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Abstract:The mechanical microenvironment of cells plays a critical role in regulating the physiological function of cells. Cells in vivo are often subjected to a variety of mechanical forces from their mechanical micro-environment, such as shear, tension, and compression. At the same time, cells can adhere to the extracellular matrix (ECM) through adhesion molecules (such as integrin-ligand binding), and further sense the stiffness of the ECM. Cell mechanics mainly studies the properties and behavior of living cells under mechanical forces, and how they relate to cell functions. This review summarized the advances in cell mechanics in 2022, focusing on integrin-ligand interactions and the effects of matrix stiffness and mechanical forces on cell physiological behavior and morphogenesis.

Abstract:Objective To explore how hyaluronic acid ( HA) in extracellular matrix regulates the adhesion ofCD44+tumor cells. Methods MDA-MB-231 cells or HL60 cells were perfused in a parallel plate chamber. Themovement of cells over immobilized HA was observed and analyzed to obtain the characteristics of cell adhesionand rolling. Results The adhesion number of MDA-MB-231 cells on HA substrate was positively regulated by HAconcentration, but not by HA molecular weight. Compared with physically adsorbed HA, immobilized HA byavidin-biotin could significantly improve the cell adhesion ratio. With the increase of shear stress in the range of30-50 mPa, the rolling velocity of cells increased and the adhesion ratio decreased, but the tether lifetime of cellswas not affected. In the same flow field, compared with MDA-MB-231 cells, HL60 cells with low expression ofCD44 rolled more quickly on immobilized HA, with shorter tether lifetime and much lower adhesion ratio(<1. 5% ). Conclusions Fluid shear stress might mediate the rolling velocity of MDA-MB-231 cells by regulatingthe CD44-HA association rate rather than their dissociation rate. The interaction between CD44 and HA is involved in the initial adhesion of HL60 cells, but it does not play a major role. This study will provide references for the design of anti-tumor drugs.

Abstract:Objective To investigate the molecular mechanism of palmitoylation modification in regulating the activity of non-receptor tyrosine kinase Fyn. Methods The intracellular Fyn activity was detected by applying fluorescence resonance energy transfer (FRET) technology, and the mechanism was investigated by combining with Fyn palmitoylation deficiency and C-terminal Src kinase ( CSK ) plasmid co-expression. ResultsExperimental data showed that single loss of either of ( C3, C6) palmitoylation sites resulted in higher Fyn activity, and C6 seemed more significant. It is known that CSK membrane translocation occurred after activation. FRET assay confirmed that CSK could down-regulate the activity of Fyn in cells, but could not effectively regulate the activity of Fyn(GSS) with the loss of palmitoylation sites. Conclusions The results in this study support the hypothesis on Fyn regulation by spatial localization, namely, non-palmitoylated Fyn (GSS) is less effective in the inhibitory regulation by CSK on cell membrane, thus promoting constitutive high activity expression

Abstract:Objective To explore the cooperative effect from β-propensity of amyloidogenic peptides on amyloid nucleation and its related products. Methods Based on a coarse-grained model for amyloidogenic peptides containing two states ( a soluble state and a β-sheet-forming state), with the consideration of two kinds of cooperative effects on β-propensity of peptides ( inhibiting and promoting the conformational conversion of peptides), the regulation of cooperative effects from amyloidogenic peptides on amyloid nucleation was analyzed through Monte Carlo simulations. Results In the case of the cooperative effect inhibiting the conformational conversion of peptides, amyloid nucleation occurred only within a certain interval of the peptide concentration, as well as inside the oligomers with certain sizes. Besides, the coexistence of on-pathway and off-pathway oligomers was observed. In the case of the cooperative effect promoting the conformational conversion of peptides, the β-sheet protofibril could be observed at physiological concentration as low as 4 μmol / L. Conclusions In this study, a more realistic coarse-grained model for amyloidogenic peptides was developed by introducing the cooperative effects of local concentration on β-propensity of amyloidogenic peptides, with observation of some intriguing phenomena not reported in previous simulations. The research findings not only improve current understandings about the mechanism of amyloid formation, but also provide theoretic references for the therapeutic strategies for curing neurodegenerative diseases

