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Abstract:From biomechanics to mechanobiology, and then to mechanomedicine in the intersection frontiers of mechanics and life and medical science, biomechanics strongly promotes the development of biomedical engineering and plays a pivotal role in disease diagnosis and treatment. Similarly, the study of dental biomechanics can help to break through the research bottleneck and solve the difficult problems in clinical practice. Combined with the latest progress in the field of oral biomechanics in 2022, this review focuses on the development and application of biomechanics in the field of stomatology from two aspects: the main mechanical organs of the oral and maxillarfacial system, and their related mechanomedicine. Special attention is given to mechanobiology effects and subsequent mechanotherapy, with the aim to facilitate transformation and application of the achievements in dental biomechanics.

Abstract:Oral biomechanics, an important fundamental discipline within orthodontics, continually evolves and expands upon traditional orthodontic mechanical systems. As advancements in new orthodontic devices and techniques persist, interest within the field progressively focuses on the investigation of biomechanical effects of various orthodontic systems. Furthermore, relentless optimization, innovation, and breakthroughs in oral biomechanics technology offer an essential pathway to simulate and understand the biomechanical impacts within orthodontic treatment more accurately. This review primarily summarized the research development from the recent years across three principal orthodontic treatment systems: fixed orthodontics, invisible orthodontics, and orthopedic treatment, including orthodontic concepts, emergence of new technologies, and implementations of novel biomechanical techniques within these systems.

Abstract:Objective To optimize the connection between the three-dimensional ( 3D) printed self-positioning titanium mesh main body and the positioning wings at both ends, including thickness, width and connection configuration of the positioning wings at the connection, and to analyze and optimize structural performance of the simulation model before and after the improvement, ultimately obtain the optimal design of a novel self-positioning titanium mesh. Methods A self-positioning titanium mesh simulation model was built in software SolidWorks to optimize and improve dimension parameters. Then, the multi-objective optimization design for thickness and width of the connection was conducted using the simulation software ANSYS Workbench. A discontinuous connection configuration was designed at the connection to obtain an optimized self-positioning titanium mesh. Results When the 40 N load was applied to outer surface of the novel self-positioning titanium mesh alveolar crest, the maximum strain at the connection did not exceed fracture strain of the titanium mesh, and the stress and deformation were within an acceptable range. When the 10 N bending force at 45° angle was applied to free end of the positioning wing on one side, the maximum strain at the connection exceeded the fracture strain of the titanium mesh, and the crack propagation path was concentrated at the connecting line. The experimental results of the virtual model were basically consistent with the results of mechanical performance verification test. Conclusions By optimizing the dimension and configuration of the individualized self-positioning titanium mesh connectome, the connectome does not break or shift significantly when the individualized titanium mesh is placed and pressed during surgery. After surgery, simply bending free end of the positioning wing can achieve a neat fracture and separation of the connector along the connecting line, with a smooth and flat cross-section. This study has achieved ideal clinical results by optimizing the dimension and configuration of the individualized selfpositioning titanium mesh connectome.

Abstract:Objective To determine the optimal layout of mandible implant fixation plates by topological optimization, and design personalized mandible implant fixation plates with high bearing capacity. Methods Taking a typical defected mandible as an example, the finite model of mandible was constructed with consideration of the properties of bone and scaffold materials. Topology optimization analysis of the model was carried out, and personalized mandible implant fixation plate was designed. The stress distributions of the mandible, plate and screw in conventional and personalized plate system were simulated to evaluate mechanical characteristics of personalized mandible implant fixation plate. Combined with Gibson-Ashby model, the porous face-centered cubic lattice structure prosthesis with elastic modulus equivalent to cortical bone was designed, and the final scaffold scheme was finally determined. Results The peak stresses of the mandible, fixation plate and screws of personalized mandible implant fixation plate system were 55.86, 291.1 and 122.53 MPa, respectively, which were 9.8%, 32.0% and 14.6% lower than those of conventional fixation plate fixation system. Combined the personalized mandible implant fixation plate with porous structure, a three-dimensional (3D) porous scaffold model with an optimal porosity of 71.6% was obtained. Conclusions The personalized mandible implant fixation plate designed in this study significantly reduced the peak stress and improved the reliability of the scaffold. Combined with selective laser melting (SLM) technology, personalized prosthesis with excellent properties can be quickly manufactured to meet tight time requirements.

