Abstract:Objective To investigate the biomechanical effects of femoral offset (FO) on total hip arthroplasty (THA) patients with developmental dysplasia of the hip (DDH). Methods Based on the musculoskeletal dynamic software AnyBody and the related data from a female patient with Crowe Ⅳ DDH, the corresponding patient-specific lower extremity musculoskeletal multi-body dynamic model was constructed to analyze both hip joint forces and abductor forces within ±20 mm variation of FOs. The dynamic finite element (FE) model of S-ROM stem with varying offsets was also established. The dynamic load during a whole walking gait cycle calculated by the multi-body musculoskeletal model was applied to this FE models, and the Von Mises stress, contact stress, and stem-sleeve micromotion were then analyzed. Results A variation of ±20 mm offset had small influences on peak forces of hip joints. However, the decrease in FO could lead to an obvious increase in peak abductor force, while the increase in FO could lead to an obvious increase in the maximum Von Mises stress, contact stress, and micromotion of S-ROM prosthesis stem. Conclusions The change in FO had an obvious influence on the abductor forces, the maximum Von Mises stress, the contact pressure and the consequent fretting wear of THA patients with DDH, which should be carefully considered by surgeons.
Abstract:Objective To study the load transfer mechanics between residual limb and prosthetic socket, as well as stress distributions below the residual limb, so as to provide a theoretical basis for designing and optimizing of prosthetic socket and improving the wearing comfort. Methods Aiming at compression-release stabilization （CRS）, the finite element software ABAQUS was used to analyze the stress distribution at the interface between the residual limb and CRS socket. The soft tissues were defined using the Mooney-Rivlin function. The interface pressures and shear stresses between the residual limb and CRS socket during mid-stance were obtained. A three-dimensional finite element model of the patellar tendon bearing (PTB) socket was established, and the results were compared. Results The interface pressures between the residual limb and CRS socket were mainly distributed at lateral tibia, media tibia and popliteal depression regions, which were similar to the main force regions of PTB socket. The mean interface pressures on the end of stump for CRS socket was increased by 19 kPa over PTB socket. Conclusions CRS socket had better breathability and reasonable stress distributions. The stress distribution of biomechanical interface was different due to the different shapes of socket. Therefore, the optimization of prosthetic socket can help to improve the wearing comfort of prosthetic limbs.
Abstract:Objective To investigate the method of modeling, finite element modeling and AnyBody musculoskeletal multi-body dynamics simulation technique analyze the biomechanics of clinical orthopaedic surgery. Methods The AnyBody software was used to establish the musculoskeletal motor model of the individualized upper limbs according to the height, weight and CT data of the volunteers. The flexion motion of the elbow in normal people was simulated, and the muscle force, joint force, torque, constraint condition of the humerus during the flexion movement were derived and used as the boundary conditions of finite element analysis.Then, the 3D reconstruction was conducted in the MIMICS software based on CT data. In the Geomagic Studio software, the humeral curved surface and position coordinate matching were completed, and grid division and material assignment were done in the HyperMesh software. Finally, the 3D reconstruction for finite element model of the humerus was introduced into ABAQUS software. The boundary condition data derived from the AnyBody software were applied and the stress calculation analysis was performed. Results The results of the stress and displacement of the humerus during elbow flexion motion were calculated in the ABAQUS software. The maximum stress and displacement of the humerus were 0.76 MPa and 20 μm when flexion of the elbow joint was about 90°. Conclusions A continuous dynamic analysis of humeral stress and displacement during elbow flexion motion was realized, which was more consistent with the requirements of human physiological anatomy and could provide an efficient analysis platform and a new way for studying clinical orthopedic problems.
Abstract:Objective To study the biomechanical properties of porous titanium cages used for different lumbar interbody fusion surgeries. Methods The three-dimensional (3D) finite element model of the lumbar spine was constructed, and mechanical parameters of porous materials were obtained by mechanical test. The biomechanical properties of porous titanium cages in anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), direct lateral interbody fusion (DLIF) were compared. Results After lumbar interbody surgery, the predicted range of motion (ROM) and the maximum stress in cage of DLIF model and ALIF model were substantially lower than those of PLIF model and TLIF model. The maximum stress in endplate of DLIF model, ALIF model and TLIF model were obviously lower than that of PLIF model. Conclusions DLIF with the porous cage showed advantages in biomechanical properties, which was simple to operate and suitable for minimally invasive surgery in clinical practice. DLIF performed the superior comprehensive properties.
