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Abstract:Animal model is an indispensable part of studying the pathogenesis and treatment of diseases. Review of the ethics and welfare is the necessary measure to ensure the quality of scientific research and promote the scientific and rational use of experimental animals. In the review practice, it is found that most applicants are difficult to accurately understand the items listed in the application form and ethical principles related to items. Therefore, a practical and feasible set of ethical guidelines for animal experiments is necessary. This review focuses on the legal and ethical basis of developing oral disease animal models, and divides the methods of establishing oral disease animal models into physical methods, chemical methods, biological methods, and combined methods, and details the key points of ethical and welfare review and model evaluation methods. Hopefully, ethical censors and project applicants may get more understanding of ethical review for disease animal models, and ultimately improve the standardization and applicability of laboratory animal models.

Abstract:The cardiovascular system is a mechanical system with the heart as the center and blood vessels as the network. Mechanical forces play a direct and key role in regulating the physiological state and pathological process of the cardiovascular system. Cardiovascular diseases such as coronary heart disease, hypertension and stroke have similar pathological basis, that is, vascular remodeling caused by vascular dysfunction and abnormal damage. Therefore, investigating how mechanical forces produce biological effects that lead to vascular remodeling, and elucidating cardiovascular mechanical signal transduction pathways and mechanical regulation pathways are of great research significance for in-depth understanding of the nature of cardiovascular disease occurrence. In this review, different mechanical forces and key mechanical response molecules were used as clues, and the latest research progress of vascular mechanobiology in 2023 was summarized. These results provide new ideas for further exploring the role of mechanical factors in the pathogenesis of cardiovascular diseases, and providing markers and potential targets for early diagnosis of the disease.

Abstract:Vascular biomechanics mainly explores how vascular cells perceive mechanical stimuli, how mechanics affects the development of diseases, and the exploitation of various mathematical models to analyze the effects of mechanical factors on diseases. In recent years, researches in the field of vascular biomechanics are developing rapidly, and various research teams have analyzed the mechanical and biological processes of blood vessels from different directions, in order to gain a deeper understanding of the regulatory mechanisms of vascular biomechanical factors affecting the progression of various vascular diseases, and provide a theoretical basis based on the mechanobiology for the prevention and treatment of cardiovascular and cerebrovascular diseases. This article summarizes and discusses the recent research hotspots and emerging trends in the field of vascular mechanobiology based on domestic and foreign expert teams and combined with our team's research work, thus providing a systematic framework for grasping hotspots and exploring new research directions in the field of vascular mechanobiology.

Abstract:Objective To study the hemodynamic effects of enhanced external counter pulsation (EECP) on typical coronary artery disease and microcirculation angina. Methods A physiological model of the right dominant coronary artery, including the coronary conduit arteries and coronary microcirculation, was established using lumped parameter models. Pathological conditions, such as one-vessel lesions, three-vessel lesions, and microcirculation angina, were simulated. EECP intervention models were established, and the hemodynamic effects of EECP on pathological models was simulated. Results The simulation results of the coronary physiological model, pathological models, and EECP intervention model established in this study were consistent with experimental data in related literature. EECP improved coronary blood flow in all three pathological conditions. For one-vessel lesions, EECP could not recover the blood flow of left main coronary artery to a normal level after the stenosis rate reached 80–85%. For three-vessel lesions, EECP treatment could not be used if the stenosis rate in one of the three vessels exceeded 90%. For microcirculation angina, EECP was effective when critical condition myocardial blood flow was >1.03 mL/min·g and coronary flow reserve was >1.64. Conclusions The model of coronary disease under EECP interference established in this study meets expectations, and the obtained simulation data have certain reference values for the clinical application of EECP.