Abstract:Objective To explore the biomechanical responses of oral mucosa under the effect of spherical bracket and conventional bracket by three-dimensional (3D) finite element analysis. Methods The 3D finite element model of lip-incisor-bracket was established. Four simulated cases were designed according to different arrangements of central incisors, and the stress and strain of the moving upper lip under the effect of spherical bracket and conventional bracket was analyzed numerically. Results The maximum stress of spherical bracket on oral mucosa was higher than that of conventional bracket when the tooth was aligned. The maximum stress of conventional bracket on oral mucosa was higher than that of spherical bracket, when the incisor was mesially rotated by 15°and 30°, as well as labially misaligned by 15°, respectively. Conclusions Compared with square conventional bracket, spherical bracket with smooth shape is more suitable for the functional movement of oral soft tissues in orthodontic patients with misaligned teeth. It is suggested that shape design of conventional brackets should be improved to reduce mechanical response of oral mucosal tissues.

Abstract:Objective To establish a method for efficient simulation of orthodontic alveolar bone reconstruction. Methods A complete dental and periodontal model of a single incisor and molar was established, and displacement-controlled and force-controlled loading for distalization was simulated. According to the external reconstruction theory and the periodontal ligament (PDL) strain theory, alveolar bone reconstruction was simulated using the UMESHMOTION subroutine in ABAQUS combined with the adaptive mesh technology (ALE). Results In displacement-controlled mode, the initial distal displacement load of 50 μm could be achieved by the bone reconstruction algorithm to achieve distal alveolar bone reconstruction displacement of 50 μm. In force-controlled mode, the final displacement of the single-rooted tooth and double-rooted tooth was 67.5 μm and 23.77 μm, respectively, under the condition of applying the 1 N initial distal force and considering the final decline to 50% of the initial force level. In both modes, the absolute maximum principal stress on PDL returned to 0 stress level after bone reconstruction, and the PDL reached a new mechanical equilibrium. This algorithm could simulate the alveolar bone reconstruction process of single-rooted tooth and double-rooted tooth in a short period. At the osteogenesis-osteogenesis ratio of 7︰5, a stable reconstruction process could be obtained when the displacement of a single iterative displacement was controlled at 0.1 μm. Conclusions The proposed method achieved the the simulation of double-rooted alveolar bone reconstruction for the first time, and the process of alveolar bone reconstruction could be simulated well under displacement and decayed force controls, thereby serving as an effective tool for designing orthodontic force systems with or without brackets.

Abstract:Objective To study the detection effect of different dental defects by using the finite element non-destructive testing method, and provide some theoretical support. Methods Based on continuous medium ultrasonic propagation method,the dG-FEM model was used in COMSOL software to simulate ultrasonic transmission and reflection patterns. The ultrasonic reflection intensity was monitored by changing dental defect types and ultrasonic detection angles inside the model. The time and intensity of detecting mutated ultrasonic waves were used to study the detection effect of dental defects. Results Dental defects could be detected within 16 μs by ultrasonic non-destructive method. For different types of dental defects, the best detection effect could be observed in rectangle-shaped defects. For different detection positions, when the ultrasound source and the defect were aligned in the main direction, the ultrasonic reflection intensity was the highest. Conclusions For defects of the tooth, the ultrasonic non-destructive testing method can be used for fast detection of defect types. The effect of defect detection can be increased by changing the detection angles, which provide theoretical references for its practical application.

Abstract:To investigate errors of force measurement system for clear Aligners and provide references for optimizing the use of this system. Methods The original model was three-dimensional (3D) printed and assembled to form the assembly model of the force measurement system, then the assembly model was scanned. The original model (Group A) and the assembly model (Group B) were used to manufacture clear Aligners with no activation by thermoforming material respectively. Overlapping analysis and measurement of arch width were performed on Group A and B models, so as to compare whether two groups of models matched well. The force measurement system was used to measure the 3D force of the resin teeth after the clear Aligners were put on, and the differences of dental force between two groups were analyzed. Results The results of overlapping analysis and measurement of arch width showed that there was an average deviation of -0.126 mm to 0.188 mm in Group A and B models. When the clear Aligners made by the original model or assembly model were put on the force measurement system, a certain amount of 3D forces would be measured. The clear Aligners made by the original model produced larger forces than that made by the assembly model. Significant differences of the forces between two groups could be observed in most sites after the clear Aligners were put on, except the labial & lingual forces of tooth 33 or 32, and vertical forces of tooth 32, 31 or 46. Conclusions The discrepancy between the original model and the assembly model will cause certain systematic errors. In order to reduce the errors generated in installation procedure, it is necessary to perform 3D scanning of the resin dentition after assembling the force measurement system, and to design clear Aligners based on the assembly model.

