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Abstract:After decades of development, ventricular assist devices (VADs) have evolved into the current generation of magnetically levitated blood pumps, achieving revolutionary progress in terms of implantation into the chest and large-scale clinical application. VADs have become an effective means of treating heart failure, which is a major global public health challenge. Despite these achievements, up to 89% of patients are readmitted within five years due to complications such as gastrointestinal bleeding, stroke, infection, and blood pump malfunction. Therefore, it is necessary to further study the mechanisms of blood damage of various blood components; to further develop and comprehensively utilize numerical simulations, in vitro bench testing, animal experiments, and other methods to more comprehensively evaluate blood pump performance. Innovative design of VADs are also needed to improve blood compatibility, meet the needs of different patient groups, and improve patients’ quality of life. In this review, the research progress on evaluation and design methods of VADs in 2024 both domestically and internationally is summarized, including advances in the study of blood damage mechanisms; the use of numerical simulations, in vitro bench testing, and animal experiments to evaluate blood pump performance; the progress in design and optimization of blood pump, new concept blood pump, and bio-coatings. The aim is to support the development of VADs and further improve their clinical therapeutic benefits.

Abstract:As a critical treatment for patients with end-stage heart failure, artificial hearts have achieved significant clinical success. However, due to the direct contact between mechanical blood pumps and circulating blood, the clinical use of artificial hearts is often associated with blood damage-related complications such as thrombosis and bleeding, which significantly affect patient outcomes and prognosis. This paper first systematically reviews the mechanisms of blood damage induced by artificial hearts, including the biomechanical processes of platelet activation caused by non-physiological shear stress, von Willebrand factor (vWF) degradation, and platelet receptor impairment. Subsequently, existing thrombosis risk assessment models are summarized in detail, including blood stasis models, platelet activation models, and advanced mathematical models incorporating dynamic changes in coagulation factors and hemostatic proteins. These models predict high-risk thrombosis regions induced by artificial hearts, providing valuable guidance for device optimization and complication prevention. Finally, recently developed bleeding risk assessment models for artificial hearts are introduced. The integration of bleeding and thrombosis risk models enables the development of a more comprehensive hemocompatibility evaluation system. By reviewing the current research progress, this study aims to provide a reference for the assessment and prediction of blood damage in artificial hearts, contributing to improved hemocompatibility, enhanced safety, and better clinical outcomes of artificial heart devices.

Abstract:Objective To investigate the impact of eccentric placement for various types of artificial aortic valves on downstream flow dynamics. Methods A physiological pulsatile circulation simulation system was emoloyed and particle image velocimetry (PIV) was utilized to analyze the downstream flow field variations for bioprosthetic and mechanical valves under two placement conditions: centralized placement (0 mm) and eccentric placement (1 mm). Hemodynamic parameters such as velocity, vorticity, and viscous shear stress were assessed to evaluate the flow field characteristics. Results By analyzing the flow field variations at four characteristic time points, namely, early systole, acceleration phase, peak systole, and deceleration phase, a significant difference in flow field distribution between bioprosthetic and mechanical valves was observed. The bioprosthetic valve exhibited a centrally symmetric jet with higher flow velocity, whereas the mechanical valve displayed a three-jet structure with a lower central flow velocity. Under eccentric placement, the blood flow in the aortic sinus region was sluggish, with a reduction in average velocity, hindering the formation and maintenance of vortices. During the peak systolic phase, the maximum viscous shear stresses in the sinus region for the bioprosthetic and mechanical valves were 0.45 and 0.67 N/m2, respectively, approaching the threshold for endothelial cell damage. Conclusions Eccentric placement of both mechanical and bioprosthetic valves resulted in reduced sinus blood flow velocity and diminished viscous shear stress, creating favorable conditions for thrombus formation. In clinical practice, careful attention should be given to the placement of valve replacements to prevent eccentric placement.

Abstract:Objective Two different venous models, one with and one without a venous sinus, each containing two pairs of adjacent orthogonal venous valves, were constructed. Using fluid-structure interaction (FSI) simulations, the influence of the venous sinus structure on blood flow in the lower limb venous system was studied, and the role of the venous sinus structure in the process of venous valve opening and closing was analyzed. Methods Based on ultrasound images and anatomical images of animals, two distinct three-dimensional (3D) geometric models of the venous system were constructed using modeling software. Using the immersed boundary method, FSI simulations of venous valves were performed to obtain hemodynamic parameters, such as changes in valve morphology, flow streamlines distribution, wall shear stress (WSS) distribution, and Q-criterion intensity distribution. Results The geometric opening area of the valve in the model with sinuses was larger than that in the model without sinuses. The distribution of blood streamlines demonstrated the existence of vortices in the sinus region and helical flow within the vessel. The same venous valve pair exhibited an asymmetric distribution of WSS, with the region of high WSS behind the venous valve and the Q-criterion intensity between the far and near end valves being smaller in the sinus model compared to the non-sinus model. Conclusions The blood flow between two adjacent pairs of orthogonal venous valves exhibits a helical flow characteristics. The venous sinus structure facilitates the opening of the venous valve and the generation of vortices in the sinus region. However, the venous sinus structure may somewhat weaken the helical flow produced by the orthogonal venous valves. The venous sinus has a critical influence on the hemodynamics of the venous system, and in the study of venous valves, the venous sinus structure should be considered as an indispensable component.