Abstract:Objective To investigate the hemodynamic effects of enhanced external counterpulsation (EECP) on cerebral arteries with different stenoses. Methods Zero-dimensional/three-dimensional multiscale hemodynamic models of cerebral arteries with different stenoses were constructed. Numerical simulations of the EECP hemodynamics were performed under different counterpulsation modes to quantify several hemodynamic indicators of the cerebral arteries. Among them, the mean time-averaged wall shear stress (TAWSS) downstream of the stenosis was in the range of 4–7 Pa, a low percentage of risk TAWSS area, and high narrow branch flow were considered to inhibit the development of atherosclerosis and create a good hemodynamic environment. Results For cerebral arteries with 50%, 60%, 70%, and 80% stenosis, the hemodynamic environment was optimal in counterpulsation mode when the moment of cuff deflation was 0.5, 0.6, 0.7, and 0.7 s within the cardiac cycle. Conclusions For 50% stenotic cerebral arteries, the counterpulsation mode with a deflation moment of 0.5 s should be selected. For 60% stenotic cerebral arteries, the counterpulsation mode with a deflation moment of 0.6 s should be selected. For 70 or 80% stenotic cerebral arteries, the counterpulsation mode with a deflation moment of 0.7 s should be selected. As stenosis of the cerebral arteries increases, the pressure duration should be prolonged. This study provides a theoretical reference for the EECP treatment strategy for patients with ischemic stroke with different stenoses.

Abstract:Objective To explore the dynamic process of fluid-structure interaction (FSI) between venous blood and valves and the physiological mechanism that guarantees unidirectional blood reflux back to the heart. Methods A three-dimensional (3D) numerical model of the venous system was established using the immersed boundary/finite element method. In the simulation, information from medical images of human lower-extremity veins and the anatomical structure and size of the bovine great saphenous vein were applied. Moreover, a hyperelastic constitutive model was used to describe the incompressible, nonlinear, and hyperelastic mechanical responses of the venous valve under physiological conditions. Results The simulations visualized the process of venous blood transport and the function of venous valves in preventing reflux. The periodic characteristics of venous valve motion and blood flow were reproduced, and important physiological data during the entire cardiac cycle were discussed and quantified, including the pressure, velocity, and flow rate of venous blood; opening area of the venous valve; and stress and strain distributions on the valve surface. Conclusions The 3D FSI model numerically reproduces the physiological dynamic process within veins and potentially provides important references and guidance for revealing the pathological mechanism of venous diseases.

Abstract:Objective To investigate the effects of force on mechanical stability of FLNa-Ig21/αIIbβ3-CT complex and the regulation mechanism. Methods The FLNa-Ig21/αIIbβ3-CT crystal structures were taken from the PDB database. The stability of the complexes in a physiological environment as well as the unfolding path and mechanical stability induced by mechanical forces were analyzed using equilibrium and steered molecular dynamics simulations. Results During the equilibration, the survival rate of most salt bridge and hydrogen bonds was below 0.5, and the interactions between FLNa-Ig21 and αIIbβ3-CT was relatively weak. During stretching at a constant velocity, the complex could withstand a tensile force of 70–380 pN, and its mechanical strength depended on the force-induced dissociation path. Under a constant force of 0–60 pN, the complexes exhibited a slipping-bond trend, and the force increase facilitated the breakage of the R995-D723 salt bridge and the activation of αIIbβ3 integrin. Conclusions The force-induced allostery of αIIbβ3-MP enhanced the complex mechanical strength and delayed FLNa-Ig21 dissociation from αIIbβ3-CT. After the 20 pN threshold was exceeded, tensile force positively regulated the activation of αIIbβ3 integrin. These results provide references for further revealing the molecular mechanism of IIbβ3 integrin activation and related targeted drug development.

