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Abstract:Objective To explore the effect of different initial state setting on a valve simulation. Methods Two-dimensional structural models were established with the initial state of the aortic valve being partially closed in one model and fully opened in the other. The time-dependent load was applied to the valve and the vessel wall of the aortic and the ventricle sides. The finite element method was used to study the maximum stress, the length of the joint, and the contact force of the closed aortic valve under two different initial states. Results The stress and contact force of the aortic valve were relatively large at the closed position when the initial state was fully opened. The closure degree of the valve was low, and the variations in stress and closure degree were large during the periodic cycle. The stress and contact force of the valve were relatively small when the aortic valve was partially closed. The closure degree was high, and the variations in stress and closure degree of the aortic valve were small during the periodic cycle. Conclusions In the case of the aortic valve partially closed in the initial state, the stability of the calculation process and the closure degree of the valve were relatively high, which should be given more consideration in numerical simulation. The results can be used to study the mechanical behavior of the valve and the biomechanical mechanism of the aortic root.

Abstract:Objective To investigate the influence of different end shapes of esophageal stents on the mechanical behavior of the stent-esophagus system. Methods Through finite element simulation, the mechanical behavior of the coupling system between braided esophageal stents with different end shapes (straight-tube-shaped, cup-spherical-shaped, double-trumpet-shaped) and the esophageal cavity was analyzed. The influences of bare stents and covered stents with three different end shapes on stress distributions in the inner wall of the esophagus and on dilatation of the esophageal stenosis zone were compared. Results The reduction in stenosis rate caused by the bare stent was larger than that of the covered stent. Moreover, the equivalent stress and the contact stress caused by the bare stent were much larger than those of the covered stent. Different end shapes had a significant influence on the stress occurring in the healthy esophageal zone. Stress concentration occurred in the zones where the esophagus contacted the central part of the cup-shaped end and the edge of the double-trumpet-shaped end. The braided esophageal stents with three different end shapes all had good apposition.Conclusions Different end shapes of stents cause different stress states in the esophagus. A larger stress involves a higher probability of occurrence of esophageal tissue hyperplasia, but a smaller possibility of stent migration. Therefore, understanding the effect of the end shapes on stent performance can provide important theoretical references for optimization design of the braided stent and its clinical selection.

Abstract:Objective To obtain the distribution of stress concentration on the microporous structure of 3D-printed materials through a mapping algorithm with low calculation cost, so as to provide a new method of finite element calculation of 3D-printed materials for the prediction of fatigue life and the optimization of structural design. Methods Node coordinates and stress values within the influential region of the single pore were extracted to calculate the stress concentration coefficients of different nodes. The nearest node to each node on the ideal model was determined by distance, and the corresponding coefficient was multiplied by its stress value. When the nearest nodes of several nodes were the same, the average of these coefficients was assigned. For the pores close to the edge, an edge coefficient must be multiplied to reduce the error. Results An error of less than 8% between the mapping result and the calculation result was achieved for the case in which the pores were not near the edge, but for the case in which the pores were close to each other near the edge, the error was less than 15%. Conclusions The mapping algorithm can effectively characterize the stress concentration of the microporous structure of 3D-printed materials, and determine the stress distribution with low cost. This novel algorithm provides the finite element result for the optimization design and fatigue analysis of implants in clinical applications.

Abstract:Objective To simulate the tightening procedure of a cancellous lag screw by using the implicit dynamic analysis method, and to evaluate the stress distributions on the screw-bone interface. Methods Finite element models of a lag screw with the surrounding bone were developed, and the implicit solver was set up for implicit dynamic analysis on the tightening procedure of the lag screw. The mechanical properties of the screw-bone interface were also analyzed according to strain and stress distributions on the screw and the surrounding bone. Results The stress of the lag screw was mainly distributed in the proximal portion of the screw thread rod. The high-stress region of the bone around the screw was located outside the outer edge of the screw, and it was approximately equal to the depth of the thread. The area of high-stress distributions on the bone was the main region that resisted screw stripping. Conclusions The method of implicit dynamic analysis can accurately simulate the mechanical properties of the screw-bone interface during screw tightening. The discovery of high-stress distributions on the surrounding bone can help researchers to further understand and improve the stability of screw insertion.

