Muscloskeletal tissues, bone, cartilage, muscles and tendons regulate and support the body's actions and are differentiated from mesenchymal stem cells. These organs generate and/or respond to mechanical stress, which is inevitable in daily life. Among these tissues, cartilages play roles in articular function in joints where shear stress is loaded in combination with cyclical or intermittent compressive force by joint action, and provides a template for bone growth under compressive stress directed along the long axis of long bones. Along with soluble factors, such as cytokines and growth factors, mechanical stress has been recognized as one of the epigenetic factors that regulates the gene expression of various types of cells. Thus, the molecular mechanisms of the mechano-sensing, mechano-transduction, and mechano-response of cells have become a focus of connective tissue biology. Here, we will discuss the mechanisms through which differentiated chondrocytes and mesenchymal cells that are differentiating into chondrocytes respond to various types of mechanical stress by altering their phenotype and how these phenotypic changes are molecularly regulated. We will focus on the roles of cell-extracellular matrix interactions through integrins and downstream signaling pathways involving mitogen-activated protein kinases.

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Ti-Ag alloys with 20 and 25 mass% Ag were prepared; their surfaces were polished using silicon carbide abrasive papers. The polished alloys were immersed in a simulated body fluid (SBF), and their surfaces were observed by scanning electron microscope (SEM) to investigate the spontaneous formation of calcium phosphates. The precipitates formed on the alloys were qualitatively and quantitatively analyzed using an electron probe microanalyzer (EPMA), with pure titanium and silver used as controls. Hardness and surface roughness, which was measured as the height parameter Ra, were examined, and their effect on calcium phosphate formation was elucidated. On immersion in SBF, calcium phosphates were formed on the Ti-Ag alloys and pure titanium but not on pure silver. The amount of the precipitate and the concentration ratios of calcium to phosphorus in the precipitates of the Ti-Ag alloys and pure titanium did not differ significantly. The Ti-Ag alloys showed significantly higher hardness and lower Ra values than pure titanium. The Ra values of the metals decreased as their hardness increased. The Ra values of the metals appeared to have very little effect on calcium phosphate formation. The results of this study have verified the biocompatibility of the Ti-Ag alloys, making them suitable for use as dental and orthopedic implants.

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In the present study, peri-implant tissue alteration was studied histologically, and then differences in the gene expression pattern of certain proteins were analyzed using cDNA microarray analysis, under the influence of static lateral load. Beagle dogs were divided into two groups: control and load. Three months after the extraction of mandibular premolars, two implants were placed in each side of the mandible. Each group was further divided into subgroups for loading times of 1, 7 and 14 days. Immediately after the implant installation, a loading device was adhered between the abutments of neighboring implants. Afterward, the expansion screw of the load group was activated by 360-degree rotation, resulting in 0.7 mm horizontal expansion. After sacrificing the dogs, peri-implant tissue was collected, then microarray analysis for the detection of gene expression was performed, as well as histology. Histology indicated that the peri-implant tissue broke down under the influence of the load. Microarray analysis demonstrated the presence of load-sensitive gene expression even after 1 day. Differences in gene expression patterns in concert with static lateral load were demonstrated, even at an early stage post-operation. Further study may help in the diagnosis of pathological overload.

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A porcine mandible was separated to prepare thin periodontium specimens, consisting of a molar, periodontal ligament (PDL), and alveolar bone. Occlusion was simulated by applying a forced compressive displacement, using a table-top material tester. We photographed images of the displacing periodontium specimen and simultaneously obtained the load-displacement curve during the test. The displacement and deformation distributions were examined using digital image correlation analysis. Then, we correlated the distribution with the load-displacement curve, which was characterized by biphasic behavior, as noted in many previous studies. We found that the displacement and deformation distributions of actual periodontium correlated with the load-displacement curve during dental occlusion. Regarding the biphasic characteristics of the load-displacement curve, we showed experimentally that the first phase indicated deformation of the PDL and the second indicated deformation of the alveolar bone and tooth.

