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Abstract:Research in cellular mechanics has rapidly advanced in recent years, uncovering how cells regulate their functions and behaviors by sensing and responding to mechanical cues from their environment. In 2023, significant breakthroughs were made in understanding the mechanical properties of cells, their mechanosensing of solid and fluid environments, and their adaptability under dynamic mechanical conditions. Meanwhile, advanced measurement techniques and mechanical models have provided new tools for investigation. These achievements have deepened the understanding of physiological and pathological processes, offering new approaches for disease diagnosis, prevention, and intervention. This review summarizes the research progress by Chinese scholars in cellular mechanics and explores the mechanical mechanisms exhibited in various biological processes in the year 2023.

Abstract:T cells play an essential role in adaptive immunity, and the specific recognition of antigens by T cell receptors (TCRs) is the key in initiating anti-tumor and antiviral immune responses. Recent studies have demonstrated that force plays an important regulatory role in T cell immune responses, laying the foundation for the emerging field of mechanoimmunology. In this review, the mechanisms by which force assists TCRs in distinguishing between specific antigens and non-specific antigens, as well as the critical role force plays in initiating TCR transmembrane signaling and triggering T cell activation are mainly discussed. The novel biophysical single-molecule tools and advanced imaging techniques that can deeply reveal the importance of mechanical forces at the molecular and/or cellular level are summarized. Based on the research results of domestic and foreign expert teams, combined with the research work of our team, this review summarizes and discusses the role of force in T cell function, so as to provide a system framework for deeply understanding the cutting-edge hotspots in the field of mechanoimunology and exploring new research directions.

Abstract:Objective To elucidate the mechanisms of interface disruption between the actin filament and membrane of the cell pseudopodium that occurs during the breakage of the pseudopodium. Methods Time-lapse images of the behavior of actin filaments and membranes during the rupture process of cell pseudopodia were captured using confocal microscopy. A theoretical model of the fracture of a cylindrical interface was developed to analyze the interface damage between the actin filament and the membrane during the breakage of the cell pseudopodium. Molecular dynamics simulations were employed to simulate the breaking process of the cell pseudopodium for comparison with the theoretical results. A finite element model considering the coupling of the tensile-torsional deformation of actin filaments was developed to simulate the torsional deformation of actin filaments under tension, both in the presence and absence of a membrane. Results The theoretical results indicated an exponential relationship between the critical load for the broken interface and crack length. The critical load increased with the interfacial strength. The effect of the fiber diameter on the critical load depended on the crack length, exhibiting different effects for small and large crack lengths. Finite element analysis suggested that the membrane substantially constrained torsional movement when the actin filament was extended. Conclusions This study revealed the breaking process of cell pseudopodia and the mechanical aspects underlying the disruption of the interface between the actin filament and the membrane. These results provide quantitative theoretical support for exploring cellular behaviors associated with pseudopodium breakage, such as the release of extracellular vesicles.

Abstract:Objective To explore the differential expression of the key microfilament cytoskeleton-binding proteins in immature dendritic cells (imDCs) during antigen phagocytosis. Methods Monocytes (MOs) were isolated from peripheral blood of healthy individuals and cultured with recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF) and recombinant human interleukin-4 (rhIL-4) for 6 days to obtain imDCs. ImDCs were co-cultured with low molecular weight (40 kDa) and high molecular weight (150 kDa) dextrans for 1, 3 and 6 hours, respectively. Flow cytometry was used to detect the percentage of imDCs phagocytosing dextran and the expression of immunophenotype molecules. The localization of filamentous actin (F-actin), PFN1, WASP, and α-actinin in cells were observed by immunofluorescence imaging. The differential expression of MCBPs at the mRNA and protein levels were respectively detected by q-PCR and Western blotting. Finally, the MCBPs with the highest component coefficients were identified based on the stepwise regression and principal component analysis methods in systems biology algorithms. Results During the process of antigen phagocytosis, imDCs phagocytized low molecular weight antigens at a faster rate, with a phagocytic duration of approximately three hours. Their cell phenotypes and morphology gradually differentiated into mDCs, and F-actin remodeling was occurred significantly. The expression of MCBPs such as PFN1, CDM, WASP, CAPZB, Filamin A, α-actinin were downregulated, while the expression of WAVE1, Arp2/3 complex, and Fascin were upregulated. The mRNA expression of signaling protein Rac1 was upregulated, while the mRNA expressions of CDC42 and RhoA were downregulated. The immunofluorescence results showed that PFN1, WASP, and α-actinin were transposed during the antigen phagocytosis process of imDCs. The results of stepwise regression and principal component analysis showed that PFN1 had the highest component coefficient. Conclusions PFN1 may be a key MCBPs involved in the process of antigen phagocytosis of imDCs, which is of great significance for further understanding the relationship between changes in the cytoskeleton structure of imDCs and their immunological functions.

