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Abstract:Objective To investigate the effect of unidirectional stretching on mechanical properties of different absorbable patches and evaluate its potential as a patch for rotator cuff repair. Methods The unidirectional stretching process was used to prepare absorbable patches with different polylactide based materials. Different unidirectional stretching temperatures (50-80 ℃) and stretching ratios (0.5-4.3) were set. The effects of different parameters on mechanical properties of the absorbable patches with different materials were studied. Their thermal properties, crystallization and surface morphology were characterized. Results The unidirectional stretching temperature and stretching ratio could adjust the tensile strength and strain, thermal property, crystalization and surface morphology of the absorbable patch. At directional stretching temperatures of 60, 70, 70 ℃ and stretching ratios of 3, 3, 4.3, respectively, the absorbable patches made of poly-L-lactide-co-glycolide (PLGA), poly-L-co-D, L-lactide (PLDLLA) and poly-L-lactide-co-ε-caprolactone (PLC) had the maximum tensile strength (74±7)，(97±6), (107±8) MPa, which were larger than the tensile strength for infraspinatus tendon of canine (40 MPa). However, only the strain of PLDLLA patch conformed to the flexibility of natural rotator cuff. Conclusions The unidirectional stretching process can improve mechanical properties of the absorbable patch. The absorbable patch made of PLDLLA has the potential to reinforce the rotator cuff tear.

Abstract:Objective To investigate the effect of microgravity on MC3T3-E1 osteoblast differentiation. Methods The differential miRNA and mRNA expression profiling of MC3T3-E1 cells during exposure to microgravity were established by RNA transcriptome sequencing technology (RNA-seq). The RNA sequencing results were validated using quantitative real-time polymerase chain reaction (q-PCR). Bioinformatic analyses were applied for further study of these differentially expressed miRNAs and mRNAs. Results Compared with control (CON) group, A total of 1 912 coding transcripts and 160 miRNAs were detected along with osteogenic differentiation in simulated microgravity (SMG) group. Bioinformatic analysis revealed 10 core regulatory genes including 7 mRNAs and 3 miRNAs. Based on the analysis and verification, one miRNA, miR-9_6666-5p, was identified, which might play an important role in osteogenic differentiation process under microgravity. Conclusions The process of osteoblast differentiation was repressed under microgravity which might be related to the changed expression profile of miRNA/mRNA. The research findings can contribute to the better understanding of the molecular mechanisms of mRNA and miRNAs in osteogenic differentiation and bone formation under the microgravity condition.

Abstract:Objective To investigate the effects of fluid shear stress on rolling adhesion of neutrophils on immobilized platelets under flows. Methods Experiments were performed at the parallel plate flow chamber. Platelets were adhered to the functionalized flow chamber bottom which were coated with vWF-A1 first, and then washed with PBS under wall shear stress (WSS) of 1 Pa for different time (0 min, 2.5 min, 7.5 min). A high-speed camera was used to observe and record the rolling adhesion events of neutrophils on immobilized platelets under 50 mPa WSS, and the adhesion parameters such as the number of adhesion events, the tether lifetime of cells and rolling velocity. Results Neutrophils could specifically bind to the immobilized platelets on vWF-A1-coated bottom of the flow chamber. Mechanical stimulation on immobilized platelets had no effects on the tether lifetime of neutrophils on the platelets, but up-regulated the adhesive ratio of neutrophils on the platelets and slowed down the rolling of neutrophils on the platelets. Conclusions Mechanical stimulation on the immobilized platelets will significantly make the circulating neutrophils to be captured easily and promote the rolling adhesion of neutrophils on platelets.

Abstract:Objective To investigate the effect of cyclic stretch on adhesion of vascular smooth muscle cells (VSMCs) with platelet-derived microparticles (PMPs), and the role of PMPs in VSMC autophagy. Methods Cyclic stretch with the magnitude of 5% (simulating physiological mechanical stretch) or 15% (simulating pathological mechanical stretch) was subjected to VSMCs in vitro by using FX-5000T cyclic stretch loading system, and the adhesion of PMPs in VSMCs was detected by using flow cytometry. Immunofluorescence was used to detect the expression of autophagy microtubule associated protein light chain 3 (LC3) after 24 h stimulation with PMPs. Western blotting was used to detect the expression of autophagy related protein (Atg) in VSMCs after 24 h stimulation by PMPs. Results Compared with 5% cyclic stretch, 15% cyclic stretch significantly increased the adhesion ability of VSMCs with PMPs. Immunofluorescence and Western blotting result revealed that PMPs stimulation significantly increased the expression of autophagy marker protein LC3 in VSMCs. Furthermore, the protein expressions of Atg5, Atg7 and Atg12 were all significantly increased in VSMCs stimulated with PMPs. Conclusions High cyclic stretch may enhance the autophagy of VSMCs by promoting the adhesion of PMPs, which will subsequently increase the expressions of Atg5, Atg7, Atg12 and LC3.