Abstract:Objective To compare the effectiveness and mechanical differences in the dynamic hip screw (DHS), proximal femoral nail antirotation (PFNA), and proximal femoral internal fixator (PFI) for fixing complex unstable proximal intertrochanteric fractures by biomechanical testing. Methods Eighteen Synbones of the proximal femur were made to simulate complex unstable femoral intertrochanteric fracture models (Evans-Jensen TypeⅢ), which were fixed by DHS, PFNA, and PFI, respectively. The models were tested using a biomechanical testing machine, in order to compare their differences and advantages for fixing fractures. Results Under the compressive loads of 300, 600, and 1 200 N, the fracture displacement of the DHS was the maximum, with a significant difference compared with PFNA and PFI (P<0.05). There were no significant differences between PFNA and PFI (P>0.05). Under torsional loads of 300, 600, and 1 200 N, the torsional displacements of DHS and PFNA at the fracture ends were the maximum, with no significant difference (P>0.05). There were significant differences between PFI and PFNA as well as PFI and DHS (P<0.05). Conclusions For complex unstable proximal intertrochanteric fractures, the stability of the compression resistance of the PFI system is similar to that of the PFNA system. However, the torsional resistance of PFI is stronger than that of PFNA. The DHS system shows the least resistance with respect to compression and torsion.

Abstract:Objective To compare the effects of preserving the posterior ligament complex (PLC) with torque loading and displacement loading on the biomechanical properties of the adjacent segments after lumbar decompression and fusion. Methods Six fresh male cadaver lumbar specimens of T12-S2 were tested in the sequence of intact, L4-5 laminotomy (preserving the PLC) with fixation and L4-5 laminectomy (destructing the PLC) with fixation, by applying both displacement loading and torque loading, respectively. Ranges-of-motions (ROMs) of the adjacent segments were measured under a noncontact photographic recording system. Results In displacement-loading mode, the flexion ROM in laminectomy group was significantly higher than that in laminotomy group, and no obvious ROM differences were found in the laminectomy and laminotomy groups under extension, lateral bending, and rotation movement. Conclusions Torque loading and displacement loading have different biomechanical effects on the adjacent segments after lumbar decompression and fusion. Compared with the laminotomy method, in which the PLC is preserved, the laminectomy method in which PLC structures are damaged can obviously lead to an increment of flexion ROMs at the adjacent segments, and also increase the ROMs of the adjacent segments under extension, lateral bending, and rotation movements, which might increase the risk of further instability of the fused adjacent segments.

Abstract:Objective To investigate the effect of Kirschner and bandage fixation on the hallux valgus (HV) after distal osteotomy of the first metatarsus. Methods A comprehensive three-dimensional finite-element model of the foot was established based on medical images of the foot of a patient with HV, including bones, sesamoid, cartilage, ligaments, soft tissues, and Achilles tendon. The models of Kirschner and bandage fixation were also established to investigate the biomechanical behavior of the foot with HV during full weight-bearing standing. Results The compressive stress (14.9 MPa) between the osteotomy fragment surfaces in bandage fixation was higher than the peak stress of the Kirschner needle (6.71 MPa). The Kirschner fixation was better than the bandage fixation from the dorsal, plantar, medial, and lateral foot. Therefore, it was more favorable for the stability of the osteotomy. Conclusions The bandage fixation can reduce the healing time of osteotomy, providing an optimal design for fixation methods after hallux valgus operations.

