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Abstract:

Abstract:Objective To discuss the mass transfer of low temperature gas in the lung bronchus, so as to provide a theoretical basis for the implementation of hypothermic ventilation cooling non-heart-beating donor (NHBD) lung program. Methods A real airway model was reconstructed based on human lung CT images, and the computational fluid dynamics (CFD) method was used to investigate the airflow characteristics inside the airway during reciprocating ventilation. The effect of ventilation frequency (0.5, 0.25, 0.125 Hz) on bronchial flow was also studied. Results The flow in the airway showed complex three-dimensional （3D） flow characteristics during reciprocating ventilation. The flow in different areas of the airway was different during inhaling and exhaling; the irregular bronchial geometry had an important effect on its internal flow; when the ventilation frequency decreased from 0.5 Hz to 0.125 Hz, the thickness of flow boundary layer would increase, and the mainstream velocity in different areas of the airway was enhanced to different degrees. Conclusions The real airway model based on CT 3D reconstruction was more accurate than the ideal circularity tube model in showing the bronchial flow. The research findings have an important guiding significance to optimize the hypothermic ventilation cooling NHBD lung technique.

Abstract:Objective To study the airflow characteristics in lower respiratory tract of acute respiratory distress syndrome (ARDS) patients with different degrees of respiratory distress by using computational fluid dynamics (CFD) technology. Methods Three-dimensional model of lower respiratory tract from a healthy subject was established based on CT image data. Standard k-ε turbulence model was used to simulate the airflow in lower respiratory tract, and the distribution characteristics of air velocity, airflow rate, air pressure and wall shear stress (WSS) in lower respiratory tract were analyzed. Results The function relationship between the pressure drop of airflow in lower respiratory tract and the respiratory intensity was fitted. The distribution characteristics of air velocity, air pressure and WSS in lower respiratory tract were obtained, and the airflow distributions in the lungs and the bronchi of each lobe were also obtained. Conclusions More detailed data of lower respiratory airflow field can be obtained by CFD simulation analysis, which provides the theoretical basis for clinical treatment of ARDS patients.

Abstract:Objective To reduce the thrombosis probability and hemolysis risk of the meglev left ventricular assist device (LVAD), so as to increase the efficiency of blood supply. Methods The influences of the pump outlet diameter, exit angle, fillet size between the outlet and the inner wall of the pump, as well as gap between the rotor and the shell on internal flow field of the pump were studied by using the computational fluid dynamics (CFD) method, so as to optimize the internal structure and improve the hydrodynamic performance of the pump. Results Compared with pump of the previous generation, the maximum wall shear stress (WSS) of the pump inner wall, the maximum WSS of the pump rotor, the area with WSS >200 Pa were reduced by 23.6%, 47.4%, 76.2%, respectively, while the outlet flow was increased by 14.4%. Conclusions For the meglev LVAD of the new generation, its internal blood flow tended to be smooth, and the hemodynamic performance of blood flow was improved comprehensively. The research findings provide references for optimization design of the meglev LVAD and related experimental researches in the future.

Abstract:Objective To investigate the transient hemodynamic changes during balloon deflation in coronary interventional operation, so as to explore the potential influence of balloon deflation on the occurrence of post-operative no-reflow. Methods An in vitro experimental apparatus was built, in which a high-speed camera was used to take snapshots of balloon deformation and flow field (marked by dyed water) during balloon deflation. Subsequently, image processing techniques were employed to derive the parameters of balloon deformation and estimate the flow velocity downstream from the balloon. A computer model of the experimental apparatus was constructed, with the incorporation of the measured balloon deformation data, to simulate the balloon deflation process under various perfusion pressure and fluid conditions. Results The balloon exhibited a highly nonlinear deformation behavior during deflation. The measured and simulated flow velocities downstream from the balloon were in reasonable agreement, both manifesting a monotonic increase with post-deflation time and perfusion pressure. Numerical simulations further revealed that when the flow velocity downstream from the balloon approached the physiological value of blood flow velocity in the coronary artery, the flow velocity in the balloon-vessel gap and wall shear stress (WSS) reached up to 8-10 times and 60-70 times of their physiological values, respectively. Conclusions Balloon deflation led to a sharp acceleration of flow in balloon-vessel gap and a concomitant abnormal rise in WSS, which might promote the stripping of plaque or thrombus flakes. In view of the fact that the balloon deflation-induced rise in WSS was augmented by the increase in perfusion pressure, taking strategies such as lowering pre-operative blood pressure or implementing balloon deflation during diastole in coronary interventional operation might help to reduce the risk of no-reflow.

