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Abstract:Objective To improve the biological fidelity of the thorax flexible body in the original MADYMO child human model, so as to further study pediatric thorax injuries of child occupant. Methods A finite element model of the six-year-old pediatric thorax was built by adopting the method of reverse modeling based on CT images. By replacing the thorax model with flexible body in MADYMO six-year-old human model, an improved human model containing biomechanical thorax model was developed. The model was verified by joint validation of two tests, including Kroell’s adult chest impact experiment combined with Irwin and Mertz’s scaling method, and Jun Ouyang’s thoracic impact test on pediatric cadavers. Results The response of this established thorax model was in good agreement with scaling method and cadaver test data, and the thorax model was much more accurate than the original flexible body model. The resilience of simulation model was consistent with cadaver test. Conclusions The validity of the model is verified, and can be further used in occupant injury analysis in vehicle frontal crash.

Abstract:Objective To study the effect of stair ascent on insert wear of total knee replacement (TKA) by finite element model, which is of great theoretical and practical significance for improvement of wear evaluation method and guidance of design of artificial knee joint prosthesis. Method A finite element analysis model of TKR wear based on Archard’s law was established and validated. The model was applied with loads under normal level walking (ISO14243) and stair ascent, respectively, to compare and analyze the influence of stair ascent on TKR wear. Results The predicted wear during level walking was consistent with experimental results reported in the literature. The volumetric wear rate during stair ascent was 37.10 mm3 per million cycles (MC), which was significantly higher than that during level walking (16.94 mm3/MC). The linear wear during stair ascent was significantly higher than that during level walking as well. Wear during stair ascent was mainly distributed in the backward area of medial platform, which was obviously different from that during level walking. Conclusions As a common daily activity with high loads and high flexion angles, stair ascent contributes an important part in TKR wear, and more attention should be paid to the testing and evaluation of TKR wear.

Abstract:Objective To analyze the influence from strut numbers on biomechanical properties of Z-shaped stent-grafts, especially on their radial support performance and flexibility, so as to provide theoretical support for the design and clinical selection of Z-shaped stent-grafts. Methods Z-shaped stent-grafts with 5, 8, 10, 12 struts were established by finite element method to simulate the process of compression and bending behavior. Radial displacements were applied on surface of the stent-graft and opposite rotations were applied around the z-axis, until a bending angle of 40°was reached. Then parameters such as stent stress, radial support force, strains in graft, cross-section deflection, bending torque were extracted to evaluate the performance of different stent-grafts. Results Compared with stent-grafts with more strut numbers, 5-strut stent-graft showed a better radial support performance with the maximum radial force during compression, and it also generated the smallest 68 N?mm torque and 67.5% cross-section deflection. The tensile strain in graft of 5-strut stent-graft during the process of bending was relatively smaller. Conclusions The struts number of Z-shaped stent-grafts has a significant influence on biomechanical properties of the stent-grafts. Especially the Z-shaped stent-graft with relatively fewer strut numbers shows an advantage in evaluating radial support performance and flexibility such as the bending torque and the cross-section deflection, and is more suitable to be anchored and fit to the tortuous blood vessel, which will play a positive role in decreasing the complication such as endoleaks and thrombosis. The research findings can guide structure design of Z-shaped stent-grafts and the operation to make an optimal selection.

Abstract:Objective To explore the effect of hypergravity on morphology and osteogenesis function of preosteoblast MC3T3-E1 cells. Methods The cultured MC3T3-E1 cells under hypergravity by different loading forces were divided into five groups, including control group, 5 g group, 10 g group, 15 g group and 20 g group. The experimental groups were loaded for 30 min each time in the three successive days, and the control group was synchronously exposed to the same surrounding except for difference in g-value. The morphology of cytoskeletal protein was observed by phalloidin staining, The alkaline phosphatase (ALP) content was examined by ALP activity assay kit, the gene expression of ALP, collagen Ⅰ(ColⅠ), osteocalcin (OC), runt-related transcription factors (Runx2) was measured by real-time quantitative PCR, and the protein expression of ColⅠ and OC was tested by Western blot. Results Under the condition of hypergravity, cell body of osteoblast became thinner, but its surface area increased significantly; with the structure of skeletal arrangement becoming loose, actin microfilament structure reduced so that arrangement of actin-like dispersion orderly lowered. The gene expressions of related indicators of osteogenic differentiation including ALP, ColⅠ, OC, Runx2 loaded by hypergravity were significantly up-regulated, which was the same as ColⅠ protein and OC protein after hypergravity loading. There was only a very minute quantity of small red-orange nodules in the control group, while the cells after hypergravity loading in experimental groups obviously formed various sizes of red-orange nodules. Conclusions Under hypergravity, changes in osteoblast morphology can be triggered by rearrangements of skeletal structure. Furthermore, osteoblast maturation and differentiation can be stimulated effectively by up-regulating differentiation-related gene and protein expressions.