Abstract:Objective To determine whether local gradient fluid shear stress (FSS) causes a specific distribution of intracellular calcium ion concentration, which ultimately determines the direction of cell migration. Methods Numerical simulations were performed using COMSOL software. The method of staining intracellular calcium ion for RAW264.7 osteoclast precursors was established. After applying gradient FSS on the cells, the distribution and dynamic changes of intracellular calcium ion concentration and cell migration parameters were analyzed. Results Osteoclast precursors tended to migrate towards regions with lower FSS, and oscillatory flow regulated the distribution of intracellular calcium ions along the direction of cell migration. After blocking phospholipase C (PLC), mechanosensitive cation-selective channels (MSCC), endoplasmic reticulum (ER), and removing extracellular calcium, the migration speed of cells towards the low FSS direction was significantly reduced, but the migration speed along the liquid flow direction was significantly enhanced. Meanwhile, the calcium ion distribution along the liquid flow direction was significantly increased. Conclusions Osteoclast precursors can sense the FSS gradient, resulting in a specific distribution of intracellular calcium ions along the direction of migration. This ultimately leads to the migration of osteoclast precursors towards regions with lower FSS. This study provides important basic data for ultimately elucidating the cellular and molecular mechanisms of bone tissue remodeling under dynamic external forces.

Abstract:Objective To explore the effects of astaxanthin on pressure injury wounds. Methods In vitro experiment: Fibroblasts were treated with different concentrations of astaxanthin and their proliferation activity was detected by CCK-8 assay. Subsequently, fibroblasts were induced by hypoxia/reoxygenation, and the optimal concentration of astaxanthin was administered. Then the intracellular reactive oxygen species (ROS) level was detected by DHE fluorescent probes and the level of TNF-α, IL-1β, IL-6, IL-10, TGF-β was evaluated by RT qPCR. In vivo experiment: To construct a pressure injury model , two circular magnets were symmetrically adsorbed on both sides of the mouse skin for 5 hours everyday. Subsequently, equal amounts of physiological saline, low-dose astaxanthin (10 mg/kg), and high-dose astaxanthin (20 mg/kg) were administered by gavage in groups. Wound images were taken regularly. After 7-day treatment, wound healing rates were counted and wound tissues were collected for histopathological staining. Results In vitro, the fluorescence intensity of DHE in the astaxanthin groups were reduced dramatically. The relative mRNA expression level of TNF-α, IL-1β, IL-6 in the astaxanthin group declined, and the level of TGF-β and IL-10 mRNA increased significantly (P<0.05). In vivo, the wound healing rate and the level of TGF-β, IL-10 in high-dose astaxanthin group increased significantly. The ROS content and the level of TNF-α, IL-1β and IL-6 dropped markedly in astaxanthin groups (P<0.05). Conclusion Astaxanthin can significanlty alleviate oxidative stress, mitigate inflammation, thus exerting a protective effect on pressure injury wounds.

Abstract:Objective To investigate vascular remodeling and low-density lipoprotein (LDL) deposition, the growth and development trends of lateral branch plaques in bifurcated vessels, and the potential locations of subsequent plaque growth due to the presence of plaques. Methods An idealized model of bifurcated vessels was established and the distribution of wall shear stress before and after the growth of edge-branch plaques was obtained using computational fluid dynamics. Seven sections were intercepted in the areas of low shear stress: planes 1–3 were the low shear stress areas on the lateral branch before plaque formation, planes 4–5 were the proximal and distal edges of the plaque, and planes 6–7 were the lower shear stress areas of the plaque. Vascular remodeling and LDL deposition in the cross section were simulated. The growth and development trends of plaques are also discussed. Results Among planes 1–3, plane 2 produced obvious negative remodeling and the highest concentration of LDL deposition (102.266 mmol/L), thereby indicating that this was the initial location of the atherosclerotic plaque. Compared to plane 4, plane 5 produced more pronounced vascular remodeling, lumen narrowing, and the highest deposition concentration (110.17 mmol/L) after plaque formation, which indicated that the patch had a tendency for eccentric growth downstream. Compared to plane 6, plane 7 (blood flow separation reattachment site) produced more negative remodeling and the highest deposition concentration (93.851 mmol/L), thereby indicating the possibility of new plaque formation near the reattachment point of blood flow separation. Conclusions Obvious vascular remodeling at low shear stress in the lateral branches leads to lumen stenosis and high LDL deposition, thus, forming atherosclerotic plaques. The lateral wall of the bifurcated blood vessels was the initial location of atherosclerotic plaque growth. After growth, the plaque tends to develop downstream, and subsequent plaques may form at the flow separation and reattachment points.

Abstract:Objective To address the problem of late strut thrombosis generated after the implantation of biodegradable vascular stents, a stochastic finite element model was established to perform biomechanical analysis from the perspectives of molecular weight and stress. Methods A mathematical model of the degradation process of biodegradable vascular scaffolds using poly lactic acid (PLA) was established and the mathematical model was imported, and a finite element model was constructed using COMSOL software. The model was stochastically used to analyze the effects on molecular weight and stress distribution in the degradation process under different stochastic parameters and standard deviations. Results During the degradation process of degradable polymer vascular scaffolds in human body, the random variables Mn0 and 8% standard deviation had the most significant effects on the distribution of molecular weights; randomization of the parameters led to a wider distribution range of the fracture strength during the degradation process of polymer vascular scaffolds, and the minimum value of fracture strength was lower. Conclusions The inhomogeneity of molecular weight distribution in polymer vascular stent materials leads to differences in mechanical properties at different locations of the stent, which in turn causes stress concentration within the material, ultimately leading to non-uniform fragmentation of the stent during degradation, which becomes a determining factor for stent thrombosis in later stages. This study provides theoretical guidance for designing next-generation biodegradable vascular stents.