Abstract:Objective To investigate the impact of variations in volute cross-sectional area on the flow characteristics and hemolytic performance of centrifugal blood pumps by designing six volute structures. Methods Computational fluid dynamics and the Lagrangian method were used to analyze flow characteristics and predict hemolysis in blood pumps with different volute designs. Results The annular volute pump showed the poorest hydraulic performance, while the hydraulic performance of the S-shaped volute was the best improving by 35.29% compared to that of the annular volute. Some volutes experienced stagnation zones at the helical inlet (0°–90°) and significant backflow at the outlet (270°–360°). The downward concave-shaped volute had the highest hemolysis index (HI), i.e., 9.59 × 10-4. Meanwhile, the HI of the annular volute was the lowest, which was 71.85% less than the concave-shaped volute. Conclusions Reducing the gradient of the area variation at the helical inlet and outlet can prevent flow stagnation and backflow. A higher HI arises due to the prolonged exposure of red blood cells to high shear stress. This study provides a theoretical basis for designing and optimizing volute structures of centrifugal blood pumps.

Abstract:Objective With considerion of aortic wall hyperelasticity and residual stress, to propose a numerical simulation method for predicting aortic blood pressure based on vascular compliance. Methods The residual stress solution method based on the closing opening angle was used to realizd the analytical solution for the pressure-radius relationship of the idealized double-layered aortic wall model. The vascular compliance was calculated, and the pressure-radius relationship was applied to the moving boundary representing the motion of the aortic wall for numerical simulation, to obtain the relationship between vascular compliance and pulse pressure. The effects of with or without residual stress, hyperelasticity or linear elasticity constitutive relationships, as well as different ages on vascular compliance and aortic blood pressure were compared. The function of the stent graft was incorporated, by considering the stented region as a rigid wall, simulating the effects of different stent numbers and stent positions on aortic blood pressure. Results Vascular compliance with residual stress was higher than that without residual stress; correspondingly, when residual stress was considered, aortic pulse pressure was slightly lower than that without residual stress. Compared to the linear elastic model, the hyperelastic model predicted a smaller aortic pulse pressure value. The vascular compliance for different age groups showed 40–49 year-old > 60–69 year-old > 70 year-old and above; correspondingly, the pulse pressure for different age groups showed 40–49 year-old < 60–69 year-old < 70 year-old and above. When a stent with 60 mm length was implanted in the aorta, as the number of stents increasing, the aortic pulse pressure continued to rise, indicating that the wider the range of stent implantation, the higher the pulse pressure. The closer the stent implantation site was to the heart, the higher the pulse pressure. Conclusions The proposed simulation method in this study can accurately predict blood pressure and evaluate aortic compliance, providing theoretical and technical support for stent design and surgical plan optimization.

Abstract:Objective To study the influence of stent and balloon shape on hemodynamics in tapered vessels with multiple stenosis. Methods The hemodynamic model was established after the implantation of vascular stent in tapered vessel with multiple stenosis. The numerical simulation method was used to study the effect of the combination of different shaped stents and balloons on postoperative hemodynamics. Results When the cylindrical stent was expanded using cylindrical balloon and tapered balloon respectively, compared with cylindrical balloon expansion, the proportion of low-speed blood flow area generated by tapered balloon expansion was reduced by 0.58%, and the proportion of low time-averaged wall shear stress (TAWSS) area was reduced by 3.22%. The use of tapered balloon for expansion could produce less low-speed blood flow and low TAWSS area. When tapered balloon was used to expand the cylindrical stent and tapered stent respectively, compared with expanding tapered stent, the proportion of low-speed blood flow area generated by expanding cylindrical stent decreased by 1.35%, and the proportion of low TAWSS area decreased by 9.73%. Conclusions The hemodynamic environment of tapered vessel with multiple stenosis was influenced by the shape of stent and balloon. The use of tapered balloon to expand the cylindrical stent in tapered vessels with multiple stenosis can achieve favorable hemodynamic environment and reduce the risk of ISR occurence. This study can provide a scientific basis for the rational formulation of clinical intervention scheme.

Abstract:Objective To investigate the mechanical characteristics and voltage output changes of microcatheter sensors during cyclic blood flow, and explore the feasibility of microcatheter sensors which can monitor pressure information and stenosis lesion information. Methods A two-way fluid-solid coupling model was constructed to perform finite element numerical simulation of the interaction between the microcatheter sensor and blood, the mechanical characteristics of the sensor in the longitudinal and circumferential directions in each key frame was analyzed, and the differences in mechanical characteristics of the sensor in healthy and stenotic vessels were compared; a PVDF force-electricity simulation model was constructed, and mechanical signals on the sensor were imported to analyze the sensor’s voltage output in two scenarios. Results The longitudinal and circumferential outputs of the sensors in healthy vessels were relatively even in magnitude, with a ratio close to 1. In vessels with stenotic lesions, the longitudinal outputs of the sensors yielded significant differences, with ratios ranging from 0.3 to 0.6, and abnormal distributions in circumferential stenotic regions, with the ratio of the stenosis-direction component to the average value much larger than 1. Force-electric simulation further revealed that the sensors could convert mechanical signals into electrical signals and output them. The force-electric simulation further revealed that the sensor could convert the mechanical signal into an electrical signal and output it, and its output value ranged from 8.01 mV to 225.2 mV. Conclusions There was a significant difference in mechanical characteristics of the sensor between healthy vessels and vessels with stenotic lesions, the location and direction of stenotic lesions could be obtained by analyzing the output of the sensors, while the PVDF sensor could convert these mechanical characteristics into electrical signals which were easier to be processed. This study provides a theoretical reference for the development and application of the novel microcatheter sensors.

