To investigate the protective effect of cerebrospinal fluid (CSF) on the spinal cord in patients with scoliosis and evaluate its buffering effect during gravitational traction surgery and in daily life, so as to provide a theoretical guidance for surgical planning and postoperative rehabilitation of scoliosis.

A three-dimensional coupled spinal cord-CSF finite element model was established to simulate the biomechanical responses of the spine under two scenarios: gravitational traction surgery and daily life. Comparative analyses were conducted for conditions with and without CSF, and the buffering effect of CSF was quantitatively assessed.

During simulated gravitational traction surgery, CSF significantly reduced the stress and deformation of the spinal cord, with the stress in spinal cord white and gray matter decreasing by 65%-90% and deformation decreasing by 70%-95%. In the daily life scenario, CSF provided greater protective effects in lateral flexion and anterior-posterior flexion directions, with stress reductions of 60%-85%. However, in torsion, the buffering effect of CSF was relatively weaker, with stress reductions of only 10%-25%.

CSF significantly reduces spinal cord stress and deformation during gravitational traction surgery and in daily life, reducing the risk of injury.

To investigate the effect of postoperative reduction quality in femoral neck fracture internal fixation on mechanical properties of the femoral head from the perspective of trabecular bone biomechanics.

From patients who underwent hip replacement surgery for femoral neck fractures, a total of 26 femoral head slice specimens were obtained. The central axis of the primary compressive trabeculae was defined as the 0° group, with the intersection point of the primary compressive trabeculae and the femoral calcar serving as the center. By rotating the specimens to simulate different reduction angles, the cut femoral head slice specimens were randomly divided into five groups: -10°, -5°, 0°, 5°, and 10°, representing femoral heads with varying reduction qualities. The specimens were subjected to single compression load tests and fatigue load tests. The load was set from 70 N to 1 400 N, at a frequency of 1 Hz, with 10 000 cycles. Axial stiffness, displacement, and the number of collapse cycles were measured, to compare the biomechanical properties of femoral head specimens under different reduction qualities.

There were differences in the axial stiffness, displacement, and number of collapse cycles among the femoral head specimens in different groups. Under 800 N load, the axial stiffness of 0° group was significantly greater than that of ±10° groups (P<0.05). The axial stiffness of 0° group was also greater than that of the ±5° groups, but the differences were not statistically significant (P>0.05). The axial stiffness of ±5° groups was greater than that of ±10° groups (P<0.05). 0° group had a lower displacement than ±5° groups and ±10° groups. However, the differences in displacement between 0° group and ±5° groups were not statistically significant (P>0.05), while the differences between the 0° group and ±10° groups were statistically significant (P<0.05). The differences in displacement between ±5° groups and ±10° groups were also statistically significant (P<0.05). 0° group had a significantly higher number of collapse cycles than ±10° groups (P<0.05). The number of collapse cycles in 0° group was also higher than that in ±5° groups, but the differences were not statistically significant (P>0.05). The number of collapse cycles in ±5° groups was significantly higher than that ±10° groups (P<0.05).

The quality of reduction after internal fixation of femoral neck fractures significantly affects the biomechanical properties of the femoral head. This study provides a scientific basis for optimizing treatment and postoperative management, aiming to improve clinical outcomes and patients’ quality of life.

To investigate the effects of inclined axial compressive force and flexion moment on the anterior and posterior shear stiffness of the lumbosacral segment.

Six fresh-frozen human cadaveric L5-S1 segments were tested under intact and two progressively impaired structural conditions: intact, a 4-mm bilateral facet joint gap, and anterior discectomy with nucleus pulposus removal plus circumferential release of the inner annular fibers (disc injury). A 300 N axial compressive force was applied either vertically downward or with a 10° or 20° anterior inclination through the disc's shear center. Anterior (0 N to 250 N) and posterior (-50 N to 0 N) shear tests were conducted using a material testing machine. These tests were repeated under a 5 N·m flexion moment. The relative motion between L5 and S1 was measured using a three-dimensional motion capture system.