Abstract:Objective To investigate the application of machine learning to predict the hemodynamic parameters of combined stenotic left coronary artery (LCA) aneurysms. Methods Parameterized modeling and simulation based on the geometric parameter range of combined stenosis LCA aneurysms in clinical statistics were conducted. The obtained simulation data was used as the dataset, and two common machine learning models were constructed and trained for optimization to predict two key hemodynamic parameters: wall shear stress (WSS) and pressure. By comparing and analyzing the performances of these models on the training and testing sets, the accuracy of each model was evaluated, and the effectiveness of the data-driven prediction of hemodynamic parameters for LCA aneurysms with concomitant stenosis was verified. Results The effectiveness of machine learning methods in inverting the hemodynamic parameters of aneurysms was determined. For WSS prediction, the trained deep learning model and random forest model achieved mean squared error (MSE), mean absolute error (MAE), and determination coefficient R2 of 0.052 8, 0.032 2, 0.988 3, and 0.078 2, 0.046 3, and 0.976 6, respectively. For pressure prediction, the accuracies of the deep learning models and random forest models were comparable, with MSE, MAE, and R2 of 4.67 × 10-6, 3 × 10-4, 0.999 7, and 1.07 × 10-5, 5 × 10-4, and 0.999 3, respectively. Conclusions Machine learning methods show high accuracy in predicting the hemodynamic parameters of combined stenotic coronary artery aneurysm models. The predictive accuracy of the model, computational efficiency, and needs of the application scenarios need to be considered in machine learning prediction so that the appropriate model can be selected according to the specific situation. This study has clinical significance, helping doctors to more accurately evaluate a patient’s condition and provide new ideas and methods for the diagnosis and treatment of cardiovascular diseases.

Abstract:Objective Based on clinical surgical statistical instances, the influence of double fenestration branch stents on the blood flow field after different depths of implantation in the diseased thoracic aorta was investigated. Methods Thoracic aorta, thoracic aorta-coated stent, and branch vessel-coated stent were established. The finite element calculation method was used to analyze the branch stent implanted into the diseased aorta at different depths (5, 10, and 15 mm), and experimental verification was performed using an in vitro tachymetry experimental platform. Results There were certain patterns for maintaining stable perfusion of the blood flow field with branch stent implantation at different depths in the thoracic aorta. The branch blood perfusion rate in Group D10-5 (the implantation depths of the left common carotid artery branch stent and left subclavian artery branch stent were 10 mm and 5 mm, respectively) was at a good level, and TAWSSmax was at the lowest level (44.94 Pa), thereby showing the best simulation results. Conclusions When the left subclavian artery branch stent implantation in the thoracic aorta was short, the depth of the left common carotid artery branch stent implantation in the aorta was appropriately increased to obtain a more stable blood flow field. This study provided a theoretical reference for the double-fenestration technique in clinical practice.

Abstract:Objective To establish and validate a biomechanical modeling method based on micro-magnetic resonance imaging (μMRI) and microstructure segmentation for noninvasively assessing microstructure behavior of the proximal femur. Methods Firstly, μMRI images were obtained from the femoral samples, and bone microstructures were segmented through regionized image processing to create the μMRI finite element model (μMRI model). Finite element analysis was performed utilizing a lateral fall posture simulation, and stress and strain were calculated. Secondly, the accuracy of μMRI image segmentation of bone microstructure was verified using micro-computed tomography (μCT), and the accuracy of μMRI model calculation results was verified using a finite element model constructed based on μCT (μCT model). Finally, the accuracy of bone surface strain calculated by μMRI model was verified through in vitro mechanical loading experiments simulating lateral falls and strain gauge measurements. Results The bone microstructure parameters BV/TV calculated by μMRI model and μCT model were significantly correlated (r=0.89, P<0.05). The maximum and minimum principal stress/principal strain percentiles calculated by μMRI model and μCT model were highly correlated (R2>0.9). The strain calculated by μMRI-FEM was highly correlated with the strain measured by mechanical experiments (R2=0.82). Conclusions The micro finite element model based on μMRI segmentation of bone microstructure can accurately characterize the micro-mechanical behavior of the proximal femur. This study provides an important tool for non-invasive assessment of hip femur microstructure degeneration and osteoporosis fracture risk in vivo.

Abstract:Objective To assess the biomechanical differences between the artificial ankle joints INBONE II and INFINITY after total ankle arthroplasty (TAA) to provide more scientific and individualized treatment options for patients. Methods A patient-individualized TAA lower extremity MSK MBD model was established using the musculoskeletal (MSK) multibody dynamics (MBD) software AnyBody. The ankle joint contact force, motion, and contact characteristics of artificial ankle joint surfaces were predicted. Results The geometric shape of the articular surface of the artificial ankle had no significant effect on the ankle contact force, but it affected the range of motion and contact characteristics of the articular surface. Compared with INBONE II, the coronal plane articular surface arc height of INFINITY was lower, and increased the inversion-eversion and external rotation-internal rotation movements by 7.91% and 2.61%, respectively. Sagittal plane matching was lower, and reduced posterior-anterior and inferior-superior movements by 21.75% and 21.23%, respectively, and medial-lateral movement increased by 49.26%. INFINITY exhibited lower matching with decreases of 18.48%, 30.42%, and 26.36% in the medial, lateral, and total joint surface contact areas, respectively. However, the center of the pressure motion trajectory was concentrated on the medial side, while avoiding edge contact stress concentration and reducing the risk of joint dislocation and premature wear of the tibial component. Conclusions The smaller geometric constraints of the INFINITY artificial ankle joint demonstrated better biomechanical performance, thereby promoting improved postoperative ankle joint functional recovery.