Abstract:Objective To compare biomechanical properties of cortical bone trajectory (CBT) screw and traditional trajectory screw for fixing upper-middle thoracic spine. Methods The tomography images were obtained by CT scanning of normal T7 and T8 segments, and the three-dimensional (3D) model of T7-8 was reconstructed by Mimics software. The finite element model of upper-middle thoracic spine was established by optimizing FreeForm model and pre-processing function of ANSYS software. On this basis, the CBT screw and pedicle screw fixation models after discectomy were established, and 5 N·m flexion, extension, lateral bending and rotation loads were applied to the two model groups, respectively. The displacement and peak stress of vertebrae and implants under different working conditions were compared and analyzed. Results Under different loading conditions, the maximum displacement of CBT screw group was lower than that of pedicle screw group, and the range of motion of CBT screw group was lower than that of pedicle screw group. The stress level of both models was close, and the stress of CBT screw group was slightly lower than that of pedicle screw group. Under the load of flexion, extension and rotation, the maximum vertebral stress of pedicle screw group decreased by 31%, 17% and 18% compared with that of CBT screw group, and under lateral bending load, the vertebral stress of CBT screw group was 20% lower than that of pedicle screw group. Under the load of flexion and rotation, the maximum stress of pedicle screw group decreased by 2% and 11%; however, the maximum stress of CBT screw group was 11% and 1% lower than that of pedicle screw group. Conclusions The stability of CBT screw was better than that of pedicle screw, and the overall stress distribution was similar to that of pedicle screw. However, the vertebral stress distribution of CBT group was slightly inferior. The research findings provide a theoretical basis for the clinical application of cortical screw fixation after the failure in pedicle screw fixation for the upper-middle thoracic vertebrae.
Abstract:Objective To study the change patterns of bone microstructural parameters around the magnesium based- implants after implantation in rabbit femur at different implantation time points. Methods The threaded and non-threaded high-purity magnesium (HP Mg, 99.99 wt.%) screws, with a 2 mm diameter and a 7 mm length, were implanted into the femoral condyle of the rabbits. The control group was the drilled and healthy group. Micro-CT scanning and analysis were performed at 8th, 12th and 16th week after operation. The obtained microstructural parameters included bone mineral density (BMD), bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp). Results At 8th week, BMD and BV/TV in non-threaded magnesium screw group were significantly higher than those in healthy group, Tb.N was significantly higher than that in drilled and healthy group, and Tb.Sp was significantly lower than that in healthy group. At 12th week, BMD, BV/TV and Tb.N in threaded magnesium screw group were significantly higher than those in drilled and healthy group, Tb.Th was significantly higher than that in healthy group, and Tb.Sp was significantly lower than that in drilled and healthy group. At 16th week, BMD, BV/TV and Tb.N in non-threaded magnesium screw group were significantly higher than those in drilled and healthy group, and Tb.Sp was significantly lower than that in drilled and healthy group. Conclusions The magnesium based-implant promoted higher BMD, BV/TV, Tb.Th, Tb.N and lower Tb.Sp of surrounding implant, indicating that osseointegration and bone growth were in good condition. Magnesium based-implant could effectively promote the regeneration of bone. The results provide a theoretical basis for the orthopedic application of magnesium based-implants in clinic.
Abstract:Objective To analyze the mechanical properties of bone tissue engineering scaffolds with different pore structure and porosity, and improve the mechanical properties of scaffolds by changing pore structure. Methods Square pore, spherical pore and cylindrical pore with different porosities from 55% to 75% were established by SolidWorks software, and the surface-volume ratio of different structures was calculated. The stress distribution and equivalent compression modulus of different scaffolds were obtained by ANSYS Workbench software. According to the stress distribution results, the scaffold with rectangular pore structure and cuboid element structure was improved instead of square pores. Results With the increase of porosity, the surface-volume ratio of the three structures increased. For the same porosity, the surface-volume ratio of square pores and spherical pores was larger, while that of cylindrical pores was the smallest. The modulus and porosity of the three structures were approximately linear. The modulus of the square pore and the cylindrical pore were similar. The stress analysis on the square pore and two improved structures with 60% porosity showed that for the two improve structures, the wall stress on 4 edges parallel to the direction of applied stresses could be reduced by 15%. Conclusions The surface-volume ratio and mechanical property of square pores were more advantageous than spherical pores and cylindrical pores with the same porosity, and the two improved structures could improve the mechanical properties of square pores. The two improved pores enriched the structure of tissue engineering scaffolds. The research findings provide the mechanical references for their clinical application.