Abstract:Objective To study the compressive mechanical properties and constitutive models of brain tissue at different strain rates. Methods Quasi-static and medium-velocity compression tests were carried out on the white and gray matter of pig brain tissue using an electronic universal testing machine, and stress-strain curves of pig brain tissue at different strain rates were obtained. The Ogden constitutive model was used to fit the test curve, the parameters of the constitutive model were determined, and the simulation was verified using finite element software. Results The brain tissue stress-strain curves showed nonlinear characteristics, with a strong strain rate correlation and sensitivity. When tissues were compressed to 0.6 strain, the stress of white and gray matter increased by 102% and 129%, respectively, at a strain rate of 5×10-4–5×10-2 s-1, and by 50.7% and 54.6%, respectively, at a strain rate of 1–1.5 s-1. At a strain rate of 1.5 s-1, the stress in the white and gray matter increased by 347% and 413%, respectively, compared with that at 5×10-4 s-1 strain rate. The R2 value of the Ogden model was greater than 0.99, and the error between the simulation and experimental results was within 15%, thereby verifying the validity of the model. Conclusions This study is helpful for the prediction of brain tissue deformation and provides an accurate scientific theoretical basis for the establishment of scientific and reasonable human simulation targets as well as the design and improvement of brain-protective equipment.

Abstract:Objective To predict the tissue-level failure strain of the cortical bone and discuss the effects of different running speeds on the mechanical properties of rat femoral cortical bone. Methods The threshold for cortical bone tissue-level failure strain was assigned, and fracture simulation under three-point bending was performed on a rat femoral finite element model. The predicted load-displacement curves in each simulation were compared and fitted with the experimental data to back-calculate the tissue-level failure strain. Results The cortical bone tissue-level failure strains at different running speeds were statistically different, which indicated that different running speeds had certain impacts on the micromechanical properties of the cortical bone structures. At a running speed of 12 m/min, the cortical bone structure expressed the greatest tissue-level failure strain, and at a running speed of 20 m/min, the cortical bone structure expressed the lowest tissue-level failure strain. Conclusions Based on the changing trends of tissue-level failure strain and in combination with the changes in macro-level failure load and tissue-level elastic modulus of cortical bone structures, the effects of different running speeds on the mechanical properties of cortical bone structures were discussed in this study. The appropriate running speed for improving the mechanical properties of the cortical bone was explored, thereby providing a theoretical basis for improving bone strength through running exercises.

Abstract:Objective To investigate the influence of different cell structures on the static and dynamic mechanical performance of porous titanium alloy scaffolds, and to provide a theoretical mechanical basis for the application of scaffolds in the repair of mandibular bone defects. Methods Porous titanium alloy scaffolds with diamond, cubic, and cross-sectional cubic cell structures were manufactured using three-dimensional printing technology. Uniaxial compression tests and ratcheting fatigue with compression load tests were conducted to analyze the static and dynamic mechanical performances of scaffolds with different cell structures. Results The elastic moduli of the diamond cell, cross-sectional cubic cell, and cubic cell scaffolds were 1.17, 0.566, and 0.322 GPa, respectively, and the yield strengths were 71.8, 65.1, and 31.8 MPa, respectively. After reaching the stable stage, the ratcheting strains of the cross-sectional cubic, diamond, and cubic cell scaffolds were 3.3%, 4.0%, and 4.5%, respectively. The ratcheting strain increased with increasing average stress, stress amplitude, and peak holding time, and decreased with increasing loading rate. Conclusions The evaluation results of the static mechanical performance showed that the diamond cell scaffold was the best, followed by the cross-sectional cubic cell scaffold and the cubic cell scaffold. The evaluation results of the dynamic mechanical performance showed that the cross-sectional cubic cell scaffold performed the best, followed by the diamond cell scaffold, whereas the cubic cell scaffold performed the worst. The fatigue performance of the scaffold is affected by the loading conditions. These results provide new insights for scaffold construction for the repair of mandibular bone defects and provide an experimental basis for further clinical applications of this scaffold technology.

