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Abstract:Objective To predict biomechanical responses of neck injuries under different loading conditions based on the finite element model of the 6-year-old pediatric neck. Methods The finite element model of the 6-year-old pediatric neck with real anatomical structural muscles was developed, according to the CT images. The model was verified by reconstructing the dynamic tensile test of different cervical spine segments, the tensile test of full cervical spine and the low speed impact experiment of the pediatric volunteers. Results The force-displacement curves, obtained from the simulations on tensile test of different cervical spine segments and tensile test of full cervical spine, were in good agreement with the experimental curves. The head angular velocity-time curve obtained from simulations on pediatric volunteer was consistent with the corridor obtained from experimental data. Conclusions The model is validated and can be used for studying the biomechanical responses and injury mechanism of pediatric neck under different loading conditions.

Abstract:Objective To study the distribution of stress, strain and effective surface pressure in the knee joint. Methods Based on CT/MR scan image data and using the Mimics/ANSYS software, a three-dimensional finite element model of the knee joint (including the upper/lower knee and the meniscus) was established with the principle of reverse engineering, and the treatment of articular cartilage and ligament was ignored in this model. The mechanical responses of the three models, i.e., the healthy knee joint, the knee joint with V-shape medial meniscal tears, the knee joint with longitudinal meniscal tears under axial loading were analyzed and compared. Results Under axial loading, the healthy knee joint would transfer the majority of the compressive stress loads, which were mainly concentrated in the lateral side of the middle part of the meniscus, and the maximum contact pressure appeared in the rear area of the middle part of the meniscus. When the meniscus was torn, the maximum stress appeared at the periphery of the tear, and the contact stress distribution of the meniscus was significantly changed due to the presence of the tear. Conclusions The meniscal tears have a significant influence on the stress distribution and peak stress of the knee joint. According to the shape of the meniscus, the doctor can determine the position of the stress concentration in the meniscus, and to determine the most important point in the treatment of the meniscus tear.

Abstract:Objective To develop an in vitro vascular tensile stress loading device and study the distributions of tensile stress and tensile strain on the elastic basement membrane (silicone sheet). Method The in vitro vascular tensile stress loading device which simulated the human hemodynamic environment was developed based on the elastic basement membrane deformation loading technology. The images of grid points before and after the stretch of the silicon sheet were recorded by camera and transformed into the digital images. The characteristics for the location of the grid points were calculated by using Matlab software, so as to obtain the strain distribution on the silicon sheet. Experiments were conducted on the silicon sheet by using the universal material testing machine, so as to calculate the mechanical parameters of the silicon sheet. The finite element model was established according to the mechanical parameters, and the distribution of tensile stress and tensile strain on the silicon sheet was simulated and calculated. The experimental results and simulative results were then compared. Results The finite element results were basically in accordance with the experimental results. The maximum value of tensile stress and tensile strain appeared on the loading point, while the stress and strain in intermediate area were comparatively homogeneous. 60% of the intermediate area in the silicone sheet could be regarded as homogeneous strain fields Conclusions The research finding can provide experimental techniques for the dynamic culture of vascular endothelial cells and the research on cell mechanics in the future.

Abstract:Objective To investigate the influence of mechanical stretch at different frequencies on proliferation and aerobic capacity of mice myoblast cells C2C12. Methods C2C12 cells cultured in vivo were exposed to mechanical strain with the magnitude of 15% at the frequency of 1 and 2 Hz, respectively, for 2 hours per day over a period of 4 days by using Flexercell Cell Tension System, while in control group C2C12 cells were cultured statically. The C2C12 cells were observed by inverted phase contrast microscope. CCK-8 Cell Counting Kit was used to estimate the proliferation of cells. After the experiment, the cells were obtained by trypsin digestion. MitoXpress-Xtra system with oxygen sensitive probe was induced to detect the extracellular oxygen consumption level. Results The morphology of C2C12 cells presented a typical long spindle under the microscope following the mechanical stretch stimulation. The cells were arranged in a certain direction, parallel to the direction of tension stimulation and growing in good condition. Compare with the control group, the cell numbers in 1 Hz group and 2 Hz group were significantly increased (P<0.05). At the 3rd and 4th day, number of cells in 1Hz group was significantly increased than that in 2 Hz group. However, the oxygen consumption capacity increased in both 1 Hz group and 2 Hz group, but no significant difference was found between experiment groups (P>0.05). Conclusions Cyclic mechanical stretch stimulation can effectively induce proliferation of C2C12 cells, which is related to the frequency of mechanical stretch, with the frequency of 1 Hz being optimum. But stretch stimulation has no significant impact on the aerobic ability of C2C12 cells.