Abstract:Objective To analyze the influence from size parameters of minimally invasive vascular clamp on mechanical properties of small arteries. Methods The finite element simulation analysis on the process of minimally invasive vascular clamp clamping small arteries was performed. The influence patterns of 5 different sawtooth spacing, sawtooth heights and sawtooth lengths on mechanical properties of small arteries were studied. Results Larger sawtooth spacing led to smaller maximum equivalent stress of the clamped artery. The maximum equivalent stress of the small artery was not linear with the sawtooth height of the vascular clamp. The maximum equivalent stress of the small artery was the smallest and the vascular injury was the minimal when the swatooth height was 75 μm. The sawtooth length of the vascular clamp had an important influence on mechanical properties of clamped small arteries. The maximum equivalent stress of the artery was proportional to the sawtooth length of the vascular clamp. Conclusions The size parameters of minimally invasive vascular clamp had an important influence on mechanical properties in the process of clamping small arteries. The research findings can provide guidance for the design of the minimally invasive vascular clamp.

Abstract:Objective To analyze the biomechanical characteristics of 3 different posterior internal fixation methods for treating thoracolumbar burst fracture by three-dimensional finite element (FE) method. Methods The FE fixation models of normal thoracolumbar, short-segment posterior fixation (SSPF), short-segment posterior fixation with intermediate screws at fractured level (SSPFI) and long-segment posterior fixation (LSPF) were established, respectively. The biomechanical characteristics of L1 centrum and the adjacent intervertebral disc under 6 kinds of motion states (spinal flexion, extension, lateral bending and axial rotation), in normal thoracolumbar model and 3 fixation models were compared by FE analysis. Results L1 centrum equivalent stress distributions in normal thoracolumbar model, SSPF model, SSPFI model, LSPF model were 31.63, 13.41, 110.35, 13.17 MPa, respectively. The maximum equivalent stress of adjacent intervertebral disc in normal thoracolumbar model was 3.84 MPa, which was located in L1-2 intervertebral disc; the maximum equivalent stress of adjacent intervertebral disc in 3 fixation models was 0.41, 0.36, 0.40 MPa, respectively, which was all located in T12-L1 intervertebral disc. Conclusions Fixation in short segment of the fractured vertebrae could lead to an increase of stress in the centrum. The stress of the adjacent intervertebral disc in 3 fixation models was smaller than that in normal spinal model.

Abstract:Objective To investigate the effect of muscle function on structural stress in patient with lumbar disc herniation (LDH), by observing the stress changes in LDH lumbar-pelvis finite element model loaded with muscle force. Methods One normal healthy volunteer and one LDH patient were selected. Their CT data were collected to establish two corresponding normal and LDH lumbar-pelvis finite element models, and their gait data were also simultaneously collected to drive the AnyBody musculoskeletal model. The muscle force around the lumbar and pelvis as well as the hip-joint force were obtained as the loading condition. Self-loading of the normal and LDH model as well as the normal model loaded with LDH muscle forces were conducted seperately. Then the stress changes in L4 and L5 intervertebral discs and sacroiliac joints under two above loading conditions were compared. Results The stress curve of normal model loaded with LDH muscle force showed a unimodal stress curve, instead of a bimodal curve, and such trend of stress-time curve was as same as the trend of the LDH model during self-loading. But the stress difference in L4 and L5 intervertebral discs and sacroiliac joint of the normal model loaded with LDH muscle force was smaller than that in the LDH model during self-loading. Conclusions Abnormal muscle function of LDH could lead to abnormal joint stress of the intervertebral discs and sacroiliac joint. Structural imbalance itself could lead to stress imbalance, and muscle as a driving factor was an important cause of anomaly structural dynamic stress, thus leading to abnormal joint motion patterns. Therefore, attention should be paid to assessment of the imbalance of peripheral muscle function in clinical treatment of LDH.

Abstract:Objective To analyze the influence of ligaments surrounding sacroiliac joints (SIJs) on stability of SIJs by finite element method. Methods The finite element lumbar spine-pelvis-femur model was established. Based on this normal model, all SIJ ligaments in both sides were removed in turn, to establish models without iliolumbar ligaments, sacroiliac anterior ligaments, sacroiliac posterior ligament, sacrotuberous ligaments, sacrospinous ligaments, sacroiliac interosseous ligaments, respectively. The models were used to simulate physiological motions of the spine. The range of motion (ROM) and average stress on the left and right SIJs were analyzed and compared with the normal models. Results Compared with the normal SIJ model, no significant differences in the ROM of bilateral SIJs were found in the models without sacrotuberous ligaments, sacrospinous ligaments and sacroiliac posterior ligaments; for the model without acroiliacinterosseous ligaments, there was no significant difference in the ROM of the left SIJs under spinal right rotation and ROM of the right SIJs under spinal extension, but the ROM of bilateral SIJs increased significantly under the other spinal physiological activities. Under the physiological activities of the spine, the average stress of the SIJ surface in the left and right sides of the model without acroiliacinterosseous ligaments significantly decreased. Conclusions Of all the sacroiliac ligaments, the sacroiliac interosseous ligaments showed the maximum influences on the stability of SIJs. The research findings are helpful to investigate the mechanism of SIJ subluxation and provide certain theoretical basis for clinical treatment of SIJ subluxation.