Abstract:Objective To study fluid flow within alveolar bone under orthodontic and occlusal loading, so as to provide references for understanding the regulatory mechanism of bone remodeling during orthodontics. Methods An animal model for orthodontic tooth movement on rats was first constructed. The finite element model of tooth-periodontal ligament-alveolar bone was established based on micro-CT images and the strain field in alveolar bone under orthodontic or constant occlusal loading was analyzed. Then finite element model of alveolar bone was constructed from the bone near the cervical margin or apical root of mesial root. The fluid flow in this model under orthodontic and cyclic occlusal loading was further predicted by using fluid-solid coupling numerical simulation. Results The fluid velocity within alveolar bone cavity mainly distributed at 0-10 μm/s, and the fluid shear stress (FSS) was mainly distributed at 0-10 Pa. FSS on the surface of alveolar bone near the apical root was higher than that close to the cervical margin. Conclusions FSS at different levels could be produced at different location within alveolar bone cavity under orthodontic and cyclic occlusal loading, which might further activate biological response of bone cells on the surface of trabeculae and finally regulate the remodeling of alveolar bone and orthodontic movement of tooth. The results provide theoretical guidance for the clinical treatment of orthodontics.

Abstract:Objective To analyze the biomechanical effects of gravity loading countermeasure garment on human lumbar intervertebral disc in microgravity environment. Methods Based on CT images of a healthy adult volunteer, the finite element model of L4-5 vertebrae was established. Through the empty load and 400 N axial loading for 4 hours on lumbar finite element model, the biomechanical effect of the non-intervention and gravity loading countermeasure garment were simulated respectively in microgravity environment. Results The central pore pressure, radial displacement and water content of the human lumbar intervertebral disc increased with time in microgravity environment. In the case of wearing gravity loading countermeasure garment, the central pore pressure, axial stress, radial displacement and water content of the lumbar intervertebral disc were reduced after 72 hours of cyclic loading compared with the non-intervention group. Conclusions Wearing gravity loading countermeasure garment can help astronauts to prevent the adverse effects of microgravity on the spine to some extent in microgravity environment.

Abstract:Department of Orthopedics, Yang Pu Hospital Affiliated to Tongji University,

Abstract:Objective To study the effect of stress on the degradation rate in vitro of novel magnesium alloy bone screw. Methods A three-dimensional （3D） model of the tibia fracture was established using the reverse engineering method. Then, based on the FE model, the in vitro degradation experimental device for bone screws was designed. The stress distribution of the screw by finite element calculation was used as the in vitro experimental load, which effectively improved the accuracy and efficiency of the experiment. The experimental samples were divided into four groups. Group A was treated as control group without force application, while Groups B, C and D were subjected to 150, 250 and 350 N axial forces. The influence of different mechanical environment on the degradation rate in vitro of bone screws was investigated. Finally, combining the stress distributions with the degradation experiment results in vitro, the curve between the stress and the degradation rate in vitro of novel magnesium alloy bone screws was obtained. Results Degradation experiments in vitro showed that Group A had the lowest weight loss and hydrogen production, and the average degradation rate was (0.315±0.005) mm/a. While in the stress groups, the weight loss and hydrogen production increased gradually with the axial force increasing. The average degradation rates of Groups B, C and D were (0.379±0.006), (0.469±0.007) and (0.547±0.009) mm/a, respectively. Conclusions When the novel magnesium alloy bone screw was degraded in mechanical environment, the greater stress on the screw would cause the faster degradation rate in vitro. The obtained relationship between the maximum stress and the average degradation rate in vitro of the novel megnesium alloy bone screw provided data support and theoretical guidance for material selection, design and clinical application of magnesium alloy bone screws.