Abstract:Objective To investigate the in vivo stress distribution of the atherosclerotic plaque at carotid bifurcation, so as to provide references for the mechanical mechanisms of plaque rupture at carotid bifurcation and the design for further medical treatment. Methods The three-dimensional geometric model of carotid bifurcation and plaque were established according to average geometric parameters of human carotid bifurcation. Residual stress of the carotid bifurcation and plague was reestablished with “thermal-structure” coupling method, and in vivo stresses of vessels with the plaque at carotid bifurcation under blood pressure and blood flow were calculated. Results Both the maximum principal stress and elastic shear stress concentrated on the shoulder of the plaque. Elastic shear stress increased with the increase of stenosis ratio and blood pressure. Wall shear stress in the upstream of the plaque was considerably higher than that of the downstream. The distribution of oscillatory shear index(OSI) was quite the opposite. The changing patterns of the elastic shear stress and flow shear stress were quite different with the change of stenosis ratios. Conclusions Tension grew gradually from the centrality to shoulder surface of the plaque. The centrality of the plaque might bear compression when the stenosis was very severe. The periodic variation of the structural stress might cause structural fatigue of the plaque, thus increasing the rupture risk. Distinction of the component and vulnerability of the plaque between upstream and downstream might be caused by differences in hemodynamic parameters of the plaque between upstream and downstream.
Abstract:Objective To study the effect of simulated microgravity on activity of the store-operated calcium (SOC) channels in osteocytes and its possible mechanism, so as to elucidate the potential mechanism of weightlessness bone loss. Methods Osteocytes (MLO-Y4) as the experimental subjects were divided into simulated microgravity (SM) group and normal gravity group (CON). After rotating for 24 h and 48 h, confocal microscope was used to detect the intracellular calcium ion concentration level to reflect activity of the SOC channels after thapsigargin (TG)-induced endoplasmic reticulum (ER) depletion. Immunofluorescence staining was used to observe the distribution of ER membrane protein IP3R and spectrin membrane skeleton, in order to preliminarily explore the possible mechanism of functional changes of SOC channels. Results During the period of calcium release from ER, ［Ca2+］i had no significant difference between SM group and CON group for 24 h and 48 h; while during the period of extracellular calcium influx by SOC channels, ［Ca2+］i of SM group had significant differences in the first 4 minutes for 24 h, as well as in the whole time for 48 h. Compared with CON group, the spectrin membrane skeleton of SM group was gathered at the rim of membrane, while ER membrane protein IP3R of SM group was gathered at the nuclear envelope of ER. These two tendencies were more obvious for 48 h. Conclusions The stimulated microgravity could inhibit activity of SOC channels in osteocytes. Changes in the distribution of the spectrin membrane skeleton and ER membrane protein IP3R under the simulated microgravity might reduce the activity of SOC channels by affecting the conformation coupling process between the membrane and ER.
Abstract:Objective To investigate a self-designed catheter pump by using computational fluid dynamics (CFD) method, so as to predict its hydraulic performance and risk of thrombosis formation. Methods The thrombosis prediction models proposed by Grigioni and Danny Bluestein were used. The shear stress and exposure time during platelet motion were calculated by CFD method, and parameters of platelet activation state (PAS) were obtained for prediction of thrombogenic performance. Results At the flow rate of 4 L/min and rotating speed of 10 000 r/min, the differential pressure of the pump reached 14.763 kPa and the hydraulic performance was proved to fit the requirement of left ventricular assist device. The PAS values of Grigioni model and Danny Bluestein model were 6.35×10-6 and 7.68×10-4,respectively, both at a very low level, indicating a low possibility of thrombus formation. Conclusions This study investigated the feasibility of thrombosis prediction based on simulation method and the predicted hydraulic performance and thrombosis will provide references for further design optimization.