Abstract:Objective To evaluate the biomechanical effects of lateral meniscus posterior root (LMPR) tears fixed at different suture positions, so as to investigate the optimal suture method for repairing LMPR tears. Methods Eight fresh cadaveric knees were used. Each knee was tested under 6 conditions: intact knee, ruptur of LMPR, suture of LMPR to the center point of root insertion, suture of LMPR posterior, interior and later 5 mm to the center point of root insertion, respectively. The peak contact pressure, the average contact pressure and contact area were evaluated using a Tek-scan sensor positioned between the meniscus and tibial plateau, under 1 kN compressive loading, at 0 degree knee extension. Results In the lateral compartment, the average contact pressure and peak pressure significantly increased under rupture of LMPR compared with the intact state (P<0.01), and the contact area decreased significantly (P<0.05). For LMPR tears fixed by four different suture methods, both the average pressure and peak contact pressure reduced, and the contact area increased. The average contact pressure, peak pressure and contact area were closer to the knee joint in the intact state when the suture positions of LMPR tears was posterior 5 mm to the center point of root insertion (P<0.05). In the medial compartment, there were no significant differences in contact pressure, peak contact pressure and contact area with the knee joint at 0 degree (P>0.05). Conclusions The average contact pressure, the peak contact pressure and the contact area between the lateral meniscus and the tibial plateau changed obviously due to the LMPR tears. When the suture position was 5 mm lateral to the center point of root insertion, similar biomechanical function with the intact knee could be obtained.

Abstract:Objective To establish the musculoskeletal multi-body dynamic foot-ground contact model and explore its applicability at different speed. Methods The gait data of the subjects at different speed were collected, and the foot-ground contact model was established based on the full body model from the musculoskeletal multibody dynamic software AnyBody. Then the calculated ground reaction forces (GRFs) and ground reaction moments (GRMs) at different speed (slow walking, normal walking, fast walking and jogging) were compared with the measurements from the force plates. Results The predicted GRFs and GRMs correlated well with the experimental measurements at slow, normal and fast speed (stride speed ranged from 0.69 to 1.68 m/s). The correlation coefficients between predicted and measured GRFs were greater than 0.875 and the correlation coefficients for GRMs were greater than 0.9. Conclusions The developed foot-ground contact model could simultaneously predict GRFs and GRMs with good accuracy, thus eliminating the dependency on force plates. The model could be applied to low-speed gait conditions, such as the elderly and pathological gait.

Abstract:Objective To analyze effects of different elastic modulus, thickness and tooth movement on deformation of the invisible dental appliance by finite element method, so as to provide theoretical references for orthodontic doctor to formulate the orthodontic treatment scheme. Methods A total of 12 finite element models of invisible appliances were established with 4 kinds of thickness and 3 kinds of elastic modulus. The displacement load of the tilting movement was applied to the 12 models, and the maximum Von Mises stress and deformation of the appliance were analyzed; the deformation of the appliance was analyzed by applying the displacement load of inclined, parallel and intrusion to the optimal model. Results The maximum Von Mises stress increased with the elastic modulus and thickness of the invisible appliance increasing. The deformation decreased with the appliance thickness increasing. When the tooth was under inclined and parallel movement, the maximum deformation was found in the corresponding part of the tooth. Some of the corresponding parts of the immovable teeth were deformed to the lip convex side and some to the tongue side with internal concave deformation, and the appliance deviated seriously to top of the crown when the tooth was under intrusion movement. Conclusions The optimum thickness of invisible dental appliance was 0.75 mm, and the elastic modulus 816.31 MPa that currently used in clinic was suitable. In the digital model, the tongue side of the teeth corresponding to the labial protruding part and the lip side of the tooth corresponding to the concave side of the tongue side can be thickened, and the invisible appliance can be optimized by using the thickened digital model.

Abstract:Objective To study the ratcheting behavior of defective cartilage under cyclic compressive loading, so as to explore the pattern of damage evolution for defective articular cartilage. Methods Fresh articular cartilage was obtained from the distal femur of adult porcine, and the cartilage samples with different depth of defect were applied under triangular wave cyclic loading with different parameters. Combined with non-contact digital image technology, the ratcheting strain at different layers of cartilage was obtained. Results With the increase of loading cycles numbers, the ratcheting strain at each layer of cartilage increased sharply at first, then increased slowly and tended to be stable, and the ratcheting strain decreased gradually from shallow layer to deep layer. The response of each layer to cycle number was different. The strain in shallow layer increased rapidly within 50 cycles, while the strain in middle layer increased rapidly within 100 cycles and the strain in deep layer increased rapidly within 75 cycles. The ratcheting strain in shallow and deep layers was positively correlated with the stress amplitude and defect depth, and negatively correlated with the loading rate, while hysteresis response occurreds in middle layer. Conclusions The ratcheting behavior of cartilage was affected by special structure of the cartilage. The defect caused the strain increasing in each layer of cartilage, which could easily result in the aggravation of damage. The experiment results provide references for the construction of tissue-engineered cartilage.

