LO-mode phonon of KCl and NaCl at 300 K by inelastic x-ray scattering measurements and first principles calculations

Longitudinal-optical (LO) mode phonon branches of KCl and NaCl were measured using inelastic x-ray scattering (IXS) at 300 K and calculated by the first-principles phonon calculation with the stochastic self-consistent harmonic approximation. Spectral shapes of the IXS measurements and calculated spectral functions agreed well. We analyzed the calculated spectral functions that provide higher resolutions of the spectra than the IXS measurements. Due to strong anharmonicity, the spectral functions of these phonon branches have several peaks and the LO modes along Gamma-L paths are disconnected

Effect of halogen ions on low thermal conductivity of cesium halide perovskite

The lattice dynamics of CsSnX3 (X = Cl, Br, and I) and CsPbI3, which are low-thermal-conductivity materials, are investigated using first-principles phonon calculations. Because of the strong lattice anharmonicity and the accompanying instability of high-temperature cubic phases, the self-consistent phonon theory, which can incorporate the effect of lattice anharmonicity at a mean-field level, is applied in this study. The calculated lattice thermal conductivity reproduced a low thermal conductivity, as shown experimentally, owing to the short phonon lifetime due to the incoherent scattering contribution of Cs atoms. The halogen ion dependence on thermal conductivity reveals that CsSnCl3 exhibits an anomalous lattice thermal conductivity that is as low as that of CsSnBr3. This indicates that the lattice dynamics cannot be explained merely in terms of the atomic mass of the compounds. The low thermal conductivity of CsSnCl3 is caused by the exceptionally short phonon lifetime; further, a bonding analysis suggests that covalent bonding contributes significantly to the unusual anharmonicity of CsSnCl3

Effects of growth on residual stress distribution along the radial depth of cortical cylinders from bovine femurs.

Residual stress is defined as the stress that remains in bone tissue without any external forces. This study investigated the effects of growth on residual stress distributions from the surface to deeper regions of cortical cylinders obtained from less-than-one-month-old (Group Y) and two-year-old (Group M) bovine femurs. In these experiments, five diaphysis specimens from each group were used. Residual stress was measured using a high-energy synchrotron white X-ray beam to penetrate X-rays into the deeper region of the bone specimens. The measurements in the cortical cylinders from Groups Y and M were performed at 0.5- and 1-mm intervals, respectively, from the outer surface to the deeper region of the diaphysis specimens at four positions: anterior, posterior, lateral, and medial. The residual stress was calculated on the basis of variation in the interplanar spacing of hydroxyapatite crystals in the bone tissue. According to the results, the diaphysis specimens from Group Y were not subjected to large residual stresses (average −1.2 MPa and 2.4 MPa at the surface region and 1.5 mm depth, respectively). In Group M, the surface region of the diaphysis specimens was subjected to tensile residual stresses (average 6.7 MPa) and the deeper region was subjected to compressive stresses (average −8.2 MPa at 3 mm depth). There was a strong significant difference between both these regions. The value of residual stresses at the surface region of the diaphysis specimens in both the groups had a positive statistical correlation with the cortical thickness at the measured locations

X-ray diffraction technique with imaging plate for detecting surface distribution of residual stress in diaphysis of bovine femurs

Stress measurements of bone are essential for evaluating the risk of bone fracture, the cure of bone diseases (e.g., osteoporosis), and the bone adaptation. Previously, a method using X-ray diffraction (XRD) was used to assess the presence of residual stress in the diaphysis of bovine and rabbit extremities. However, the previous method required a complicated experimental setup, long irradiation time, and limitations of the sample size. To profoundly enhance the understanding of distribution and biomechanical implications of bone residual stresses, it is necessary to develop an alternative method that features a simple setup without limitations on the sample size and shape. An imaging plate (IP) can obtain the two-dimensional distribution of hydroxyapatite crystal deformation and has the potential to resolve the previously mentioned issues. The aim of this study was to develop a measurement system using an XRD technique with an IP for obtaining the surface distribution of residual stress in the diaphysis of extremities. A mid-diaphysis specimen taken from an adult bovine femur was irradiated with characteristic Mo-K alpha X-rays under no external forces and the diffracted X-rays were detected by an IP in the reflection side. The residual stress in the bone axis was calculated from the XRD pattern. As a result, tensile residual stresses were detected at the diaphyseal surface, corresponding to the results of the previous method. The developed system reduced the irradiation time by two thirds and the limitations of the sample size were removed