Abstract:Objective To study the mechanical response of tibial prostheses and the distal tibial cancellous bone after implantation of radial and axial functionally graded materials (FGM) into the ankle joint. Methods Three FGM were used: titanium alloy-bioactive glass composite FGM (FGM-I), titanium (Ti) alloy-ideal bone elastic composite FGM (FGM-II), and Ti alloy-hydroxylapatite composite FGM (FGM-III). A three-dimensional finite element model of total ankle arthroplasty (TAA) was established, and the simulation software ABAQUS was used for secondary development based on Fortra. By changing the volume fraction, the mechanical properties of the FGM tibial prosthesis can be adjusted both axially and radially. The stress distributions of the tibial prosthesis and cancellous bone after FGM axial and radial tibial component implantation in the standing position were analyzed. Results Compared with Ti alloy tibial prosthesis, three kinds of FGM could effectively reduce the stress concentration on the tibial prosthesis, and the overall effect of FGM-III tibial prosthesis was better than that of FGM-I and FGM-II tibial prosthesis; the radial distribution of FGM could effectively reduce the maximum von Mises stress of the prosthesis. For the tibial cancellous bone, the three types of FGM radial tibial prostheses and FGM-III axial tibial prostheses could effectively increase the distal stress, thus, relieving the stress shielding on the cancellous bone; the FGM-III radial tibial prosthesis was the most effective in improving the stress level of the cancellous bone. Conclusions FGM-III radial ankle prosthesis can effectively reduce the stress concentration phenomenon and the stress shielding effect on the prosthesis to prolong its life, with potential application prospects.

Abstract:Objective To evaluate the mechanical behavior of the internal soft tissues of the elbow at different healing stages of a posterior capsular injury. Methods A finite element model of the elbow joint considering muscle activation behavior was established to simulate elbow flexion without injury and at 2nd, 4th, 6th, and 8th week after posterior capsule injury. The von Mises effective stress variations in the articular capsule, ulnar cartilage, and ligaments were analyzed. Results Before injury and at 2nd, 4th, 6th, and 8th week after injury, the stress on the articular capsule at 60° of flexion was 8.23, 7.87, 8.27, 8.99, and 10.5 MPa, respectively. When the elbow flexion angle was 30°, the ulnar cartilage stress increased by 13.0%, 28.3%, 41.3%, and 45.7% at 2nd, 4th, 6th, and 8th week after injury, respectively, compared with that before injury. At the 4th week after injury, the stress of the radial collateral ligament at 15°, 30°, 45°, 60°, and 75° flexion was reduced by 12.5%, 22.2%, 13.6%, 3.2%, and 10.6%, respectively, compared to that at the 2nd week. Conclusions This study provides a theoretical basis for the prevention and treatment of capsular contracture and development of rehabilitation aids.

Abstract:Objective To investigate the therapeutic effect of segmental decompression combined with corrective short-segment fusion surgery for the treatment of degenerative lumbar scoliosis. Methods In total, 124 patients with degenerative lumbar scoliosis were selected and divided into short- and long-segment fusion groups using the random number table method, with 62 patients in each group. Posterior short-segment decompression, fixation, and fusion were performed in the short-segment fusion group; the fusion segment was the adjacent lumbar vertebra. Posterior long-segment decompression, fixation, and fusion were performed in the long-segment fusion group; the fusion segments included multiple adjacent lumbar vertebrae. At the 6th month after surgery, the coronal Cobb angle of lumbar convexity, sagittal Cobb angle of lumbar lordosis, intervertebral foramen height, intervertebral space height, intervertebral foramen area, spinal canal area, spinal canal diameter, Japanese Orthopedic Association (JOA) score, Oswestry Disability Index (ODI), degree of pain in the lower back and lower limbs, and postoperative complications were compared between the groups. Results The Cobb angle of the coronal lumbar scoliosis in the short- and long-segment fusion groups was significantly higher than that before surgery (P < 0.05). At the 6th month after surgery, the intervertebral foramen height, intervertebral space height, intervertebral foramen area, spinal canal area, and spinal canal diameter in both groups increased, and those in the short-segment fusion group were higher than those in the long-segment fusion group (P < 0.05); at the 6th month after the operation, the JOA scores of the short-segment and long-segment fusion groups were higher than those before surgery, and the JOA score of the short-segment fusion group was higher than that of the long-segment fusion group (P < 0.05). The ODI score was lower than that before surgery in the short- and long-segment fusion groups, and the ODI score in the short-segment fusion group was lower than that in the long-segment fusion group (P < 0.05). At the 6th month after surgery, the pain scores of the lower back and lower limbs in the short- and long-segment fusion groups were significantly higher than those before surgery (P < 0.05). There were two cases of dural tears during decompression caused by lamina dura adhesion in the long-segment fusion group, and no serious complications were observed in the short-segment fusion group. Conclusions Both short- and long-segment decompression fixation fusion using a posterior approach can achieve good therapeutic effects for treating degenerative lumbar scoliosis. However, compared to the long-segment fusion group, the short-segment fusion group undergoing short-segment decompression fixation fusion through a posterior approach had a shorter surgical period, lower intraoperative blood loss, better recovery of lumbar function, and a lower risk of postoperative complications.