Abstract:Objective To explore the relationship between shoe comfort and foot loading characteristics in two types of basketball shoe during different basketball footwork. Methods Two Kistler 3D force platforms and Medilogic insole plantar pressure system were used to collect the kinetic data of 12 healthy male basketball players wearing two types of basketball shoe (shoe L and shoe N) during three varieties of basketball footwork (side-step cutting, 90° varied-direction running, lay-up), including peak impact force, peak loading rate, and peak plantar pressure. The perception test scale was used to evaluate comfort for two types of basketball shoe during three kinds of basketball footwork. Results For the two types of basketball shoes, there was no significantly difference in the impact force during the three kinds of basketball footwork, but the plantar pressure of shoe L was significantly greater than that of shoe N during side-step cutting and lay-up. Shoe N was significantly more comfortable than shoe L, with a significant difference in preference (heel stability, heel responsiveness, forefoot cushioning, heel cushioning, and overall liking) and intensity (forefoot and heel cushioning) on a dynamic scale. Conclusions The plantar pressure and comfort show significant differences in the two types of shoes; however, none of the shoes appeared definitively superior in the two evaluations. It is suggested that the biomechanical characteristics of the shoes and the subjective evaluation of the athletes should be considered in the overall design and evaluation of specialized shoes.

Abstract:Objective To investigate the E-selectin mediated-calcium response of neutrophils under flow fields. Methods A parallel-plate flow chamber combined with a fluorescence microscope was used to observe the adhesion and subsequent calcium response of neutrophils on E-selectin at different concentrations under fluid shear stress (FSS) of 0-600 mPa. Results E-selectin could capture neutrophils from the flow to the chamber substrate and induce further intracellular calcium flux of firmly adhered cells. The arrested cell and activation ratio increased gradually as the concentration of E-selectin increased. Only immobilized E-selectin could conduct the external force-signal to trigger the calcium response of neutrophils effectively. By increasing FSS, not only was the activation ratio increased from 23% to 70%, but the calcium response intensity also increased from 0.92 to 1.45, while the delay time from cell adhesion to calcium response was greatly reduced from 70 s to 27 s. Conclusions FSS can modulate the calcium response of neutrophils in cooperation with E-selectin, and it positively regulates the activation rate and level of calcium response. This study may deepen the understanding of the immune response of leukocytes under a hemodynamic environment.

Abstract:Objective To investigate changes in the collagen expression and elastic modulus in scleral tissues of experimental high myopia, so as to further explain the mechanism of high myopia. Methods Twenty one-month-old New Zealand white rabbits were monocularly treated by eyelid suturation randomly to build an experimental high myopia eye model. Eyes without such operation were set as the normal control. After 60 days, the experimental high myopia eye models were successfully established by measuring the eye axis. The eyeballs were obtained to assess three regions of the sclera (anterior, equatorial, and posterior area). The three regions of the scleral tissues were separately divided into four groups. The first group was made into scleral strips for elastic modulus measurement using an Instron5544. The second group was hematoxylin-and-eosin stained for observation of the scleral structures. The third group was used for electron microscopy to observe the size distribution of collagen fibrils. The last group was homogenized, and the concentration of hydroxyproline was measured to determine the collagen content. Results The elastic modulus, collagen content, and diameters of the collagen fibrils of each scleral region increased with age. The posterior sclera of high myopia had looser collagen fibril arrangement, less hydroxyproline concentration, and lower elastic modulus than the normal eyes. However, there was no significant difference as for the anterior and equatorial sclera. Conclusions The remodeled posterior sclera of high myopia has a looser collagen fibril arrangement, less collagen, and lower elastic modulus, which easily causes expansion and deformation and thus lead to high myopia. The research findings provide the theoretical guidance for high myopia prevention by targeting the collagen during early development.