Abstract:Objective To study the damage propagation and evolution mechanism of cartilage under compressive load. Methods The fiber-reinforced porous elastic model of cartilage with micro-defect was established by using finite element method, and the process of damage evolution under compressive load was simulated and analyzed with parameters. The patterns of stress and strain distributions on cartilage matrix and collagen fiber at different damage extension stage were obtained. Results The strain in surface and the forefront of cartilage damage increased significantly with the increase of compression displacement, and they were obviously in positive correlation; in the process of damage evolution, there was a trend that cartilage extended to the deep and both sides simultaneously; cracks and damage in cartilage extended preferentially along the fiber tangent direction. With the aggravation of cartilage damage, the lateral extension speed was significantly faster than the longitudinal extension speed. Conclusions The process of cartilage damage extension has a close relationship with the distribution of fibers. And the damage in matrix and fiber promote each other. The evolution speed and degree of cartilage vary constantly in different layers and at different stages. These results can provide the qualitative reference for prediction and repair of cartilage damage, as well as the theoretical basis for explaining clinical pathological phenomena of damage degeneration and treatment.

Abstract:By developing a novel endoscopic succession closing device to overcome the shortcomings of existing devices that cannot deploy several clips at a time, to perform structural analysis on different clamp structures and to validate their performances in tissue closure through finite element analysis. Methods Comparative analyses of three clamp structures, namely, the aligning tooth structure (original, clamp A), the staggered tooth structure (clamp B), a combination structure with page break angle and staggered tooth (clamp C), were performed to analyze pressure and its distribution on tissues when clamping the stomach wall. Displacement of 7.5 mm was then applied on the clamps to simulate the effect of the operating procedures of the device and tissue kick-back. Results The maximum stresses of the clamp A and B were located on the first pair of teeth which was closest to the rotating shaft, with the stress being 10.39 kPa and 10.11 kPa, respectively. The maximum stress (11.35 kPa) of the clamp C was located on the second pair of teeth. For clamp A and B, the longer the distance to shaft, the larger pressure on stomach tissues. While for clamp C, the pressure on device-tissue interface showed little change along the path. Under tensile displacement, clamp A and B slipped off from the tissue when displacements reached to 5 mm and 6.5 mm, respectively, while clamp C did not. Conclusions　Clamp with page break angle and staggered tooth can exert the uniform max pressure to tissues and provide a larger contact area away from the rotating shaft, thus improving anti-slippage and performance of the novel endoscopic closing device.

Abstract:Objective To analyze stress distribution changes in patellofemoral joints before and after arthroscopic surgery by lateral retinacular release and medial retinaculum placation using three-dimensional (3D) finite element method. Methods The 3D finite element model of pre-and post-operative patellofemoral joints for patients with patellofemoral joint disorders were constructed, and the maximum stress and stress distributions on patellofemoral joints at different flexion angles (30°,60°,90°,120°) under the load of 120 N were calculated and analyzed. Results The maximum stress of patellofemoral joints at different flexion angles after arthroscopic surgery significantly smaller than that before arthroscopic surgery. The stress concentrated on the lateral patellofemoral joints before the surgery, but was redistributed after the surgery. Conclusions The stress on patellofemoral joints at different flexion angles is reduced after arthroscopic surgery by lateral retinacular release and medial retinaculum placation, which provides an objective theoretic reference for arthroscopic surgery to effectively restore stress balance between lateral and medial patellofemoral joints. It is suggested that patients with early patellofemoral joint disorders and abnormal force line should be treated with surgery intervention as early as possible.