Abstract:Objective To investigate the effects of different salt ion concentration, polyethylene glycol (PEG) and force on structure of double DNAs braids. Methods Taking the 10 kb DNA as the research object, the effects of different concentrations of salt ions(Na+, K+, Mg2+), PEG and different forces on variation of relative extension of twisted double DNAs with rotation turns were investigated by flow chamber experiment of magnetic tweezers. Results The structure of double DNAs braids was sensitive to salt ion concentration but insensitive to PEG. With the increase of ion concentration, the extension of braids changed more gently with the rotation turns, and the electrostatic shielding saturation concentration of Mg 2+ was much lower than that of the monovalent cation. The effect of crowded environment on DNA was mainly the compression of contour length. The twisted structure of DNA was more stable under high force (above 4 pN), and fluctuated greatly under low force (lower than 2 pN). Conclusions The braiding structure and mechanical properties of DNA are affected by ion concentration in the solution and forces. The results may help to elucidate the mechanism of chromatin torsional torque affected by solution environment, and provide references for the function of topoisomerase under different solution conditions.

Abstract:Objective To study stability of the deterministic tumor-immune system with time delay by means of linear stability analysis method. Methods In tumor-immune system, since it took some time for immune cells to recognize tumor cells and respond appropriately, time delay was considered in this process, then the model was simplified by using Taylor expansion of small delay, and the equilibrium points were solved out. By linear stability analysis method, the stability of these equilibrium points was studied. Finally, the trajectory of the system and that around each equilibrium point were simulated by numerical calculation method, so as to verify the result of theoretical analysis. Results The system had four meaningful equilibrium points with small delay, including a stable focus, a stable node, and two saddles. Moreover, the type and stability of these equilibrium points were not affected by the delay. Numerical simulation demonstrated the conclusion from theoretical analysis. Conclusions Under the condition of small delay, the type and stability of equilibrium points in the system are not affected by the delay. The results are helpful to further understand dynamic mechanisms of tumor immune response, and provide references for tumor growth and treatment

Abstract:Objective To investigate the effects of groove topography on morphology and migration speed of cervical cancer HeLa cells. Methods HeLa cells were cultured on PDMS substrates with four different surface features, namely, flat substrate, 10 μm width parallel groove, 20 μm width parallel groove, bifurcate groove. Immunofluorescence technique was used to transfect F-actin in HeLa cells, and specific probes Mito-Tracker Green were used to label mitochondria. The location, morphology of cells and distribution of mitochondrial at different moments were obtained through the living cell system. Results Compared with 20 μm width parallel groove and flat substrate, HeLa cells in 10 μm width parallel groove were more orderly arranged and more elongated, but their migration speed was much slower. HeLa cells at the bifurcation protruded into branches and mitochondria were mainly distributed at the protrusion and around the nucleus. The bifurcation reduced the average migration speed of HeLa cells in 10 μm width parallel groove. Conclusions Groove topography has a significant effect on morphology and migration speed of HeLa cells. The research findings help to understand the role of topography in in vivo microenvironment during migration of HeLa cells, and provide references for the subsequent research on invasion and metastasis of cervical cancers.

Abstract:Objective To explore the effects from the synergy of substrate stiffness and hypoxia on epithelialmesenchymal transition (EMT) of colon cancer cells SW480 by simulating the microenvironment of human colon cancer tissues. Methods Polyvinyl alcohol gels with different stiffness ( 4. 5, 20, 40 kPa) were prepared to simulate the stiffness of each part of colon cancer tissues. The morphological change of cells on substrate with different stiffness was detected under simulated hypoxia ( CoCl2 ) environment. The expression of hypoxiainducible factor (HIF-1α), and EMT markers E-cadherin, Vimentin, Snail 1 were detected by Western blot. The mRNA expression of E-cadherin, Vimentin, Snail 1, matrix metalloproteinase-2 ( MMP-2), and MMP-9 was detected by quantitative real-time PCR ( qRT-PCR). Results Under simulated hypoxia environment, with the increase of substrate stiffness, the SW480 cells spreading area increased, and transformed from round shape into irregular polygon. The EMT of SW480 could be enhanced through up-regulating expression of Vimentin, Snail 1, MMP-2, MMP-9, and down-regulating expression of E-cadherin. Conclusions This study is important for exploring the synergistic effect of substrate stiffness and hypoxia on the EMT of colon cancer cells as well as the molecular mechanism.