Abstract:Objective To study the mechanical properties of titanium mesh and three-dimensional (3D)-printed metal vertebral body substitutes (VBS) to provide guidance for the selection and structural optimization of artificial vertebral implants in clinical practice. Methods The equivalent elastic modulus, equivalent yield strength, and structural failure mode of titanium mesh and 3D-printed porous, truss, and topologically optimized VBS were systematically investigated using compression tests. Results The elastic modulus of the titanium mesh (2 908.73 ± 287.39 MPa) was only lower than that of the topologically optimized VBS. However, their structural strengths and stabilities were inadequate. The yield strength of the titanium mesh (46.61 ± 4.85 MPa) was only higher than that of the porous VBS and it was the first to yield during compression. The porous VBS was insufficient for use as the vertebral implant owing to its poor mechanical strength (18.14 ± 0.17 MPa–25.79 ± 0.40 MPa). The truss VBS had good elastic modulus (2 477.86 ± 55.19 MPa–2 620.08 ± 194.36 MPa) and strength (77.61 ± 0.50 MPa–88.42 ± 1.07 MPa). However, the structural stability of the truss VBS was insufficient, and instability occurred easily during compression. The topologically optimized VBS had the highest elastic modulus (3 746.28 ± 183.80 MPa) and yield strength (177.43 ± 3.82 MPa) among all the tested VBS types, which could provide improved security and stability for artificial vertebral implant in vivo services. Conclusions Topology optimization results in a high strength and high stability VBS design. Moreover, it provides a large design space and great safety margin to provide increased possibilities for lightweight and new material design of future artificial vertebral implants.

Abstract:Objective To study the corrosion-fatigue properties of a novel low modulus Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloy subjected to simulated body fluid (SBF). Methods Ti-6Al-4V (TC4) alloy was used as the control group. The electrochemical corrosion polarization curves of the two titanium alloys were measured in SBF. The pre-corroded TC4 and TLM titanium alloy samples were subjected to rotational bending fatigue tests. The loading stress amplitude and fatigue fracture cycle relationship was established using the experimental data, and the stress life curves were drawn. Subsequently, the fracture mechanism was analyzed by analyzing the corrosion fatigue micro-fracture morphology of the sample, and fatigue analysis on the titanium alloy sample was then conducted combined with the finite element software. Results The self-corrosion potential of the TC4 titanium alloy under stress annealing was lower than that of the TLM titanium alloy after heat treatment. The TLM titanium alloy was most sensitive to changes in cyclic stress. A comparison between the simulation and experimental results showed that the TC4 titanium alloy under stress annealing had a higher fatigue strength and stronger resistance to crack propagation than the TLM titanium alloy did after heat treatment, whereas its corrosion resistance was the opposite. Compared to the specimens without pre-corrosion treatment, the brittleness of the TLM titanium alloy increased, and its fatigue performance decreased after pre-immersion in SBF. Conclusions Through comparative analysis, the reliability of the test results proved to be high, and the COMSOL finite element software could effectively predict the fatigue life of titanium alloy materials.

Abstract:Objective A?novel?variable-diameter cortical threaded screw used?in a modified cortical bone?trajectory?(MCBT)?was?designed to verify?its mechanical properties using the MCBT technique. Methods According?to?MCBT?technology,?the?screw?pitch?was fixed?at 2 mm, the total length was 45 mm, the diameter of the thick rod was 5.5 mm,?the diameter?of?the?thin?rod was?4.0–4.5 mm,?and?the?length?of?variable-diameter position connecting the?thick?rod?and?the?thin?rod?was?2 mm. The parameters?were?set based on three?aspects: variable-diameter position,?thread?depth, and?thread?type. Three-factor?and?three-level?L9?tests were conducted and??screw?models?were established.?The?torsion and the bending?and pull-out force?of?the?designed screws?were?calculated?based on?the?finite?element?method,?the?results?were analyzed using range analysis,?and?then?the?screw?models?were?determined. The three-dimensional (3D)?model?of?L4?vertebral?body?in?osteoporosis?specimens?was?established?and?screws were?placed?according?to?the MCBT?technique.?The pull-out force of the novel variable-diameter cortical threaded screw was compared with that of a conventional non-variable-diameter cortical threaded screw. Results?Range?analysis showed that screw?No.6?(variable-diameter position:?24 mm?from?the?screw?head,?thread?depth:?0.7 mm,?45° symmetrical?thread)?was the?optimal?screw. The anti-pull-out force of the No.6?variable-diameter cortical threaded screw?was?13.1%?higher?than that?of?the 4.5 mm?conventional?non-variable-diameter?cortical?threaded screw,?and?no statistical?difference in anti-pull-out force was found between?the No.6 variable-diameter cortical threaded screw and the 5.5 mm?conventional?non-variable-diameter cortical threaded screw. Conclusions The variable-diameter position has the smallest influence?on pull-out?force?of?the?screw,?the?thread?type?has?the?largest?influence?on?pull-out?force, and?the?thread depth has?the largest influence?on?torsion?and?bending.?Compared with that of?the conventional non-variable-diameter cortical?threaded screw,?the?variable-diameter cortical?threaded screw had a?smaller?front?end,?which?prevented?splitting?at the entrance point?of the screw.?The?screw?has?a large?diameter at rear?end, thereby showing?improved?pull-out?performance. The?results?provide?a new theoretical?basis?for?the?clinical?application?of?MCBT?technology.