Abstract:Objective To analyze the force condition of a single microparticle in blood vessel and the factors that influencing its motion. Method The microparticles in blood vessel during targeted drug delivery were studied, and the fluid flow in blood vessel was simplified as the Poiseuille flow in parallel plate flow chamber. Specific methods for calculating each force subjected on the single microparticle in the flow field were analyzed. The motion equations of the single microparticle were determined through calculation of its force balance and torque balance. The relationship between the force subjected on the single microparticle and the particle diameter/flow rate as well as the critical motion conditions of the particle diameter and flow rate were obtained by numerical calculation. Results The single microparticle was more subjected to the motion of rolling, sliding and ascending with the increase of flow rate and particle diameter. In flow rate and particle diameter diagrams, the critical curve of ascending motion located above that of sliding motion, while the rolling curve was located at the bottom.Conclusions The microparticle will not do the ascending motion under the condition of blood flow rate in human. As the blood flow rate reduces, the motion of microparticle with given diameter will be transfered from sliding to rolling, and will be entirely still under the condition of elastic deformation. Therefore, the proper selection of mircoparticle diameter and its surface adhesivity is critical for the drug particle to transport to the target location.

Abstract:Objective To study the frictional contact force properties of articular cartilage by modified silicon probes of the atomic force microscopy (AFM). Methods Modification was conducted on the silicon nitride probes of AFM by the micromanipulator, and the glass microsphere was glued on the probe by glass adhesive as the pinhead. Micro-tribology properties of human and bovine articular cartilage were then investigated by using the modified AFM probes. Results With the increase of load, the friction force of human and bovine cartilage also increased gradually. When the sliding speed increased from 0 to 100 /s, the friction force between specimens and probes increased quickly; when the sliding speed increased from 100 /s to 300 /s, the friction force increased slowly. Conclusions Articular cartilage had an obvious fibrous structure in its surface. There was a direct relationship between the surface roughness of articular cartilage and the measuring range. When the load or sliding speed increased, the friction forces of human and bovine cartilage show an increase with the same variation range. The investigation on mechanical and tribological properties of articular cartilage in micro-frictional experiment will contribute to understanding the injury mechanism of articular cartilage and developing wear-resistant materials for medical artificial joints.

Abstract:Objective To establish 5 different finite element models of the proximal femur based on CT images, and analyze the influences of element size on materials distribution and biomechanical behavior of the proximal femur model. Methods The proximal femur was scanned by spiral CT. The images, stored as DICOM format, were extracted by Mimics to obtain 3D geometric data, and then meshed separately by Mimics, 3-Matic and ICEM software to establa voxel element model, a tetrahedral element model and 3 hexahedral element model (with element size of 2, 1, 0.5 mm). These meshed models were assigned materials by Mimics, and their mechanical behavior was analyzed by Abaqus eventually. Results For the proximal femur model with material assignment based on CT images, the influence of element size on the total mass of all the 5 models was not significant. The nodal Mises stress and nodal displacement along the same path in 5 models showed a similar tendency, while the Mises stress at each node displayed an obvious deviation. The nodal Mises stress in the hexahedral element model with the element size of 0.5 mm showed accordance with the voxel element model. Conclusions The element size has a small influence on the total mass and nodal displacement when the material assignment is attributed to the model based on CT gray values, while decrease in the element size will affect the materials distributions and stress distributions of the model. When the element size of the proximal femur model is close to its voxel size, the mass distributions and mechanical behavior of the femur can be preferably reflected.