Abstract:Objective To analyze thoracolumbar vertebral fractures (A3) treated by multiple manipulations using the finite element method and to explore the feasibility and advantages of the composite surgical method for treating thoracolumbar vertebral fractures (A3). Methods For three-dimensional reconstruction of thoracolumbar vertebral fractures (A3), the model was loaded with simulated hyperextension posture restoration, simple press restoration, press restoration under hyperextension posture, and composite manipulation. Subsequentially, the stress distribution of the model and displacement of the fractured vertebral body were observed. Results The equivalent stress under composite manipulation was 111.88 MPa, which was greater than that under other manipulations, and the stress under composite manipulation was more concentrated in the anterior and middle columns of the vertebral body. The peak stress under composite manipulation was 122.53 MPa, which was greater than that under other manipulations, and the stress was centrally distributed in fracture region of the fractured vertebral body. The fracture displacement under composite manipulation was 3.94 mm, which was greater than that under other manipulations, and the displacement distribution decreased from the posterior column to the anterior mid-column. The anterior longitudinal and intertransverse interligamentous ligaments of the fractured vertebral body experienced the greatest stress under composite manipulation, and the joint capsule ligaments experienced the greatest stress under hyperextension postural restoration, simple press restoration, and press restoration under the hyperextension posture. Conclusions Compound manipulation for treating thoracolumbar vertebral fractures (A3) has obvious advantages over other manipulative restorations and is a reasonable program for the current treatment of thoracolumbar vertebral fractures (A3).

Abstract:Objective To analyze the correlation between the sagittal orientation of lumbar pedicle screws and screw loosening based on the craniocaudal cyclic load and artificial vertebra, and to provide a reference for the improvement of screw orientation during surgery, consequently reducing the incidence of screw loosening postoperatively. Methods Pedicle screws were inserted into artificial vertebrae in the cranial, parallel, and caudal orientations. After the artificial vertebra was installed in the material testing machine, the model was subjected to a 100 N preload and 166 N cyclic load for 10 000 cycles. During loading, displacements were recorded and cycle-displacement curves were drawn. After the test was completed and the screws were removed, the screw hole volume was measured and the screw hole volume ratio (the ratio of screw hole volume to the volume of the screw inserted into the vertebra) was calculated. Results The cyclic displacement curve showed that the cranial group had the largest displacement, followed by the parallel and caudal groups. The screw-hole volume ratio results showed that the cranial group had the highest ratio, followed by the parallel and caudal groups. Correlation analysis showed a negative relationship between screw sagittal orientation and terminal displacement (displacement corresponding to the 10 000th cycle) (P = -0.897, P = 0.02) and screw hole volume ratio (P = -0.902, P = 0.01). Conclusions There is a negative correlation between the sagittal orientation of the lumbar pedicle screw and screw loosening. Namely, when the screw sagittal orientation is adjusted from a cranial tilt to a parallel and even caudal tilt at a certain angle range, the incidence of screw loosening is reduced.

Abstract:Objective To establish preoperative and postoperative femoral-pelvic-lumbar spine models of patients with developmental dysplasia of the hip (DDH) and healthy volunteers and to study the biomechanical effects of curved periacetabular osteotomy on the lumbar spine. Methods: Preoperative and postoperative femoral-pelvic-lumbar spine DICOM and Communications in Medicine data from four patients with DDH and one healthy volunteer were acquired using CT scanning technology, and a three-dimensional finite element model was constructed. The offset method was used to divide the cortical and cancellous bones in Geomagic and the lumbar cartilage, sacroiliac joint, pubic symphysis, and other cartilages were added to SolidWorks. The model was analyzed using ANSYS for finite element analysis, and the gait was the mid-stage of single-leg support during slow walking. The biomechanical changes in the lumbar spine of patients with DDH before and after surgery were analyzed and compared, and the biomechanical data of the lumbar spine of patients after surgery were compared with those of healthy volunteers. Results The femoral-pelvic-lumbar spine models of four patients and a healthy volunteer were established. The results obtained by the established models under each working condition were within the range of the referenced literature, and the validity of the models was proved. The postoperative stresses on the lumbar spine, femoral neck, annulus fibrosus, and nucleus pulposus were much smaller than those of the patients in the preoperative state, and the postoperative stresses on the lumbar spine, femoral neck, annulus fibrosus, and nucleus pulposus of the patients were similar to those of healthy volunteers. Conclusions: Curved periacetabular osteotomy significantly reduced the stresses on the lumbar spine and intervertebral discs. Additionally, the stresses on the annulus fibrosus were more uniform after surgery, which indicated that curved periacetabular osteotomy will adjust patients to a healthy state. This study provides a biomechanical basis for the clinical treatment of DDH and helps optimize surgical plans.