Abstract:Objective For patient-specific open-wedge high tibial osteotomy (OWHTO), a novel anatomical fixation plate was designed, and the effects of geometric parameters and material selection on biomechanical fixation were studied. Methods A patient-specific OWHTO anatomical fixation plate was designed and constructed, and the effects of design parameters (thickness, width, and length of the fixation plate) and four different materials (stainless steel, titanium alloy, magnesium alloy, and PEEK) on the biomechanics of the OWHTO fixation system were studied using finite element analysis. The biomechanical differences between the anatomical fixation plate and TomoFix fixation plate were also compared. Results The thickness had a greater effect on the micromotion of the osteotomy space than the length and width of the fixation plate did. Titanium alloy or magnesium alloy fixation plates were more conducive than stainless steel and PEEK materials in obtaining reasonable stability and mechanical transfer simultaneously. Compared with that of the TomoFix plate, the maximum von Mises stress of the anatomical fixation plate was reduced by 13.5%; the maximum von Mises stress of the screws and tibia was increased by 9.8% and 18.4%, respectively; and the micromotion at the maximum osteotomy space cc was increased by 49.3%. Conclusions Anatomical fixation plates have a positive effect on reducing the stress-shielding effect and improving biomechanical properties under the premise of ensuring stability. This study provides a reference for the development of OWHTO anatomical fixation plates.

Abstract:Objective To calculate the nonlinear features of motion in patients with chronic vestibular syndrome (CVS) using the largest Lyapunov exponent (LLE), and to verify the classification model’s validity through machine learning algorithms. Methods A three-dimensional (3D) motion capture system was used to capture the joint motion trajectories of the subjects, which were determined using the LLE. The features of the chaotic trajectories were calculated as the input, and seven classifiers, namely the ID3 decision tree, Adaboost, C45 decision tree, Bayesian classification, Naive Bayes, and support vector machine, were used for classification. Results A total of 17 sets of trajectories from 16 joints were in the chaotic state, and the average energy, enhanced wavelength, and kurtosis of the motion trajectories in the experimental group showed significant differences (P < 0.05). The ID3 decision tree classifier showed optimal performance with 100% prediction accuracy, recall, and F1-score. Conclusions Chaotic features may contain high personality differences in patients with CVS and can improve the accuracy of machine learning algorithms for recognition. These findings provide a reference for early identification and motor rehabilitation of patients with CVS.