Abstract:Objective To obtain biomechanical conditions of the tibia section with different osteotomy thickness under different activity states, so as to provide theoretical basis for osteotomy thickness in total knee arthroplasty (TKA) and activities of patients after operation. Methods The three-dimensional models of the lower limb were reconstructed and the proximal tibia was resected by 0 mm,5 mm,7 mm,9 mm respectively based on the principle of bone resection in TKA. The tibia model after osteotomy were assigned the material properties and the stress and strain of the tibia cross-section were analyzed under the following activity states: standing, walking, running and going upstairs. Results The stress and displacement of the tibia cross-section increased with the increase in osteotomy thickness under the same activity state. The maximum stress and displacement of tibia cross-section increased in general with the same osteotomy thickness, when the strength of activity increased. Conclusions During TKA in clinic, the stress and strain on tibia cross-section became larger as the tibia osteotomy became thicker and the postoperative activity became stronger. Excessive osteotomy in TKA and high intensive activity after TKA should be avoided, so as to reduce stress and strain of the tibia plateau and promote long-term life of the prosthesis.

Abstract:Objective To investigate the influence of barefoot running and shod running with different foot-strike patterns on characteristics of plantar pressures. Methods Kistler force plates and Medilogic insole plantar pressure system were used to collect and compare the kinetic data from a total of 12 healthy male volunteers under shod and barefoot conditions with heel-toe run and toe-toe run at the speed of 3 m/s, including the GRF, loading rate, plantar pressure and impulse. Results (1) Shod running with heel-toe strike significantly reduced the maximum loading rate and extended the time to reach the peak of impact force. Under forefoot strike pattern, shod running significantly increased the maximum push-off force than barefoot running. (2) More plantar pressure parameters were influenced by the foot-strike patterns as compared to those under the shod conditions, and there was a significant difference in the peak pressure and the time to reach the peak pressure in the mid-foot and heel region between the two foot-strike patterns. Conclusions The foot-strike pattern shows a more obvious influence on plantar pressure during jogging than the shod conditions. Shod running with heel strike can reduce the impact force, while barefoot running with forefoot strike can cause an excessive concentration of plantar pressure on the forefoot region, which indicates that a suitable pair of sports shoes is needed for both foot-strike patterns to reduce plantar pressure during jogging.

Abstract:Objective To establish a three-dimensional(3D) finite element model of cervical vertebrae (C1-7), and study its biomechanical properties under muscle force by cervical traction, so as to provide references for clinical treatment. Methods On the basis of nonlinear finite element model of normal cervical vertebrae and combined with clinical traction methods, cervical traction at the extension angle of 0°, 10°, 20°, 30°, 40° under the same traction weight, was simulated by finite element analysis (FEA) software to obtain and select the joint force and muscle force that were appropriate for FEA on the model. Results In the process of cervical extension by traction, under the muscle force, the average maximum equivalent stress of cervical vertebrae, intervertebral disc and uncovertebral joints increased by 4.86, 1.79, 0.69 MPa, respectively, and the average maximum relative displacement of cervical vertebrae in sagittal and vertical axis direction increased by 11.1, 1.26 mm, respectively. The biomechanical properties of cervical traction were similar to the FEA results reported in the literature. Conclusions Neck muscles play an active role in promoting the stress and displacement of cervical vertebrae, intervertebral discs and uncovertebral joints and it should be taken into consideration when performing cervical traction in clinic. In addition, the traction angle should not be too large: 0°-20° is generally recommended as a relatively safe angle range at the initial stage.

Abstract:Objective To study the middle ear damage caused by high pressure. Methods The finite element model of human middle ear was established based on CT scanning, and the change of stress, strain and displacement of the tympanic membrane and the stapes footplate was analyzed when the model was applied with time-varying pressure. Results The satisfactory agreement between the computational results and the corresponding experimental data in the literature indicated the validity of the model. High pressure would cause damage to the middle ear, and the damage would increase with the pressure increasing. Rapid pressurization could severely damage the middle ear, but with a small effect on the inner ear. Slow pressurization could also lead to the middle ear damage, but the inner ear might be damaged before the damage to the middle ear. Conclusions High pressure can easily lead to the ear damage; therefore, the pressurized rate should be controlled strictly during pressurization in order to protect the hearing.