Abstract:Objective To analyze the differences in static balance plantar pressure characteristics between female adolescent idiopathic scoliosis (AIS) patients with moderate Lenke 3CN and healthy adolescents of the same age, and provide a scientific basis for scoliosis screening, assessment, treatment, and prognosis evaluation. Methods A total of 30 female patients with moderate Lenke 3CN AIS as the AIS group and 30 healthy female adolescents of the same age as the control group were selected, respectively. The plantar pressure data of the subjects were collected, and the characteristics of equilibrium plantar pressure distributions in two groups were comparatively analyzed. Results Regarding the plantar pressure characteristics, the average pressure (P<0.05) and hindfoot pressure (P<0.05) of the left and right foot in the AIS group were significantly greater than those of the control group, the forefoot pressure was significantly lower than that of the control group (P<0.05), and the symmetry index (SI) of both feet was significantly greater than that of the control group (P<0.05). The plantar pressure of the left foot in the AIS group was significantly larger than that of the control group in the medial mid-foot area and 1st toe area (P<0.05), and significantly smaller than that of the control group in the 1st, 2nd, 3rd, 4th and 5th metatarsal areas (P<0.05); the plantar pressure of the right foot in the AIS group was significantly greater than that of the control group in the medial heel area and the1st toe area (P<0.05), and significantly smaller than that of the control group in the lateral mid-foot area, the 3rd, 4th, 5th metatarsal area and 3rd, 4th, 5th toe area (P<0.05); and the plantar pressure in the right foot of the AIS group was significantly smaller than that of the control group in the medial heel area and 1st toe area (P<0.05). The plantar pressures at lateral midfoot area, the 3rd, 4th, 5th metatarsal area and the 3rd, 4th, 5th toe area of the right foot were significantly larger than those of the control group (P＜0.05). Regarding the center of pressure (COP), the length of the COP trajectory, the ellipse area of the 95% confidence interval, the maximum distance of COP left-right movement (COP-X), and the maximum distance of COP anterior-posterior movement (COP-Y) of the AIS group were significantly larger than those of the control group (P<0.05). Conclusions There are significant differences in static balance plantar pressure characteristics between female AIS patients with moderate Lenke 3CN and healthy female adolescents of the same age, with foot pressure favoring the side of the lateral convexity, poorer symmetry and stability of the feet, and weaker balance control.

Abstract:Objective Wearable inertial measurement unit (IMU) technology and random forest (RF) algorithm were used to detect the fatigue level of long-distance walking with backpack load, and the feasibility of fatigue detection of load-bearing walking and optimal IMU combination scheme were explored. Methods Thirty healthy male college students were recruited to carry out long-distance backpack walking. Xsens MVN Link inertial motion capture system and Borg-RPE fatigue scale were used to collect kinematic data and subjective fatigue values of load-bearing walking, and fatigue was divided into 3 levels: without fatigue, moderate fatigue and severe fatigue. The original data were extracted; gait segmentation, data screening and feature extraction were carried out; and RF model was used for machine learning of sample features. Finally, the accuracy rate, precision, confusion matrix and AUC (area under the curve) were calculated to evaluate the detection effect of different IMU combinations. Results The accuracy of one right femur IMU was 82.55%, and the accuracy of five IMU combinations was 87.94%. In a combination of IMUs, at least one upper body IMU was included, and the left limb had more IMUs than the right limb. The RF model had a higher level of fatigue detection for load-bearing walking; when four IMUs were used, the AUC of 3-level fatigue was 0.99, 0.97 and 0.99, respectively. Conclusions IMU technology and RF algorithm have high accuracy and classification ability in the 3-level fatigue detection task of walking with backpack load. In practical application, it is recommended to use 1–5 IMUs, and the combination of upper body IMU and lower limb IMU configuration scheme is preferred.

Abstract:Objective This study investigated lower limb biomechanics and lateral asymmetry during the continuous vertical jump (CVJ) landing process in individuals with unilateral functional ankle instability (FAI) and compared these characteristics with those of healthy individuals. Methods Fourteen males with unilateral FAI were selected as the experimental group, and 14 males without ankle joint injury were matched to the control group. Both the groups performed 30 CVJ landing tasks. Lower limb kinematic and kinetic characteristics during the 1st, 15th, and 30th CVJ landings were synchronously collected using Vicon and Kistler equipment, and a 2 × 3 mixed analysis of variance was adopted for the data. Results In the execution of CVJ landing tasks, patients with FAI demonstrated no significant differences in the kinematic and kinetic characteristics of the affected limbs compared with healthy controls. However, a greater degree of lateral asymmetry was observed in the FAI group, particularly in the symmetry index (SI) of the vGRF peak. Despite the increase in the number of jump landings and consequent increase in fatigue levels, which led to adjustments in lower limb movement patterns, these adjustments did not appear to have a significant impact on the biomechanical characteristics and asymmetry of the affected limb in patients with FAI. Conclusions This study provides a theoretical basis for the prevention of recurrent ankle sprains in patients with FAI, as well as rehabilitation training prior to their return to sports. These findings underscore the importance of addressing lower limb asymmetry in the rehabilitation training of patients with FAI to reduce the risk of potential long-term injuries. When formulating rehabilitation plans for patients with FAI, particular attention should be paid to the correction of lower limb asymmetry with consideration of biomechanical adaptability under different states to achieve a more comprehensive rehabilitation outcome.

