The biomechanics of peripheral nerve plays an important role in physiology of the healthy and pathology of the diseased such as the diabetic neuropathy, the cauda equine compression and the carpal tunnel syndrome. The other application is recent development of neural prostheses. The goal of this paper is to review researches done by members of Taiwanese Society of Biomechanics on the biomechanics of peripheral nerves in the past two decades. First, a brief introduction of the anatomy of peripheral nerve is given. Then experiment designs and mechanical models for testing the nerves are presented. The material properties ranged from linear elastic to nonlinear visco-elastic and scales ranged from organ level to tissue level are reviewed. Implications of these studies to clinical problems will be addressed and the challenges and future perspective on biomechanics of peripheral nerve are discussed.
In recent years, orthodontic treatments have become increasingly popular. In these treatments, orthodontic forces, which cause the absorption and deposition of alveolar bone, are applied through brackets and teeth in order to move the teeth to the expected position. The periodontal ligament (PDL) has a determinative role in dental biomechanics; however, the difficulty of predicting PDL behavior has limited the advancement of dental biomechanics. Therefore, this study intends to measure the biomechanical behavior of the PDL and then develop an analytical model to predict the holistic force-displacement relationship of the tooth. In this study, a porcine premolar, including the tooth, periodontal ligament, and alveolar bone, was harvested for experimental purposes. A custom-made apparatus was designed to measure the force-displacement relationship of the PDL. Three analytical models, including linear, exponential, and power functions, were adapted to fit the experimental results. In addition, three-dimensional finite element models were constructed from micro-CT sectional images, and the hyperelastic behavior (Mooney-Rilvin equation) of the PDL was simulated. The results showed that the PDL exhibited nonlinear biomechanical behavior. The power function was found to be a good fit for the force-displacement relationship of the PDL. Furthermore, it was found that the hyperelastic model could predict the biomechanical behavior of the PDL for tension less and equal to 20 N.
Detecting selective electromyography (EMG) signals is important for minimizing errors in muscle information from crosstalk and delivering movement intension orders clearly. In this paper, we propose a circular-array EMG system for detecting the orientation of muscle fibers and recording maximal EMG amplitude. This system records six-channel bipolar EMG signals using a circular array grid consisting of twelve Au electrodes. We evaluate the performance of this system by hypothesizing that: (1) this system can detect the fiber orientation of forearm muscles (including flexor carpi radialis (FCR), extensor carpi radialis (ECR), pronator, and supinator) and record the maximal EMG amplitude; (2) it minimizes EMG amplitude error caused by twisting between the orientations of electrodes and muscles during complex movement from a body part with multi-degrees of freedom (DOF); the normalized root mean squares (Normalized RMS) were used to analyze the six-channel EMG signals to verify these three hypotheses. It was concluded that the circular array EMG system is superior to other systems in its acquisition of selective EMG signals. It could be a useful technique for improving the DOF in movement and obtaining accurate muscle information.
With the extension of life span and advances in medical technology, there has been an increasing number of operations and procedures for human organs that were previously impossible. Successful completion of complex surgery requires considerable trial and error and medical training, which is costly and risky. To deliver a realistic feeling in virtual surgery, it is essential to know the distribution of the stresses to produce the repulsive force associated with the deformation of the organ. However, it is not possible to measure or calculate in real-time stresses of the necessary parts while observing the actual organ movements during the operation. We propose a method called the cell element method, which calculates the real-time stress by applying an external load to a soft tissue specimen. A combination of an image-processing technique along with a camera and the cell element method based on finite element method makes it possible to provide the calculated stresses as the loadings apply. For the verification of the method, we used the method of calculating the stress by measuring the strain by applying the load using the specimen made of PVC. The results are relatively close to those of finite element simulations under the same mechanical conditions.
The rupture of the atherosclerotic plaque is related to the mechanical stress and structural integrity of plaque wall tissues. In order to investigate the longitudinal asymmetry across the stenosis of the arterial plaque wall, asymmetric plaque wall models were constructed by skewing the lipid core distribution in the upstream direction. Wall stress and blood flow in the coronary artery models were computationally analyzed considering fluid and structure interaction. The values of maximum cap stress increased, and its location moved toward the proximal cap as asymmetry increased. Hemodynamic wall shear stress (WSS) did not change much owing to negligible changes in luminal geometry, but the maximum WSS and the spatial gradient of WSS were higher in the asymmetry models than in the symmetry model. The pressure drop and pressure gradient across the stenosis were also higher in the asymmetry models. Because higher peak wall stress, wall strain, increased WSS, WSS gradient, pressure drop, and pressure gradient are correlated with weakening and rupture of the plaque wall, we suspect that longitudinal asymmetric distribution of the lipid core in the plaque could affect plaque wall stability and vulnerability.
We constructed an experimental system that can observe bovine sperm motility in three dimensions, simultaneously from the vertical and horizontal directions. The comparison of the experiments conducted using cover glass and square tubing indicates that the effect of the cover glass on the sperm motility is not negligible. Based on this result, we investigated a three-dimensional trajectory of a motile sperm in the square tubing by simultaneously observing through two high-speed cameras. In addition, we investigated the effect of different viscosities of the surrounding fluid on the sperm motility. The experimental results indicate that the increasing viscosity causes a decline in the sperm motility. Furthermore, we focus on the width of the sperm head and the flagellar shape. At low viscosity, the time variation of the head widths is relevant with the two directions and varies periodically. In contrast, at high viscosity, an almost constant value is maintained and periodical time variations are not observed for both directions. Moreover, a difference in the viscosity is observed for the tortuosity of the flagellum shape. These results suggest that the three-dimensional flagellar structure of the bovine sperm is a helix whose cross-sectional shape is an ellipse with quite a large aspect ratio. Further, the results state whether the rotation or nonrotation of the sperm is dependent on the balance between the viscous resistance acting on the sperm and the torque due to the flagellar shape. The experimental results obtained will be useful in clarifying the mechanics of sperm motility under their actual environmental conditions at high viscosity.