Abstract:Objective To investigate the effects of element size and type, material property distributions of vertebral cancellous bone and simulation methods of cortical bone structure on the finite element (FE) results during the finite element modeling of lumbar vertebral body. Methods Based on QCT images of lumbar spine, 22 FE models of L2 without posterior structure were built by 6 element sizes (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 mm), 2 heterogeneous material distribution methods of cancellous bone (300, 150) and 2 cortical bone modeling methods. The maximum displacement, strain energy, average stress and axial stiffness of these models were obtained to analyze and verify the results. Results When the element size was 0.5 mm, the axial stiffness of models with 10, 150 and 300 kinds of heterogeneous materials showed obvious differences; for the vertebral cancellous bone with 150 kinds of materials, the variation of average stress was not distinct under different element sizes; the average stress of the model using the outermost hexahedral elements to simulate the cortical bone structure was larger than that appending the skin to the outmost of the model. Conclusions It is more reasonable and effective to build the FE model of lumbar vertebral body with the method by 0.5 mm element size, 8-noded hexahedral elements, 150 kinds of heterogeneous materials, and using the outermost hexahedral elements to simulate the cortical bone structure. The research findings will lay a foundation for building subject-specific FE models of lumbar vertebral body on a large scale in future.

Abstract:Objective To compare the biomechanical differences in 3 posterior fixation methods with or without crosslink for treatment of thoracolumbar fractures, so as to find the optimal posterior fixation methods. Methods On the basis of the validated finite element model of T12-L2 segments to simulate L1 vertebra burst fracture, the superior 1/2 cortical bone of T12 segment was removed and the superior 1/2 cancellous bone was assigned with the material damage property of cancellous bone. Then 6 thoracolumbar fracture models by intermediate unilateral pedicle screw fixation without or with crosslink (Model A1, A2), traditional short-segment pedicle screw fixation without or with crosslink (Model B1, B2), intermediate bilateral pedicle screw fixation without or with crosslink (Model C1,C2) were established, respectively. The range of motion (ROM) as well as the maximum Von Mises stress of the pedicle screw and rod for 6 models under various physiological loading conditions were compared. Results The ROM under flexion-extension and lateral bending in Model A and Model C was obviously smaller than that of Model B. Under flexion-extension, no significant difference was found in ROM between Model A and Model C; under lateral bending, the ROM of Model C was smaller than that of Model A. The stress was concentrated in the root of upper screw and the rob located between upper screw and intermediate screw; the maximum stress of upper screw in Model C was smaller than that in Model A and Model B. The crosslink could increase the stability of all fixation groups under axial rotation stress condition, and decrease the maximum stress on upper screw and rod under axial rotation stress condition, but no significant difference was found under flexion-extension and lateral bending. Conclusions Additional pedicle screws at the level of fracture vertebra can achieve the better biochemical stability. The additional crosslink not only increases the torsional rigidity, but also decreases the maximum torsional stress of the screw and rod, which is a better choice as the treatment of thoracolumbar fractures.

Abstract:Objective To analyze the effect of different bone defect types on stress distributions of the implant- bone interface and bone-Bio-oss interface under dynamic loads by finite element method. Methods The finite element models for four types of bone defects (fenestrative bone defect, dehiscent bone defect, circular bone defect, vertical bone defect) without the first molars were established, then the models of grafting bone and implants corresponding to each model were established. The vertical load of 100 N and Oblique load of 200 N were used to simulate the dynamic chewing process of 5 stages in a masticatory cycle, and the maximum Von Mises stresses at the implant-bone interface and bone-Bio-oss interface were analyzed. Results In a masticatory cycle, from stage 2 to stage 4, the stresses on implant-bone interface increased by 81.6%, 90.7%, 182%, 106%, respectively, while the stresses on Bio-oss bone and natural bone interface increased by 26%, 13%, 6%, 56.25%, respectively. Conclusions The sequence of bone graft stability for the models with four types of bone defects is: circular bone defect> dehiscent bone defect>fenestrative bone defect>vertical bone defects. In clinic, doctors should screen the high-risk patients according to the sites of the bone grafts, and choose different methods for fixing the bone grafts so as to improve the stability of bone grafting. The axial loading will be more beneficial to the stress distributions on the interface, and the oblique loading should be decreased or avoided in clinical design for the superstructure of implant denture.