Abstract:Objective To study the fall risk of older adults stepping over obstacles of different heights with their dominant or non-dominant legs and provide references for developing fall prevention measures for the elderly during obstacle-crossing. Methods Sixteen older adults randomly stepped over obstacles at 15%, 30%, and 45% of their leg heights with their dominant and non-dominant legs. A three-dimensional (3D) motion capture system and 3D force platform were used to record kinematic and kinetic data. Results When older adults used their non-dominant leg to step over obstacles, the dynamic stability in the anterior-posterior direction of the trailing leg at 30% of leg length height was significantly lower than that at 15% of leg length height (P < 0.05, Cohen’s d = 0.628); the vertical toe clearance of the trailing leg was significantly smaller than that of the dominant leg (P = 0.041, Cohen's d = 0.516), and the vertical toe clearance (P<0.001, Cohen's d = 0.685) and anterior-posterior toe clearance (P = 0.043, Cohen's d = 0.616) of the leading leg were significantly greater than those of the dominant leg. Conclusions Compared to stepping over obstacles with the dominant leg, older adults have a greater risk of falling in the anterior-posterior direction before obstacles when using the non-dominant leg. There is also a greater risk of the trailing leg tripping over obstacles of different heights.

Abstract:Objective To observe the effects of 12-week pilates exercise and trunk strength training on the scores of visual analog scale (VAS) and Roland-Morris disability questionnaire (RMDQ), trunk extension/ ?exion strength and dynamic balance of female college students with chronic non-specific low back pain (CNSLBP), so as to offer a practical-based evidence for the rehabilitation treatment for female college students with CNSLBP. Methods A total of 45 female college students with CNSLBP were randomly divided into pilates (n = 22) and strength training groups (n = 23). Then, the scores of VAS and RMDQ, trunk extension/?exion strength and dynamic balance were measured before and after the exercise. Results After the 12-week exercise program, compared with the pre-exercise period, the VAS and RMDQ scores in the pilates and strength training groups were significantly decreased; the extensor peak torque (EPT) at 30°/s and 90°/s angular velocities in both groups and the flexor peak torque (FPT) at 90°/s angular velocities in the Pilates group were significantly increased, and the ratio of flexor/extensor (F/E) at 30°/s and 90°/s angular velocities in both groups were significantly decreased. In the eyes-open condition, only the anterior/posterior stability index (APSI) significantly decreased in the Pilates group. With eyes closed, the APSI, stability index (SI), and medial/lateral stability index (MLSI) significantly decreased in the pilates group, and only the APSI significantly decreased in the strength training group. After 12-week exercise, compared with strength training group, the VAS scores and F/E at 30°/s and 90°/s angular velocities decreased significantly in the pilates group, and EPT at 30°/s and 90°/s angular velocities increased significantly. In the eyes-closed condition, the SI, APSI, and MLSI in the pilates group were significantly lower than those in strength training group. Conclusions Compared with strength training, pilates exercise can significantly increase and balance the trunk flexion/extension muscle strength of female college students with NSLBP, enhance dynamic balance ability under eyes-closed conditions, and improve the low back pain of CNSLBP female college students with CNSLBP.

Abstract:Objective To quantify the lower limb muscle synergy characteristics of athletes during the abdominal take-off phase before and after exercise-induced fatigue (EIF) and reveal the impact of EIF on the lower limb muscle synergy characteristics of athletes during the abdominal take-off phase. Methods The surface electromyographic data of the lower limbs during the abdominal take-off phase of 10 second-level male athletes in track and field special classes before and after EIF intervention were compared. Muscle synergy structures were analyzed before and after EIF. The paired sample t-test was used to compare the differences in synergy parameters before and after EIF. Results Two synergistic elements were extracted before and after EIF, and alternate activation of the muscle synergy structures was observed. After EIF, the degree of activation of synergy element 2 decreased significantly from 53.21 ± 7.90 to 43.44 ± 10.23. However, there was no significant change in synergy element 1. After EIF, the contribution of the rectus femoris muscle of synergy element 1 significantly increased from 0.37 ± 0.04 to 0.44 ± 0.07, and the contribution of the semitendinosus muscle decreased significantly from 0.13 ± 0.05 to 0.08 ± 0.05. Conclusions During abdominal take-off, as fatigue increases, the activation degree of the synergistic elements of each lower limb muscle decreases, and the contribution of the rectus femoris muscle in the synergy element to absorb the ground reaction force increases. This indicates that the rectus femoris muscle is at risk of sprain, and prevention of rectus femoris muscle injury should be strengthened.

Abstract:Objective To explore the muscle force characteristics of the knee joint during a Taekwondo roundhouse kick in Korea. Methods Kinematic and dynamic data from twelve elite Taekwondo athletes were collected using the DaeDo electronic scoring system, Vicon optical motion capture system, Kistler three-dimensional force plates. The OpenSim software was used to simulate these movements and calculate the muscle forces, joint torques, joint stiffness, and muscle coordination patterns of the knee. Results During the knee-lifting and striking phases, the coronal torque of the knee joint in the attacking leg was significant, and the sagittal torque peaked during the strike. For the supporting leg, the highest coronal torque of the knee joint occurred during knee lifting, with the sagittal torque reaching its peak during strike. In terms of muscle activity, the semimembranosus and long head of the biceps femoris in the attacking leg exerted greater force during the striking phase, whereas the semimembranosus and medial head of the gastrocnemius in the supporting leg were more active during the recovery phase. Five muscle synergy patterns were observed during the Taekwondo roundhouse kick. Conclusions Significant differences were found in the muscle forces and knee joint torques of the attacking and supporting legs when athletes performed the roundhouse kick, and there was a complex muscle synergy.