Abstract:Objective To investigate the effect of exosomes, derived from periodontal ligament cells (PLCs) under stretch loading on osteoblast differentiation, and the role of these exosomes in force-related periodontal tissue remodeling. Methods After 20% strain was applied to human PLCs cultured in vitro, exosomes from the supernatant were extracted and co-cultured with osteoblasts, then the differentiation of osteoblasts was detected, and miRNA which played a regulatory role in exosomes was explored. Results Exosomes secreted by PLCs under stretch loading could up-regulate the expression of osteogenic-related factors including alkaline phosphatase(ALP), transcription factor Osterix（osterix, Osx）, type I collagen (Col-1), Runt-related transcription factor 2 (Runx2), osteocalcin (Ocn), and bone morphogenetic protein 2 (BMP2) in osteoblasts, as well as promote osteogenic differentiation of cells. Among the miRNAs differentially expressed in PLC exosomes under stretch loading, the expression of miRNA-181d-5p was up-regulated by 107 times, and the expression of osteogenic-related factors including ALP, Osx, Col-1, Runx2, Ocn and BMP2 was also increased in osteoblasts transfected with miRNA-181d-5p. Conclusions This study preliminarily reveals the role of exosome miR-181d-5p secreted by PLCs under stretch loading in regulating the differentiation of osteoblast, which is of scientific significance for clarifying the signaling pathway in force-related periodontal tissue remodeling.

Abstract:bjective To reveal the mechanism of mechanical regulation of platelet surface CD40L expression mediated by vWF-A1 in flow filed. Methods The prokaryotic systems expressing proteins, flow cytometry, and parallel plate flow chamber technique with cellular immunofluorescent antibody staining were selected, so as to investigate the activation and subsequent expression of CD40L induced by vWF-A1 in platelets under different shear environments. Results The vWF-A1 did not activate platelets under resting conditions. Fluid shear stress (FSS) was the initiating switch for vWF-A1-mediated platelet CD40L expression. With the increase of shear stress accumulation (SSA), the expression level of platelet CD40L showed a trend of increasing and then decreasing, and when SSA reached 2 Pa·min, the expression of platelet CD40L reached its peak. Conclusions The expression of CD40L on platelet surface is regulated by vWF-A1, FSS and SSA. SSA promote the ability of platelets to express CD40L.

Abstract:Objective To study kinetics of extracellular regulated protein kinase (ERK) activity in Jurkat T cells and the effect of matrix stiffness on ERK activity. Methods ERK activity in cells was visualized by fluorescence resonance energy transfer (FRET) biosensor, and the cells were embedded into type I collagen (COL) hydrogel to detect the biomechanical effect. Results Pulsation of ERK activity was found in a sub-group of Jurkat cells, the frequency was about three times per hour, and the average change in oscillating magnitude was about 20%. Under the condition of T-cell receptor (TCR) activation with antibodies, ERK pulse still existed, but the frequency and amplitude did not change significantly. ERK showed a decreased frequency of pulsation in COL hydrogel with an increased stiffness. Conclusions ERK has autonomous pulsating activity in Jurkat T cells, and preliminary experiments show that the frequency is regulated by matrix stiffness. The physiological implication of ERK oscillation and underlying molecular mechanism need further study.