Abstract:Objective The biomechanical model for the musculoskeletal system of a human knee joint was established using a numerical simulation method. The kinematic and dynamic information captured during jumping motion simulated by the human dynamic model was used as driven data of the knee biomechanical model, followed by further analysis of the stress field distribution characteristics of the meniscus under different thermal-force coupling knee brace conditions. Methods Based on computed tomography and magnetic resonance imaging of the subject, a realistic human knee model, including bone, articular cartilage, meniscus, ligaments and peripheral soft tissues of the knee joint, was constructed. Furthermore, two gaits, namely taking-off and landing-on, of jumping motion with an increased risk of meniscus injuries were selected according to mechanical features in full-cycle jumping motion. Subsequently, the stress field characteristics of the knee meniscus under four different thermal-force coupling knee braces were analyzed, the changes of the peak stress of the meniscus and its stress concentration area were discussed, and the protective efficacy and mechanical basis of meniscal injuries and wearing knee braces were explored. Results The anterior part of the medial knee meniscus was a vulnerable area under concentrated stress. Under the knee brace thermal-force coupling condition, the stress concentration area of the medial meniscus was transferred from its narrow and weak anterior part to its wide and thick middle part, and the peak stress was also significantly reduced. The peak stress on the medial meniscus and that on the lateral meniscus were similar, indicating that the two parts of the meniscus bore the external load evenly, and the meniscus stress concentration area decreased. Conclusions Thermal-force coupling knee braces have good protective effects against knee meniscus injury. The numerical simulation provides theoretical support and technical guidance for the design of multifunctional thermal knee braces.

Abstract:Objective To investigate the effect of trunk control on the biomechanical characteristics of lower-extremity movements during Asian squats (AS) and Western squats (WS) in young adults to provide empirical support for the application and promotion of deep squat training. Methods Twenty-four healthy young male collegiate students performed AS and WS with and without bar control, and their lower-extremity kinematic and kinetic characteristics were collected using an infrared light-point motion capture system and a three-dimensional (3D) dynamometer. The 3D angles of the lower extremities were obtained using Cortex-642.6.2 software, based on the calculation of Euler angles, and the 3D moments were obtained by applying the inverse dynamics method. The effects of trunk control and deep squatting posture on the lower-extremity kinematic characteristics were examined using a two-factor analysis of variance with a 2 × 2 repeated design. Results There was no significant interaction between trunk control and the deep squatting posture for either kinematic or kinetic parameters (P > 0.05). The WS group had a large knee flexion angle, peak patellofemoral contact force, and ratio of peak hip and knee extension moments, and small ankle dorsiflexion and hip flexion angles (P<0.05). The deep squat with a bar had a large ankle dorsiflexion angle, peak patellofemoral contact force, and hip flexion angle as well as a small knee flexion angle and ratio of peak hip and knee extension moments (P<0.05). Conclusions WS is helpful for training hip extension muscle groups, whereas AS is helpful for training knee extension muscle strength. The peak patellofemoral joint contact force of the WS is significantly greater than that of the AS; therefore, it is recommended that patients with patellofemoral joint pain use the AS. A squat with a bar can compensate for the body’s balance; thus, people with limited ankle dorsiflexion range of motion or anterior tibial muscle weakness may consider trunk control training, such as a deep squat with a bar. This may help improve lower-extremity stability during squats.

Abstract:Objective To investigate the effects of different foot-strike patterns during running on Achilles tendon (AT) morphology and mechanical loading. Methods Fourteen habitual rearfoot strike runners and 14 habitual forefoot strike runners were recruited. Morphological characteristics (tendon length, cross-sectional area, and thickness) of the AT were collected using ultrasound imaging. The AT loading characteristics (plantar flexion moment, tendon force, load rate, impulse, and stress) of subjects wearing cushioned running shoes while running at a speed of 10 km/h were collected and calculated using a three-dimensional force measurement treadmill. Results Compared to habitual rearfoot strike runners, habitual forefoot strike runners showed a significant increase in peak plantar flexion moment of ankle joint, AT peak force, average loading rate, and peak loading rate (P < 0.05). However, the differences in AT length, cross-sectional area, and thickness between the two groups were not statistically significant (P>0.05). Conclusions Long-term forefoot strike patterns can adaptively enhance the mechanical loading characteristics of the AT during repetitive stretch-shortening cycles.