Residual stress distribution in rabbit limb bones

The presence of the residual stresses in bone tissue has been noted and the authors have reported that there are residual stresses in bone tissue. The aim of our study is to measure the residual stress distribution in the cortical bone of the extremities of vertebrates and to describe the relationships with the osteon population density. The study used the rabbit limb bones (femur, tibia/fibula, humerus, and radius/ulna) and measured the residual stresses in the bone axial direction at anterior and posterior positions on the cortical surface. The osteons at the sections at the measurement positions were observed by microscopy. As a result, the average stresses at the hindlimb bones and the forelimb bones were 210 and 149 MPa, respectively. In the femur, humerus, and radius/ulna, the residual stresses at the anterior position were larger than those at the posterior position, while in the tibia, the stress at the posterior position was larger than that at the anterior position. Further, in the femur and humerus, the osteon population densities in the anterior positions were larger than those in the posterior positions. In the tibia, the osteon population density in the posterior position was larger than that in the anterior position. Therefore, tensile residual stresses were observed at every measurement position in the rabbit limb bones and the value of residual stress correlated with the osteon population density (r=0.55, P<0.01)

Nanostructure and elastic modulus of single trabecula in bovine cancellous bone

We aimed to investigate the elastic modulus of trabeculae using tensile tests and assess the effects of nanostructure at the hydroxyapatite (HAp) crystal scale on the elastic modulus. In the experiments, 18 trabeculae that were at least 3mm in length in the proximal epiphysis of three adult bovine femurs were used. Tensile tests were conducted using a small tensile testing device coupled with microscopy under air-dried condition. The c-axis orientation of HAp crystals and the degree of orientation were measured by X-ray diffraction. To observe the deformation behavior of HAp crystals under tensile loading, the same tensile tests were conducted in X-ray diffraction measurements. The mineral content of specimens was evaluated using energy dispersive X-ray spectrometry. The elastic modulus of a single trabecula varied from 4.5 to 23.6GPa, and the average was 11.5±5.0GPa. The c-axis of HAp crystals was aligned with the trabecular axis and the crystals were lineally deformed under tensile loading. The ratio of the HAp crystal strain to the tissue strain (strain ratio) had a significant correlation with the elastic modulus (r=0.79; P<0.001). However, the mineral content and the degree of orientation did not vary widely and did not correlate with the elastic modulus in this study. It suggests that the strain ratio may represent the nanostructure of a single trabecula and would determine the elastic modulus as well as mineral content and orientation

Irradiation conditions for fiber laser bonding of HAp-glass ceramics with bovine cortical bone.

Orthopedic implants are widely used to repair bones and to replace articulating joint surfaces. It is important to develop an instantaneous technique for the direct bonding of bone and implant materials. The aim of this study was to develop a technique for the laser bonding of bone with an implant material like ceramics. Ceramic specimens (10 mm diameter and 1 mm thickness) were sintered with hydroxyapatite and MgO-Al2O3-SiO2 glass powders mixed in 40:60 wt% proportions. A small hole was bored at the center of a ceramic specimen. The ceramic specimen was positioned onto a bovine bone specimen and a 5 mm diameter area of the ceramic specimen was irradiated using a fiber laser beam (1070-1080 nm wavelength). As a result, the bone and the ceramic specimens bonded strongly under the irradiation conditions of a 400 W laser power and a 1.0 s exposure time. The maximum shear strength was 5.3±2.3 N. A bonding substance that penetrated deeply into the bone specimen was generated around the hole in the ceramic specimen. On using the fiber laser, the ceramic specimen instantaneously bonded to the bone specimen. Further, the irradiation conditions required for the bonding were investigated