Abstract:Objective To explore the role of miR-199a-3p in osteoblast proliferation induced by fluid shear stress (FSS) and the potential molecular mechanism. Methods Osteoblast MC3T3-E1 was treated with 1. 2 Pa FSS with time gradients of 0, 15, 30, 45, 60, 75 and 90 min, respectively. MC3T3-E1 cells were transfected with miR-199a-3p mimic or miR-199a-3p inhibitor. MC3T3-E1 cells were transfected with miR-199a-3p mimic and itsnegative control and then treated with 1. 2 Pa FSS for 45 min. The pc DNA NC, pc DNA-CABLES -1, si RNA NC and si RNA CABLES-1 were transfected into MC3T3-E1 cells. The pc DNA-CABLES-1 and mir-199a-3p mimic and SI NA-cables-1 and miR-199a-3p inhibitor were co-transfected, respectively. Cell activity was detected by CCK-8 assay. Real-time quantitative PCR (RT-qPCR) was used to detect expression levels of CABLES-1, miR-199a-3p, CDK 6, Cyclin D1 and PCNA. Luciferase reporting assay was used to detect targeting relationship between CABLES-1 and miR-199a-3p. Immunofluorescence was used to detect protein expression of CABLES-1.Western blot was used to detect protein expression of CABLES-1, CDK 6, PCNA and Cyclin D1. Results Mir- 199a-3p in MC3T3-E1 cells was significantly down-regulated by FSS. Over-expressed miR-199a-3p inhibitedosteoblast proliferation, and down-regulated miR-199a-3p expression promoted osteoblast proliferation. miR-199a- 3p could reverse the FSS-induced proliferation in osteoblasts. Dual luciferase assay showed that miR-199a-3p targeted to CABLES-1 and over-expressed miR-199a-3p inhibited expression of CBALES-1 protein. CABLES-1 could promote proliferation of osteoblasts. miR-199a-3p inhibited osteoblast proliferation induced by FSS through CABLES-1. Conclusions FSS-induced osteoblast proliferation can be realized by down-regulated miR-199a-3p expression via targeting CABLES-1. The findings in this study provide new direction for researches on mechanism of FSS-induced osteoblast proliferation, as well as new ideas for future research on clinical application of mechanical loading in the treatment of bone and joint diseases.

Abstract:Objective Aiming at the problem of significant anisotropy in the three-dimensional ( 3D) printed polyether-ether-ketone ( PEEK) bone substitutes manufactured by material extrusion technology, taking the femur, the main load-bearing long bone of the lower limb, as an example, the biomechanical properties of the femoral model under different direction in the build chamber were evaluated by the combination of finite element analysis and in-vitro mechanical experiment. Methods A left femoral model was obtained by reconstruction from CT data. The stress and displacement of the 3D printed PEEK femur with different directions in the build chamber under five physiological postures in the human gait cycle were simulated by varying the orthogonal anisotropy mechanical properties. An in-vitro mechanical experiment was conducted to investigate the safety and stability of the femur through a 3D printed PEEK femur. Results When the long axis of the femur model was perpendicular to the building platform of the 3D printer, a better mechanical property was obtained, and the maximum von Mises stress was 46. 56 MPa, which was lower than the yield stress of PEEK, while the maximum displacement was larger than that of the natural femur under same loading condition. Therefore, the 3D printed PEEK femur met the strength requirement, but the stability needs to be improved. Conclusions The long axis is recommended to be perpendicular to the building platform when the material extrusion technology was used for the substitute of the load-bearing long bone, and the effect of its anisotropy on service performance of the substitute should be carefully considered when the 3D printing technology is used for load-bearing bone substitute.

Abstract:Objective To evaluate biomechanical properties of the nickel-titanium (NiTi) memory alloy stent and its in vitro biomechanical properties for lumbar interbody fusion. Methods The mechanical properties of the NiTi memory alloy stent were tested on mechanical testing machine. Moreover, lumbar interbody fusion was simulated on fresh lumbar specimens, and biomechanical properties of the NiTi memory alloy stent with matching bone graft for used for lumbar interbody fusion were analyzed and compared with the traditional box-shape cage. Results The maximum compressive strength of the NiTi memory alloy stent was ( 12 964 ± 962) N. The maximum deformation within the effective range of memory characteristics was (4. 68±0. 03) mm. The recovery rate of the NiTi memory alloy stent was up to 99. 86% . Compared with the intact lumbar model, the stability of the operative segment after the simulated lumbar interbody fusion using NiTi memory alloy stent alone was increased in the direction of anterior flexion, posterior extension, lateral flexion and rotation, which was equivalent to the boxshape cage group (P>0. 05). After the combined use of autogenous bone granule and absorbable bone cement the ROM of the operative segment was further reduced (P<0. 05), which was equivalent to the box-shape cage+ unilateral posterior fixation group (P>0. 05). The pull-out strength of the NiTi memory alloy stent with matching bone graft group was significantly stronger than that of the box-shape cage group (P<0. 05). Conclusions The NiTi memory alloy stent in this study was designed with a matched bone granule-absorbable bone cement graft,which provided a new idea for the further optimization and development of lumbar interbody fusion. With excellent support and deformation properties, this NiTi memory alloy stent is biomechanical equivalent to the traditional boxshape cage for lumbar interbody fusion, and can greatly improve the stability of surgical segment and the pull-out strength of implants after the combined use of autogenous bone granule and absorbable bone cement.

