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Abstract:All professional or amateur athletes sustain different kinds of acute or overused injuries, which vary with sports events. Biomechanics plays the key role in determining risk factors and elucidating injury mechanisms for sports injuries. Three kinds of research methods, experimental test, modeling and computer simulation and statistical simulation, are generally used in biomechanical studies of sports injuries. This paper firstly reviews the epidemiology of sports injuries, and then comprehensively summarizes the related researches on injury biomechanics, in purpose of providing theoretical basis for studies on sports injury biomechanics, prevention of sports injuries, and clinical treatments and rehabilitation.

Abstract:Objective To explore the brain injury mechanism and enrich the database of human finite element (FE) biomechanical model by developing the FE model of one-year-old toddler head. Methods Based on CT data from Chinese one-year-old toddler head with substantial and detailed information, the head model with detailed anatomical structure was constructed by using the medical software Mimics to get the head geometry data, as well as the reverse engineering software to divide NURBS surface and build the geometric model. Finally, the FE pre-processing software was used mesh the model. The FE model of one-year-old toddle head was validated by data from anatomic and cadaver experiments, and was used for preliminary analysis on damage mechanism of one-year-old toddler head. Results The FE model of Chinese one-year-old male toddler head was developed, which included and distinguished the gray matter and white matter of brain and cerebellum, hippocampus, fontanel, sagittal suture, coronal suture, brainstem and ventricles. The cadaver head static compression experiments and drop experiments were reconstructed by using this head model, and the results showed that the FE model of head had similar mechanical properties with the cadaver, which proved the validity of the FE model. Simulation results showed that skull stiffness and skull injury severity varied with different compression rates. Conclusions The FE model of one-year-old toddler head with detailed anatomical structures is of great biofidelity. The FE head model can be used to further investigate the detailed injury mechanism of deep brain tissues, especially for the closed craniocerebral injury, which provides an effective way and tool for the related research and clinical application.

Abstract:Objective To determine the hyperelastic constitutive equation of biological soft tissues and study the mechanical responses during the clamping process of biological tissues. Methods The destructive uniaxial tensile test was performed on fresh porcine liver and the uniaxial tension experiment was simulated in ABAQUS. The hyperelastic constitutive equation of porcine liver was determined by comparing the simulation results with the experimental data. Based on this equation, the sharp teeth-shaped and wave-shaped chucks were used to simulate the clamping process. Results The simulation results of the tensile experiment with the 4th-order Ogden model were in good agreement with the experimental data. The results of tissue clamping simulation showed that stress concentration was more likely to occur when the sharp teeth-shaped chuck was adopted. Conclusions The 4th-order Ogden model can be used to describe the hyperelasticity of porcine liver and determine the relevant para-meters. Using the sharp-shaped chuck is more likely to cause tissue clamping damage, and there is a linear relationship between tissue stress and clamping feed distance. These research findings provide references for the design of surgical clamp.

Abstract:Objective To study the effect of time delay on tumor-immune system in tumor growth through theoretical approaches. Methods A mathematical model of the tumor-immune system interactions was established, and a time delay in the logistic growth term was introduced to investigate the processes of the interaction between immune system and tumor cells through qualitative analysis and numerical simulations. The relationship between the states of tumor and time delay was analyzed and the results were compared with the stages of the cancer immunoediting. Results Qualitative analysis and numerical simulations indicated that the tumor-immune system was a stable equilibrium state if the time delay was small. With the time delay increasing, the tumor-immune system entered equilibrium and escape stages of the cancer immunoediting, which described the alteration from dormant state to malignant state. Conclusions The time delay plays a key role in the interaction between immune system and tumor cells. The different time delays can result in different behaviors of tumor. The results will help to deepen clinical understanding of the tumor-immune system and provide references for the analysis and treatment of tumor.

