Masahiko Kawabe

Micro-Brillouin Scattering Measurements in Mature and Newly Formed Bone Tissue Surrounding an Implant

The evolution of implant stability in bone tissue remains difficult to assess because remodeling phenomena at the bone-implant interface are still poorly understood. The characterization of the biomechanical properties of newly formed bone tissue in the vicinity of implants at the microscopic scale is of importance in order to better understand the osseointegration process. The objective of this study is to investigate the potentiality of micro-Brillouin scattering techniques to differentiate mature and newly formed bone elastic properties following a multimodality approach using histological analysis. Coin-shaped Ti-6Al-4V implants were placed in vivo at a distance of 200 μm from rabbit tibia leveled cortical bone surface, leading to an initially empty cavity of 200 μm×4.4 mm. After 7 weeks of implantation, the bone samples were removed, fixed, dehydrated, embedded in methyl methacrylate, and sliced into 190 μm thick sections. Ultrasonic velocity measurements were performed using a micro-Brillouin scattering device within regions of interest (ROIs) of 10 μm diameter. The ROIs were located in newly formed bone tissue (within the 200 μm gap) and in mature bone tissue (in the cortical layer of the bone sample). The same section was then stained for histological analysis of the mineral content of the bone sample. The mean values of the ultrasonic velocities were equal to 4.97×10(-3) m/s in newly formed bone tissue and 5.31×10(-3) m/s in mature bone. Analysis of variance (p=2.42×10(-4)) tests revealed significant differences between the two groups of measurements. The standard deviation of the velocities was significantly higher in newly formed bone than in mature bone. Histological observations allow to confirm the accurate locations of the velocity measurements and showed a lower degree of mineralization in newly formed bone than in the mature cortical bone. The higher ultrasonic velocity measured in newly formed bone tissue compared with mature bone might be explained by the higher mineral content in mature bone, which was confirmed by histology. The heterogeneity of biomechanical properties of newly formed bone at the micrometer scale may explain the higher standard deviation of velocity measurements in newly formed bone compared with mature bone. The results demonstrate the feasibility of micro-Brillouin scattering technique to investigate the elastic properties of newly formed bone tissue.

Measurement of Wave Velocity in Bovine Bone Tissue by Micro-Brillouin Scattering

To evaluate microscopic bone elasticity without contribution from macroscopic structures, a micro-Brillouin scattering technique was used. Our micro-Brillouin scattering system enables the measurement of wave velocities in the GHz range over a minute area (diameter: approximately 10 µm). We have applied this technique to thinly sliced bovine trabecular bone and collagen film. The average wave velocity in one trabecula was approximately 4.8 ×103 m/s, which was much higher than the velocity in the collagen film. The velocity anisotropy near the trabecular nodes was weak but complicated. In addition, these velocities were also higher than velocities in the cortical bone, which were in the MHz range. These investigations show the possibility of using the Brillouin scattering technique to evaluate microscopic bone elasticity, which is closely related to the quality of bone matrix.

Measurement of Wave Velocity Distribution in a Trabecula by Micro-Brillouin Scattering Technique

Ultrasonic wave velocities in small trabeculae of bovine femur were investigated using a micro-Brillouin scattering technique. Our micro-Brillouin scattering system enables the measurement of wave velocities in the GHz range over a minute area (diameter: approximately 10 µm). Using thin trabecular specimens with a thickness of about 150 µm, the distribution of longitudinal wave velocity in a trabecula was observed. In the direction parallel to the trabecular alignment, the velocity changed depending on the measurement position. We measured 20 different trabeculae in our specimens, and the average wave velocities in each trabecula were similar at approximately 4.92×103 m/s. In addition, the difference in average velocity was not statistically significant between trabeculae that align in the bone axis or anterior–posterior directions. These data tell us the possibility that the average wave properties are similar in all trabeculae.