Abstract:Objective To accurately measure the motion angels of hand-related joints during manipulations of acupuncture needle thrusting-pulling and twirling, so as to provide quantitative references for acupuncture manipulation. Methods Six acupuncturists with over 3-year acupuncture experience and one volunteer were enrolled in this study. The angles of the forearm, wrist, metacarpophalangeal & interphalangeal joints of the thumb and index finger in each acupuncturist when performing thrusting-pulling and twirling manipulation were measured by the video motion capture (VMC) system, and the different ranges of above-mentioned angles among the 6 acupuncturists when performing 10 trails of thrusting-pulling and twirling manipulations on the volunteer’s thigh were compared. Results There was no significant difference in the ranges of relevant hand-related angles in the acupuncturist (P>0.05). The manipulation of thrusting-pulling was mainly managed by the wrist joint, with the range of (7.23±1.87)°, while the manipulation of twirling was mainly managed by the interphalangeal joints of the index finger, and the range of the first and second interphalangeal joints of the index finger was (28.33±2.18)°and (10.43±1.69)°, respectively. Conclusions The VMC can be a reliable method to quantify the parameters of acupuncture manipulation. Different acupuncture manipulation shows particular variation of the joint angles, which can be used as a reference to quantify the acupuncture manipulation.

Abstract:Objective To investigate the effect of pathologically elevated cyclic strain induced by hypertension on proliferation of vascular smooth muscle cells (VSMCs) and the role of long non-coding RNA (IncRNA)-XR007793 during this process. Methods Flexcell-4000 tension system was used to apply physiologically (5% magnitude) and pathologically (15% magnitude) cyclic strain with frequency of 1.25 Hz on VSMCs for 24 h respectively. qRT-PCR was used to detect the expression of XR007793 and 4 co-expressed genes: signal transducer and activator of transcription 2 (STAT2), cell division cycle associated 8 (CDCA8), proto-oncogene LMO2 and interferon regulatory factor (IRF7). Western blot was used to detect the proliferating cell nuclear antigen (PCNA) level in VSMCs. RNA inference was used to inhibit XR007793 expression. The cell cycle of VSMCs was measured by flow cytometry in static condition and the cell proliferation was detected by Brdu-Elisa in cyclic strain loading condition. Results Compared with 5% cyclic strain, 15% cyclic strain remarkably decreased the XR007793 level and increased the proliferation of VSMCs，along with the increasing expression of STAT2 and CDCA8. XR007793 specific siRNA transfection under static condition decreased the expression of XR007793 and increased the VSMC proliferation. Under 15% cyclic strain, XR007793 specific siRNA transfection also increased the VSMC proliferation and the expression of CDCA8 compared with the non-specific siRNA control. Conclusions Pathologically elevated cyclic strain decreases the XR007793 expression level and increases the CDCA8 expression level to modulate VSMC proliferation. These results provide new experimental evidence for the study of mechanobiological mechanism during hypertension and potential targets for hypertension therapy.