Abstract:Objective To investigate the circulatory supporting effect of the third generation fully magnetically levitated China Heart ventricular assist device (CH-VAD) under heart failure (HF) condition. Methods An in vitro mock circulatory system (MCS) was developed. This system could simulate a healthy adult under resting state and a patient with heart failure, and incorporate the CH-VAD to evaluate the assisting performance under continuous flow mode. Furthermore, CH-VAD was equipped with a pulsatile flow controller and its initial performance was accessed. The pulsatile mode was obtained by using sinusoidal velocity waveform of the pump which synchronized the CH-VAD with the ventricle simulator of the MCS. Results CH-VAD under continuous flow mode could recover the hemodynamic parameters (arterial pressure and cardiac output) under HF condition to normal range. Preliminary pulsatile test results showed that amplitude of current pulse speed had a minor influence on the hemodynamic performance. CH-VAD under continuous flow and pulsatile flow mode could obtain comparable mean arterial pressure, systolic arterial pressure, diastolic arterial pressure and mean flow. Conclusions CH-VAD can generate a certain degree of speed pulse via appropriate pulsatility control, so as to provide sufficient support on ventricular function. Further optimization on pulsatile controller of CH-VAD is required to conform to natural physiology. The developed MCS can be utilized as an effective and controllable in vitro platform for design, optimization and verification of VADs or other mechanical circulatory support devices.

Abstract:Objective To study the expression of caspases in stretch-induced apoptosis in human periodontal ligament cells (HPDLCs). Methods HPDLCs in vitro were subjected to mechanical stretch with 20% strain for 6 h or 24 h. The apoptotic rates were analyzed by flow cytometry. The protein expression of caspase-3, -5, -7, -8 and -9 was detected by Western blot, and the activity of caspase-3, -5, -8 and -9 was measured using colorimetric assay. Results Mechanical stretches with 20% strain for 6 and 24 h could induce apoptosis in HPDLCs. Compared with non-stretching control group, the protein expression level and activity of caspase-3, as well as the protein expression level of caspase-7 were up-regulated by 24 h-stretch. The protein expression level and activity of caspase-5, -8, -9 were up-regulated after stretches for 6 h and 24 h. Conclusions Mechanical stretch with 20% strain can induce apoptosis in HPDLCs in vitro, with the activation of caspase-3, -5, -7, -8 and -9.

Abstract:Objective To investigate the effect of fluid shear stress (FSS) on VWF-A1A2A3-mediated expression of platelet surface P-selectin. Methods Using a parallel plate flow chamber system and mouse anti-human CD62P: FITC as the indicator of P-selectin expression, the alteration of platelet P-selectin expression level with increasing exposure time under different FSS conditions (0, 1, 2 Pa) specifically mediated by VWF-A1A2A3 was observed and analyzed by fluorescence microscope to obtain the activation characteristics. Results FSS triggered platelet activation and P-selectin expression. The activation ratio of platelet was positively regulated by FSS and their exposure time, reaching the maximum value, 9.42% and 14.59% under FSS of 1 Pa and 2 Pa, respectively. The level of P-selectin expression exhibited two-phase tendency with the shear stress-exposure time increasing, uplifted at first, then decreased, with the best action time at 7.5 min. The fluorescence peak intensity increased when FSS was enhanced. Conclusions The level of platelet P-selectin expression is co-regulated by VWF-A1A2A3 and FSS, and is closely related to force-signaling exposure time.

Abstract:The implantation of an intravascular stent has become a widely used minimally invasive treatment for coronary heart disease due to its low invasiveness and high efficiency. But the long-term outcomes are often compromised by in-stent restenosis (ISR), which severely restricts its effectiveness in practical. In this paper, the formation mechanism of ISR was given, and the effects of mechanical environment on ISR were analyzed from the view of solid mechanics. The research progress of stent expansion in vessels with 4 different shapes, including straight vessel, tapered vessel, bifurcation vessel and curved vessel was reviewed. Moreover, the correlations between vessel stress and vessel shape change caused by stent expansion and ISR were reviewed. Finally, based on the influence of different vessel shapes on stent expansion, a multi-objective optimization design method was proposed to improve stent expansion performance and reduce the occurrence of ISR.

Abstract:Osteoporosis (OP)-related vertebral fractures often occur in the transitional thoracolumbar region, which are the earliest signs of OP deterioration in elderly patients. Such fractures can be regarded as a physical incident that occurs when the vertebral stress load exceeds the mechanical structural strength. To OP patients, preventing the occurrence of OP fracture is the primary goal for preventative measures, treatment and research of OP. This paper reviews the biomechanical research progress of osteoporotic vertebra compressive fracture (OVCF), and advocates early prevention of OVCF in OP patients, who should avoid activities that might exceed the security scope of the vertebral body load in daily life, so as to prevent subsequent fractures of the vertebral fracture cascade.