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Currently, β-type Ti-Nb-Ta-Zr alloys are gaining attention owing to their feasibility for use as biomedical materials. However, the deformation behaviors of these alloys have not yet been clarified. In this study, the Nb content of the Ti-30Nb-10Ta-5Zr (TNTZ) alloy was altered between 1.0 and 3.0 mass% from 30 mass%, and the corresponding changes in the superelasticity and shape-memory characteristics were investigated by tensile loading-unloading tests, X-ray diffraction (XRD) analysis, and microstructural analysis using a transmission electron microscopy (TEM). When the Nb content is less than approximately 29 mass%, the loading-unloading stress-strain curves show two-step gradients and are similar to those of common shape-memory alloys such as Ti-Ni alloys; these gradients result from stress-induced martensitic transformation and its reversion. When the Nb content is approximately 30 mass%, the tensile loading-unloading curves show a nonlinear gradient corresponding to superelastic behavior, which can not be explained by XRD and TEM microstructural analyses on stress-induced martensitic transformation and its reversion in the present state. When the Nb content is approximately 31 mass%, the tensile loading-unloading curves show a single gradient. The elastic deformation is mainly caused by the elastic strain in the lattice. Changes in the chemical content of Nb in TNTZ within a very narrow range are found to alter the superelastic behavior of this alloy.

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The polymerization shrinkage of dental restorative resin composites in cavities was studied using a digital image correlation method. The cylindrical and semi-cylindrical cavities in bovine teeth were used to examine the shrinkage behavior on the top free surface and the simulated cross section, respectively. The cavities filled with the resin after spreading a bonding agent were irradiated using a visible-light curing unit and photographed with a CCD camera as a function of time. The two images photographed were correlated to study the deformation during the polymerization process. Experiments were also performed on the cavities without the bonding agent, and its effect on the bonding strength at the interface between the resin and tooth structure was examined.

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Previously, a few models have been proposed to predict bone resorption process due to stress shielding in long bones such as proximal femur; however, there are almost no reports on finite element analysis of loss of marginal dental bone that is caused mainly by occlusive overload. In this work, the stress, strain and strain energy density (SED) criteria were separately applied to simulate overload-induced bone resorption in a jawbone/implant system by means of the finite element analysis. A simplified dental bone/implant model was created, with the bone composed of a cortical bone and a cancellous bone and the implant having the detailed screw structure. The results demonstrated that the simulations according to the equal SED criterion reproduce bone resorption patterns that are more realistic to actual clinical situations, when compared to the equal stress or strain criterion. It was shown that bone resorption starts initially in the cortical bone around the implant neck, then extends downwards, and lastly enters the cancellous bone after passing through the interface of the cortical and cancellous bone. A symmetric bone resorption pattern was revealed under the condition of axial loading, whereas an asymmetric resorption prototype was demonstrated under the oblique loading condition. Moreover, in the case of oblique loading, bone resorption is faster and the amount of resorbed bone is larger, which leads to more micromotion of the dental implant than in the case of axial loading.

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Newly approach using the formation process of polymer foam is introduced in this study to prepare porous hydroxyapatite (HAp) scaffolds for bone tissue engineering applications, which could provide a better control over the microstructures of scaffolds and enhance their mechanical properties. The scaffolds prepared have an open, relatively uniform and interconnected porous structure with a pore size ranging 50 to 300 µm. A compressive strength of 5 MPa for the scaffolds with HAp content 80 wt% and higher porosity of 77% was achieved. The pore morphology and size of the scaffolds were characterized using a scanning electron microscopy. X-ray diifraction was used to determine the crystal structure. Scaffolds with desired porosity, pore size, and geometry could be prepared by using the formation process of polymer foam with controlling process parameters.

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Ni-free type Ti-based metallic glass evaluated in this study has imposing performances for biomaterials that is based on high bulk forming ability (BFA) for implantable materials, superior specific strength, low Young's modulus as hard tissue replacements and excellent workability. Especially, surface characteristics of Ti-based bulk metallic glass for corrosion resistance exhibit a high potential for application to be used as dental implants in the oral cavity. We also made an examination of chemical stability for human cell test with osteoblasts (SaOS2) in vitro. Results of the good biocompatibility and high glass forming ability evaluated in this study are expected to increase utility value for biomedical application