Abstract:Objective Taking Chinese college students as the target group, this study detected the distribution of plantar pressure in different gait groups and analyzed the distribution characteristics of plantar pressure in in-toeing gait populations, to provide references for their orthopedic rehabilitation. Methods Ten subjects with typical in-toeing and normal and out-toeing gaits were selected to participate in the plantar pressure testing experiment. The maximum force, pressure, and contact time during natural standing and during one walking gait cycle were measured using a Zebris foot plantar pressure measurement system. Gait parameters, including step length, step width, step speed, step direction angle, gait center line, and force change curves, were collected, and a hazard analysis was conducted. Results During natural standing, the swaying interval area of the center of pressure was 939.0 252.4 mm2 for the in-toeing gait group and 1 120.2 101.6 mm2 for the out-toeing gait group, which was larger than that for the normal group (240.7 130.6 mm2). The in-toeing gait further weakens the human body’s ability to maintain stability. The dynamic and static plantar pressures in the three gait groups exhibited different distribution characteristics. During static standing, the pressure center of the in-toeing gait group shifted to the hindfoot, which accounted for 70% of the plantar pressure and was higher than that of the normal group. During dynamic walking, the absolute value of peak pressure in the tripodal area of the foot in the in-toeing gait group was higher than that in the other two groups. Conclusions The in-toeing gait group had poor static maintenance ability, and to a certain extent, the distribution of plantar pressure in the foot tripodal area and plantar zone pressure were different compared with that of the normal gait. This led to poor stability, easy muscle fatigue, and ankle and knee joint injuries in the in-toeing gait group under equal-intensity exercise conditions.

Abstract:Objective To study the injury risk and fatigue status of firefighters with different training postures under load-bearing conditions to reduce the occurrence of physical injuries and occupational diseases. Methods First, a questionnaire was administered to investigate the training injury conditions of firefighters in a fire-rescue brigade. Considering the exercise fatigue factor, which accounts for the highest proportion of injury causes, lower back analysis, static strength analysis, fatigue analysis, comfort analysis, and other human factor analysis tools in Jack software were used to analyze four common firefighter water-shooting training postures. Training postures while climbing a five-storey building with loads and a hooked ladder were also simulated. Results Injury caused by exercise fatigue accounted for 69.8% of injuries and was the most important injury-causing factor. The risk of knee and ankle joint injuries increased in all four water-shooting postures. The comfort levels of the four water-shooting postures from high to low were shoulder, standing, kneeling, and lying postures. For the entire dynamic training process, while climbing the five-storey building with loads and climbing the hooked ladder, firefighters did not have an increased risk of lower back injury but had an increased risk of ankle and knee joint injuries. Conclusions Some training postures are uncomfortable for firefighters, and they experience body discomfort during firefighting training with loads, thereby increasing injury risk. These results provide scientific references for the prevention and reduction of firefighter training injuries, reasonable training plans, and targeted protective measures.

Abstract:Objective To analyze the lumbar/hip imaging and surface electromyography data of professional equestrian riders, to understand the incidence of chronic diseases in the hip and lower back of the rider, and to explore the causes of chronic pain in riders. Methods Twenty-five equestrian riders from the Shanghai Equestrian Sports Management Center were divided into chronic lower-back pain and chronic hip pain groups. Twelve healthy subjects without hip or lower-back pain were included in the control group. Medical history, X-ray, and magnetic resonance imaging of the hip and lower back, and surface electromyography data of the core muscle were collected. Results The JOA score of the lumbar spine in patients with chronic lower-back pain was significantly lower than that in the control group (P < 0.05). The riders had relatively mild chronic hip pain, but the Harris score was significantly lower than that of the control group (P<0.05). The JOA score of the equestrian rider’s waist significantly correlated with the Pfirrmann grading. However, the visual analog scale and Harris hip pain scores were not significantly correlated with imaging parameters. The root mean square amplitudes of the rectus abdominis, erector spinalis, rectus femoris, gluteus medius, and multifidus were greater in the riding position than in the normal sitting position (P < 0.05). Conclusions The cause of chronic lower-back pain in riders may be related to soft tissue overwork and lumbar degeneration. Changes in the lumbar-hip sagittal sequence pelvic and sacral inclination angles can reflect the degree of lumbar stiffness of the riders.