Abstract:Objective To investigate the influence of thrombus entrance shape, suction rate and blood flow velocity on thrombus aspiration of rotary cutting and suctioned thrombectomy devices, so as to provide theoretical support for the design and optimization of such devices. Methods Three models with different thrombus entrance shapes (‘L’-style, ‘8’-style and ‘0’-style) were established to study the influence of thrombus entrance shape on the thrombectomy; different suction rates (75, 100, 125, 150 mL/min) and different blood flow velocities (0-10 cm/s, at interval of 1 cm/s) were set to discuss how the suction rate and blood flow velocity affected the thrombectomy based on ‘8’-style thrombus entrance. Results The thrombus could not be aspirated evenly in ‘L’-style model, and there was no significantly difference in aspiration between ‘8’ -style model and ‘0’-style model. But the ‘8’-style model was better than ‘0’-style model in lateral thrombus suction. The suction rate that was greater than 100 mL/min provided a limited effect on improvement of thrombectomy effect. The best suction effect was reached when blood flow velocity was less than 1 cm/s, and the effect of thrombectomy was decreasing gradually with blood flow velocity increasing. Conclusions The thrombus entrance shape, suction rate and blood flow velocity had a great impact on thrombectomy greatly. A wide and short thrombus entrance shape, an appropriate increase of suction rate and decrease of blood flow velocity would contribute significantly to the improvement of thrombectomy effect. These results can be used as guidance for the optimal design of rotary cutting and suctioned thrombectomy devices.
Abstract:Objective To evaluate the mechanical responses of human neck tissues under the influence of massage head by modeling and simulation, so as to provide guidance for the design of massage apparatus. Methods Gray images of human tissues under application of message head were obtained through CT scanning, and the three-dimensional (3D) model for these tissues was established with reverse engineering method. Changes in strain, stress and message force of muscles and cervical vertebrae under the application of message head with the radius of 15 mm and 10 mm and pressed depth from 0 mm to 10 mm, as well as its damage and influence to bones and tissues were analyzed by finite element method. Results When 15 mm-radius massage head moved in depth of 6 mm and 7 mm, the maximum local stress was 3.0 MPa and 3.4 MPa, which was beyond damage limit of the vein. In contrast, when 10 mm-radius massage head moved in depth of 6 mm and 7 mm, the maximum local stress was 3.2 MPa and 3.7 MPa, which was beyond damage limit of the vein. To derive 1 MPa stress in cervical spine, the 15 mm- and 10-mm radius massage head should move in depth of 8 mm and 6 mm, respectively. Conclusions To avoid the local tissue damages, the pressed depth of massage should not be greater than 5 mm and 7 mm with the 10 mm- and 15 mm-radius message head, respectively. The message head with a larger radius could produce a larger action range and a more moderate massage force.
Abstract:Objective To compare the three-dimensional （3D） gait characteristics of patients with medial meniscus injury of the knee before and after arthroscopic surgery. Methods Fifteen patients with medial meniscus injury and fifteen healthy subjects were included in the study. The 3D gait parameters were collected, including spatiotemporal parameters, kinematic parameters and kinetic parameters. Results (1) The preoperative walking speed and step length of the injury group were significantly lower than those of the control group. There was no significant difference in walking speed and step length after surgery between the injury group and the control group. (2) In the sagittal plane, the preoperative knee flexion-extension range of motion (ROM), the maximum flexion angle in load-bearing phase and swinging phase were significantly lower than those in the control group (P＜0.001). The maximum knee flexion in load-bearing response phase was significantly increased after surgery (P＜0.05), but the maximum flexion angle in swing phase and the knee flexion-extension ROM after surgery were still significantly lower than those of the control group (P＜0.05). In the coronal plane, the preoperative knee adduction-abduction ROM and the maximum adduction angle in gait cycle were significantly lower than those of the control group (P＜0.001). The postoperative parameters significantly increased compared with the preoperative ones (P＜0.05), but they were still significantly lower than those of the control group (P＜0.001). (3) In the sagittal plane, the postoperative first and second peaks of knee flexion moment in stance phase of the injury group increased, compared with the preoperative ones (P＞0.05), but they were still significantly lower than those of the control group (P＜0.05). In the coronal plane, the postoperative first and second peaks of knee adduction moment in stance phase of the injury group increased, compared with preoperative ones, but they were also significantly lower than those of the control group (P＜0.05). Conclusions Patients with medial meniscus injury have their own unique gait patterns, usually with stiffening gait to reduce the knee load. Arthroscopic meniscusplasty can significantly improve knee gait characteristics, but patients still cannot return to normal gait in a short period of time.