Abstract:Objective To propose a novel mechanical method and index to in-vivo characterize the health status of cancellous bone during the percutaneous kyphoplasty, and validate its feasibility and consistency. Methods According to the theory of elasticity, the expression and physical significance of the mechanical index K were given. Then using clinical images of the lumbar spine L4, three-dimensional finite element simulations were conducted to verify the validity of the theoretical results, as well as the consistency of the methodology and the indexes were verified for studies of different balloon shapes and puncture routes. Results The internal pressure of the balloon linearly varied with the injected fluid volume. The mechanical index K was closely related to the bone shear modulus and could well reflect the health status of cancellous bones. The balloon shape had a trivial influence on the K results, and the relative difference between the cylindrical and ellipsoidal shapes was less than 2%. The influence of surgical access route on the K results was also very small, and the relative difference between the routes by vertebral pedicle and by lateral margin of vertebral pedicle was less than 0.5%. Conclusions The in-vivo mechanical method and the mechanical index K can characterize the bone health of patients with good consistency. This study has a great significance for providing guidelines of the optimization of PKP operation plan and postoperative rehabilitation, collecting in vivo data of bone mechanical properties, and improving the diagnosis and treatment of osteoporosis in clinic.

Abstract:Objective The stress distribution of the lumbar spine L1–5, fibrous rings and nucleus pulposus of the patient in mid-phase of single-leg support under slow-walking gait was studied, to determine the optimal correction angle of the osteotomy block in curved periacetabular osteotomy (CPO), and provide an individualized plan for clinical surgery. Methods The femur-pelvis-lumbar spine DICOM data of a patient and a healthy volunteer were obtained using CT scanning to construct a three-dimensional finite element model. The cortical bone, cancellous bone, and a series of cartilages were delineated using the modeling software, and the model was analyzed by finite element method using simulation software. The patient’s lateral center edge angle (LCEA) and anterior center edge angle (ACEA) were 15°, and 16 different postoperative models (LCEA=15°,25°,35°,45°and ACEA=15°, 25°, 35°, 45°) were obtained by computer simulation of the surgical osteotomy process. The stress differences in the regions of interest of the model were compared and analyzed, which were also compared with those of patient before surgery and the healthy volunteer, so as to obtain the optimal surgical plan. Results The stresses applied to the lumbar spine decreased with increasing LCEA and ACEA angles, with the lowest stresses applied to the lumbar cones, nucleus pulposus, and annulus fibrosus in the LCEA=35°, ACEA=35°models; then, the stresses applied increased with increasing angles. Conclusions The optimal correction angle for LCEA and ACEA can be obtained using the finite element method, this method is of great significance to improve the accuracy and efficiency of CPO for different patients.

Abstract:Objective To explore the failure criterion that can accurately simulate the tensile and compressive fracture of hollow cortical bone structure. Methods Based on the previous compression and bending experimental data, the predicted results using different failure criteria were compared to determine the simulation accuracy. Results Under the compressive load, the differences in the fracture load between the simulations using the equivalent and invariant strain failure criteria and the experiment were less than 5%, indicating that these two failure criteria were suitable for predicting the cortical bone failure; under the bending load, the differences in the fracture load between the simulations using the equivalent and invariant strain failure criteria and the experiment were less than 5%, indicating that these two failure criteria could accurately predict the failure process. Conclusions The prediction accuracy using different failure criteria mainly depends on whether the strain growth rate conformed to the actual bone deformation. Unbefitting strain growth rate will lead to premature or delayed structural fracture. The fracture simulation adopted in this study is suitable for most cortical bone structures, and can be used to determine the suitable failure criterion under different loads, so as to assist in obtaining the strength limit of cortical bone in various parts and provide data support for improving the simulation accuracy and grasping the condition of fracture occurrence in clinical practice.

Abstract:Objective To explore the relationship between plantar fascia stiffness and windlass mechanism and their impact on the arch, and provide a biomechanical mechanism explanation for plantar fascia and arch-related problems. Methods A foot-plate model with 30° flexion angle at the metatarsophalangeal joint was constructed. The musculoskeletal model combined with the three-dimensional finite element analysis method was used, and the dynamic data of the foot during walking at the speed of 5 km/h was obtained using dual fluoroscopic imaging system (DFIS). The finite element model was verified, and the influence of plantar fascia stiffness on the capstan mechanism and arch-related mechanical parameters was explored. Results The finite element simulation analysis results were highly consistent with the foot data obtained by DFIS, confirming the validity of the model. With the increase of plantar fascia stiffness, the windlass effect and the stiffness of the longitudinal arch of the foot both showed an increasing trend, but the flexion angle of the metatarsophalangeal joint decreased, the distal stress of the plantar fascia gradually decreased, and the proximal stress increased; when the plantar fascia stiffness was 25%–150%, the width of the transverse arch of the foot increased with the increase of plantar fascia stiffness, while the height of the transverse arch decreased with the increase of plantar fascia stiffness; when the plantar fascia stiffness was 150%–200%, the width of the transverse arch of the foot decreased, the height increased, and the stiffness also increased. Conclusions An increase in plantar fascia stiffness can enhance the windlass mechanism to some extent, but it also leads to a reduction in metatarsophalangeal joint flexion. The stiffness of the plantar fascia affects the metatarsophalangeal joint flexion, thereby impacting the windlass mechanism and the distal tensile force of the plantar fascia. Together with the ground reaction force at the distal end of the metatarsals, these factors collectively influence the stiffness of the transverse arch of the foot.