Abstract:Objective To compare the differences in long-term jogging and Tai Chi in terms of neuromuscular latency and time to peak of surface electromyography (EMG) in older males during lateral sudden perturbation. In addition, an effective means to enhance neuromuscular response and muscle contraction efficiency of older males during lateral postural challenges was investigated. Methods Postural reactions of young males, older sedentary male controls (without regular exercises), older male joggers (with long-term jogging practice), and older male Tai Chi participants (with long-term Tai Chi practice) were evoked by means of a sudden unpredictable lateral translation platform. Surface EMG signals of peroneus longus, anterior tibialis, gluteus medius, and erector spinae were collected by an EMG detection and analysis system. Results The latencies of peroneus longus, anterior tibialis, and gluteus medius were delayed in the older sedentary male controls compared with those in young males. The neuromuscular reactions of anterior tibialis and erector spinae in older Tai Chi male participants were faster than those of older sedentary male controls. The contraction speeds of peroneus longus, anterior tibialis, and gluteus medius in young males were higher than those in three older groups during sudden lateral perturbations. Conclusions Long-term Tai Chi practice can enhance the responses of ankle and trunk muscles of older males during lateral postural challenges, but it has little effect on the muscle contraction efficiency of older males.

Abstract:Objective To study effects of different types of high-impact exercises on the increment of bone mineral density (BMD) and bone mineral content (BMC) . Methods Thirty-nine male volunteers, including 13 hoopsters, 13 paratroopers, and 13 common college students as the control, were recruited and divided into two subgroups (subgroup 1:20-22 years old; subgroup 2:23-25 years old). Their BMDs and BMCs on calcaneus, first through fifth metatarsus, hip, and lumbar spine (L1-4) were evaluated. Results The BMC of calcaneus, the first and second metatarsals, total lumbar spine, and total hip in the hoopster group was significantly higher than that in the control group and paratrooper group. The hoopster group obtained statistically higher BMD at the lumbar spine, hip, and femoral neck than the other two groups. However, the BMCs and BMDs of the paratrooper group and control group had no significant differences at almost all measured anatomical locations. Conclusions BMC and BMD are not always in positive correlation with vertical ground reaction forces during normal exercises. Compared with parachuting training, playing basketball as a kind of variable load exercise can effectively increase BMC and BMD, and is more beneficial for reducing the risk of osteoporotic fracture.

Abstract:The description for load-displacement characteristics of in vitro spinal specimens in three-dimensional (3D) motion is the foundation of spinal biomechanical research. How to simulate the load and movement of spine in vivo as accurately as possible is the difficulty of in vitro spinal biomechanical research. Domestic and foreign scholars have carried out extensive research on theories and equipments of spinal biomechanical test. Currently, the spinal 3D motion test is mainly divided into load control, displacement control and hybrid control according to the control method. Based on different control method, the test equipments are also developing and perfecting constantly. The operation principle for current in vitro spinal loading devices are summarized, and their advantages and disadvantages are also analyzed, so as to provide references for the research on in vitro spinal biomechanical loading devices.

Abstract:Large-conductance Ca2+-activated K+ (BKCa) channels, activated by stress, exhibit mechanosensitivity and are involved in stress-regulated cellular function. For different types of cells, they will have different expression and activity changes due to their BKCa channels responding to different stress patterns. Correspondingly, the mechanism underling channel activation behaves differently, which is activated by the elevation in Ca2+ concentration or changes in membrane bilayer and cytoskeleton. In this review, the research progress in mechanosensitivity of BKCachannels was summarized from 3 aspects, including its molecular structure basis, manifestation and stress activation mechanism.

Abstract:Vascular endothelial cell glycocalyx is a layer of glycoprotein complex located on the surface of endothelial cells, forming a selective permeation barrier on the surface of endothelial cells. In the present review, after a brief introduction of glycocalyx, the relationship between glycocalyx and mass transport under fluid sheer stress (FSS), especially the relationship between glycocalyx and macromolecules such as low density lipoprotein (LDL) has been discussed. This relationship was reflected as following: on the one hand, the thickness and integrity of the glycocalyx affects the concentration polarization of LDL and its transendothelial transport and heparan sulfate proteoglycan (HSPG) participates in the whole process of residual lipoproteins metabolism. On the other hand, ox-LDL, an oxidized product of LDL, destroys heparan sulfate (HS) which is a major component of the endothelial cell glycocalyx. The study on relationship between vascular endothelial glycocalyx and lipoproteins will provide a new clue to elucidate the pathogenesis of atherosclerosis and provide more evidence to view the glycocalyx as a new control target.