Abstract:Objective Aiming at the medial prosthetic loosening failure and lateral cartilage degeneration after unicompartmental knee arthroplasty ( UKA), the effects of prosthetic installation errors of joint line in UKA on knee contact mechanics and kinematics during different physiologic activities were studied using musculoskeletal multi-body dynamic method. Methods Taking the medial natural joint line as 0 mm error, six installation errors ofjoint line including ±2 mm, ±4 mm and ±6 mm were considered respectively, and seven musculoskeletal multibody dynamic models of medial UKA were established, to comparatively study the variations in knee contact mechanics and kinematics during walking and squatting. Results At 70% of walking gait cycle, compared with 0 mm error, the medial prosthetic contact force was increased by 127. 3% and the contact force of the lateral cartilage was decreased by 12. 0% under 2 mm elevation in joint line, the medial prosthetic contact force was close to 0 N, but the lateral cartilage contact forces were increased by 10. 1% under 4 mm reduction in joint line. The tibiofemoral total contact forces were increased by 19. 7% and decreased by 14. 2% under 2 mm elevation and 2 mm reduction in joint line, respectively. At the 100°knee flexion during squatting, compared with 0 mm error, the medial prosthetic contact force and the tibiofemoral total contact force increased by 31. 6% and 11. 1% under 2 mm elevation in joint line, and decreased by 24. 5% and 8. 5% under 2 mm reduction in joint line, respectively. The change in the lateral cartilage contact force was not marked. Moreover, at 70% of walking gait cycle, the varus angle decreased, the internal rotation and the anterior translation increased along with the elevation of joint line in UKA, while it was just the opposite along with the reduction of joint line in UKA. The trends of the varusvalgus movement and anterior-posterior translation during squatting were consistent with those during swing phase of walking, but the trend of the internal-external rotation was opposite. Conclusions In order to reduce the risk of medial prosthetic loosening failure and lateral cartilage degeneration, it is recommended that the installation error of joint line in UKA should be controlled in the range of -2 mm to +2 mm. This study provides theoretical basis for UKA clinical failure caused by changes in joint line

Abstract:Objective To compare biomechanical characteristics of external fixator, Kirschner’s wire, elastic stable intramedullary nailing (ESIN) for fixing proximal humeral fractures in children by finite element method.Methods The CT scanning data from the healthy humerus of an 8-year-old patient with proximal humeralfractures were collected, and the image data were imported in Mimics 21. 0 to establish the rough humeralmodel, which was imported in Geomagic 2013 to construct the three-dimensional (3D) model of cancellous and cortical bones of the humerus. After the model was assembled with 3 fixators ( external fixator, Kirschner’swire, ESIN), it was imported in ANSYS 2019 to simulate the upper limb under quiet, abduction, adduction, flexion, extension, external rotation, internal rotation working conditions. The maximum displacement of the distal humerus, the maximum stress of the fixture, and the maximum displacement of the distal fracture surface were analyzed. Results The minimum values of the maximum displacement of the distal humerus in models fixed by external fixator, Kirschner’s wire, ESIN appeared under extension (2. 406 mm), external rotation (0. 203 mm), external rotation (0. 185 mm) working conditions, respectively. Conclusions External fixator is the most unstable fixation of proximal humeral fractures in children, and the biomechanical performance of ESIN is better than that of external fixator and Kirschner’s wire fixation

Abstract:Objective To investigate the relationship between lesion size of solitary bone cyst ( SBC) and pathological fracture of calcaneus, so as to provide references for the treatment of SBC. Methods The threedimensional (3D) finite element model of foot and ankle was established based on CT images. Four models with gradient spherical bone defects were constructed in the focal area to simulate different SBC lesion sizes, and the biomechanical characteristics of calcaneus in different gait phases were analyzed. Results With the increasement of SBC size, the kinematics of calcaneus did not change significantly, but the peak stress of calcaneus increased gradually. When the SBC size exceeded 75% of the calcaneal width, the stress in calcaneal sulcus and cortical bone below SBC increased by 1. 48 times and 7. 74 times, respectively. Conclusions The risk of pathological fracture increases when the SBC diameter exceeds 75% of the calcaneal width, and early surgical intervention should be recommended. The calcaneal sulcus and the cortex bone below SBC are stress concentration regions and can be used as important areas to evaluate pathological fractures.