In the intact state, the inclination of the axial compressive force did not significantly alter anterior or posterior shear stiffness. However, the application of a flexion moment increased anterior shear stiffness by 49.3%. Progressive structural damage resulted in incremental increases in anteroposterior shear translation and corresponding reductions in stiffness. Notably, under combined loading with axial compression and flexion moment, anterior stiffness decreased from 939 N/mm (intact) to 224 N/mm (disc injury), while posterior stiffness decreased from 572 N/mm to 217 N/mm. Within the low-load range, no significant differences in shear stiffness were observed across any structural conditions, regardless of axial force inclination or combined with a flexion moment.

This study supports the clinical view that retro-inclination of the pelvis serves as a compensatory mechanism to enhance segmental shear stability. However, this compensatory capacity gradually diminishes and ultimately fails as spinal degeneration progresses.

To address the limitations of conventional physics-informed neural network (PINN) in handling hemodynamic boundary constraints, an improved hard boundary-constrained PINN (HBC-PINN) framework was proposed to achieve precise prediction of blood flow fields within stenotic arteries.

An idealized stenosed vessel geometry model was established and computational fluid dynamic simulation was performed to obtain a validation dataset. Appropriate boundary dependent trial functions were designed according to the hard constraint method to embed the flow boundary conditions into the network output. Thus, an HBC-PINN model with the hard boundary constraint method was constructed to predict the velocity field and pressure field of stenosed blood flow. Meanwhile, an original PINN model with the soft constraint method was also built for comparison. By evaluating the accuracy of the two models on the validation dataset, the capability of the HBC-PINN model to simulate hemodynamics without using any labeled data for training was verified.

The effectiveness of the HBC-PINN method in predicting hemodynamic parameters in stenosed blood flow tasks was validated. The relative L₂ errors of the flow velocity and pressure predicted by the HBC-PINN in two different stenosis scenarios were both lower than 0.5%, representing an improvement of over 48.8% in accuracy compared to the original PINN model. Additionally, the prediction accuracy of the transverse velocity also increased by more than 35.4%.

Implementing hard constraints on boundary conditions in the PINN modeling process can effectively improve the prediction accuracy of hemodynamic parameters and the efficiency of model solving.

To investigate stress distributions of the knee joint at 0 and 15^th day after anterior cruciate ligament reconstruction (ACLR) under a compressive force through the axis of the femoral shaft onto the proximal femur.

A three-dimensional (3D) finite element model of the human knee joint incorporating viscoelastic material properties was developed. The one-dimensional (1D) Prony series viscoelastic constitutive model parameters for articular cartilage, menisci, ligaments, and anterior cruciate ligament (ACL) grafts were determined by fitting experimental creep curves. The viscoelastic parameters of ACL grafts at 15^th day after ACLR surgery were extrapolated. Finite element simulations were then performed to analyze the von Mises stress distributions in knee ligaments, ACL grafts, articular cartilage, and menisci under 1.5 kN vertical downward compressive load applied to the femur, with loading durations of 1 second and 600 seconds.

At 15^th day after ACLR surgery, the initial relaxation modulus and equilibrium modulus of human ACL grafts remained elevated compared to native ACL tissues, resulting in a significantly higher stress concentration within the grafts relative to healthy ACL. Despite the compromised mechanical properties of the grafts after ACLR surgery, the vertical downward compressive force applied to the femur under both short-term (1 s) and prolonged (600 s) loading durations, exhibited a minimal biomechanical impact on articular cartilage and meniscal structures.

Following ACLR, vertical compressive loads during weight-bearing rehabilitation exercises such as standing demonstrate minimal impact on articular cartilage and meniscus, while promoting fibrous regeneration of the graft. This renders such exercises a prudent early-stage rehabilitation strategy. Graft preparation requires balanced consideration of elastic and viscous properties, with grafts exhibiting higher relaxation modulus and viscosity coefficient than healthy ACL proving more effective in maintaining early postoperative knee stability.