Abstract:Objective To conduct a comparative study on the biomechanical performance of using sutures for repairing inferior pole patellar fractures. Methods Compared to the normal patellar structure ( Group A), four repair methods, namely, ‘ Krackow’ suture ( Group B), “ Kessler” fixation ( Group C), ‘ 8 - figure’ mesh method (Group D), and modified suture bridge ( Group E) were adopted. The static stiffness and dynamic stability of inferior pole patellar fractures fixed by each repair method were measured at 30°, 60°, and 90° knee flexion. Results The stiffness at all flexion angles in Group E was closer to that in Group A, compared to other repair groups, followed by Group B, then Group D, and finally Group C. After the first cycle, at 30° knee flexion, Group C showed the greatest displacement, while Groups B and E had slightly larger displacements than the Group A, and the displacement of Group D was smaller than that of Group A. At 60° and 90° knee flexion, the displacement in all repair groups was smaller than that of Group A. After 200 cycles in the subsequent three cycles, displacement changes in all repair groups were smaller than those in Group A. Conclusions All repair methods were effective. In terms of biomechanical fixation performance, the modified suture bridge was superior to the ‘Krackow’ suture and ‘8-figure’ mesh, with Kessler fixation being the least effective. However, factors such as the injury severity, incision location, and surgical time should be comprehensively considered in actual clinical use, and it is recommended that the repair method should be selected in the following order: E, B, D, and C.

Abstract:Objective To establish two osteoarthritis models of destabilization of the medial meniscus (DMM) and chronic ankle instability (CAI) in mice, and compare the effects of knee osteoarthritis with varus deformity on ipsilateral ankle cartilage degeneration. Methods Thirty 6-week-old C57BL/6J male mice were randomly divided into a control group and two surgical groups (DMM group and CAI group), respectively. The progression of ankle joint degeneration was quantitatively evaluated through behavioral observation, imaging techniques and histopathology analysis in each group of mice over a 12-week period. Results A decline in gait stability and balance was observed in two surgical groups. Compared to the control group, the time required to cross the balance beam was increased by 23.20%, and the number of slips was increased 43.26% at 12th week postoperatively in the DMM group. The bone volume fraction and bone mineral density of ankle joints also increased. Meanwhile, wear and tear of the ankle cartilage were found, with the formation of osteophytes, and OARSI score was increased by 88.89%. These changes in ankle joint were more pronounced in the CAI group. Conclusions This mouse model-based study revealed a coupling relationship between the knee and ankle motion. Knee osteoarthritis with varus deformity could lead to a significant ankle joint degeneration, while the damage was less severe than that observed in CAI.

Abstract:Objective To investigate the correlation between the change of muscle tissues and bone mineral density (BMD) in elderly women with hip fracture, with consideration of the impact of muscle mechanics on bone mass changes. Methods A total of 79 elderly patients with hip fracture were selected as the fracture group, and 45 physical examination personnel as the control group. Analyze the total muscle mass, total body fat, trunk muscle mass, trunk fat mass, arm muscle mass, arm fat mass, leg muscle mass, leg fat mass, as well as BMD at the lumbar spine (L1-4), femoral neck, hip joint, and whole body. Results Muscle content and fat content of the whole body, upper limb and lower limb, fat content of the trunk, relative skeletal muscle index (SMI) and BMD of the whole body in fracture group were significantly lower than those in control group (P<0.05). The incidence rate of sarcopenia for elderly women in fracture group was higher than that in control group. BMD of femoral neck of the affected side was significantly lower than that of the intact side in women with intertrochanteric fractures. Logistic regression analysis found that SMI in elderly women with hip fracture was negatively correlated with age, and positively correlated with body mass index (BMI), BMD of the femoral neck and whole body. Conclusions The rate of sarcopenia was significantly higher in elderly patients with hip fracture, and SMI was closely related to BMD of the femoral neck and whole body. Therefore, sarcopenia should be highly emphasized in the prevention and treatment of osteoporotic fracture in elderly people.

Abstract:Objective To evaluate the safety and therapeutic efficacy of three-dimensional-printed personalized cervical correction pillows for treating cervical spondylotic radiculopathy. Methods A finite element model was established to simulate and analyze the biomechanical changes in cervical spine before and after using the pillow. Additionally, 20 patients with chronic neck pain were included to analyze changes in visual analogue scale (VAS) scores, neck disability index (NDI), pressure pain threshold (PPT), Borden value, cervical lordosis, T1 slope, cervical slope, and thoracic inlet angle before and after using the pillow. Results Finite element analysis indicated that the maximum stress on vertebral bodies increased by 64.35% and the maximum stress on cartilage tissues by 5.09% after using the pillow. The Borden value improved by 45.75%. Clinical studies showed a significant reduction in VAS scores, NDI, and PPT after treatment (P<0.05), while PPT, Borden value, cervical lordosis, T1 slope, and thoracic inlet angle significantly increased (P<0.05). Conclusion The 3D-printed personalized cervical correction pillow is safe and effective in alleviating neck pain and improving cervical curvature. It provides a new and effective non-surgical treatment option for cervical spondylotic radiculopathy, with significant clinical implications.