Abstract:Objective To study the effect of the icariin on apoptosis and cytoskeleton of osteoblasts in response to overload damage. Methods The four-point bending loading device was used to simulate the mechanical environment of overload damage and establish the cell overload damage model. According to whether the drugs were added before or after mechanical loading, the experiment was divided into blank control group, icariin group, damage group, damage prevention group and damage treatment group. Cell apoptosis was detected by flow cytometry. The specific fluorescent dyes were used to label the actin filament and the nucleus, and the changes of cytoskeleton were observed under laser scanning confocal microscope. Results Compared with control group, the apoptosis rate of damage group was the highest, and the icariin group was the lowest (P<0.05). Compared with damage group, the apoptosis rate of the damage prevention group was the lowest (P<0.05). The damage group showed cell shrinkage deformation, microfilaments disorganization, loosely arranged skeleton with vague outline, even broken skeleton. The morphological changes of cytoskeleton in damage prevention group were not significant, and there was no obvious change in cell nucleus. Conclusions Icariin can inhibit the apoptosis of osteoblasts after overload injury and maintain the stability of cytoskeleton to some extent.

Abstract:Objective To investigate the effects of changes in elastic modulus of dental implants on stress distributions in implants and peri-implant bone by 3D finite element analysis, so as to supply experimental evidence for new implant system. Methods The model of the mandible with implant bone was constructed based on CT data. The elastic modulus of implants was set as 110, 90, 70, 55 and 40 GPa, respectively. The model was applied with static load of 300 N in vertical direction, 100 N in horizontal direction and 130 N in oblique direction, respectively, to stimulate occlusal state. The stresses on different parts of implants with different elastic modulus and peri-implant bone under 3 kinds of loads were calculated and analyzed. Results As the elastic modulus of implants declined, stresses in cortical bone around implants under horizontal and oblique loads decreased, and stresses in the implants showed a decreasing tendency as well. Conclusions The decrease in elastic modulus of implants can benefit the transferring of load from the implants to the surrounding bone, and reduce the risk of long-term implant failure.

Abstract:Objective In the computational fluid dynamics software FLUENT, the independently developed user defined function (UDF) dynamic mesh program is called to achieve the mobile update of grid note based on the wall shear stress (WSS). Then this method is applied to simulate the development process of atherosclerosis (AS). Methods The UDF program by secondary development could extract WSS results of every note on the wall during the computing process, and if the threshold value criterion condition was met, the node would be adjusted to a new position. The mesh regeneration method combining with the spring smoothing and the local remeshing was adopted to control the update of the grid, so as to ensure the grid quality during deformation. Results The UDF program successfully extracted the WSS and arranged the corresponding deformation for the grid. The morphology of local extension in the proximal part and restenosis in the distal end were resulted from the vortex in the rear of the initial stenosis. Those features were similar to the indication of clinical angiography. Conclusions The independently developed UDF program has reached the expected effects, depicting the topography characteristics of AS influenced by WSS. In future researches, more influential factors should be considered in dynamic mesh deformation control to provide numerical references for clinical prognosis and risk evaluation of AS.

Abstract:Objective To analyze the relationship of closed staple height with tissue damage and compression pressure, so as to provide theoretical references and guidance for the surgeon to choose the appropriate staple cartridge and height, as well as improve the safety of operation. Methods The finite element model of stapled colorectal end-to-end anastomosis was established based on analysis of staple-tissue interaction. Large intestine tissues with different wall thicknesses (1.0-1.5 mm) were compressed by closed staples with 4 different height to compare changes in stress distributions and average radial pressure. Results When the tissues were compressed by closed staple with height of 1.0, 1.1, 1.2 and 1.5 mm, respectively, the average radial stress of compressed tissues with wall thicknesses of 1.2, 1.3, 1.4, and 1.5 mm were 56.0, 58.6, 59.7 and 57.3 kPa, respectively, which was close to the optimal compression pressure. Stress concentrations were found in contact area of the staple and tissues，with the maximum stress being 2 783, 1 750, 1940 and 2 030 kPa, respectively. Conclusions Tissue damage cannot be completely avoided in anastomotic surgery, and stress concentration is generally located near contact region of the staple and tissues. The optimal closed staple height ranges in 50%-60% of the uncompressed tissue height.

Abstract:Objective To reveal the characteristics of dynamic response from stresses in lumbar intervertebral discs during getting up. Methods A finite element model of lumbar vertebrae (L1-5) with consideration of nonlinear and anisotropic material properties was established and validated by comparing the experimental data. Based on this model, the complete process of getting up from supine lying, rising and turning left to sitting up on the bedside were simulated, and the distributions and dynamic changes of stresses in the model during getting up were calculated. Results The stress and its distributions in annulus fibrosus, nucleus pulposus, and endplate of lumbar vertebrae during getting up changed constantly. The stresses were mainly concentrated on the dorsal part of lumbar vertebrae, and the maximum stress was located at L4-5 intervertebral disc. Peak stresses occurred when the body trunk turned about 35° -62° from supine lying, which were 3 times and 17 times of those during sitting firmly and supine lying, respectively. Conclusion As a high incidence area of injury and degeneration, the dorsal part of L4-5 intervertebral disc in daily activities may be subjected to an extensive stress, which is higher than that predicted by static experiments and calculations. Dynamic simulation can help to further understand the loading characteristics of intervertebral discs and provide a scientific reference for prevention and treatment of related lumbar disease.