Cell migration is an important process both in physiological and pathological conditions. Migrating cells in vivo respond to various extracellular environmental factors and change their migratory behavior. Thus, it is important to take into account extracellular environmental factors in studies on cell migration. This study specifically focused on fibroblast migration in a three-dimensional microenvironment. We fabricated a polydimethylsiloxane cell culture substrate with intersecting grooves as a model to mimic a feature of the complex porous microenvironment experienced by fibroblasts in vivo. The sizes of the grooves allowed fibroblasts to penetrate into the grooves. The effects of branched grooved structures on cell migration, and on cellular organization of the actin filaments and phosphorylated myosin light chain, were analyzed. Fibroblasts migrated along intersecting lattice grooves that were 5 μm wide, 13 μm deep, and spaced 10 μm apart. Analysis of the cellular distribution of actin filaments and phosphorylated myosin light chain demonstrated two effects of the intersecting grooved structure on actin cytoskeletal organization in the fibroblast. One was the enhancement of filopodia protrusions into the branched groove at the junction, and the other was the formation of stress fibers to cross the opening of the junction. These results suggest that the filopodia protrusions are guided by the groove and are followed by the cytoplasmic protrusion, then the rear of the cell retracts due to stress fiber contraction, leading to fibroblast guided migration in the branched intersecting groove.
Macrophages infiltrated in the walls of abdominal aortic aneurysms (AAA) are subjected to cyclic stretching due to pulsatile deformation of blood vessels and low oxygen conditions caused by intraluminal thrombus. These conditions could induce aberrant changes in macrophage functions and lead local weakening of AAA walls. We previously reported that the combination of 10 % cyclic stretching and 2.2% O2 conditions caused an increase in matrix metalloproteinase-9 (MMP-9) production in macrophages as well as changes in morphological responses to cyclic stretching. In the present study, we investigated the effects of oxygen concentrations on MMP-9 productions and morphological changes of macrophages subjected to cyclic stretching. Macrophages differentiated from THP-1 cells were subjected to 10% cyclic stretching under 5% or 1% O2 conditions for 24 h, and gelatinolytic activity of MMP-9 in the conditioned medium was assessed by zymography. Cells showed spread and rounded shape under static conditions and elongated and oriented to the direction of stretching after exposure to cyclic stretching, and there were no obvious effects of oxygen concentrations in cell morphology. An O2 concentration of 5% did not change MMP-9 productions of macrophages in static culture and subjected to cyclic stretching compared to normal cell culture condition of 20% O2. In contrast, 1% O2 condition stimulated MMP-9 production of macrophages both under static culture and cyclic stretching conditions. We also found that treatments of inhibitors for extracellular signal-regulated kinase (ERK) and Rho associated protein kinase (Rho kinase) suppressed the increased MMP-9 productions of macrophages by 1% O2 condition. These results suggest that lower oxygen conditions such as 1% O2 stimulate MMP-9 production in macrophages through signaling pathways involving ERK as well as Rho kinase-mediated actin cytoskeletal contractility.
In this paper, the proposed study aims to achieve a better understanding of neuronal tolerance and contribute to the prediction of the secondary degeneration of diffuse axonal injury (DAI). Therefore, a uniaxial stretching device which subjected cultured neurons to uniaxial stretch was employed to evaluate the effect of strain and strain rate along axon to realize the injury threshold. Neurons differentiated from mouse neuronal stem cells were injured and the morphology was observed before and after stretching with strains of 0.10, 0.12, 0.18, 0.23 at strain rates of 8, 11, 19, 26 s-1 respectively. Results suggest that the threshold for axonal dysfunction is around 0.18 strain whereas the threshold for axonal disruption is around 0.23 and the results of strain rate effect investigations on axonal dysfunction and disruption around these threshold values indicated that higher strain rate values such as 50 s-1 may have diminishing effects on threshold for axonal disruption.
In the present study, an image correlation method was used to determine the site-dependent strain in the porcine anterior cruciate ligament (ACL). In particular, the strain of the ACL in the femoral and tibial attachment areas was quantified when the eight knees were subjected to a maximum of 50 N anterior tibial load that was applied using a 6-DOF robotic system. The ACL strains in the anterior, central, and posterior bundles of the medial, middle and lateral layers were determined as a function of the applied anterior load. In addition, the surface of the ACL was observed using a light microscope under no loading condition. Results revealed that the strain in the medial layer of the ACL increased gradually and almost linearly with the increase of anterior load in the midsubstance area. In contrast, the strain in the femoral and tibial attachment areas of the medial layer of the ACL increased rapidly at the beginning of anterior loading and gradually thereafter with significant differences in slope of strain-anterior load curve found in the anterior and posterior bundles. The largest strain in response to 50 N of anterior force was found in the tibial attachment area in medial and middle layers, while the maximum strain was found in the femoral attachment area in the lateral layer. Microscopic observation indicated that crimp structure was more clearly observed in the femoral and tibial attachment areas than in the mid-substance. These microstructural features of the ACL were may be attributable to the higher and load-dependent, nonlinear strain observed in the attachment areas. Our study suggested that the strain in the ACL at full extension is site- and load-dependent in a non-linear manner at the femoral and tibial attachment areas.
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