Abstract:Objective To analyze the plantar pressure distribution of knee osteoarthritis ( KOA) patients after medial opening wedge high tibial osteotomy ( MOWHTO), so as to provide biomechanical references for the surgical treatment and rehabilitation of patients. Methods A total of 31 patients with medial single compartmental KOA after unilateral MOWHTO treatment were selected as the experimental group, and 35 healthy subjects at same age were selected as the control group. The Pedomedic 40 ?? pressure measuring system was used to test dynamic plantar pressure. By comparing the maximum pressure ( pmax ), force-time integral ( FTI) and contact area (CA) of different plantar zones between the experimental group (operative side and unoperated side) and the control group during walking, the changes of plantar pressure in patients with medial single compartmental KOA after MOWHTO were evaluated. Results Compared with the unoperated side and the control group, the CA and FTI of the 1st metatarsal head (MH1) were higher (P<0. 05), the CA of the 4th metatarsal head (MH4)was smaller (P<0. 001), the pmax and FTI of the 5th metatarsal head (MH5) were smaller (P<0. 05), the CA of the lateral middle foot (MF-L) was smaller (P<0. 001), and the CA of the medial rear foot (RF-M) was larger (P<0. 05). Compared with the control group, the pmax of MH1 and MH2 was smaller (P<0. 05), the CA and FTI of MH5 were larger (P<0. 05), the pmax of MF-L was larger (P<0. 001), and the FTI of lateral rear foot (RF-L) was larger (P<0. 05). Conclusions Compared with healthy people, patients with medial single compartmental KOA have abnormal plantar pressure residual after MOWHTO. In clinical practice, targeted intensive rehabilitation therapy is necessary to restore the normal plantar distributions of patients.

Abstract:Objective To analyze the differences of von Mises stress distribution in knee cartilage and meniscus in female with generalised joint hypermobility (GJH) and healthy female during drop jump landing. Methods The kinematic and ground reaction force (GRF) characteristics of knee joint in female with GJH and healthy female at the moment of peak vertical GRF (VGRF) during loading phase of drop jump landing were collected. The knee joint reaction force was calculated via inverse dynamics, and the combined force of knee joint along long axis of the femur was applied as the load. Based on three-dimensional (3D) finite element model of a female knee joint, numerical simulations were performed separately during drop jump landing of subjects in two groups, and von Mises stresses and stress distribution of knee cartilage and meniscus were calculated. Results At the moment of peak VGRF during drop jump landing, knee flexion and valgus angles in GJH group and control group showed a statistical significance (P<0. 05). Compared with control group, knee flexion angle decreased and valgus angle increased in GJH group. During drop jump landing, GJH group bore larger stress inside the knee joint, and stress distribution in weight-bearing areas of the medial and lateral tibiofemoral compartments was uneven, while the lateral femoral cartilage lateral condyle, the anterior and middle lateral of lateral tibial cartilage, the anterior angle and body lateral margin of lateral meniscus were stress concentration sites. Conclusions For females with GJH, the stability of knee joint decreases and force lines change in jumping events, due to the increased range of motion of knee joint and relaxation of joint capsule, which increases the risk of cartilage and meniscal injury in lateral knee joint. During jumping sports, females with GJH should especially prevent knee joint injury caused by altered force lines in frontal plane of knee joint.