Abstract:Objective To compare characteristics of stress variations in 3D finite element models of normal and degenerative lumbar vertebrae and the dose-effect relationship, and analyze the mechanism of mechanical balance by traditional Chinese medicine (TCM) manipulation on degenerative lumbar vertebrae. Methods The 3D finite element model of intact, real human degenerative lumbar vertebrae (L4-5) was established to simulate the physiological activity of flexion and extension in lumbar vertebrae. The characteristics of stress variation in degenerative lumbar vertebrae under external loading, namely, the TCM manipulation was analyzed, and the stress variation in degenerative lumbar vertebrae under gradual increasing-external loading was analyzed as well, which was compared with the stress and strain variation in normal lumbar vertebrae under different motion status. Results Under different motion status, the stress distributions on lumbar disc as well as the elastic modulus of nucleus pulposus and fiber ring showed a gradually increasing tendency with lumbar degeneration increasing. TCM manipulation could change the stress distributions on lumbar disc, enlarge the space of spinal canal to a certain degree, and decrease the stress on nerve root. Stresses on small joints of the vertebral body and vertebral pedicle under posterior extension were larger than those under anterior flexion, while stresses on intervertebral disc under anterior flexion were greater than those under posterior extension, which showed a gradually increasing trend from top to bottom. Conclusions The mechanical environment of human lumbar vertebrae can be balanced by TCM manipulation, for the purpose of improving and treating lumbar disc diseases. The comparison with the 3D finite element model of normal human lumbar vertebrae and investigation on lumbar degeneration from perspective of changes in biomechanical environment and characteristics can provide scientific basis for clinic application of TCM manipulation in prevention and treatment of lumbar degenerative diseases, as well as new research idea for studying mechanical mechanism of TCM manipulation in effective prevention and treatment of lumbar lesions.

Abstract:Objective To study the influence of follower load on contact force of facet joints under various postures of lumbar spine. Methods A 3D nonlinear finite element model of lumbar spine (L1-S1) was developed, with consideration of the non-uniform thickness and nonlinear material properties of the cartilage layer in facet joints. The model was then applied with different follower preload (0, 0.5, 0.8, 1.2 kN), under pure moment of 7.5 N?m in different directions (flexion, extension, lateral bending, extension and torsion). The contact forces of facet joints on the two sides of each segment under different loading conditions were compared. The asymmetry influence of follower load on contact force of facet joints was also quantitatively studied. Results The follower preload increased the facet force under flexion-extension and bending (ipsilateral), while decreased the force on the contralateral facet under lateral bending. All the effects of follower load on facet force became weaker with the increase of preload. For torsion loading, the preload had almost no effect on facet force. The greatest asymmetry influence of follower load on facet force was under bending (the ipsilateral side), followed by flexion, bending (contralateral side), extension and torsion. Conclusions The follower load shows obviously different effects on contact force of facet joints with different postures. The asymmetry of facet joints should be fully considered in biomechanical studies of lumbar spine, especially in studies on post-structures of lumbar spine under physiological loads.

Abstract:Objective To study the effect of typical middle ear diseases on sound compensation of round window (RW) stimulation, so as to provide references for the optimal design of middle ear implants by RW stimulation. Methods The finite element model of the middle ear and cochlea was built by CT scanning and reverse engineering technique, and its reliability was also verified. On the basis of the model and by changing material properties of corresponding tissues, three typical middle ear diseases were simulated: hardening of stapedial annular ligaments, abnormal stapedial bone growth and hardening of anterior mallear ligaments. Then the response from displacement of basilar membrane (BM) was compared to analyze the impact of 3 types of middle ear diseases on sound compensation of RW stimulation. Results The stapes with abnormal bone growth severely deteriorated the equivalent sound pressure (ESP) of RW stimulation at higher frequencies, while the hardening of stapedial annular ligaments and the hardening of anterior malleus ligaments prominently decreased ESP of RW stimulation at lower frequencies. Among the 3 types of middle ear diseases, hardening of stapedial annular ligaments affected the sound compensation of RW stimulation more significantly with the amount of the ESP reduction up to 17 dB. Conclusions Middle ear diseases can deteriorate the sound compensation of RW stimulation seriously with large deterioration, Therefore, the output stimulation of the actuator should be targeted to improve the design of the middle ear implants by RW stimulation.

