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Abstract:Objective To investigate the role of receptor for activated C kinase 1 (RACK1) in vascular smooth muscle cells (VSMCs) proliferation modulated by co-cultured endothelial cells (ECs) and shear stress. Methods Using EC/VSMC co-cultured parallel plate flow chamber system, two levels of shear stress, i.e. low shear stress (LowSS, 0.5 Pa) and normal shear stress (NSS, 1.5 Pa), were applied for 12 h. BrdU ELISA was used to detect the proliferation of VSMCs, and Western blot was used to detect the protein expressions of RACK1 and phosphor-Akt. Under the static condition, RNA interference was used to suppress the expression of RACK1 in VSMCs, and then the proliferation of VSMCs and expressions of RACK1 and phosphor-Akt were detected. By using co-culture model (ECs/VSMCs) and separated culture model (ECs//VSMCs), the effect of ECs on expressions of RACK1 and phosphor-Akt in VSMCs was further analyzed. Results Comparative proteomic analysis revealed that LowSS increased the expression of RACK1 in rat aorta. In vitro experiments showed that LowSS induced the proliferation, expressions of RACK1 and phospho Akt in VSMCs co-cultured with ECs. Target RNA interference of RACK1 significantly decreased the proliferation of VSMCs, and the phosphorylation of Akt. In comparison with ECs//VSMCs (separated culture) group, the expression of RACK1 and phosphor-Akt were both up-regulated in the VSMCs co-cultured with ECs (ECs/VSMCs group). Conclusions The expression of RACK1 in VSMCs was modulated by shear stress and neighboring ECs, which might induce cellular proliferation via PI3K/Akt pathway. The investigation on VSMC proliferation and the involved biomechanical mechanism will contribute to understanding and help preventing the pathogenesis and progress of atherosclerosis.

Abstract:Objective To study the biomechanical effect from pulley tissues of extraocular muscles on super adduction of the eye. Methods By the coordinate parameters of extraocular muscles reported in the literature and based on the mechanical equilibrium of eye movement, two mechanical models, active pulley model and non pulley model (as control), were established to simulate eye adduction in the range of 30°-45°. Results For the contribution of medial rectus muscle, the non pulley model produced more force than the active pulley model to control eye adduction, and its corresponding force value increasingly exceeded the physiologically safe threshold (0.5 N). At the maximum simulative adduction of 45°, the force of medial rectus obtained by active pulley model and non pulley model was 0.508 N and 0.782 N, respectively, and the latter was 56% greater than the safe threshold. For controlling eye adduction, the active pulley model consumed much less energy than the non pulley model. Conclusions Due to the existence of pulley tissues, extraocular muscles could control eye adduction by consuming less biological energy and reinforce the ocular derivation. In addition, with the active pulley, the medial rectus muscle could maintain its mechanical advantage under super adduction of the eye.

Abstract:Objective To design mechanical structure of exoskeleton which simulates physiological structure and kinematic characteristics of lower limbs according to kinematics analysis of human body, and investigate biomechanical properties of exoskeleton under two different phases of human gait period, so as to provide references for such exoskeleton design and optimization. Methods Based on clinical gait analysis of lower limbs, the mechanical structure of exoskeleton was first established by using 3D modeling software. Then the physical model was assembled, meshed and materialized by 3D modeling software, and surface to surface contact relationship between each component was also constructed to simulate and analyze the stress distributions of exoskeleton. Results Under the load of 1 kN, the maximum stress of double stance (calculating condition I) was 91.45 MPa and the maximum stress of vertical tibia (calculating condition II) was 154.55 MPa, occurring at the back support and hip, respectively, and such results were in accordance with the analysis results of force transmission mechanism got before design. Conclusions The stress distributions of exoskeleton under different calculating conditions were obviously different. Some uncertain factors such as some shock caused during the walking period, which have not been taken into account in the calculation, should be considered for the design and optimization of exoskeleton and multiplied by a certain safety coefficient.

Abstract:Objective To further understand the biomechanical relationship between activities of cervical spine and blood flow of vertebral artery (VA) by developing the VA finite element model and calculating the fluid-structure interaction. Methods Based on the normal model of cervical spine and the developed C0-T1 finite element model with bilateral VA, the flexion and extension, right and left lateral bending, right and left axial rotation movement of cervical spine at physiological velocity were simulated. The effects of cervical activities on stress of vertebral arterial wall were observed, and the biomechanical interaction between the vessel wall and fluid was calculated by fluid-structure interaction equation to obtain the hemodynamic parameters. Results The maximum stress was usually concentrated on the both sides of C2 transverse foramen, where the second arc of vertebral arterial wall protruded into the cranial direction during cervical activities. The maximum strain of the vessel wall was most obvious during the extension and lateral bending movement, with strain ratio of 23.04% and 35.5%, respectively. The maximum stress on the vessel was located in the position of contralateral transverse foramen during lateral bending movement, while the maximum strain on the vessel was located in the position of ipsilateral transverse foramen during rotation movement. In aspect of cervical spine range of motion (ROM), the minimum volume flow rate occurred within 30%-40% of the physiological ROM. The volume flow rate-time curve of bilateral VA was similar during flexion and extension movement, when the circulation of flow rate was completed for two times within 0.5 s. The peak and valley of ipsilateral blood flow in volume flow rate-time curve occurred earlier than that of contralateral blood flow during lateral bending movement, while the results of rotation movement were opposite. Conclusions The obtained stress features of bilateral VA vessel and the law of the volume flow rate-time curve validated the experimental results with those in the literature, which could reasonably explain the clinical phenomenon. The established model would provide an ideal platform for researches on vertebral artery-related diseases.