Abstract:Objective Aiming at the problems of lacking initiative in upper limb rehabilitation training equipment, single training mode, and low active participation of patients, an upper limb continuous motion estimation algorithm model based on multi-modal information fusion was proposed, so to realize accurate estimation of elbow joint torque. Methods Firstly, the surface electromyography (sEMG) signal and posture signal of participants were collected at four angular velocities, and the time domain characteristics of the signal were extracted. The principal component analysis was adopted to multi-feature fusion. The back propagation neural network (BPNN) was optimized through the additional momentum and the adaptive learning rate method. The particle swarm optimization (PSO) algorithm was used to optimize the neural network and a continuous motion estimation model based on PSO-BPNN was constructed. Finally, the joint torque calculated by the second type of Lagrangian equation was used as the accurate value to train the model. The performance of the model was compared with the traditional BP neural network model. Results The root mean square error (RMSE) of the traditional BP neural network model was 558.9 N·m, and the R2 coefficient was 77.19%, Whereas the RMSE and the R2 coefficient of the optimized model were 113.6 mN·m and 99.12%, respectively.Thereby, the accuracy of torque estimation was improved apparently. Conclusions The method for continuous motion estimation of the elbow joint proposed in this study can estimate the motion intention accurately, and provide a practical scheme for the active control of upper exoskeleton rehabilitation robot.

Abstract:Objective To study stress relaxation behaviors of cartilage scaffolds under different degradation cycles by using finite element analysis combined with theoretical models. Methods Based on the established degradation theoretical model, the elastic modulus of the scaffold was calculated under different degradation cycles. The finite element model of cartilage scaffolds was established and stress relaxation simulation was performed to analyze the variation of scaffold relaxation stress with time. The stress relaxation constitutive model was established to predict mechanical properties of the scaffold. Results The elastic modulus of cartilage scaffolds at 14 th, 28th, 42nd, 56th day after degradation was 32. 35, 31. 12, 29. 91, 28. 74 kPa, respectively. The upper layer for cartilage scaffolds was the largest. The overall relaxation stress of the scaffold decreased rapidly with time and then tended to be stable. At 8th week after degradation, the stress which the scaffold couldwithstand was still within the physiological load range of the cartilage. The predicted results of the stress relaxation constitutive model were in good agreement with the finite element simulation results. Conclusions The elastic modulus of the scaffold gradually decreases with the increase of degradation time. The longer the degradation period is, the less stress the scaffold can withstand. At the same degradation period, the larger the applied compressive strain, the larger the stress on the scaffold. Both the finite element simulation and stress relaxation constitutive model can effectively predict stress variations of cartilage scaffolds under degradation

Abstract:Objective To investigate tumor cell killing effect of superparamagnetic Fe3O4 nanoparticles with cubic phase through magneto-mechanical force under a low-frequency vibrating magnetic field ( VMF). Methods A kind of strong magnetic and irregular-shaped Fe3O4 nanoparticles with cubic phase was synthesized by coprecipitation method. The Fe3O4 nanoparticles were exposed to a self-developed VMF and cell killing efficiency of the Fe3O4-mediated magneto-mechanical force was investigated. Results VMF alone had no effects on cell viability. After Fe3O4 nanoparticles were added, the cell viability significantly decreased with prolonging the VMF treatment time and increasing the Fe3O4 nanoparticle concentration. Lactate dehydrogenase released by damaged cells also increased with prolonging the VMF exposure time. Conclusions The irregular-shaped Fe3O4 nanoparticles can transfer magneto-mechanical force to tumor cells under VMF, cause structural damage of cells and result in cell death. The VMF generator developed in this study has simple structure and it is safe for use and convenient for operation. The developed magnetic nanoparticles and the corresponding cancer cell killing technique have the potential for clinical transformation.

Abstract:Objective To investigate the effect of different optimization algorithms on accurate reconstruction of traffic accidents. Methods Non-dominated sorting genetic algorithm-II ( NSGA-II), neighborhood cultivation genetic algorithm (NCGA) and multi-objective particle swarm optimization (MOPSO) were used to optimize the multi-rigid body dynamic reconstruction of a real case. The effects of different optimization algorithms on convergence speed and optimal approximate solution were studied. The optimal initial impact parameters were simulated as boundary conditions of finite element method, and the simulated results were compared with the actual injuries. Results NCGA had a faster convergence speed and a better result in optimization process. The kinematic response of pedestrian vehicle collision reconstructed by the optimal approximate solution was consistent with the surveillance video. The prediction of craniocerebral injury was basically consistent with the cadaver examination. Conclusions The combination of optimization algorithm, rigid multibody and finite element method can complete the accurate reconstruction of traffic accidents and reduce the influence of human factors.