Abstract:Objective To explore the biomechanical safety of applying traditional Chinese orthopedic manipulation therapy after anterior cervical discectomy and fusion (ACDF) surgery, so as to provide a theoretical basis for clinical treatment in biomechanics. Methods Based on CT data, a three-dimensional finite element model of the normal C0–T1 cervical spine was established, and an ACDF postoperative finite element model of the C5–6 segment was constructed on this basis. Cervical spine rotation manipulation was simulated at the C4 and C7 segments of both models, and the von Mises stresses of the vertebral body, bilateral facet joints, intervertebral discs, and internal fixation system under manipulation loading of the C4 and C7 segments in both models were compared and analyzed. Results The study found that when the C4 segment was manipulated, the stress on the C5, C6, and C7 vertebral bodies in the ACDF postoperative model decreased by 12.3%, 11.5%, and 26.4% ,compared to the normal model. The stress on the left facet joints of the C4–5, C5–6, and C6–7 segments decreased by 12.3%, 58.8%, and 15.4%, and the stress on the right facet joints decreased by 16.6%, 92.1%, and 17.2%. The stress on the C4–5 and C6–7 segments decreased by 13.2% and 4.0% , while the maximum stress of the fusion cage, titanium plate, and screws in the C5–6 segment were 9.349, 111.9, and 300.8 MPa. When the C7 segment was manipulated, the stress on the C4, C5, and C6 vertebral bodies in the ACDF postoperative model increased significantly compared to the normal model, especially the C5 vertebral body, with an increase of nearly 18 times. Except for the stress on the left facet joint of the C4–5 segment increased by 57.7%, the stress on the bilateral facet joints of other segments generally decreased, but the stress on the C4–5 and C6–7 segments increased by 43.2% and 21.7% and the stresses on the fusion cage, titanium plate, and screws in the C5–6 segment were 2.926, 205.4, and 256.2 MPa. Conclusions The safety of performing manipulation on the upper vertebral body of the fusion segment after ACDF surgery is relatively high, but performing manipulation on the lower vertebral body of the fusion segment may lead to stress concentration and increase the risk of injury. When postoperative conservative treatment is implemented, the manipulation safety and indications should be considered to avoid operations in high-risk areas, and more precise and safe manipulation intervention treatment should be implemented based on the specific postoperative biomechanical state of the patient.

Abstract:Objective To study the characterization of surface electromyographic signals of upper limb force-generating muscles operated by rolling manipulation of Tuina doctors. Methods Surface electromyographic signals during rolling manipulation were collected from beginners and proficient operators for comparative analysis, and the patterns, similarities, and differences were summarized. Results The iEMG ratio of the ulnar lateral wrist extensor muscle in the proficient group was significantly higher than that in the beginner group (P<0.05), while that of the middle deltoid fascicle in the beginner group was significantly higher than that in the proficient group (P<0.05). There was no statistical difference in the iEMG ratios of other muscle groups (P>0.05). The proficient group mainly used the ulnar wrist extensors, lateral head of triceps brachii, pectoralis major, and ulnar wrist flexors, while the beginner group mainly used the lateral head of triceps brachii, pectoralis major, and radial wrist flexors. Conclusions The proficient group and the beginner group shared common features in the electromyographic signals of the rolling manipulation. The proficient group increased the angle of ulnar deviation by recruiting more ulnar wrist extensors to increase the angle of palmar flexion and the dorsal contact area of the hand, and the proficient group used the middle and posterior deltoid fasciculus muscles less intensively and mastered the ‘sinking shoulder’ principle better.

Abstract:Objective Two neural network algorithm models were constructed to estimate the three-dimensional (3D) ground reaction force (GRF) and center of pressure (COP) during walking, and the estimation results of the two algorithm models were compared, so as to provide a solution for the acquisition of gait dynamics data without force plate. Methods A total of 1 384 gait data were selected. Multi-layer perceptron (MLP) and convolutional neural network (CNN) were applid to construct models for estimating GRF and COP components based on the 3D trajectory of whole-body markers. 100 samples were randomly selected as the test set, and the estimation performance was evaluated by the correlation coefficient (r), relative root mean square error (rRMSE). Paired-sample t-tests were used to compare the estimation performance of the two neural network models. Results The r values of each components of GRF estimated by MLP were 0.954–0.993, and the rRMSEs were 4.36%–9.83%. The r values of each component of GRF estimated by CNN were 0.979–0.994, and the rRMSEs were 3.06%–6.69%. The r values of each component of COP estimated by MLP were 0.888–0.992, and the rRMSEs were 4.78%–16.63%. The r values of each component of COP estimated by CNN were 0.944–0.995, and rRMSEs were 3.06%–10.85%. The RMSEs of CNN in estimating the medio-lateral component of GRF , the medio-lateral and antero-posterior components of COP during right stance phase, as well as the medio-lateral and antero-posterior components of COP during left stance phase were all lower than those of MLP (P<0.01). The RMSEs of MLP in estimating the anterior-posterior component of GRF during right stance phase, as well as the anterior-posterior component of COP and the vertical direction of GRF during left stance phase were lower than those of CNN (P<0.01). Conclusions Both MLP and CNN achieved good estimation accuracy in estimating GRF and COP during walking based on the trajectory of whole-body markers. The estimation accuracy of MLP in estimating the anterior-posterior components and vertical component of GRF was better than that of CNN, while the estimation accuracy of CNN in estimating the medio-lateral component of GRF, the anterior-posterior and medio-lateral components of COP were better than that of MLP.