Abstract:Objective To develop the three-dimensional (3D) finite element (FE) models of pelvis and fracture fixation, and test their validity. Methods Based on CT scan images, the 3D FE model of the pelvis was built by software of Mimics, ANSYS ICEM, Hypermesh and ABAQUS. A uniformly distributed load of 600 N was applied in vertical direction on the upper lamina of S1 vertebrae to simulate the stresses on the pelvis in standing position and to verify the validity of the pelvis model. T-shaped acetabular fracture models with 3 types of fixation were also established to verify the validity of internal fixation. ResultsBoth the stress and displacement distributions were found to be bilaterally symmetrical on the pelvis in standing position, with the Von Mises stresses mainly distributed in the beginning of arcuate line, pubic branch and posterior-superior area of acetabulum. The largest displacement occurred in the center of the sacral crest, and became relatively smaller in iliac fossa and femur, which was reduced gradually to the femur. Each of the three fixation types in acetabulum showed good biomechanical stability. Conclusions The established hexahedral grid-3D FE model can accurately simulate mechanical properties of the femur in standing position, which would provide an intuitive basis for clinical study.

Abstract:Objective To investigate mechanical performances of two different drug eluting stents (DES) during compression process, so as to provide a scientific guideline for design of DES. Methods Using Solidworks, two kinds of stent models, namely the common DES without slots in outside surface (Stent I) and the targeted DES with slots in outside surface (Stent II) were established, respectively. The important mechanical properties of the two stents during compression process, such as rebound ratio of radial contraction, rebound ratio of axial contraction, the inhomogeneity of compression and the distribution of residual stress, were analyzed by ABAQUS. Results With the same outer radius, the difference values of rebound ratio of radial contraction, rebound ratio of axial contraction and inhomogeneity of compressing for the two stents were 0.07%-0.12%, 0.016%-0.033% and 0.013 %-0.048%, respectively; there was a bigger low-stress area on the support of Stent II. Conclusions Compared with the traditional DES, the targeted DES could maintain the same mechanical performances while reducing drug-loading capacity, which shows a good prospect in clinical application of the treatment for cardiovascular stenosis diseases.

Abstract:Objective To build a 3D finite element model of the whole cervical spine by using Simpleware software, as well as validate and analyze the model, so as to provide a reliable model for exploring the mechanism of cervical spine injury. Methods The 3D entity model of the whole cervical spine C1-7 was established based on CT tomography images, medical image processing software Simpleware, reverse engineering software Geomagic, which was imported to Hypermesh for meshing, adding ligaments and introducing facet joint contact relation, etc., thus to establish the finite element model of the whole cervical spine C1-7. Biomechanical properties of the cervical spine under flexion, extension, lateral bending and torsion were simulated by ANSYS. Results The established model was proved to be accurate and reliable, and its range of motion (ROM) under flexion, extension, lateral bending and axial rotation was similar to in vitro experiment and finite element analysis results in related literatures. The stress of intervertebral disc was concentrated on the compression side of the vertebral body, and the cervical spine C4/5 was more prone to have a stress concentration. Conclusions The finite element model of the whole cervical spine C1-7 can effectively simulate the biomechanical characteristics of the cervical vertebra, which establishes a good foundation for the follow-up studies on whiplash injury of the cervical spine.

Abstract:Objective To introduce the design principles and functional modules of a self-programmed software system for designing customized hip stem prosthesis based on X-ray films. Methods Some femoral anatomical feature points (e.g. the peak of trochanter minor, the center of femoral head, trochanteric fossa), two planned points on osteotomy line (a boundary point at the side of trochanter major and the lowest point on the osteotomy line), and some key location points for designing (e.g. the hip stem far-end location point, the highest point of neck shaft connecting section) were extracted from X-ray films by using image processing methods to predict the patient’s proximal femoral cavities. The customized hip stem prosthesis was designed by inputting the design parameters (e.g. the neck-shaft angle, anteversion angle, thickness of reserved cancellous bone, radiuses of the cross-section in matching area of the prosthesis, height of transition area of the prosthesis). Two-dimensional cross-section verification on matching area of the customized hip stem prosthesis and three-dimensional overall verification were conducted. Results According to the verification results, the design parameters were adjusted to regenerate point cloud data of the hip stem prosthesis model, which could make the designed hip stem prosthesis match the patient’s femoral cavity and finally meet the requirements for the customized purpose. Conclusions The program system introduced in this paper can be used to design customized hip stem prostheses for patients. With the much shorter design cycle and relatively lower cost, this program system can promote the application of customized hip stem prosthesis in clinic and further prove the life quality of patients.