Abstract:Objective To investigate the influence of implant location and axial direction on stress distributions at the implant bone interface of maxillary central incisors with different alveolar fossa morphology by immediate implantation under immediate weight-bearing. Methods With reference to dental cone beam computed tomography (CBCT) image data from a healthy adult, the three-dimensional ( 3D) finite element models of maxillary central incisors with three types of alveolar fossa ( buccal, mediate, and palatal type) by immediate implatation under immediate weight-bearing were established. Different implant sites ( apical site, palatal / labial site) and axial directions (long axis of the tooth, long axis of the alveolar bone) were simulated. The established models were subjected to 100 N force at different angles (0°, 30°, 45°, 60°, 90°). The stresses in the alveolar bone around the implant were analyzed by the ANSYS software. Results Twelve 3D finite element models of maxillary central incisors with different alveolar fossa morphology by immediate implantation under immediate weight-bearing were successfully established. When alveolar fossa with buccal and mediate shape was applied with immediate implantation under immediate weight-bearing, it was easier to obtain good biomechanical properties of the implant-bone interface when implants were placed at palatal site along long axis of the alveolar bone. When alveolar fossa with palatal shape was applied with immediate implantation under immediate weightbearing, the equivalent stresses on peri-implant alveolar bone were much smaller than those on apical site, regardless of whether the implant was placed along long axis of the tooth or the long axis of the alveolar bone. Conclusions Different alveolar fossa morphology, implant location and axial direction will affect characteristics of implant-bone interface of maxillary central incisors with immediate implantation under immediate weight-bearing. In clinical practice, surgical planning on different axial direction and location of implantation should be developed for alveolar fossa with different morphology.

Abstract:Objective To explore hemodynamics of the aortic arch and supraarch vessels after thoracic endovascular aortic repair with fenestration and parallel grafts techniques, and compare the differences of these techniques. Methods Four patients with aortic arch lesions whose supraarch vessels were reconstructed by different surgical techniques (fenestration, chimney and periscope) were studied, and three-dimensional (3D) geometric models were established based on postoperative image data. The physiological flow obtained from twodimensional (2D) phase contrast magnetic resonance imaging were imposed on the ascending aorta inlet and the supraarch vessels outlets. The pressure waveform of 3-element Windkessel model was imposed on the descending aorta outlet. Through computational fluid dynamics ( CFD ) simulations, the hemodynamic parameters were obtained, including the pressure of supraarch vessels, the velocity vector of the stent inlet, and the relative residence time. Results The pressure change of the periscope stent was the largest, followed by the fenestration stent, and the pressure change of the chimney stent was the smallest. The velocity of the fenestration and periscope stent inlet was uneven, which might form vortex. The velocity of the chimney stent inlet was even. The high relative residence time concentrated in distal end of the fenestration stent outer wall, the ‘gutter’ part, and the place where the chimney and periscope stent adhered to the vessel wall. Conclusions The pressure difference between the inner and outer walls of the fenestration and periscope stent was high, so it was recommended to use the balloon-expandable stent. The pressure difference between the inner and outer walls of the chimney stent was low, so it was recommended to use the self-expanding stent. The predicted location of thrombosis was consistent with the clinical follow-up data, so it may be used for surgical planning and risk assessment of interventional treatment of aortic arch lesions.

Abstract:Objective A program-controlled flexible multi-point temperature measurement device was selfdeveloped for collection and analysis of skin temperature signals of diabetic patients and healthy subjects under resting and heating conditions so as to assess vasodilation function of the microcirculation, Methods With reference to the endothelial regulation spectrum of human body, wavelet analysis was performed on skin temperature signals, and the temperature fluctuation amplitudes in diabetic group and healthy control group were compared at different time periods after thermal stimulation. Results The temperature fluctuation amplitude in endothelial spectrum of diabetic group was smaller than that of healthy control group, and the decrease in skin temperature fluctuation after the power-off of thermal stimulation was remarkably smaller than that of control group, indicating that the response to thermal stimulation for diabetic patients was slower. Conclusions Vasodilation function can be quantitatively evaluated by using the fluctuation of skin temperature signals in endothelial spectrum band. Skin temperature monitoring is a potentially easy-implemented method for the health management and early diagnosis of microvascular diseases in diabetic patients.