Abstract:Objective To investigate the injury mechanisms of three-year-old child occupants by reconstructing a real traffic accident. Methods A traffic accident case from the CIREN database was reconstructed using a vehicle finite element model and a three-year-old child occupant injury bionic model (TUST IBMs 3YO-O). The Δv, mass of the vehicle, and deformation energy were comprehensively analyzed to calculate the collision velocity of the vehicle. This accident was simulated to present injuries to a child occupant, and the injury mechanisms were analyzed in depth. Results The TUST IBMs 3YO-O fully reconstructed the injuries of the child occupant in this case. The kinematic and biomechanical responses of the children's heads differed. The biomechanical response of the internal tissues and organs in the chest cavity showed no injury, however, the resultant chest acceleration at 3 ms reached 54 g, which exceeded the threshold. Conclusions In the future, it will be necessary to adopt biomechanical parameters for occupant safety evaluations. The application of human biomechanical models with high biofidelity to reconstruct occupant injuries in traffic accidents can not only be used to observe the kinematic responses of the occupant in the accident and analyze the injury mechanisms in depth, but also to provide references for virtual testing, as well as for the research and development of child occupant protection devices and the formulation of safety regulations.

Abstract:Objective A precise microinvasive robot system coupled with a cooperative robot matrix and an end effector of a wire-controlled microvariable path robot was proposed. A puncture needle structure, including the rigid body of the outer needle, non-uniform flexible body of the inner needle, force control wire, internal imaging of the image fiber, and other components, was designed to verify the feasibility of this system. Methods By constructing the puncture structure of the puncture robot, the structural optimization design of the key components affecting the variable-path precision puncture needle was analyzed by constructing the puncture structure of a puncture robot. Based on the orthogonal experimental design method, a three-factor and three-level experiment that primarily affected the accuracy of the puncture needle was designed, namely, the starting distance of the hole center from the edge, the diameter of the hole, and the distance between the two holes. The experiment is verified and simulated using a real object. Results The displacement of the titanium-nickel needle tip had a significant relationship with the starting distance of the hole center from the edge, and the main and secondary influencing factors were as follows: starting distance of the hole center from the edge> hole diameter>hole distance. When the starting distance of the hole center from the edge was 1 mm, the diameter of the hole was 0.2 mm, and the distance between the two holes was 2.6 mm, the displacement of the titanium-nickel needle tip was the maximum value. Conclusions The experiment verified the functional applicability of the designed system and the linear elastic hysteresis characteristics of variable path puncture, providing a reference for further in vivo experiments and system optimization.

Abstract:Cellular force transducer plays a crucial role in normal development of the follicles, which consists of integrin, focal adhesion, signal pathways and cytoskeleton. In follicle development, cellular force transducer converts force stimulation into biochemical signal, and activates the signal pathways to make cytoskeleton respond to stimulation. This process promotes various biological functions of germ cells, such as migration, meiosis and ovulation. This review summarizes the mechanism of follicles’ development from two aspects, the role of cellular force transducer in the development of follicles and the related signal pathways, so as to provide a new idea for the further study of follicle development.

Abstract:Mechanical ventilation (MV) provides life support for critically ill respiratory patients, but in the meantime can cause fatal ventilator-induced lung injury (VILI), and the latter remains a major challenge in respiratory and critical care medicine, because the pathological mechanism has not been fully elucidated. Recent studies show that on the one hand, in the lung with VILI, there exists airway collapse at multi-sites of an individual airway, which can not be explained by traditional airway collapse models. But on the other hand, under MV conditions, airway smooth muscle cells (ASMC) exhibit abnormal mechanical behaviors, accompanied by regulation of Piezo1 expression and endoplasmic reticulum stress. These phenomenons indicate that the MV-induced abnormal mechanical behavior of ASMC is closely related to multiple airway collapse and VILI. Therefore, by studying the MV-induced changes of ASMC mechanical behaviors and their relationship with airway collapse in lung injury, as well as the related mechanochemical signal coupling process, it is expected to reveal a novel mechanism of MV-associated airway collapse and lung injury from the perspective of cell mechanics. In this review, the recent research progress of airway collapse during MV, the regulation of ASMC mechanical behavior by MV-related high stretch, especially the related mechanochemical signal coupling mechanism is summarized. These advances may provide a novel insight for exploring the roles of ASMC abnormal mechanical behavior in the pathological mechanism of VILI, alternative targets of drug intervention for prevention and treatment of VILI, as well as for optimizing the ventilation mode in clinical practice.

Abstract:Anterior cruciate ligament reconstruction (ACLR) is the preferred treatment to restore the original activity level of patients. The single-leg drop jump can not only identify high-risk exercise strategies, but also provide a standard for the rehabilitation process of ACLR. In this review, a combined search of ‘single-leg drop jump’ ‘anterior cruciate ligament reconstruction’ ‘biomechanics’ was conducted through CNKI, PubMed, Embase and other databases, and the biomechanical changes of single-leg drop jump after ACLR and related intervention methods are summarized. The research findings will help adjust rehabilitation strategies after ACLR and avoid high-risk actions with secondary injuries. The analysis of single-leg drop jump after ACLR can guide clinicians and rehabilitation therapists to formulate and adjust rehabilitation treatment plan, improve the postoperative rehabilitation efficiency of ACLR , and help patients return to exercise early.