To investigate the dynamic balance ability of healthy young adults under different obstacle-crossing strategies, thereby providing a theoretical basis for fall prevention training and public facility design.

Twenty healthy young adults participated in the experiment using F-scan plantar pressure analysis insoles. The subjects were required to cross three obstacles with different combinations of height and width. With their dominant foot serving as the leading foot and the non-dominant foot as the trailing foot, the subjects performed both lateral and forward crossing maneuvers, and their plantar pressure data were collected.

Different crossing strategies significantly affected the adjustment speed of the leading foot's center of pressure in the medial-lateral direction (COP_ML), the area of the 95% confidence circle, ML amplitude, and anterior-posterior (AP) amplitude (P<0.05). These strategies also significantly impacted the trailing foot's COP_ML adjustment speed, the area of the 95% confidence circle, and the range between the maximum and minimum swings (P<0.05). For the leading foot, during lateral and forward crossing, the balance parameter values under different heights and widths were statistically significant (P<0.05), increasing as the height and width increased. For the trailing foot, during forward crossing, the balance parameter values under different heights were statistically significant (P<0.05), increasing with height, while during lateral crossing, the differences in balance parameter values were not statistically significant (P>0.05).

Healthy young adults demonstrate better balance ability with the leading foot during forward obstacle crossing, which aligns with the movement habits of the dominant foot and daily activity patterns. The trailing foot exhibits a more stable plantar pressure distribution during lateral obstacle crossing, likely due to a larger contact area and more even center of gravity distribution.

The biological characteristics and action mechanisms underlying the excellent performance of skeletal muscles were studied through experiments to provide a scientific basis for the development of flexible actuators with performance comparable to that of skeletal muscles.

A frog skeletal muscle sample was contracted by applying electrical stimulation, and then tensile load was applied to it to analyze the relationship between the driving properties (such as contraction length and output force) of skeletal muscle and its structure from three aspects: skeletal muscle dimensions, tendon, and epimysium.

The contraction lengths of these skeletal muscle samples were approximately 28.92% and 20% under unloaded conditions and under 50% of their maximum output force, respectively. When the load on the skeletal muscles did not exceed 20% of their maximum output force, they also exhibited the property of rapid reduction (approximately 1.25 s). The active tendon increased contraction by approximately 19.68% compared with the inactive tendon, and the integrity of the epimysium protected the force transfer efficiency of skeletal muscles.

By simulating the structural and biomechanical properties of skeletal muscles, flexible actuators can achieve better driving performance, thus greatly promoting the development of bionic robots.

By applying the long short-term memory (LSTM) neural network model and using lower body landmark coordinates obtained from a markerless motion capture system as inputs, to estimate ground reaction force (GRF) curves during running.

The video images and GRF data of 59 amateur runners during running were collected by the markerless motion capture system and three-dimensional (3D) force plates. The LSTM model was established, and the 3D coordinates of 11 lower body landmarks, obtained via the Theia3D markerless system, were used as inputs to estimate the 3D GRF curves during the stance of running. The estimation performance was evaluated using correlation coefficients r, root mean square error (RMSE), and normalized root mean square error (nRMSE) by comparing LSTM model estimation and force plate measurement. Statistical parametric mapping was used to analyze differences in GRF curves estimated by the LSTM model and measured by the force plate, while paired t-tests were used to assess differences in GRF characteristics between model estimation and actual measurement.

A strong correlation (r>0.85, P<0.001) and lower error (RMSE<0.3 body weight, nRMSE<15%) was found between the LSTM model estimation and actual measurements. No significant difference was found in GRF curve intervals between LSTM model estimation and actual measurements. There was no significant difference in GRF characteristics between LSTM model estimation and actual measurements (P>0.05).

Based on the LSTM model, the 3D GRF curves can be effectively estimated by lower body landmark coordinates obtained from the makerless motion capture system, thereby acquiring the highly accurate GRF characteristics. The LSTM model developed in this study can be used to monitor injury risks during running in outdoor environments.