Abstract:Objective To develop a data-driven model for estimating tangential ground reaction force (GRFt) from lower limb kinematic data and select the most suitable input based on a balance between input quantity and estimation accuracy, with the aim of measuring GRFt in outdoor gait experiments. Methods Gait data from ten subjects walking at five different inclines (-10°, -5°, 0°, 5°, 10°) were used to train two data-driven models, namely a backpropagation neural network (BPNN)-based model and a polynomial sparse identification (PSI)-based model. The performance of these models was evaluated using eight kinematic data combinations and the normal ground reaction force (GRFn) as inputs to determine the optimal model and input combination. Results Under the same input dimensionality, the combination of hip-knee joint angles proved more accurate in estimating GRFt than the knee-ankle joint angle combination. Specifically, the BPNN and PSI models based on the former combination predicted GRFt with errors of 1.61%BW (body weight) and 1.84%BW, respectively, while the latter combination resulted in errors of 2.82%BW and 3.15%BW. When GRFn and all joint angles were used as inputs, the model’s prediction error was only 1.46%BW. Conclusions The combination of GRFn and hip-knee joint angles achieves an optimal balance between computational complexity and estimation accuracy. This study supports the accurate estimation of GRFt in outdoor gait testing.

Abstract:Objective To investigate the effects of wearing high-heeled shoes at different heel heights on ankle joint motion control during walking in women with chronic ankle instability (CAI). Methods The Vicon infrared motion capture system and a three-dimensional force plate were used to synchronously collect kinematic and kinetic parameters within 200 ms before and after foot contact for 20 healthy females and 20 CAI females while walking on flat ground wearing high-heeled shoes at different heel heights (1, 3, 5, and 7 cm). Two-way repeated measures ANOVA was applied to analyze the data statistically. Results There was an interaction effect between group and heel height on the peak inversion angular velocity and peak inversion angle during foot strike. Post-hoc tests revealed that within the healthy group, compared to a 1 cm heel, the 5 cm (P=0.002) and 7 cm (P=0.002) heels had significantly greater peak inversion angular velocity within 200 ms before and after foot strike; there were significant differences in peak inversion angle between the 1 cm and 5 cm (P=0.018), 7 cm (P<0.001) heels. In the CAI group, compared to a 1 cm heel, the 5 cm (P=0.002) and 7 cm (P=0.002) heels had significantly greater peak inversion angular velocity within 200 ms before and after foot strike; there were significant differences in peak inversion angle between the 1 cm and 3 cm (P<0.001), 5 cm (P<0.001), 7 cm (P<0.001) heels. There was a significant main effect of height on peak plantarflexion angle (P<0.001), peak external rotation angle (P<0.001), peak external rotation angular velocity (P<0.001), and peak plantarflexion torque (P=0.048) within 200ms before and after foot strike; there was a significant main effect of group on peak eversion torque (P<0.001). Conclusions Compared to healthy individuals, women with CAI have reduced ankle joint control while walking with high-heeled shoes. As heel height increases, the ankle stability decreases. It is recomended that women with CAI should wear high-heeled shoes with a heel height of 3 cm or below.

Abstract:Objective To develop a three-compartment kinetic fatigue model for the isometric muscle endurance of the hip, knee, and ankle joints at 50% IPT (isometric peak torque), so as to provide a theoretical basis for simulation-based assessments and load evaluations in biomechanics and sports science. Methods The IPT of the hip, knee, and ankle joints was measured in 40 male university students. Isometric endurance tests were then performed on all three joints at 50% IPT until exhaustion. Electromyography data and endurance time (ET) of major lower limb muscles were collected concurrently. The differences between ETs predicted by models based on previously recommended F and R parameters and actual ETs were analyzed. Subsequently, experimental ETs were used in a grid search to optimize F and R parameters, allowing for the development of an accurate three-compartment kinetic model. Results The ET of the hip and ankle joints was significantly longer than that of the knee joint (P<0.001). Models using previously recommended F and R parameters overestimated ET, with significantly higher predicted values than experimentally measured ET (P<0.001), as well as elevated root mean squared error (RMSE) and mean relatvie error (MRE) values. The grid search successfully identified F and R parameters for the three-compartment model in isometric endurance tests of lower limb joints , with no statistical difference between model-predicted ET and experimental ET (P>0.05). Conclusions The developed model in this study can serve as an indirect measurement tool for evaluating load in similar activities.