Abstract:Objective To propose a new multi-joint series venipuncture system, explore the mechanics and kinematics-based related control problems involved in needle insertion and needle picking during the puncture process, and verify feasibility of this system. Methods A puncture manipulator was built, and needle displacement control algorithm was proposed by combing with the puncture mechanics model. The the forward kinematics was calculated by using DH method, so as to obtain the tip coordinates. Then the inverse kinematics was calculated by using the geometric method. The forward and inverse processes were closely connected. The position error of the end coordinates before and after needle picking was compared by using the method of kinematics positive solution-inverse solution-re-positive solution. Finally, experimental verification and simulation were conducted by combining with the physical object. Results Through simulation and experiments, accuracy of the theoretical model was verified. The needle insertion algorithm could be used to achieve success with only one needle insertion, which provided theoretical basis for the control of robot arm. The position error before and after needle picking could be controlled within 1 mm from the end trajectory. The end needle tip of robot arm was almost kept fixed during the needle picking process. Therefore, this needle picking scheme was feasible and could basically verify that the needle picking action of robot arm met the accuracy and safety requirements. Conclusions The venipuncture manipulator truly simulates the needle insertion and needle picking action during the puncture process, and can safely and accurately realize the needle insertion and needle picking action with needle tip as the fixed point, indicating that it has certain clinical value.

Abstract:Objective To analyze characteristics of motoneurons controlling the extension of a single finger in different individuals, and obtain the similarity and difference of micro-motoneurons characteristics in different individuals. Methods The motoneurons were decomposed by blind source separation algorithm. The twodimensional (2D) features of the neurons were quantified, and the fingers were classified by the features of the neurons decomposed by different individuals. In addition, the proportion of shared motor neurons was used to study characteristics of motoneurons innervating the coordinated movement of different fingers between individuals. Results There were significant differences in spatial distribution of motoneurons between the index finger and the middle finger for different individuals, but the activation area was similar. Using data from different people as training sets and testing sets, the average accuracy of finger classification was 86. 99% , and it was significantly improved to 90. 07% after using transfer component analysis (TCA) calibration. Through analysis on the proportion of shared neurons in different individuals, it was found that the proportion of shared neurons between index finger and other three fingers (middle finger, ring finger and little finger) was relatively low, while that between ring finger and little finger was high. Conclusions The spatial discharge characteristics of motoneurons controlling different fingers in different individuals are similar and have small individual differences. This study reveals the internal neural mechanism of different individuals during finger movement, and provides references for clinical neural mechanism analysis of patients with finger movement disorders and the related engineering applications

Abstract:Objective A 2-PSU/ RR parallel ankle rehabilitation robot was designed, and the biomechanical properties of human muscles were also analyzed, so as to study rehabilitation strategy of the ankle rehabilitation robot. Methods The actual workspace of the robot was obtained by numerical discrete search method, and the effect of structural parameter changes on the height of robot moving platform was explored. Then the human biomechanical responses such as muscle force and muscle mobility were obtained by human biomechanical simulation software AnyBody, so as to investigate the effect of moving platform height changes on muscle behavior. Results The robot could meet the demand of ankle plantarflexion/ dorsiflexion and inversion/ eversion motion. Appropriately increasing the initial inclination angle and decreasing the length of the fixed-length bar enabled the ankle rehabilitation robot to have a lower overall height. The height of the moving platform was decreased by 10 mm in turn, and the muscle force and muscle activity of the human body involved in the movement were decreased to a certain extent. Conclusions This study provides a new design solution for ankle rehabilitation, offers theoretical guidance for motion analysis of the ankle rehabilitation robot, and accelerates rehabilitation of the patients’ ankles by modifying the mechanism parameters.

Abstract:The rotator cuff is an important structure to maintain movement and dynamic stability of the shoulder joint. Rotator cuff injury changes its unique biomechanical effects, resulting in shoulder pain and mobility disorders. Although great progress has been made in suture technology and fixation method, the rate of postoperative retear is still very high. Understanding the biomechanical mechanism of normal rotator cuff and restoring the special biomechanical effect of rotator cuff after injury are the key to prevent postoperative retear. This article reviewed biomechanical researches on rotator cuff repair in recent years, in order to provide some theoretical guidance for clinical operation.

Abstract:Mechanical stimulation in micro-environment ( such as matrix stiffness, surface topography, cyclical stretch) can be perceived by macrophages through receptors on cell membrane, transmitted to the nucleus along the adhesion protein molecular chain and cytoskeleton, and also converted into biochemical signal to stimulate gene transcription. Mechanical stimulation drives various biological functions in macrophages, such as adhesion, proliferation, migration, and polarization, thereby playing a corresponding role in disease progression and tissue regeneration. This study demonstrates the role of micro-environment mechanics in macrophages polarization and function, and elucidates the related mechanism of mechanotransduction pathway in macrophages, so as to provide molecular biomechanics insights into the development of macrophage-targeting immunomodulatory biomaterials.