Abstract:Objective To develop a microfluidic chip analysis system which can be used to evaluate the inhibitory effect of antiplatelet drugs on platelet activation and aggregation induced by pathological high shear. Methods Polydimethoxane (PDMS)-glass microchannel chip was fabricated by soft lithography. The anticoagulant human whole blood was flowed through the microchannel chip at 1 500 s-1 shear rate, and the platelet aggregation behavior downstream of the narrow channel was photographed by fluorescence inversion microscope. The platelet aggregation coverage rate, total aggregation area, average size of thrombus and number of thrombus were obtained by image analysis. The whole blood flowing through the microfluidic chip was collected and the expression of platelet surface activation markers (P-selectin and PAC-1) was analyzed by flow cytometry. The inhibitory effect of antiplatelet drugs (aspirin, tirofiban, tirofiban) on platelet aggregation and activation downstream of stenosis was also evaluated. Results With the increase of input shear rate, the ability of platelet aggregation increased gradually. Aspirin could not inhibit platelet activation and aggregation induced by pathological high shear, while tigrel and tirofiban could significantly inhibit platelet activation and aggregation. Conclusions The microfluidic chip model developed in this study can be used to simulate the local characteristics of arterial stenosis and study the effects of different shear force gradients on platelet aggregation, as well as to evaluate the inhibitory effect of antiplatelet drugs on platelet activation and aggregationunder pathological high shear stress. Different from the traditional turbidimetry and thromboelastography in the detection of platelet function under static conditions, this study provides an in vitro model closer to the real flow environment in patients with arterial thrombotic diseases, as well as a related analysis method for the detection of platelet function in patients with percutaneous coronary intervention (PCI) or atherosclerosis.

Abstract:Objective To design a bileaflet mechanical valve with the function of generating helical flow, so as to prevent postoperative complications by improving its hemodynamic characteristics. Methods Based on the structure of guiding-vane type spiral flow generator, the leaflets were used as the guiding vane and the leaflet wrap angle was defined to explore the valve configuration with better hemodynamic performance. The finite element analysis software was used to simulate the aortic flow field under the state of peak systolic flow. Then the flow velocity, effective orifice area (EOA), flow asymmetry and helicity, wall shear stress (WSS) distribution and other hemodynamic characteristics in each group were compared. Results Compared with the control valve, the helical-flow generated valve had a larger EOA and a smaller pressure difference across the valve. The helical-flow generated valve with leaflets within a certain wrap angle could promote the generation of right-handed helical flow and make the blood flow approach the center of the channel. The WSS distribution was more uniform and the peak WSS was relatively smaller in the helical-flow generated valve, with fewer low-stress and high-stress areas. For the aortic model in this study, the leaflet wrap angle for optimal hemodynamic performance was 15°-20°. Conclusions This novel artificial aortic valve can adjust blood flow characteristics in the aorta, reduce the risk of aortic dilatation and aortic aneurysm caused by aortic valve replacement, and it has guiding significance for configuration design of mechanical valve in the future.

Abstract:Objective The mechanical properties of polymeric vascular stents considering size effect were investigated, and the influence laws of stent structure on mechanical properties of the stents and size effects during stent deformation were further analyzed, so as to provide the theoretical basis for structural design of the stents. Methods The Cosserat theoretical model of poly lactic acid (PLA) considering size effect was established, and combined with the finite element method, the bending stiffness and radial support stiffness of the stents were obtained by three-point bending and flat plate compression, and the influence laws of rib thickness and rib width of the stents, radius of curvature and axial spacing of the support unit on radial support performance and size effect of the stents were further analyzed. Results There was a significant size effect on the polymeric vascular stent during bending and compression. The radial support stiffness of the support unit was negatively correlated with the radius of curvature and axial spacing, and positively correlated with the rib thickness and rib width, and the smaller the radius of curvature and axial spacing of support unit, rib thickness and rib width of the stents, the larger the size effect during compression. Conclusions The radial support performance of the stent is mainly determined by the structure stiffness, and affected by the size effect during stent deformation. With smaller characteristic dimensions of the stent geometric structure and greater bending and torsional deformation of the stent, more obvious size effects will be obtained, which leads to a greater increase in the radial support performance of the stent.

Abstract:Objective To investigate the effects of different degrees of left anterior descending (LAD) stenosis and bifurcation vessel curvature on hemodynamics. Methods An ideal model with different bifurcation radii of curvature and stenosis rates of LAD branches was developed. The effects from different radii of curvature and different stenosis rates on blood flow and wall shear stress (WSS)-related parameters were evaluated using the fluid-structure interaction (FSI) method. Results After stenosis occurred at the LAD, the regions of high oscillatory shear index (OSI) and high relative residence time (RRT) were mainly distributed on contralateral sides of the LAD bifurcation ridge, proximal downstream of the stenosis location at lateral sides of the bend, and distal downstream at medial sides of the bend. And with the increase of the degree of stenosis, such areas and degrees would be expanded. As the radius of curvature decreased, high OSI and RRT in medial side of the bend were distributed distally at downstream of the LAD, and the average decrease of high RRT area relative to the whole vascular area could reach 35.68%. With the increase of the stenosis degree Conclusions The presence of LAD stenosis increases the risks of secondary stenosis at downstream of the stenosis location and contralateral side of the LAD bifurcation ridge. The decrease in curvature promotes the formation and development of plaque at medial side of the bend. Still, it will decrease the probability of plaque formation for the entire vessel. The results may provide the theoretical reference for protocol design and optimization for treating LAD lesions and preventing secondary stenosis.