Abstract:Objective To establish the precise finite element model of the head and neck based on human anatomical structure, so as to study neck injuries caused by rear impact at different speeds. Methods The model was based on CT scan images of the head and neck of human body. The Mimics software was used to reconstruct the three-dimensional (3D) bone, and the 3D solid ligaments, small joints and other tissues of the neck were improved and meshed by HyperMesh. The generated models included the head, 8 vertebrae (C1-T1), 6 intervertebral discs (annulus, nucleus pulposus and upper and lower cartilage endplates), facet joints (cartilage and joint capsule ligaments), ligaments, muscles, etc. Finally, the model verification and post-collision calculation were completed in the finite element post-processing software. Results The simulation results of the models under axial impact, front and back flexion and lateral flexion were compared with the experimental data to verify the effectiveness of the model. Then post-collision simulation at the speed of 20, 40, 60 and 80 km/h was conducted. At the speed of 20 km/h, there was no damage to the neck. At the speed of 40, 60 and 80 km/h, the ligament was the first to be damaged. As the speed increased, the stress on tissues of the neck increased continuously. At the speed of 80 km/h, the maximum stresses of the dense bone, cancellous bone and annulus of the cervical vertebrae were 226.4, 11.5, and 162.8 MPa, respectively. When the ligament strain reached the limit, tearing began to occur. Conclusions The finite element model of the head and neck established in this study has high bionics and effectiveness, and can be used for studying neck injury analysis in traffic accidents, which is helpful for the diagnosis, treatment and prevention of cervical spine injury to a certain extent.

Abstract:Objective To prepare biofilm scaffolds by using mesenteric acellular matrix, so as to investigate their physicochemical and biological characteristics. Methods The mesenteric tissues were subjected to trypsin digestion, and the mesenteric cells were removed after repeated freezing and thawing of mesenteric tissue. Mesenteries were divided into mesenteric matrix group (Group A) and acellular mesenteric matrix group (Group B). The physical and chemical properties of mesenteric matrix in two groups were tested by HE staining, electron microscopy, DNA detection, cytotoxicity test and tensile mechanics test. The blood flow of the vessels was detected by ultrasonography at 1st week, 1st month and 2nd month, and the vessels were observed by pathological examination. Results HE staining and electron microscopy showed that the mesentery of Group B was loose in acellular mesentery matrix, and the arrangement of fibers was neat, with no cells remaining. Compared with Group A, the expression level of DNA in Group B was lower, with more completely decellularized cells. CCK-8 cytotoxicity test showed that there was no cytotoxicity in Group A and Group B. FDA-PI fluorescence staining showed no cytotoxicity of cells in both groups. Cells in Croup A and Group B survived well, and no dead cells were found. Tensile mechanics test showed that there were no significant differences in maximum tensile force, maximum elongation, yield strength, yield point elongation between Group A and Group B. The early patency of acellular mesenteric stent implantation was good, and endothelial hyperplasia was obvious at 2nd month after stent implantation. Conclusion sMesenteric cells were removed by freeze-thaw and enzymatic digestion. Mesenteric stroma was completely removed without cytotoxicity, which showed good mechanical characteristics. Mesenteric stent implantation had good early patency and endothelial proliferation after 2 months.

Abstract:Objective To analyze stress distributions of alveolar bone around implants with different types of implant thread shapes and thread depths during dental immediate implantation, so as to provide references for the design and selection of implants. Methods The simplified model of mandible bone block, implants and mandibular molar were established by Geomagic Studio, SolidWorks and ANSYS Workbench, and vertical and oblique loads were applied on this model, respectively. Stress distributions on implants with different thread shape and thread depth as well as alveolar bone around implants were calculated. Results Under vertical loading, the peak stresses of implants, cortical bone and cancellous bone were in the range of 120.51-129.63 MPa, 9.94-13.25 MPa and 3.92-8.01 MPa, respectively. And the stress of cortical bone around V-shaped, rectangular, buttress or reverse buttress implant remained stable in the range of 0.40-0.45 mm thread depth. Under oblique loading, the peak stresses of implants, cortical bone and cancellous bone were in the range of 220.23-286.51 MPa, 33.39-45.08 MPa, 4.96-12.5 MPa, respectively. Among the models, V-shaped, buttress, reverse buttress implant with 0.45 mm thread depth showed the minimum stress. Conclusions The V-shaped, buttress or reverse buttress implant with a thread depth of 0.45 mm, or the rectangular implant with a thread depth of 0.40 mm had better biomechanical properties.