Abstract:Objective To compare mechanical responses from mandibular canine with different movement types in orthodontic treatment with Invisalign. Methods Based on computed tomography images of the teeth and their supporting tissues, the finite element model of the mandible and periodontal ligaments was established. The translation, inclination and rotation movements of the canine in buccolingual direction were simulated to obtain displacements and stresses of the canine and periodontal ligaments under the three different movements. Results The initial movements of the canine and stress distributions on periodontal ligaments were mainly determined by different movement types of the canine. The stress distributions on periodontal ligaments were similar when the canine was in translation and inclination movements. The bodily movement trend of the canine was much larger in rotation movement than that in translation movement under the same displacement magnitude. Conclusions The mechanical responses and its degrees from canine would be different under different movement types. To get better understanding with such different responses can help design more reasonable orthodontic treatment with Invisalign, avoid the damage to periodontium and achieve the orthodontic treatment with less time.

Abstract:Objective To investigate the effects of overweight and obesity on the gait of primary school children by comparing the kinematic parameters between overweight/obese children and normal weight children during level walking. Methods Forty overweight/obese children (age: (9.6±1.72) year; height: (142.16±12.19) cm; BMI: (24.32±2.96) kg/m2) and 50 normal weight healthy children (age: (10.26±0.72) year; height: (139.0±7.50) cm; BMI: (17.08±1.25) kg/m2) were recruited as the subjects. All of the subjects completed 3 walking trials at preferred speed along a 10 m walkway with barefoot. A digital video camera was used to record these subjects’ level walking images, and their gait parameters, such as step length, stride length and joint angle of the lower extremity, were obtained through Shixun motion analysis system. SPSS 16.0 was used for data analysis. A paired t-test was used to assess differences of all the variables between lefe side and right side for the subjects. An independent t-test was used to assess differences of all the variables between the overweight/obese and normal weight children. Statistical significance was defined as P<0.05. Results (1) There were significant differences between overweight/obese children ((0.44±0.001)) and normal weight children ((0.45±0.001)) for relative step length (P<0.05). (2) There were significant differences in left hip and knee joint angle in the frontal plane between overweight/obese children (left hip angle: (165.36±5.29)°, left knee angle: (178.82±5.51)°, right knee angle: (177.84±5.25)°) and normal weight children (left hip angle: (161.99±4.28)°, left knee angle: (174.67±4.91)°, right knee angle: (174.67±4.91)°) during heel strike phase (P<0.05). Significant differences were found in the left ankle joint angle of the frontal plane during toe off phase between overweight/obese children((121.73±8.03)°) and normal weight children((118.44±6.70)°)(P<0.05). Conclusions Relative step length of overweight/obese children was significantly smaller than that of normal weight children during level walking. The left hip and knee joint angle in the frontal plane of overweight/obese children during heel strike phase were significantly larger than those of normal weight children. The left ankle joint angle in the frontal plane of overweight/obese children during toe off phase was significantly larger than that of normal weight children. These differences may affect the function of the lower extremity in overweight/obese children.

Abstract:Objective To detect the blood viscosity values and find out the statistically significant influencing factors of blood viscosity and their fitting formulas among the middle aged and elderly people with high incidence of cardiovascular diseases. Methods The subjects’ blood was collected in the hospital, together with their physiological and pathological information, and LG-R-80 series rotary viscometer detector was used to detect blood viscosity. The statistically significant factors of blood viscosity and their fitting formulas were obtained by using SPSS. Results Blood viscosity increased with age and body mass index (BMI) and reached its peak value in 60 year-old males (5.35 mPa?s) and 50 year-old females (4.45 mPa?s), respectively, then the variation of blood viscosity would be stabilized, with no more increase; the blood viscosity values of males in all groups with different ages were significantly higher than those of females, with difference value in the range of 0.28-0.90 mPa?s; the blood viscosity values were obviously higher in hypertension group than those in normal group, with statistically significant differences (P<0.1). Conclusions The blood viscosity distribution in people with high incidence of cardiovascular diseases has certain regular pattern, and the obtained fitting formula between blood viscosity and influencing factors in this study would provide useful references for further study such as variation of blood viscosity under different physiological conditions, effects of different viscosities on some cardiovascular diseases, and non-invasive detection of blood viscosities.