Abstract:Objective To compare and study contact mechanics and wear performance of mobile- and fixed-bearing unicompartmental knee arthroplasty (UKA) under ISO 14243-1:2009 force control standard test condition by computational simulation. Methods The contact stress and von Mises stress of mobile- and fixed-bearing UKAs under the test condition were analyzed by finite element methods. The linear wear depth and wear volume of both UKA inserts were obtained after simulating gait with 5 million cycles (MCs) using wear prediction model. Results The maximum contact stresses of mobile- and fixed-bearing UKAs before wear were 15.7 MPa and 44.3 MPa respectively, and the maximum von Mises stresses were 11.94 MPa and 23.33 MPa respectively. With the increase of wear, the maximum contact stress and von Mises stress of the mobile-bearing UKA decreased first and then became stable, while that of the fixed-bearing UKA remained basically unchanged. The linear wear depth of fixed-bearing UKA was 1.5 times that of mobile-bearing UKA. But the wear volume of mobile-bearing UKA was 5.4 times that of fixed-bearing UKA, and the wear volume on backside surface accounted for 70% of the total wear volume of mobile-bearing UKA. Conclusions Compared with the fixed-bearing UKA, the mobile-bearing UKA had lower contact stress and von Mises stress, but larger wear volume. The backside wear of mobile-bearing UKA was an important source of increased wear debris.

Abstract:Objective The biomechanical comparison between the novel scapular neck anatomical locking plate (SNALP) and the Watson reconstruction plate (WTRP) was conducted, so as to observe characteristics and advantages of the SNALP in the aspect of biomechanics. Methods Twelve preserved and moistened adult scapula cadaver specimens (7 males and 5 females) were selected and molded into scapular neck fracture (Miller's type II B) specimens, which were randomly divided into experimental and control groups according to the order of specimen collection and gender: the SNALP for internal fixation was used in experimental group, and the WTRP for internal fixation was used in control group. The specimens were placed on the biomechanical testing machine, then the scapular neck tensile test, plate screw anti-pullout test and dynamic fatigue test were conducted respectively. The experimental data were collected by the computer connected to the experimental terminal, and the stress-displacement curves and cycle-displacement curves were plotted. Results In the scapular neck tensile test, the average tensile strength of experimental group [(356.50±32.19) N ] was better than that of control group [(193.83±29.39) N] (P<0.05). In the anti-pullout test of scapular neck plate and screw, the average anti-pullout force of experimental group [(263.83±22.85) N] was better than that of control group [(135.50±15.40) N] (P<0.05). In dynamic fatigue test, the average displacement of experimental group was smaller than that of control group within 300 cycles (P<0.05), and no fracture and loosening of the steel plate and screw occurred. Conclusions The novel SNALP is better than the WTRP in terms of tensile, pullout and dynamic fatigue biomechanical properties, and can provide a more ideal internal fixation system for clinical treatment of scapular neck fractures.

Abstract:Objective To analyze stress distributions of vertebral implants with chiral honeycomb sandwich structure by finite element method, so as to provide a theoretical basis for the clinical treatment of vertebral compression fractures. Methods The three-dimensional (3D) finite element model of the vertebral implant with trichiral honeycomb sandwich structure was constructed.The structural parameters were optimized by combining orthogonal experiment with the in-plane and out-of plane size effects,and the stress and stress distributions under five different working conditions were analyzed. Results The combination of structural parameters with the minimum peak stress was as follows: cell wall thickness 0.28 mm, panel thickness 0.8 mm, cell height 0.2 mm, ligament length 0.6 mm.The peak stress occurred at the edge of the honeycomb core near the upper and lower panels, and the maximum strain was located at the edge of the upper panel which was not supported by the honeycomb core. Conclusions After optimized design, the chiral honeycomb sandwich structure could meet the physiological load of human body, and the peak stress after vertebral implantation was smaller than that of the regular hexagonal honeycomb sandwich structure, and the stress distribution was more uniform, which was suitable for the basic structure of vertebral implants.