Application of a micro-Brillouin scattering technique to characterize bone in the GHz range

The evaluation of elastic properties of bone matrix has been investigated using several techniques such as nanoindentation and scanning acoustic microscopy (SAM). These techniques make use of good spatial resolution, which can prevent effects due to microstructures at the level of several hundreds of microns. In this paper, micro-Brillouin scattering (μ-BR) is introduced as another possible technique to characterize the elastic properties of bone. This technique is well known as a non-contact and non-destructive method to evaluate viscoelastic properties of transparent materials in the GHz range. Using thin, translucent bone specimens with thicknesses of around 100 μm, and the reflection induced optical geometry, ultrasonic wave velocities in the GHz range were obtained. Because this technique optically measures thermal phonons in the specimen, we can easily measure in-plane anisotropy of wave velocities by rotating the specimen. In a single trabecula, the site matched data between SAM and μ-BR showed good correlation, revealing the applicability of this technique to characterize material properties of bone. Some recent results on the anisotropy in a trabecula and the elasticity evaluation of newly and matured bones are also introduced.

Comparative investigation of elastic properties in a trabecula using micro-Brillouin scattering and scanning acoustic microscopy.

Micro-Brillouin scattering (μ-BR) and a 200 MHz scanning acoustic microscope (SAM) with similar spatial resolutions were applied to evaluate tissue elastic properties in two directions in a trabecula. Acoustic impedance measured by SAM was in the range of 5-9 Mrayl. Wave velocities determined by μ-BR were in the range of (4.75-5.11) × 10(3) m/s. Both exhibited a similar trend of variation across the trabecula and were significantly correlated (R(2) = 0.63-0.67, p < 0.01). μ-BR is useful for the evaluation of tissue stiffness within a trabecula. Combined with SAM or nanoindentation, it can provide additional information to assess elastic anisotropy at the micro-scale.

Acoustic-Wave Velocities and Refractive Indices in an m-Plane GaN Single-Crystal Plate and c -Axis-Oriented ScAlN Films Measured by Brillouin Scattering Techniques

We have experimentally investigated wave velocities and refractive indices in bulk and film samples [a GaN single-crystal plate and c-axis-oriented ScxAl(1-x)N (x = 0.00 - 0.63) films] by Brillouin scattering (BRS). All of the piezoelectrically unstiffened elastic constants and the ordinary refractive index of the GaN single-crystal plate were determined from the reflection-induced ΘA(RIΘA) scattering geometry and the combination of 90R and 180° scattering geometries. The uncertainties of the measured wave velocities were approximately 0.17% (RIΘA) and 2.5% (combination technique). In addition, the longitudinal-wave velocities of ScxAl(1-x)N films propagating in the normal direction were obtained by the combination technique. The maximum uncertainty was approximately 3.3%. The shear-wave velocities and refractive indices of ScxAl(1-x)N films were also investigated by the 90R scattering geometry using velocities measured by high-overtone bulk acoustic resonators. The softening trends of the elasticity were obtained from the measured longitudinal- and shear-wave velocities, although there were large uncertainties in the Brillouin measurement system owing to thermal instability.We have experimentally investigated wave velocities and refractive indices in bulk and film samples [a GaN single crystal plate and c-axis-oriented ScxAl(1-x)N (x = 0.00-0.63) films] by Brillouin scattering. All of the piezoelectrically unstiffened elastic constants and the ordinary refractive index of the GaN single crystal plate were determined from the reflection induced A (RIA) scattering geometry and the combination of 90R and 180° scattering geometries. The uncertainties of the measured wave velocities were approximately 0.17% (RIA) and 2.5% (combination technique). In addition, the longitudinal wave velocities of ScxAl(1-x)N films propagating in the normal direction were obtained by the combination technique. The maximum uncertainty was approximately 3.3%. The shear wave velocities and refractive indices of ScxAl(1-x)N films were also investigated by the 90R scattering geometry using velocities measured by high-overtone bulk acoustic resonators. The softening trends of the elasticity were obtained from the measured longitudinal and shear wave velocities, although there were large uncertainties in the Brillouin measurement system owing to thermal instability.

Gigahertz acoustic wave velocity measurement in GaN single crystals considering acousto-electric effect

The resistivity¿frequency characteristics of longitudinal wave velocities propagating parallel to the c-axis in a GaN single crystal were theoretically estimated by considering the piezoelectric acousto-electric effect. The temperature and frequency dependences of longitudinal and shear wave velocities in conductive and semiconductive GaN single-crystal samples were experimentally investigated by Brillouin scattering. The temperature dependence of longitudinal and shear wave velocities had a linear tendency in the conductive sample, whereas in the semiconductive sample, those had a similar tendency to the predicted velocity changes resulting from the piezoelectric stiffening effect. However, the temperature dependence of shear wave velocity, which does not possess piezoelectric coupling, had a tendency similar to that of the longitudinal wave in the semiconductive sample, unexpectedly. The frequency dependence of longitudinal wave velocities in the semiconductive sample had a tendency similar to the predicted velocity changes resulting from the piezoelectric stiffening effect.