Abstract:Objective To record the drilling feed force on different layers of fresh porcine femur, so as to provide reference for collecting and outputting the feedback signals of drilling feed force for orthopedic virtual surgery system. Methods The biological bone drilling feed force testing system was established by modifying the universal material testing machine and adjustable speed electric drill (drill bit Φ5.0 mm). The feed forces on 6 fresh porcine femoral shafts with a total of 162 drilling markers were collected at 3 different rotate speeds (n＝500, 800, 1 200 r/min) and 3 feed speeds (v＝30, 50, 70 mm/min), and their variation with corresponding tissues and locations were also analyzed. Results At the same drill marker of the fresh porcine femur, the drilling feed force on bilateral cortical bone was the largest (fmax＝103.63~142.59 N), while that on marrow cavity was the smallest, which was almost close to zero, and the drilling feed force on the middle part (f4,5,6＝124.69 N) was larger than that at two ends (f1,2,3,7,8,9＝121.84 N); the drilling feed force was smallest (f＝106.04 N) at v＝30 mm/min, n＝1 200 r/min, while the largest drilling feed force (fmax＝139.84 N) appeared at v＝70 mm/min、n＝500 r/min. Conclusions The modified drilling feed force testing system could efficiently collect the biological bone drilling data. The drilling feed force had a close relationship with bone structure, feed speed and rotate speed of electric drill as well. A larger bone density, smaller rotate speed of electric drill and higher feeding speed would lead to a larger drilling feed force, and vice versa. The accurate drilling feed force data and its variation tendency on porcine femoral obtained in this experiment could provide a reliable basis for force-feedback signal output in the virtual orthopedic surgery system.

Abstract:Objective To study the injury cases of armored biological target by bullet and its causes, and provide references for revealing the wound mechanism of armored human by bullet and the corresponding medical treatment. Methods A 60 kg live pig was selected as the biological target, and the testing physical quantity and specific location within the biological target were identified by reference to the vulnerability in the head and chest of the soldier with armor. Three rounds of 9 mm Bala Baerum pistols in 25 meter-range were shot, respectively, on the head and chest of the biological live target with armor, and the multi-mechanical parameters (acceleration, pressure, loads, etc.) that played an important role in blunt trauma of armored biological target under pistol impacts were measured. Results (1) Blunt injury to the head of the biological target by pistol generated negative pressure pulse inside the calvarium with far reaching effects, and pressure pulse appeared in the spine and carotid; (2) Blunt injury to the chest of the biological target by pistol caused high-G impact on the heart, with high pressure wave in the lungs. Conclusions The measurement results in this study provided the basis for quantitatively understanding the injury mechanism of the pistol impacted by live armored target.

Abstract:Objective To design a percutaneous left heart assist device (blood pump) which can be used in critical cardiovascular diseases. Methods According to the aerofoil theory, a percutaneous left ventricular assist device was designed. The flow produced by blood pumps with 3 different design parameters (rotation angle of the blade, distance of the outlet from the blade, length of the outlet ) was measured so as to choose the optimal design of the blood pump. Results The flow was measured with a simple flow measurement device. When the blood pump was designed to adopt a single blade with the rotation angle of 720°, or the distance between the outlet and the blade was 0 mm, or the length of the outlet was 4 mm, the flow of the blood pump was the maximum. Conclusions To choose the design parameters that produce the maximum flow can contribute to manufacture a percutaneous left ventricular assist device with the function of pumping in vitro, which will provide a theoretical and data support for the eventual development of the percutaneous left ventricular assist device in clinic.

Abstract:Brain and neck injury has become the most severe injury during vehicle collision accident due to its high fatality rate. Finite element (FE) model has been widely used in the study on biomechanical mechanism of traumatic brain injury (TBI). In this paper, recent literatures on biomechanics of skull-brain-neck FE model were reviewed, advance in the evolution and biomechanical studies of TBI in road traffic accidents was elaborated, and protection methods of head and neck injury were explored, so as to provide a theoretical basis for biomechanical research and development of appropriate car safety devices for TBI in the event of vehicle collision accident.

Abstract:Cell biology experiments in space are indispensable for investigating the effects of microgravity environment on living organisms. As an important technological means of supporting life science researche, space cell bioreactor may directly influence the data quality of space cell biology experiments and research level. To date, space cell bioreactor techniques are still under development, and lack of standard rationale. In this article, the technical progresses of space cell bioreactor were reviewed, by introducing the operational principle of several typical space cell bioreactors, analyzing the mode of culture medium supplying and character of fluid mechanics environment in space, as well as the relevant supporting techniques about the parametric controlling on temperature, dissolved oxygen and pH value and on-line microscopic imaging, so as to discuss the future perspective about space cell bioreactor techniques.

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