Abstract:Objective Aiming at the problem that the strong coupling characteristics of knee-ankle-toe active prosthesis system in stance phase will lead to the decrease in control precision of prosthesis system, the method of exact feedback linearization was proposed to decouple the active transfemoral prosthesis system. Methods Gait data of human lower limbs were collected. Stance phase was divided into the early and middle stance phase and the last stance phase. The dynamic model of two stance phases was established. The prosthesis system in stance phase was decoupled based on exact feedback linearization decoupling. The integral sliding mode controller was designed to control the active transfemoral prosthesis. The co-simulation platform was built to verify effectiveness of the method. Results The decoupled system could improve the control accuracy. After decoupling, the calculated mean absolute error (MAE ) of knee and ankle in the early and middle stance phase was reduced to 0.001 1 ° and 0.002 6°respectively. Root mean square error ( RMSE ) was reduced to 0.014 7°and 0.023 6° respectively. At the last stance phase, the MAE of knee, ankle and toe was reduced to 0.011 1°,0.005 1° and 0.006 5° respectively, and the RMSE was reduced to 0.021 9°,0.021 0° and 0.012 9° respectively. The overall control error was reduced and the response speed was accelerated, and the prosthesis could operate stably in the co-simulation environment. Conclusions The decoupling method proposed in this study can effectively realize the decoupling of the transfemoral prosthesis system and lay the foundation for the prosthetic system.

Abstract:Objective To improve the static and dynamic matching precision of OpenSim biomechanical models, and further improve the reliability for calculation of kinematic and kinetic parameters. Methods Model nonlinear scale based on kinematic experimental data was implemented by position adjustment, interpolation function calculation. For the verification of this method, two open dataset (GC3 and GC5) were used to build the nonlinear scaled models and calculate the limb lengths and joint reaction forces. The results were compared with those calculated by anatomical landmark scale (ALS) and linear scale method. Results The maximum discrepancies between limb length of nonlinear scaled model and actual model were 14.74 mm, which were in the range (4.0±13.8) mm reported by other literature. Marker errors of scale and inverse kinematic calculation could fulfill the requirement of OpenSim. As for calculated joint reaction forces, the root mean square errors (RMSEs) (GC3: 0.40 BW, GC5: 0.34 BW, BW was abbreviation of body weight) were smaller than those of anatomical landmark scale (ALS) (GC3: 0.64 BW) and OpenSim linear scale method (GC5: 0.40 BW). Besides, the results of Monte Carlo analysis indicated that, with the variation of initial positions of model markers, the range of joint reaction forces errors was smaller and limb lengths fluctuated within 5%. Conclusions The nonlinear scale method in this study is effective, and it can improve the efficiency of kinematic and kinetic modeling process and raise the precision of simulation results under current verification condition.

Abstract:Objective To study the effect of strength loss in ankle muscles on injured and healthy side of knee joint muscles in patients with chronic ankle instability (CAI). Methods The inverse dynamic models of CAI patients and healthy subjects were established. The strength loss of ankle muscles at different degrees was simulated by changing the maximum isometric contraction force of muscles, and the change patterns for peak muscle strength and cumulative muscle strength of knee joints during a gait cycle were analyzed. Results The strength loss of plantar flexor muscle in CAI patients would affect both the quadriceps and hamstring muscles of the injured side and the healthy side. The strength loss of dorsal flexor muscle mainly affected the hamstring muscles of the injured side and the healthy side in CAI patients. The cumulative load on the affected side and the healthy side of knee joint muscles increased, and models with different strength loss of ankle muscles showed that the cumulative load of quadriceps femoris on the affected side was greater than that on the healthy side. The cumulative load on hamstring muscle of the healthy side was greater than that of the affected side. Conclusions CAI will not only affect the patients’ injured side of knee joint muscle strength, but also affect their healthy side. Strengthening the ankle muscles and protecting the bilateral knee muscles may have a positive effect on the rehabilitation of CAI.