Abstract:Objective To explore limb coordination patterns and energy flow strategies during the sit-to-stand (STS) transition in individuals with patellofemoral pain (PFP), so as to provide a theoretical evidence for the pathogenesis of PFP and subsequent formulation of treatment and rehabilitation strategies for PFP patients. Methods A totoal of 36 participants was recruited for the STS test. They were divided into the unilateral PFP group (unilateral group), bilateral PFP group (bilateral group), and control group, based on the number of limbs affected by PFP. An infrared motion capture system and a three-dimensioanl force plate were used for motion capture. Visual 3D and Matlab software were used to calculate the trunk and pelvis angles, angular velocities, linear velocities, and proximal and distal joint forces. Additionally, the angles, torques, and joint forces of the hip, knee, and ankle joints, along with the angular and linear velocities of the thigh and shank, were computed. Coupling angles was used to represent coordination patterns via vector coding; the segmental net energy integration method was used to calculate energy flow within segments at each stage. Results For the coordination pattern at frontal plane, the proximal coordination mode frequency of the pelvis-hip coordination in the flexion momentum phase (FMP) was higher in unilateral group than that in bilateral group (P=0.024). In the momentum transfer phase (MTP), the frequency of in-phase coordination in the trunk-pelvis coordination was higher in unilateral group than that in bilateral group (P=0.023), while the frequency of distal coordination was higher in control group than in that in unilateral group (P=0.032). For the knee-ankle coordination pattern, the frequency of distal coordination in control group was lower than that in unilateral and bilateral groups (P=0.025, P=0.005). In segmental energy flow, during the FMP, the energy output from the pelvis during extension phase (MP) was higher in bilateral group than that in control group (P=0.021). Conclusions PFP affects energy flow patterns and coordination patterns at frontal plane during the STS transition. Individuals in unilateral group may engage in lateral pelvic and ankle movements as a dynamic compensation for patellofemoral joint pressure, whereas individuals in bilateral group appear to increase pelvic region energy output and employ a more complex whole-body coordination pattern to compensate for functional deficits in the knee caused by PFP.

Abstract:Objective The finite element pelvis model with detailed anatomical structures which meets the Chinese human 95th percentile characteristics is developed, and the influence of cortical bone modeling methods on the biomechanical response of the real pelvis is explored. Methods Based on the pelvic medical images of a 95th percentile male volunteer, the two finite element pelvis models with real hip bone cortical bone thickness (REA-M) and 2 mm uniform cortical bone thickness (CON-M) dominated by hexahedral elements were constructed. Using simulation methods to reconstruct the loading conditions of cadaver experiments, the validation of models was verified by comparing the experimental results and simulation results, and biomechanical response differences of the two models under different working conditions were discussed. Results The simulation data showed that there was a strong correlation between overall biomechanical responses of the two pelvic models and the cadaver experiment, and the mechanical response difference between the two models was mostly within 8%, and the correlation score difference between the two models was smllaer than 2%. Conclusions The validation of the two pelvic models established in this study is verified by rebuilding multiple simulation experiments. Although biomechanical responses of the two models are different, the difference in the mechanical responses of CON-M and REA-M models were small. From the perspective of model simplification, the CON-M model can be used to study the biomechanical response of the pelvis.

Abstract:Objective To explore the frequency domain characteristics of pedestrian head dynamic response in vehicle collisions and investigate the correlation between frequency domain parameters and time domain injury criteria. Methods Finite element modelling based on human body model was used to simulate the process of pedestrian head-vehicle impacts, and the wavelet packet signal analysis method was employed to obtain the frequency domain response of pedestrian head in the simulations. Results The head energy under impacts at the bonnet area was mainly dispersed in the 0–300 Hz frequency band, while the head energy under impacts at the windshield area was mainly concentrated in the 0–5 Hz frequency band. The peak energy of frequency band for pedestrian head generally increased with the increase of linear and rotational speed, and the influence of rotational speed on the peak energy of frequency band was more significant when the linear speed was higher. The linear correlation R2 between the peak energy of the head frequency band caused by the collision between the bonnet and windshield area and the time-domain criterion for skull injury were 0.85 and 0.61, respectively. But their correlation with the time-domain indicators for brain injury evaluation was relatively low (R2<0.5). Conclusions The frequency domain response characteristics of pedestrian heads are affected by collision speed and location. The peak energy of the frequency band can potentially characterize the risk of skull injury, but the frequency band and concentration of the peak energy in the frequency band are not related to the risk of head injury. This study can provide references for the evaluation of head blunt injury combined with time-frequency response.

Abstract:Objective To study the effects from varying stenosis degrees of the mesencephalic aqueduct on intracranial cerebrospinal fluid ( CSF) flow field. Methods Based on the clinical magnetic resonance image sequences of a male volunteer, a complete normal CSF circulation model was reconstructed by using semiautomated image segmentation technique. Subsequently, eight ideal models representing different stenosis degrees of the mesencephalic aqueduct were manually created. Computational fluid dynamics (CFD) was then performed to simulate the CSF flow field in the nine models. Results The stenosis degree of the mesencephalic aqueduct was positively correlated with the maximum pressure difference between the aqueduct upstream and downstream and the maximum velocity of CSF within the stenosed aqueduct. In the normal model, the maximum pressure difference was 0. 84 Pa and the maximum velocity was 11. 4 mm / s. While in the maximum stenosed model, the maximum pressure difference and velocity were 21. 36 Pa and 60. 3 mm / s, respectively. Compared to the normal model, the maximum pressure difference and velocity were approximately increased by 25 times and 5 times, respectively. Moreover, the maximum pressure difference was inversely proportional to the stenosis area square of the aqueduct, and there was a linear relationship between the pressure difference and the quadratic the maximun CSF velocity. Conclusions The pressure difference and velocity of the stenosed mesencephalic aqueduct was not apparently increased with mild stenosis with respect to the normal aqueduct, while the great aqueductal stenosis increased the risk of hydrocephalus. This study provides a theoretical framework which contributes to understanding the development of obstructive hydrocephalus and intracranial hypertension.