Abstract:Objective To observe the effect of paraformaldehyde fixation on viscoelastic properties of the vertebrae in rats, so as to find the best methods of preserving cancellous bone samples from the perspective of biomechanics. Methods Twenty 8-week-old healthy female Sprague-Dawley rats were selected, and their whole L4 and L5 vertebra were separated by surgery. The total 40 vertebrae were randomly and evenly divided into experimental group and control group. The experimental group was fixed with 4% paraformaldehyde for 72 h, and the control group was transferred to 5 mL EP tube and cryopreserved at -20 ℃. Ten vertebrae were randomly selected from each group for stress relaxation and creep experiments. After 7 200 s, the samples were collected and their micro-structure changes were analyzed by micro-CT. Results The relaxation creep curve of experimental group was smoother than that of control group, the time to reach steady state was shorter, and the total amount of relaxation creep at 500 s and 7 200 s was significantly decreased (P<0.01). Micro-CT results showed that relaxation and creep experiment could cause trabecular rupture, and trabecular damage was more severe in experimental group than that in control group. Conclusions Paraformaldehyde significantly reduce the viscoelasticity of rat vertebrae, and it is more easily to cause microstructure damage under mechanical stimulation, which is detrimental to cancellous bone preservation.

Abstract:Objective To measure the dynamic parameters of pushing manipulation with one-finger (PMOF), and provide the quantitative basis for evaluation and measurable criteria of PMOF. Methods A multi-film pressure measurement system was used to test and record the graphics of the operator when performing PMOF, and the data of corresponding parameters were recorded and analyzed. Results For PMOP, the maximum force was (11.75±0.88) N, the operation frequency was (111.7±6.98) times/ min, the cycle was (539±35.73) ms, the effective work ratio was greater than 0.28, and the waveform homogeneity was greater than 0.927. Conclusions The requirement of being permanent, forceful, homogeneity during PMOP can be objectively measured thorough graphics and quantitative indicators, but there is still a lack of quantitative indicators to measure and evaluate the requirement of being soft, deep and thorough for PMOF.

Abstract:Objective To study the effects on anterosuperior stability of the shoulder joint when the coracoacromial arch is damaged at different degrees. Methods Thirty-six specimens of the fresh frozen adult shoulder joints were randomly and evenly divided into 3 groups. Group 1, reserving integrity of the coracoacromial ligament of the shoulder joint; Group 2, dissecting half of the coracoacromial ligament attachment sector on the acromion; Group 3, grinding all the coracoacromial ligament attachment sector on the acromion. The specimens of the shoulder joint were fixed on test bench of the biomechanical testing machine. The axial pressure was applied on the humeral shaft, and the humeral head was pushed to move in anterosuperior direction. The displacement distance of the humeral head under 50 N pressure was then recorded. Results Under 50 N pressure, the displacement distance of the humeral head in Group 1, 2, 3 was (2.50±0.59), (5.38±0.71), (6.49±0.81) mm, respectively, which showed significantly statistic differences among 3 groups (P<0.05). Conclusions The damage to the coracoacromial arch will affect the anterosuperior stability of the shoulder joint. The greater damage to the coracoacromial arch will lead to the lower anterosuperior stability of the shoulder joint.

Abstract:Osteoporosis, a skeletal disorder of low bone density and disrupted bone architecture leading to fractures, is a common and costly condition among postmenopausal women. The biomechanical properties of bone are determined by the amount and quality of bone material and the arrangement of the material in space, mainly affected by the bone cortex, trabecular bone and collagen. When osteoporosis occurs, the cortex, trabecular bone and collagen all have the corresponding changes, which lead to the changes in biomechanical properties of bone. In this review, the changes of bone cortex, trabecular and collagen are summarized, to provide the comprehensive understanding about the changes of bone biomechanical properties in osteoporosis.