Abstract:Objective To explore the regulation strategy of human standing stability from linear and nonlinear perspectives. Methods Sixteen healthy male subjects were recruited and required to stand normally or stand with closed eyes, stand on foam pad with open eyes or closed eyes for a period of 30 s on the balancer. The linear and nonlinear characteristics of plantar COP (center of pressure) trajectory during standing with different interference factors were analyzed by spatio-temporal parameters, trajectory approximate entropy and wavelet transform. Visual × proprioceptive repeated measures ANOVA was used to compare the linear and nonlinear characteristics of COP trajectory between the interference condition (visual interference, proprioceptive interference and visual and proprioceptive interference) and normal standing. Results For linear index, the COP trajectory length, trajectory rate and C90 area during closed-eye standing, unstable standing and closed-eye unstable standing were all higher than those during normal standing (P<0.05). The average offset of C90 area and that in mediolateral (MP) and anteroposterior (AP) directions under three interference modes had no significant changes compared with that during normal standing (P>0.05). For nonlinear index, in MP and AP directions, there was no significant difference in approximate entropy between closed-eye standing, unstable standing and closed-eye unstable standing compared with that during normal standing pressure center track (P>0.05). For frequency domain index in MP direction, visual interference increased the energy weight of the intermediate frequency, low frequency and sub-low frequency bands (P<0.05), and decreased the ultra-low frequency energy weight (P<0.05). The energy weight of three frequency bands during proprioceptive interference was not different from that of normal standing (P>0.05), while the energy weight of intermediate frequency, low frequency and sub-low frequency increased (P<0.05), while that of ultra-low frequency decreased (P<0.05). For frequency domain index in AP direction, the sub-low frequency energy decreased (P<0.05) and ultra-low frequency energy increased (P<0.05) after visual interference compared with that during normal standing. The energy weights of intermediate frequency, low frequency and sub-low frequency of proprioceptive interference, visual and proprioceptive interference increased (P<0.05), while that of ultra-low frequency decreased (P<0.05). Conclusions For healthy people, the closed-loop control mechanism of lower frequency band is dominant during standing, and the interference of external signal input will not change the complexity of COP trajectory, in which visual information interference has an obvious effect on ML direction, proprioceptive information interference has an obvious effect on AP direction. When standing is disturbed, the energy weight of higher frequency band of open-loop control mechanism increases, and shaking amplitude and speed of the body become larger.

Abstract:Objective To investigate the effect of aging on mechanical work patterns of lower extremity joints in older adults during stair descent, so as to enrich the fall-prevention theory of stair walking. Methods Vicon infrared motion capture system and Kistler platform were synchronized to collect the kinematic and kinetic data. The mechanical work was quantified by using parameters such as joint angle, moment, power, and mechanical work contribution of lower joints. Results Older adults demonstrated a consistent trend in joint angle, moment and power of lower limbs with young adults during stair descent. Compared with young adults, older adults showed decreased peak hip flexion moment, the first peak and second peak of knee extension moment, the first peak of ankle plantarflexion moment, the first and second peak peak of knee negative power, peak ankle negative power, net mechanical work of hip, knee, and ankle joints (P<0. 05). Significantl increase was found in peak hip extension moment, peak hip negative s power, and the mechanical work contribution of ankle joint among older adults (P< 0. 05). There was no significant difference in mechanical work of hip and knee joints between two groups (P> 0. 05). Conclusions The mechanical characteristics of lower extremity joints in older adults were significantly reduced during stair descent. Older adults adopted a strategy in mechanical work which was different from young adults. They would increase hip extension to resist the excessive trunk leaning forward, together with the mechanical work of ankle joint as the compensatory mode, so as to improve body stability during stair decent. It is suggested that older adults should mainly increa

Abstract:Objective To investigate gait characteristics of older adults during stair ascent and descent, and mechanical properties of lower extremity joint movement. Methods A total of 17 young adults and 15 old adults were required to ascend and descend a five-step staircase at natural walking speed. The gait parameters, lower limb joint angles and ground reaction force were obtained using infrared high speed motion capture system and three-dimensional force platform, the joint moments and powers were calculated by inverse dynamics approach, and the influence of age on those parameters was analyzed by independent samples t-test. Results Compared with young adults, older adults had a relatively longer gait cycle, as well as an obviously lower walking speed and frequency during stair ascent and decent (P<0.05). Meanwhile, the support phase and swing phase in older adults during stair ascent and decent were obviously prolonged and shortened respectively (P<0.05). The change trend for joint angle, moment and power of lower limbs during stair ascent and decent was consistent in both young and older adults. However, during stair ascent, older adults were mainly maintained by the generation of ankle and knee joint power, while young adults were mainly maintained by the energy at the proximal limb, especially more knee power was used. For older and young adults, energy absorption during stair decent played an important role in knee joints. Conclusions With aging, lower limb function and muscle strength will decrease. Older adults are afraid of falling down during stair ascent and decent, and try to compensate for the instability of the body by reducing swinging time. The research findings provide references for rehabilitation management and functional assessment on fall prediction of older patient populations in clinical practice.