Abstract:Objective Based on fibroblast cell model and photopolymerized hydrogel substrate with moderate gradient stiffness, to analyze the effect of process and performance parameters on cell migration and provide theoretical guidance for artificial scaffold design and fabrication. Methods A mathematical model of the test system was built and the corresponding numerical program was compiled, including viscoelastic dynamic finite element of the cell model, reaction kinetic equation of focal adhesions, and the strategy to deal with dynamic boundary and multi-scale time. Results The relationship between process parameters and performance parameters was formulated based on experimental data; cell migration speed and traction increased with the substrate stiffness increasing and were accompanied by rapid fluctuation when stiffness gradient was constant, then cell movement gradually stabilized with the extension of observation time. Increasing stiffness gradient moderately obviously promoted cell migration, and cells could maintain a limited speed on substrate with a large stiffness gradient. Smaller photomask opacity gradient resulted in larger substrate stiffness gradient and less time spent for cell to reach the target. These results agreed with the experimental results reported in the literature. Conclusions The experimental result provided an effective digital simulation platform to test the influence of process and performance parameter of photopolymerized hydrogel substrate with moderate gradient stiffness on cell migration.
Abstract:Objective To investigate the differences in stress distribution at the bone-implant interface of dental implants with different length-diameter ratios, so as to provide references for the design of novel dental implants. Methods The three-dimensional finite element model of mandible was established using Geomagic studio, SolidWorks and ANSYS Workbench software. The mandibular molars were applied with different vertical or oblique forces, to compare and analyze stress distributions on dental implants and the surrounding bone tissues. Results Under the same length-diameter ratio, the maximum peak equivalent stress of implant under oblique loading was significantly higher than that under vertical loading. The Von Mises stresses of implants in Group A and Group B occurred in the neck under oblique and vertical loading. Under oblique loading, the implant stress variation in Group A and Group B was 144.74-374.67 MPa and 161.52-475.38 MPa, respectively. Under vertical loading, the implant stress variation in Group A and Group B was 101.28-187.40 MPa and 110.08-210.32 MPa, respectively. The maximum Von Mises stress of Group A was significantly smaller than that of Group B. Conclusions Dentists should focus on a length-diameter ratio of 2.67 to select the standard implants, and the jawbone quality of patients should be taken into full account.
Abstract:Microfluidic technology refers to the technique of precise fluid control by manipulating submillimeter-scale fluids. In recent years, the use of microfluidic technology has realized the construction of organ-on-chips. The organ-on-chip refers to a micro-model with physiological functions, and cultivating living cells in a continuously perfused micro-chamber to simulate the physiological functions of tissues and organs. As the physiological function of the organ-on-chip has many advantages such as definite function, controllable microenvironment, rich measurement information, low chemical consumption, low cost, promising automation and high throughput, it has a huge application prospect in the field of drug development to solve the bottleneck problems in cellular and animal experiments, which has caused a great concern in the academic community. Although the organ-on-chip is still a very young research field, some microfluidic organ-on-chips have been developed and their potential applications are explored, including drug target optimization, drug screening and toxicity tests, and biomarker identification. In this review, the progress made in microfluidic organ microchips and their potential significance in clinical research were analyzed.
Abstract:As mechanoreceptors, cells can sense and transmit mechanical forces exerted on their surfaces, meanwhile adjust their own mechanical properties to maintain stability. The mechanical force is transferred from cell surface or cytoplasm to the nucleus depending on the complete cytoskeletal system. This cytoskeletal system consists of cytoplasmic skeleton and nuclear skeleton, and these two parts are connected mechanically by the LINC complex (linker of nucleoskeleton and cytoskeleton complex), which plays an important role in cellular mechanotransduction. This review discusses the basic structure of mechanical transmission part in LINC complex and the changes in the nuclear morphology, the location of transcription factor, and the spatial conformation of chromatin induced by mechanotransduction, so as to lay a foundation for further exploring the role of LINC complex in cell mechanotransduction and gene expression.
Abstract:Bone is a dynamic organ, and the morphology, structure and function of bone can vary with the size, direction and form of mechanical stimulation. Appropriate mechanical stimulation is the key to maintain the dynamic balance of bone formation and bone resorption. However, with aging, the senescence of bone tissues causes a series of changes, including bone microenvironment, osteocyte morphology, signaling pathways in the osteocyte, etc., which weakens its mechanical response ability and then leads to osteoporosis and other diseases. Therefore, it is of great significance to study how aging affects the mechanical response of osteocyte. This review mainly discusses the influence of aging on mechanical response of the osteocyte.