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Calcium phosphate coating films were fabricated on blast-treated titanium plates and screw-type titanium implants using RF magnetron sputtering. A uniform and dense coating film with a thickness of 0.5 µm could cover the blast-treated titanium plate efficiently, maintaining the surface roughness of the substrates. The as-sputtered coating films consisted of amorphous calcium phosphate (ACP) or oxyapatite (Ca₁₀(PO₄)₆O, OAp). Heat treatments of the OAp coating films were conducted in a silica ampoule or in air, and it was observed that the crystallinity of the coating films increased after the heat treatment. The bonding strength between the as-sputtered coating films, subjected to heat treatment in air, and the blast-treated titanium plates exceeded 60 MPa. An immersion test was conducted and alkaline phosphatase (ALP) activity of osteoblasts was investigated in vitro. The dissolution rate of the coating films in the 0.9% NaCl solution decreased with an increase in their crystallinity. The ACP coating film exhibited high ALP activity. As the in vivo evaluation, the coated and non-coated titanium implants were implanted into the femur of Japanese white rabbits. The percentage of bone-implant contact and the removal torque value of the coated titanium implants were greater than those of the non-coated titanium implants.

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Control of the gliding directions of kinesin-driven microtubules (MTs) in vitro has good feasibility for the development of nano-scale transport systems. A requirement for the control of transporters in these systems includes detecting the positions of gliding MTs; however, no studies have reported on the monitoring of the positions of gliding MTs. Here, we suggest an algorithm to detect tip coordinates of gliding MTs by binarization, skeletonization, and filtration of fluorescent images of MTs. The algorithm was first applied to artificially drawn segments with given lengths (10-80 pixels), widths (1-10 pixels), and curvature radii (20-120 pixels) to verify the effect of the sizes of MTs on accuracy of tip coordinates extracted by the algorithm, and error was estimated by referring to the true coordinates. The estimated errors were as small as 2 pixels in the width and were not affected by the length and the curvature radius, indicating that our algorithm is useful to extract the tips of MTs. The algorithm was subsequently applied to images of gliding MTs. Since distances from the trajectories of the MTs to the centers of gravity of the MTs (3.7 ± 2.1 pixels) were significantly larger than those to the tips (1.9 ± 0.5 pixels), the use of the tips as representative points of gliding MTs was verified. A detection method using tips of MTs, as suggested in this study, may be a useful technique for monitoring each MT in nanoscale transport systems.

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Displacement of actin filament and its binding proteins in mouse myoblasts under locally applied deformation was analyzed by manual method or digital image correlation method. Cyotoskeletal components labeled by immunofluorescent technique or green fluorescent protein-fused protein were deformed via the movement of a glass needle which was poked into a cell. First, we confirmed the digital image correlation method is able to use to analyze displacement map by comparison of the manual method. Next, we examined whether the applied deformation isotropically propagates into cell body. At focal adhesions, fluorescent signals from the deformed area unchanged under the application. Mainly, focal adhesions around the poked area were moved to the direction of the movement of the needle. In addition, some adhesions away from the poked area were moved. Similar results were observed in phalloidin-stained cells. Finally, we applied the local deformation to live cells. However, displacement at the locally deformed area was not observed due to the disappearance of fluorescent signals. These results indicate that applied deformation propagated heterogeneously into a cell, and may imply that biochemical signals disrupt actin fibers under local deformation.

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Propelling handcart tasks, such as pushing a wheelchair with an occupant or a handcart with heavy objects are well seen and met in our daily life and occupational works. Office workers and attendants in propelling wheelchairs are physically weaker than workers in industries. Also, aged persons propelling wheelchairs for aged spouses increase in recent aged society in advanced industrialized countries around the world. In this paper, we proposed the linear signal model of worker-cart system based on steady propelling state, and produced the experimental device for investigating the propelling activity in daily life. We analyzed the mechanism of the steady propelling behavior at steady state with the model and device. From experimental results with three subjects in his 20s, we found followings; The proposed model is useful in walking speed 1km/h above. Maximum estimated forces by single leg is around 50N against maximum road resistance, and the force decreases proportionally in walking speed 1km/h above against the decrease of the resistance. Also, autonomous natural pushing force in maximum mechanical power 25-40W, are carried out under exercising heart ratio (EHR) 30%, which shows light load activity to be able to continue over 20min.