Abstract:Objective To evaluate the effect of transforming growth factor β1 (TGF-β1) on early tendon-bone healing after reconstruction of rotator cuff tears in Wistar rats. Methods The models of rotator cuff supraspinatus tendon by full-thickness transverse tears at the greater tuberosity point in bilateral upper limbs of 54 Wistar rats were established and reconstructed. TGF-β1 induced by fibrin glue was injected at the tendon-bone interface to release osteogenesis after 6 weeks. The rats were randomly divided into low-dose TGF-β1 group, high-dose TGF-β1 group and control group, and then executed randomly at 1st, 2nd and 3rd week to make the supraspinatus specimens for biomechanical testing. Results The rupture point was formed within the suture of rotator cuff in each group by visual observation. The maximum tensile strength, maximum loading percentage, stiffness and maximum cross-section area of tendon-bone interface in high-dose group were higher than those in low-dose group and control group (P<0.05). The maximum loading percentage，maximum tensile strength, stiffness, stiffness percentage and the maximum cross-section area of tendon-bone interface in low-dose group were significantly higher than those in control group (P<0.05). High-dose TGF-β1 could promote the healing during early reconstruction of rotator cuff tears, the tensile strength and stiffness at the tendon-bone interface would increase with the rehabilitation period prolonging. Conclusions TGF-β1 can increase the maximum tensile strength, maximum loading percentage, stiffness and maximum cross-section area of tendon-bone interface, induce the fractured section to directly generate complex structure, thus promote the healing of rotator cuff tears.

Abstract:Objective To analyze the present status, subject and characteristics of biomechanical studies on injury prevention of anterior cruciate ligament (ACL), which has a practical guiding significance in promoting prevention and control of ACL injuries. Methods Biomechanical studies on ACL injury prevention were conducted by scientometrics based on the Web of Science, CNKI database for statistic analysis. Results Cumulative numbers of issued papers on biomechanical studies of ACL injury prevention well complied with the exponential growth rule year by year in general, which mainly focused on sports science, orthopedic science, surgery, rehabilitation and other disciplines. From the countries participating in the studies, the United States of America was unique, followed by Canada, UK and Japan. Timothy E. Hewett contributed the largest number of issued papers among all the authors participated in the studies. Topics of biomechanical studies on ACL injuries could be identified into four groups: risk factors and incidence, ACL injury of the female, neuromuscular training and control, ACL injury assessment. Conclusions Researchers should broaden their research fields, take advantage of the national and local governments to lead the role in the rehabilitation medical treatment, and pay more efforts in biomechanical studies of ACL injury prevention.

Abstract:Costal cartilage, auricular cartilage and nasal septal cartilage are widely used in plastic operation. Costal cartilage is used in ear reconstruction and augmentation rhinoplasty, while the auricular cartilage and nasal septal cartilage are applied in the nasal plastic operation. The maintenance of postoperative form is closely related to the biomechanical characteristics of the cartilage. Meanwhile, ultrastructure, especially extracellular matrix, determines the mechanical properties of cartilage. This review mainly focuses on the biomechanical properties and ultrastracture of the cartilages and summarizes the basic data of different cartilages in biomechanical testing, including tissue engineered-auricular cartilage. However, the procedure of biomechanical testing on cartilages currently needs further standardization, and the use of the finite element method should be promoted, so as to offer a better clinical diagnosis and treatment.

Abstract:The biomechanical studies on the temporomandibular Joint（TMJ）are of great importance to understand the origin and progression of TMD disorders. The finite element method can be used to analyze stress/strain distribution patterns in the TMJ tissues after application of force or deformation. However, due to the delicate and complicated anatomical structures of TMJ, modeling research were always time-consuming, expensive and non-repeatable. To explore a more rapid and accurate method for establishment of 3D finite element model of TMJ, the relevant factors such as geometric similarity, biomechanical environment simulation for improving the accuracy of TMJ finite element modeling were summarized.

Abstract:Hip fracture is one of the major causes of death and injuries of the elderly, and its occurrence rate is increasing with the progress of aging population, which becomes a heavy economic burden on the family and society. The main treatment for proximal femoral fractures includes fracture fixation and hip arthroplasty. This review is focused on the relationship between anatomical structure and load transfer mechanism of the proximal femur, mechanical distributions on cortical and cancellous bone in the proximal femur, and the latest progress in biomechanical research on risk prediction of hip fracture both in China and abroad, which will contribute to understand hip fracture from a biomechanical perspective, improve the accuracy of risk prediction of hip fracture in the elderly, as well as treatment of hip fracture, the correct selection and application of othopaedic implants.