Abstract:Objective To investigate the influence of gravity levels on lower limb motions during human walking. Methods A suspended microgravity simulation system was designed for the experiment. Kinetic parameters from lower limb joints of twelve volunteers during walking were measured by the motion capture system and 3D force plate under simulated Mars gravity (1/3 G), lunar gravity (1/6 G) and earth gravity (1 G). Results Under simulated Mars and lunar gravity, the ranges of motion (ROMs) of hip and knee joints in sagittal plane significantly decreased (P＜0.01) while the ROMs of ankle joints obviously increased (P＜0.05). The ROMs of hip, knee and ankle joints in sagittal plane under earth gravity were 45.2°, 67.7°, 32.5°, respectively, while the ROMs of hip, knee and ankle joints under lunar gravity were 25.1°, 50.8°, 42.4°, respectively. In addition, the force and torque of lower limb joints in sagittal plane under lower gravity also decreased significantly (P＜0.01). Conclusions The results obtained by this study were almost the same as the research findings obtained by using treadmill. Astronauts can use the treadmill and microgravity simulation system for walking exercises under lunar gravity on the earth.

Abstract:Objective To obtain kinetic parameters of the plantar pressure in different age groups during normal walking, so as to provide theoretical references for designing insoles and sports shoes for different age groups, and maximally minimize the risk of foot injuries. Methods Footscan force plate was used to test the peak plantar force and pressure of 120 subjects in 4 different age groups (15 male and 15 female in 20-30, 30-40, 40-50, 50-60 age group, respectively). Results The peak plantar force constantly changed with age, showing a rising tendency, except that at the first phalanx area, the peak plantar force gradually decreased with age. For female subjects, the peak plantar pressure in the first phalanx area was gradually decreasing. Most subjects had significantly higher force on the 2nd and 4th bones than the 1st and 5th metatarsals. The 2nd metatarsal peak plantar force in male 50-60 age group was also significantly higher than that in male 20-50 age group (P<0.05). Only the peak plantar force of the 1st phalanx gradually decreased with age increasing, and the rest of the plantar region showed an increasing tendency. A significant change in the peak plantar pressure was observed, especially in the 2nd and 3rd metatarsals, which showed a rising tendency (P<0.05). Conclusions The plantar force and pressure on each part of human foot constantly changed with age. To find out the characteristics of plantar pressures in different age groups can help to design corresponding sports shoes and exert the functions of sports shoes in a better way.

Abstract:Lubricin is widely expressed in tissues in the musculoskeletal system, including articulate cartilage, tendon and synovium, which shows a close relationship with the structure and pathology of these tissues. Lubricin plays an important role in lubrication, anti-adhesion, proliferation inhibition and inflammation regulation, which may facilitate the healing of impaired tissues in the musculoskeletal system. This article reviews the research progress on expression and regulation of lubricin as well as its structure and function in wound repair of the musculoskeletal system, so as to provide theoretical evidences for further researches on the role of lubricin in the musculoskeletal system with its related mechanisms and the clinical application of lubricin.

Abstract:Vascular diseases including cardiovascular and cerebrovascular diseases and peripheral vascular diseases of the lower extremities are serious threats to human health. The emergence of compression therapy is of great significance for the effective prevention and treatment of these vascular diseases and the therapeutic value of compression therapy has been confirmed by many research results at present. Compression therapy is a non-invasive physical therapy implemented through a series of compression therapy devices, including external counterpulsation for the treatment of various ischemic diseases, intermittent pneumatic compression for the treatment of some peripheral vascular diseases in the lower extremities, graduated compression stockings for the treatment of deep vein thrombosis, and so on. This review summarizes clinical applications of these typical compression therapies in cardiovascular and cerebrovascular diseases and peripheral vascular diseases of the lower extremities, analyzes their advantages and limitations, and discusses the necessity and significance of biomechanical research on compression therapies.

Abstract:The research progress in fatigue protocols and biomechanics of lower extremity and its relationship with injury induced by exercise-induced fatigue was reviewed in this paper. At present, fatigue protocols can be divided into the traditional fatigue-induced protocol and the functional fatigue-induced protocol under laboratory condition. The former mainly includes power-cycling model, treadmill run model and step-ups model, while the latter is closer to what is experienced during competition, which is usually shown as multidirectional movements. In addition, the biomechanical measures of exercise-induced fatigue mainly include kinematics, ground reaction force, joint mechanics and electromyography. Different fatigue protocols do not uniformly produce alterations in lower limb biomechanical factors. The refinement of fatigue protocols and specific indicators should be considered in future studies, in order to compare the induced effects of fatigue protocols and provide references for the selection of fatigue protocols in laboratory tests. Meanwhile, the relationship between the response of brain-nerve system and the activation of musculoskeletal system for specific athletic task should be focused, so as to understand the difference of biomechanical mechanisms between fatigue protocols and further explore the effect of exercise-induced fatigue on sports injuries.