Abstract:Objective To design a occluder suitable for the anal fistula internal mouth occlusion surgery, study structural design of the occluder, as well as the interaction between implants and tissues, and evaluate performance of the internal mouth occlusion. Methods The overall structure of the occluder was designed and the prototype was manufactured. The finite element model of occluding was established to study the stress distribution and damage area of tissues during occlusion; the tissues puncture experimental platform was built to verify the simulation model and results; the pull-out force test platform was built to evaluate the occlusion effect of the internal mouth. Results During the occlusion process, the maximum torque of the feeding mechanism was 36 mN · m, the maximum stress of the tissues was 19.75 MPa, and the damage area was 1.35 cm2. The finite element model was basically consistent with the experimental results, and the maximum pull-out force reached 5.11N. Conclusions The area of tissues damage in the process of occlusion meets the requirements of minimally invasive treatment of anal fistula. The minimally invasive anal fistula occluder designed in this study can effectively occlude the internal mouth, which is helpful for doctors to perform minimally invasive surgery for anal fistula more conveniently, quickly and effectively.

Abstract:Objective To quantitatively investigate the motor dysfunction after brain stem pyramidal tract injury in rats by grasp strength (GS)-motor evoked potential (MEP). Methods Thirty healthy male SD rats were randomly divided into 1.25 m injury group, 2.25 m injury group and normal group. The classical marmarou model was used to make the traumatic axonal injury model of pyramidal tract. In injury group, the limb GS signal and MEP were detected at 1st , 3rd, 5th , 7th , 14th, 28th and 42nd day after injury, and the control test was carried out at the corresponding time after anesthesia. Results With the increase in injury degree, the MEP amplitude and maximum GS decreased significantly in injury group. The measured values of GS and MEP under two heights had obvious positive correlation. When the damage degree was relatively small, MEP was more sensitive at early stage, but MEP was not sensitive at late stage. When the damage degree was relatively large, MEP changes at both early and late stages were more sensitive. Conclusions The combined evaluation of GS-MEP can provide an data support for the quantitative evaluation of motor dysfunction after pyramidal tract injury.

Abstract:Frequency plays an important role in biomechanical responses of traumatic brain injury (TBI). Impact loading can amplify brain deformation and aggravate neurological dysfunction due to resonance behavior. This paper summarized the main research methods for frequency response characteristics of brain injury. Specifically, different mathematical methods for the study of frequency response characteristics of brain injury, as well as current understanding on frequency response characteristics were investigated. Then some suggestions for further researches on frequency response characteristics of brain injury were put forward. The results show that finite element method, reduced order model and fluid-solid coupling model are feasible in the study of frequency response characteristics of brain injury. However, there is still a lack of unified understanding about the natural frequency of brain injury, and frequency response characteristics have not been applied in brain injury criteria. Therefore, improving mechanical evaluation of brain injury based on frequency response characteristics is still the research focus.

Abstract:Hepatocellular carcinoma (HCC) is a malignant disease that seriously endangers human health. The stiffness of the extracellular matrix (ECM) in liver is increasing in the occurrence and development of HCC. In recent years, studies on the role of biomechanical factors in HCC have shown that the increase of ECM stiffness plays an important role in the occurrence and development of HCC. This article mainly reviewed the changes of ECM stiffness as well as the causes of such changes in the occurrence and development of HCC, and the effect of increased ECM stiffness on HCC-associated cells and the mechanotransduction therein, so as to provide new ideas and directions for the clinical treatment of HCC.

Abstract:Chinese massage is a method based on the theory of viscera and meridians of traditional Chinese medicine, which regulates the physiological and pathological conditions of the body by applying different techniques to specific parts of body surface to achieve the therapeutic purpose. The study on Chinese massage can reveal the biomechanical mechanism of manipulation, and it is of great significance to normalization, standardization and innovation of manipulation?of?massage. This paper summarized the biomechanical research progress of Chinese message from the aspects of description, dynamic analysis, massage force effect and comparative analysis of manipulation, in order to provide references for follow-up researches in the related fields of traditional Chinese massage.