Abstract:Objective To explore the accuracy of the multiplication coefficient method and the moment synthesis method for determining the spatial position of the center of gravity (CoG) of the human body based on machine vision. Methods The mechanical measurement platform was built, and the three-dimensional (3D) human body CoG measurement methods under static and dynamic conditions were designed to calculate the space coordinates of the CoG. Through experiments, the calculation accuracy of the multiplication coefficient and moment synthesis method were studied and analyzed. Results In the static experiments, the calculation results of the torque synthesis method were more accurate than those of the multiplication coefficient method for each dimension. The errors in the 3D CoG of the human body in the X, Y, and Z directions calculated using the torque synthesis method were 3.9%, 4.1%, and 8.5%, respectively. In the dynamic experiment, the average and relative errors of the torque synthesis method in the X or Y direction were lower than those of the multiplication-coefficient method. When the action decomposition method was used to analyze the height direction of the CoG along the Z axis, the final rendering effect of the torque synthesis method improved. Conclusions The accuracy of the 3D CoG calculated by the moment synthesis method was relatively high, and was closer to the measurement data of the mechanical measurement platform. The 3D CoG calculated using the moment synthesis method can replace the mechanical measurement platform and can be used in subsequent studies.

Abstract:Objective A finite element simulation analysis of a bracketless orthodontic appliance was carried out to determine the correction amount under different working conditions. A design scheme for the bracketless orthodontic appliance was also formulated to create an orthodontic appliance formed by the fused deposition process with a personalized orthodontic effect. Methods Combined with the computed tomography data of the patient, a tooth model was reversely reconstructed. The correction amount of the tooth under tilting, twisting, and translation working conditions was established using the finite element method. Materials with different elastic moduli were chosen to make three-dimensional (3D) shaped bracketless orthodonitc appliance, and the orthodontic force was measured. Results Different correction amounts could be designed according to different working conditions so that the orthodontic appliance had a personalized treatment effect. The orthodontic force of the bracketless orthodontic appliance increased with elastic modulus and thickness. Under the given working conditions, the orthodontic force was minimal (90 mN) when the orthodontic material was at the minimum (90 mN). The orthodontic force reached its maximum value when the orthodontic material was at the maximum (61.66 N). Conclusions According to the patient’s tooth condition and the size of the orthodontic force required for each step of correction in the whole correction process, the design should consider bracketless orthodontics with different elastic moduli and thicknesses to treat deformed teeth to realize the effect of staged orthodontic correction.

Abstract:Walking downstairs and running are common actions in daily life; however, older adults with functional decline are prone to falls or injuries. To cope with various situations and avoid falls, the first neuroprotective motor mechanism activated by the body is the regulation of lower-extremity stiffness. Hence, this study retrieved and collected relevant research results from databases such as China Knowledge, Wanfang, Google Scholar, and Web of Science, using keywords such as elderly and lower-extremity stiffness, and summarized the similarities and differences in changes in lower-extremity stiffness in different action tasks. The findings show that interventions on controllable factors can improve changes in lower-limb stiffness to prevent falls in older adults. However, owing to the small number of related studies, it is necessary to further investigate the effects of action interventions on lower-limb stiffness in older adults to obtain reliable regularity features and references.

Abstract:During the occurrence and development of various heart diseases, continuous deterioration of myocardial fibrosis leads to remodeling and dysfunction of the cardiac structure. As a newly discovered mechanically sensitive ion channel, Piezo1 has opened up a new field of research on cellular mechanical transduction. Piezo1 combines a fine force transducer with Ca2+ influx and participates in the regulation of cellular mechanical transduction, thereby regulating cellular biological functions. Recent studies have shown that the biomechanical changes induced by myocardial injury regulate the expression of Piezo1 in cardiomyocytes and cause an imbalance in calcium homeostasis, which plays an important role in the positive feedback loop of myocardial fibrosis. This review summarizes the theoretical basis and related studies of Piezo1 in regulating cardiac fibrosis and suggests that the Piezo1 channel may become a new target for the treatment of cardiac fibrosis, thereby providing a new research horizon for the prevention and treatment of cardiac fibrosis.