Assessment of the biomechanical properties of newly formed bone tissue using micro-Brillouin scattering

The assessment of implant stability in bone tissue remains difficult because remodelling phenomena in the vicinity of the implant are still poorly understood. The present multimodality study investigates the potentiality of micro-Brillouin scattering technique to differentiate mature and newly formed bone microscopic elastic properties following an approach coupled with histological analysis. Coin-shaped Ti-6Al-4V implants were placed in vivo in rabbit tibia. After seven weeks of implantation, bone samples were removed, embedded in methyl methacrylate and sliced into 190 µm thick sections. A micro-Brillouin scattering technique was used to measure ultrasonic velocities in 10 µm diameter regions located in mature and newly formed bone. The same section was then stained for histological analysis of the mineral content of the bone sample. The mean values of the ultrasonic velocities were equal to 4.98 10−3 m/s in newly formed bone tissue and 5.20 10−3 m/s in mature bone. ANOVA (p=0.029) tests revealed significant differences between the two groups of measurements. Histological observations showed a lower degree of mineralization in newly formed bone than in mature cortical bone. The higher ultrasonic velocity measured in newly formed bone tissue compared to mature bone might be explained by the higher mineral content in mature bone, which was confirmed by histology. The results demonstrate the feasibility of micro-Brillouin scattering measurements to investigate the elastic properties of newly formed bone tissue.

Measurement of longitudinal wave velocity in articular cartilage by micro Brillouin scattering

Articular cartilage is composed of cartilage cells and extracellular matrix (mainly collagen type II and proteoglycan). When stress is applied, the cartilage releases water and the stress is distributed [1]. The extra-cellular matrix structure is important to perform normal cartilaginous functions. It is then important to evaluate the elasticity and anisotropy of the cartilage, in addition to the heterogeneity. In this study, longitudinal wave velocity distribution, velocity anisotropy and the effect of water on the velocity in the cartilage were investigated using a micro-Brillouin scattering technique.

Rapid and simple measurement of hypersonic wave velocity by Brillouin scattering with induced phonons

Brillouin scattering is a non-contact method to measure wave velocities in the GHz range. One problem of the Brillouin scattering technique is weak light scattering from thermal phonons, which results in the long measurement time and necessity of a complex tandem Fabry-Perot interferometer. To overcome this problem, we have proposed techniques to make use of induced strong coherent phonons from a high frequency transducer. In this study, we have tried to induce strong longitudinal coherent phonons by a ScAlN film transducer (composition of the film : Sc0.41Al0.59N), which has a high electromechanical coupling coefficient. The transducer was fabricated on the quartz sample and composed of the ScAlN film grown by an RF magnetron sputtering and electrodes. The transducer was deposited on one side of the sample. Due to the induced phonons, the scattered light became much stronger than those of thermal phonons and could be observed by a simple confocal Fabry-Perot interferometer. The measured frequency shift of the Brillouin scattering peak was equal to the excitation frequency of the ScAlN transducer (883 MHz). This technique enables easy, rapid and simple measurement of wave velocity in the GHz range, which can be applied for the 2D velocity imaging of the sample. Brillouin scattering is a non-contact method to measure wave velocities in the GHz range. One problem of the Brillouin scattering technique is weak light scattering from thermal phonons, which results in the long measurement time and necessity of a complex tandem Fabry-Perot interferometer. To overcome this problem, we have proposed techniques to make use of induced strong coherent phonons from a high frequency transducer. In this study, we have tried to induce strong longitudinal coherent phonons by a ScAlN film transducer (composition of the film : Sc0.41Al0.59N), which has a high electromechanical coupling coefficient. The transducer was fabricated on the quartz sample and composed of the ScAlN film grown by an RF magnetron sputtering and electrodes. The transducer was deposited on one side of the sample. Due to the induced phonons, the scattered light became much stronger than those of thermal phonons and could be observed by a simple confocal Fabry-Perot interferometer. The measured frequency shift o...