Micro-cantilever bending for elastic modulus measurements of a single trabecula in cancellous bone

Mechanical tests performed on small bone specimens such a single trabecula remain challenging because their isolation, fixation, and precise loading are complicated. Hence, we describe a novel experimental method to measure the elastic properties of a single trabecula using micro-cantilever bending (MCB) testing. The method does not require specimens to be completely separated from the cancellous bone, and the specimen can be easily fixed during the test. In total, 10 trabecular specimens taken from the proximal epiphysis of an adult bovine femur were used in the present study. Measurements were conducted using a small testing device comprising a 1-axial stage, load cell, optical microscope, and small plate with a taper bore for applying load at the edge of the specimen. Each specimen was positioned at the edge of the bore and was deformed by displacing the stage. The deflection of the specimen was observed by optical microscopy. The elastic modulus of the specimen was calculated on the basis of the force-deflection relationship, assuming that the shape of the specimen was a vertical circular cylinder. As a result, an average elastic modulus of 9.1 +/- 5.4 GPa was obtained for a single trabecula, including the values in literature. Thus, the MCB test is a novel simple method for biomechanical analysis of a single trabecula

An EMG-CT method using multiple surface electrodes in the forearm

Electromyography computed tomography (EMG-CT) method is proposed for visualizing the individual muscle activities in the human forearm. An EMG conduction model was formulated for reverse-estimation of muscle activities using EMG signals obtained with multi surface electrodes. The optimization process was calculated using sequential quadratic programming by comparing the estimated EMG values from the model with the measured values. The individual muscle activities in the deep region were estimated and used to produce an EMG tomographic image. For validation of the method, isometric contractions of finger muscles were examined for three subjects, applying a flexion load (4.9, 7.4 and 9.8 N) to the proximal interphalangeal joint of the middle finger. EMG signals in the forearm were recorded during the tasks using multiple surface electrodes, which were bound around the subject’s forearm. The EMG-CT method illustrates the distribution of muscle activities within the forearm. The change in amplitude and area of activated muscles can be observed. The normalized muscle activities of all three subjects appear to increase monotonically with increases in the load. Kinesiologically, this method was able to estimate individual muscle activation values and could provide a novel tool for studying hand function and development of an examination for evaluating rehabilitation

Influence of osteon area fraction and degree of orientation of HAp crystals on mechanical properties in bovine femur

Cortical bone has a hierarchical structure, spanning from the macrostructure at several millimeters or whole bone level, the microstructure at several hundred micrometers level, to the nanostructure at hydroxyapatite (HAp) crystals and collagen fibrils levels. The aim of the study is to understand the relationship between the HAp crystal orientation and the elastic modulus and the relationship between the osteon area fraction and the deformation behavior of HAp crystals in cortical bone. In the experiments, five strip specimens (40×2×1 mm3) aligned with the bone axis were taken from the cortical bone of a bovine femur. The degree of c-axis orientation of HAp crystals in the specimens was measured with the X-ray diffraction technique with the imaging plate. To measure the deformation behavior of HAp crystals in the specimens, tensile tests under X-ray irradiation were conducted. The specimens were cut at the X-ray measurement positions and osteon area fraction and porosity at the transverse cross-sections were observed. Further, the volume fraction of HAp of the specimens was measured. Results showed the degree of c-axis orientation of HAp crystals was positively correlated with the elastic modulus of the specimens (r=0.94). The volume fraction of HAp and the porosity showed no statistical correlation with the elastic modulus and the tensile strength. The HAp crystal strain εH increased linearly with the bone tissue strain ε. The average value of εH/ε was 0.69±0.13 and there was no correlation between the osteon area fraction and εH/ε (r=−0.27, p=0.33). The results suggest that the degree of c-axis orientation of HAp crystals affects the elastic modulus and the magnitude of HAp crystal strain does not depend on the osteon area fraction