Abstract:Objective To investigate the biomechanical effects of tropoelastin on self-assembly and degradation of the collagen in vitro. Methods The real-time dynamic scanning with atomic force microscopy was utilized to observe and analyze the changes in microstructure, orientation, area fraction, and average diameter of collagen fibrils during the self-assembly process. The D-band structure of collagen fibrils was characterized using transmission electron microscopy. Finally, data analysis was performed using Gwyddion and Matlab software to assess the structural characteristics and degradation resistance of collagen fibrils. Results Compared to the control group, the addition of tropoelastin not only promoted the collagen self-assembly and significantly increased the area occupied by the assemblies, but also caused a shift in their orientation from unidirectional to multidirectional. Upon the addition of collagenase, the assemblies underwent degradation; however, the degradation half-period decreased with the inclusion of tropoelastin, indicating that tropoelastin accelerated the degradation of collagen assemblies. Conclusions The addition of tropoelastin promotes the collagen self-assembly, and increases the area occupied by the self-assembled structures. However, the consistency of orientation in the assemblies is weakened, resulting in a reduced resistance of collagen fibrils to degradation by collagenase. This study lays a theoretical foundation for the preparation of collagen-based biomimetic functional materials.

Abstract:Objective To investigate the effects of implant length, diameter, and abutment angle on bone stress around maxillary central incisors, elucidate the significance of each factor on maxillary stress and determine the optimal parameter combination. Methods A three-dimensional (3D) model of the maxilla was reconstructed based on CBCT data. Using an orthogonal table, a total of 16 dental implant 3D models were established, varying in length, diameter, and abutment angle. These models were assembled with the maxillary and rigid-body models. Finite element analysis was performed using the transient dynamics module of ANSYS. Orthogonal experiments and one-way analysis of variance (ANOVA) were conducted on the obtained stress data. Results The implant diameter showed a statistically significant effect on the maximum von Mises stress in cortical bone (P=0.010), while implant length (P=0.229) and abutment angle (P=0.844) did not demonstrate a statistical significance. The optimal parameter combination for cortical bone stress was 5.0 mm implant diameter, 12 mm implant length, and 0° abutment angle. In cancellous bone, implant length (P=0.001), diameter (P=0.011), and abutment angle (P=0.013) all had statistically significant effects on the maximum von Mises stress. The optimal parameter combination for cancellous bone stress was 14 mm implant length, 5.0 mm implant diameter, and 5° abutment angle. Conclusions Implant diameter significantly affects the stress of both cortical and cancellous bone. Clinically, a larger diameter should be preferred to reduce the stress peak. Implant length is the next most important factor, while abutment angle has the least effect.

Abstract:The triceps surae muscle-tendon unit (MTU) is the key for effective force generation, transmission, and energy storage and release in human movement, impacting efficiency, but its injury rate remains high. This paper provided an overview of MTU function and its biomechanical adaptations during running, aiming to deepen the understanding of MTU’s role in movement and to explore how external factors influence its biomechanical properties, offering scientific insights for improving running performance and preventing injuries. During running, forefoot striking and wearing shoes with greater stiffness, such as shoes with carbon plate, the contraction or return energy could be achieved through a more economical MTU behavior, namely reduce energy consumption by more economically muscle contraction and more energy storage of elastic element and the muscle contraction was exerted at a length closer to the optimal muscle fascicle length and reduce energy consumption caused by muscle contraction. However, adopting forefoot striking, barefoot running, or wearing minimalist shoes during running could increase the mechanical loads on the MTU. After gait retraining, the MTU could contract or recoil energy more efficiently while running, while the impact of other training methods on it is relatively poor, and the research in this area is still not sufficient. Therefore, future research should focus on optimizing the biomechanical properties of the MTU, MTU interaction and balanced development through changes in movement patterns, equipment, and training methods to enhance performance and reduce injuries.

Abstract:Knee adduction moment (KAM) is a key biomechanical index in knee joint biomechanics research, which is closely related to the occurrence and development of knee osteoarthritis (KOA). Therefore, understanding the factors influencing KAM is important for the diagnosis and treatment of KOA disease. This article summarizes the factors that may affect KAM based on relevant research.

Abstract:This study reviews recent publications on the biomechanical causes and treatment of flat foot, through searching PubMed, Web of Science, CNKI, Wanfang and other databases. The reasons for the formation of flat footinclude congenital factors and acquired factors, while the treatment methods mainly include orthopedic insoles, physical therapy, surgical therapy and exercise therapy. These methods, to a certain extent, can correct foot structural abnormalities, optimize biomechanical properties and improve foot stability and range of motion. For future research, the advanced imaging and simulation technology will be used for accurate assessment, the application of novel materials and non-surgical therapies will relieve long-term symptoms, genetic researches will promote the development of early diagnosis and personalized treatment, and the use of intelligent orthosis will realize real-time monitoring and dynamic adjustment, to provide more and more effective methods and means for the evaluation, intervention and treatment of flat foot.

Abstract:In order to fully consider the physiological characteristics and movement mechanism of the human body under the premise of ensuring the function and practicality of the product, the human-fabric contact finite element model based on biomechanical feedback plays an important role in the design of ‘people-oriented’ health protection products. This review focuses on the design of protective products made of flexible materials, and discusses the application status and development trend of human finite element model in the design of protective products. The construction process of finite element models of different parts of the human body in recent years is summarized from the perspective of human biomechanics. Secondly, from the contact models established between the human head, torso, upper limbs and lower limbs and protective devices, the application status and challenges of finite element method in the design of health protective products are sorted out. Finally, the problems existing in the use of finite element method in such researches are discussed. It is pointed out that in the context of pursuing accuracy, real-time and realism, finite element contact models with the advantages of high efficiency, precision and reusability still have a broad application prospect.