretch combined with IL-1β may facilitate the corneal tissue damage, thereby contribute to the development of keratectasia.

Abstract:Objective To observe the effect of cervical rotatory manipulation on tensile mechanical properties of atherosclerotic carotid artery in rabbits, so as to provide safety references for such manipulation. Methods Twenty male New Zealand rabbits were randomly divided into control group (n=10) and experimental group (n=10), then all fed with high-cholesterol diet for 12 weeks. The rabbits in experimental group were then applied with cervical rotatory manipulation (rotating on each side once a day during a total of 4 weeks), while no manipulation for rabbits in control group. The bilateral carotid arteries were obtained after all the rabbits were executed, and measured for the maximum load, the maximum displacement, the average load, the elastic modulus, elongation at break and stress-strain by the material testing machine. Results The maximum tension, the maximum displacement, the average tension, the elastic modulus and elongation at break in experimental group were (1.36±0.35) N, (6.84±2.08) mm, (0.44±0.30) N, (4.30±2.66) MPa and (83.08±51.32)%, respectively, while the corresponding data in control group were (2.92±0.65) N, (9.23±2.62) mm, (1.17±0.63) N, (3.71±0.60) MPa and (154.19±34.32)%. The maximum load, the average load and elongation at break in experimental group were obviously smaller than those in control group (P<0.05), while no statistical differences in the maximum displacements and elastic modulus between two groups were found (P>0.05). Conclusions The tensile mechanical properties of atherosclerotic carotid artery after cervical rotatory manipulation were declined; thus, intensity and magnitude of cervical rotatory manipulation should be proper so as to avoid harm to carotid artery.

Abstract:Objective To investigate elastic modulus of double-stranded DNA (dsDNA) biofilm adsorbed on microcantilever substrate. Methods Parsegian’s empirical potentials based on mesoscopic continuum liquid crystal theory was employed to describe the interaction energy among coarse-grained DNA cylinders; Monte Carlo method was used to simulate the distribution pattern of DNA chains before and after loading. The thought experiment method combined with the compression bar model in the sense of macroscopic continuum mechanics was adopted to predict the elastic modulus of DNA biofilm. Results The elastic modulus of dsDNA biofilm ranged from 0.1 MPa to 80 MPa. Conclusions It was found out that the classic hypothesis with uniform hexagonal pattern may underestimate the elastic modulus of DNA biofilm when compared with that in random pattern. Moreover, either the increase of packing density or the decrease of buffer salt concentration will help to enhance elastic modulus of DNA biofilm. These results have great significances in further understanding the mechanical properties and regulation rules of DNA biofilm related with clinical work.

Abstract:Objective To measure the cancellous bone mineral density and axial elastic modulus from multiple anatomic sites, then build the constitutive equation between them, so as to provide specific data for finite element modeling of Chinese people. Methods Ten fresh adult cadavers were taken as sample sources. In every fresh cadaver, 5 different anatomic sites were selected: proximal tibia, greater trochanter, femoral neck, humeral head and lumbar vertebra. The raw samples were processed into standard specimens, which were approximately 6 mm in diameter and 30 mm or 40 mm in length. Both the size and volume for the cancellous bone specimens were measured, and their mineral densities were obtained with computed tomography. The mechanical properties of such specimens were tested with biomechanical testing machine for analyzing the elastic modulus of the cancellous bone at different anatomic sites. The linear and power regression between mineral density and axial elastic modulus were analyzed on SPSS 18.0. Results A total of 169 cancellous bone specimens which were availably tested were collected, including 52 proximal tibia, 31 greater trochanter, 15 femoral neck, 17 humeral head and 54 lumbar vertebrae. The analysis on measurement results showed that the mineral density and axial elastic modulus in cancellous bones from 5 anatomic sites were different, and had a solid linear relationship (0.850>r2>0.785), with 3 sites (proximal tibia, greater trochanter, lumbar vertebra) showing a solid power correlation (0.871>r2>0.825), and the other 2 sites (humeral head and femoral neck) showing relatively weak power correlation (0.671>r2>0.643). Conclusions There are solid linear and power relationship between mineral density and axial elastic modulus, while no significant difference is proved between the r2 values of the two regressions in this research. This discovery can be applied to detect patients’ bone quality in vitro and identify the precise position of bone loss, and further to predict fracture risk with the help of finite element modeling.

Abstract:Objective To investigate the process and method of making an individualized limited contact dynamic compression plate (LC-DCP) and template for fixing tibial fracture, as well as its preliminary effect in clinic. Methods The custom-made tibia LC-DCP and the template used in minimally invasive percutaneous plate osteosynthesis (MIPPO) surgery were developed by 3D reconstruction of CT images, computer-aided design/manufacturing (CAD/CAM) and computer numerical control (CNC) technology, and then applied in 6 patients with tibial fractures. Results The individualized tibia LC-DCP was successfully used in clinic. The average 20-month follow-up showed that all fractures were healed in 6 patients, with 5 reaching excellent and 1 reaching good standard, according to criteria of Johner-Wruhs. Conclusions The production process of such individualized plate is simple and practicable, and has the advantages of simple operation, less injury, satisfactory reduction and fixation, high healing rate, less complexity when treating tibial fracture in MIPPO surgery. Therefore, it is worth of clinical application.

Abstract:The dynamic dummy plays an important role in the research of protecting human beings from impact environment. To collect data from dummy in dangerous impact tests is the fundamental method used in developing protection equipment and systems in aerospace, automobile and other industries. The performances of a dummy depend on its simulation degree, as well as the quality and quantity of sampled signals. The dummy technology abroad is now indispensable in developing the protection of aviation ejection and rescue system, and also beneficial to automobile and other industries. China had no Chinese characterized dummy applied until the year of 2003 when the dynamic dummy was created in Institute of Aviation Medicine, and the dummy has equivalent high performance as that made by the United States and has been availably exerted in aviation. For evaluating the impact injuries on Chinese human beings, it is necessary to further develop Chinese characterized dummy series, and to establish the all-around criteria by strengthening application of digital virtual dummy in impact environment study.

Abstract:Road traffic injuries have become a major social issue. With the development of technology, legislation and safety consciousness, the fatal rate of brain and chest injuries has been declined. However, as to prevent foot and ankle injuries of occupants still no effectual protective devices have been developed. In this paper, research progress on foot and ankle injuries of occupants was reviewed, which found out that most of such injuries in the frontal motor vehicle crashes occurred more easily to the drivers, which was possibly due to the special loading on their lower extremity during braking. Although there still exists a continuing debate about taxonomy of the frontal motor vehicle crashes, researchers have approached unified understanding that foot and ankle injuries are usually caused in the real-world narrow object frontal crashes. Until now, studies on foot and ankle injury and its protective mechanisms in various types of crashes are rarely conducted. A combination of the in-vitro experiment and computational modeling would be an ideal method to solve this issue.