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The purpose of this study is to test a hypothesis that involvement of the low-magnitude, high frequency strain components in the walking-induced bone strain is essential to elicit the osteogenic response of osteoblasts to the bone strain. To this end, a strain waveform recorded in vivo on a radius of a walking dog (original strain) was used to stimulate osteoblasts cultured in a porous, hydroxyapatite-deposited collagen matrix. The cells were loaded under three different strain waveforms: the original strain with 0 - 50 Hz components, and low-pass filtered strains limited to either 0-5 Hz components or 0-2 Hz components. We found that the original strain and the 0-5 Hz strain elevated significantly mRNA levels of stress-sensitive or bone-formation related genes such as c-fos, cyclooxygenase 2, egr1 and osteocalcin. There was no significant difference between these two strains in the mRNA levels. The 0-2 Hz strain increased significantly only osteocalcin mRNA level, but the level was about 30% of those in the original and the 0-5 Hz strains. It was concluded that involvement of strains from 2 to 5 Hz is essential, but high-magnitude, lower frequency strains from 0 to 2 Hz and low-magnitude, higher frequency strains from 5 to 50 Hz are not, to elicit the osteoblastic response to the walking-induced bone strain.

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Hip protectors can reduce the incidence of hip fractures. However, low user acceptance and compliance in use remain a major obstacle in the effective use of hip protectors, due to its discomfort and extra effort needed to wear it, etc. A leak-allowed air cushion is an air-bubble cushion designed to have one or some orifices on the side. In this cushion, an impact load is shunted to open air with airflow through orifice(s), and the energy is dissipated by the friction of the airflow. With the lightness, the flexibility, and the inexpensiveness, this cushion has a potential to be accepted by the target users at high levels of compliance. The purpose of this study was to evaluate a potential of the cushion as a hip-protector material by comparing with other three commercially-variable impact attenuation materials: polyethylene elastmer; silicon gel; and porous polyurethane. To this end, we performed impact tests for pads made of the materials using a falling-mass impact loader. The pad made of leak-allowed air cushions reduced the peak impact force from 7700N (recorded with no pad) to 1213 N, which was 38—64 % lower than the attenuated peak forces recorded in the other material pads. We concluded that the leak-allowed air cushion could be a novel hip protector material with high capacity of impact-force attenuation.

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To get a deeper insight into the factors affecting the vascular hemodynamic, the propagation coefficient (γ) should be calculated. However, results from estimated method of this quantity are conflicting. Using numerical tools, three methods permitting an estimation of this complex number were investigated. We studied the influence of peripheral resistance, fluid and wall viscosities, stiffness, cross-sectional area, vessel length and measurements errors on the accuracy of these methods. Results obtained from this analysis demonstrated that the three methods provide exact value of propagation coefficient when analysing accurate flow velocity and diameter data. Conversely, in realistic condition (i.e. inaccurate data) significant errors related to the degrees of inaccuracy within the data arise. These errors are systematically larger on the values of propagation coefficient obtained by the three-point method than the error on the values calculated by two-point methods. Hence, we believe that difference in sensitivity of each method to the measurements errors may be the main source of the disparity of results reported in literature. In addition, the small value of attenuation and time lag seem to be the sources of the large difference between calculated and theoretical values of this parameter. Our finding doesn't support previous works which attributed the disparity of results to the high reflection or/and to the failure of the methods themselves. In realistic condition, it seems that two-point methods are more reliable than the three-point method for the estimation of the true propagation coefficient.

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The maximum peak value of traction coefficient between a shoe sole and a floor at heel-strike period |F_h/F_n|_h and that at toe-off period |F_h/F_n|_t for normal-style and Nanba-style walking were investigated in this paper. The Nanba-style walking is known as Japanese traditional walking style. The characteristics of the Nanba-style walking different from the normal-style walking are knee flexion, anteversion of the upper body and small swing of the arms. Gait experiments were carried out on a dry level walkway. Four healthy male adults participated in the gait experiments, and they were asked to walk in the normal-style and the Nanba-style walking under a wide range of step length and walking speed. Ground reaction forces and full body kinematics were captured. The results indicated that |F_h/F_n|_h of the Nanba-style walking was significantly (p<0.05) smaller than that of the normal-style walking under a wide range of walking conditions. Kinematic analysis of the Nanba-style walking indicated that reduction in friction requirement for such walking style would be due to anteriorly displacing the whole body COM as compared with that of the normal-style walking, resulting in decrease of the distance between the whole body COM and the COP in horizontal-plane. While a statistically significant difference of |F_h/F_n|_t between these two walking styles were not observed, mean |F_h/F_n|_t of the Nanba-style walking was smaller than that of the normal-style walking under a wide range of walking conditions.

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