Abstract:Objective To investigate the role of Bmi1 on the migration of human umbilical vein endothelial cells (HUVECs) in response to low shear stress. Methods A parallel plate flow chamber system was used to generate low (0.5 Pa) or normal (1.5 Pa) laminar shear stress. HUVECs were isolated, cultured and exposed to flow for 12 hours. The mRNA and protein levels of Bmi1 were analyzed by real-time PCR and Western blot, respectively. Meanwhile, wound healing assay was performed to determine the migration of HUVECs. Bmi1 specific small interference RNA (siRNA) was used to silence Bmi1 gene. Results Low shear stress (0.5 Pa) significantly inhibited migration of HUVECs compared with normal shear stress (1.5 Pa). Similarly, compared with HUVECs exposed to normal shear stress, the expression of Bmi1 significantly increased in HUVECs exposed to low shear stress. Small interfering RNA knockdown of Bmi1 attenuated low shear stress-induced inhibition of HUVECs migration. Conclusions Low shear stress may inhibit the migration of HUVECs through up-regulation of Bmi1 expression. Knockdown of Bmi1 may reverse the HUVECs migration inhibited by low shear stress．

Abstract:Objective To develop an innovative device for endothelial cell culture in vitro, namely, to develop a vascular endothelial cell culture device based on hemodynamic environment, so as to introduce the development and experimental study of endothelial cell culture device in vitro. Methods A device of dynamic culture system for endothelial cells in vitro on the basis of the existing research was designed with the theory and method of hemodynamics. The shear stress, positive stress and tensile stress existed at the same time in the flow environment. The development and experimental research of the device were described in detail from 5 aspects, such as the development background, structure and composition, design principle, theoretical basis and experimental research. Results The device could accurately simulate the hemodynamic environment of endothelial cells at normal level, with precise control of shear stress in 0-12 Pa range, positive stress in 0-15.96 kPa range, and tensile stress in 0-0.5 MPa range. Conclusions The device can provide a hemodynamic environment which is closer to the physiological conditions of human body, as well as a more ideal experimental environment and means for further exploring the mechanism of vascular intimal injury.

Abstract:Modern vehicle safety design and safety regulations are mostly based on 50th percentile populations. However, with the increase of obese populations, it is very important to investigate the injury mechanism and protection of obese occupant. Methods such as traffic accidents statistics, cadaver experiments, multi-body modeling and finite element modeling, are currently used to study the injury mechanism of obese occupants. Different hypotheses including cushion effect, body geometrical effect and mass increasing effect have been put forward to explain the effect of obesity on occupant injury mechanism, which means that its mechanism is still uncertain. The impact injury mechanisms of obese occupant were comprehensively summarized. Furthermore, the problems confronted by the research of current obese occupant impact injury and future investigations were proposed in this study.

Abstract:With the increasing life span of the population and the increasing proportion of the elderly population, the elderly with osteoporosis are prone to hip fractures, which brings heavy economic burdens to the family and society. The progress in predicting hip fractures from the aspects of the proximal femur geometry, bone mineral density (BMD), fracture risk assessment tool (FRAX) and finite element analysis (FEA) based on computed tomography (CT) imaging was reviewed, in order to understand the influencing factors of fracture risk, improve the accuracy of hip fracture risk prediction for the elderly, detect the high fracture risk group at an early stage, and hence to reduce the occurrence of fractures with appropriate preventing measures, and provide theoretical references for the prevention and treatment of hip fractures.

Abstract:Orthopedic sutures are vital medical devices in repair surgeries of tendons and ligaments. Properties especially mechanical properties of orthopedic sutures have great impacts on the effects of tendon/ligament repairs. In this paper, clinically used orthopedic sutures including absorbable sutures and non-absorbable sutures were summarized firstly, by exploring literature about orthopedic sutures, and the mostly used orthopedic sutures are non-absorbable sutures. Then, based on the particularity of the repaired sites of orthopedic sutures, the in vitro mechanical test devices and evaluation method of orthopedic sutures were reviewed, mainly including the mechanical properties of sutures, suture-tissue, and suture-anchor. In addition, the characteristics of different evaluation method or test devices were compared. It was still difficult to evaluate the mechanical properties of orthopedic sutures due to the lack of instruments and test criteria.