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PubMed2005

Can reliable torsion elastic constants be determined from FPA data on 24 and 27 base-pair DNAs?

Torsion elastic constants obtained from fluorescence polarization anisotropy (FPA) measurements on fifty-three 24 and 27 base-pair (bp) DNAs were recently reported [F. Pedone, F. Mazzei, D. Santoni, Sequence-dependent DNA torsional rigidity: a tetranucleotide code, Biophys. Chem. 112 (2004) 77-88; F. Pedone, F. Mazzei, M. Matzeu, F. Barone, Torsional constant of 27-mer DNA oligomers of different sequences, Biophys. Chem. 94 (2001) 175-184]. The problem of extracting reliable torsion elastic constants (alpha) from FPA measurements on such short DNAs is examined in detail. The difficulty is illustrated by two (fictitious) 24 bp DNAs with approximately 5-fold different torsion elastic constants and 10% different initial anisotropies (r(0)), which exhibit practically indistinguishable anisotropy decays for all t>1 ns. FPA data were simulated for 24 bp DNAs with different input values of alpha and r(0) in the presence and absence of Poisson noise, and were fitted using different choices of the adjustable and fixed parameters. Experimental data for a 24 bp DNA were fitted in a similar manner. For either the simulated or experimental FPA data, it was not possible to determine both the initial anisotropy, r(0), and the torsion elastic constant, alpha, in a reliable (i.e. statistically significant) manner in the presence of Poisson noise. When r(0) is assumed to be fixed at any particular value in the fitting protocol, a unique best-fit value of alpha is obtained, but that best-fit alpha is extremely sensitive to small deviations of the assumed fixed value of r(0) away from the input r(0)-value of the simulated data. Pedone et al. fitted their FPA data by assuming that r(0)=0.360, and adjusting alpha, the hydrodynamic radius (R(H)), and effective length (L). In fact, the reported best-fit values of R(H) and L lay significantly outside their expected ranges. When this same fitting protocol is applied to simulated data for 27 bp DNAs, better overall agreement with the reported experimental values (alpha, R(H), and L) is obtained for a model, wherein all DNAs have the same typical input alpha=5.9 x 10(-12) dyn cm, R(H)=10.0 A, and L=27 (3.4)+2.7=94.5 A, but a 1.00- to 1.13-fold range of r(0)-values, than for the model of Pedone et al., wherein all DNAs have the same input r(0)=0.360, R(H)=10.0 A, and L=94.5 A, but a approximately 3-fold range of alpha-values. It is concluded that, in the absence of reliable independent estimates of r(0) for every DNA, the alpha-values reported for 24 and 27 bp DNAs cannot be regarded as experimentally justified. The reliability of the torsion elastic constants reported for the 136 distinct tetranucleotide steps, which are inferred from the values reported for the fifty-three 24 and 27 bp DNAs, is also briefly discussed.

Anisotropy↗
PubMed2006

17beta-estradiol increases volume, apical surface and elasticity of human endothelium mediated by Na+/H+ exchange.

OBJECTIVE: 17beta-estradiol is known to delay the onset of atherosclerosis in women but cellular mechanisms are still unclear. Estrogens bind to specific receptors and initiate a signaling cascade that involves the activation of plasma membrane Na(+)/H(+) exchange. We hypothesized that estrogens interfere with ion transport across the plasma membrane and thus control endothelial structure and function. Therefore, we investigated the effects of the sex steroids 17beta-estradiol, progesterone, and testosterone on volume, apical surface and elasticity in human endothelium. METHODS: The atomic force microscope was used as an imaging tool and as an elasticity sensor. We applied the antiestrogen tamoxifen, the Na(+)/H(+) exchange blocker cariporide and the epithelial Na(+)channel blocker amiloride to elucidate the role of transmembrane ion transport in hormone-treated human umbilical vein endothelial cells (HUVEC). RESULTS: Incubation with 17beta-estradiol for 72 h led to a dose-dependent increase of endothelial cell volume (41%), apical cell surface (22%), and cell elasticity (53%) as compared to non-17beta-estradiol treated controls. Block of the 17beta-estradiol receptor by tamoxifen and of plasma membrane Na(+)/H(+) exchange by cariporide prevented the hormone-induced changes. Progesterone and testosterone were ineffective. CONCLUSIONS: 17beta-estradiol increases HUVEC water content and HUVEC elasticity mediated by activated estrogen receptors. The estrogen response depends on the activation of plasma membrane Na(+)/H(+) exchange. The increase in endothelial cell elasticity could be one of the vasoprotective mechanisms postulated for 17beta-estradiol.

Amiloride↗
PubMed2006

Effect of short-term water storage on the elastic properties of some dental restorative materials--A resonant ultrasound spectroscopy study.

OBJECTIVES: This study was aimed to determine if short-term water storage would change elastic properties of dental composite materials. METHODS: Particulate filler composite resin and continuous unidirectional E-glass FRC materials were photopolymerized and additionally post-polymerized by heat for testing elastic properties with the Resonance Ultrasound Spectroscopy method as a function of time in water storage. The test specimens were stored in 37 degrees C water for up to 30 days. RESULTS: About 1% weight increase due to water sorption was observed in both materials with both polymerization methods. Water sorption did not change the resonance frequencies towards lower values, indicating no significant decrease in elastic properties in these materials. Because of high damping of the polymer composite materials leading to wide resonance peaks and low number of the recorded peaks, accurate determination of the elastic properties was not possible. SIGNIFICANCE: Results suggest that the most likely explanation for the previously observed decrease in bending stiffness of FRC materials is the decreased yield limit of the hydrated polymer matrix. It is important to recognize that water sorption has the effect on mechanical properties of dental composite materials by changing the yield limit of the matrix rather than by changing the elastic properties of the material.

Absorption↗
PubMed2006

Mapping age-related elasticity changes in porcine lenses using bubble-based acoustic radiation force.

Bubble-based acoustic radiation force aims to measure highly localized tissue viscoelastic properties. In the current investigation, acoustic radiation force was applied to laser-induced bubbles to measure age-related changes in the spatial distribution of elastic properties within in vitro porcine lenses. A potential in vivo technique to map lens elasticity is crucial to understanding the onset of presbyopia and develop new treatment options. Bubble-based acoustic radiation force was investigated as a technique to measure the spatial elasticity distribution of the lens in its natural state without disrupting the lens capsule. Laser-induced optical breakdown (LIOB) generated microbubbles in a straight line across the equatorial plane of explanted porcine lenses with 1mm lateral spacing. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. A two-element confocal ultrasonic transducer applied 6.5 ms acoustic radiation force-chirp bursts with the 1.5 MHz outer element while monitoring bubble position within the lens using pulse-echoes with the 7.44 MHz inner element. A cross-correlation method was used to measure bubble displacements and determine exponential time constants of the temporal responses. Maximum bubble displacements are inversely proportional to the local Young's modulus, while time constants are indicative of viscoelastic properties. The apparent spatial elasticity distributions in 41 porcine lenses, ranging from 4 months to 5 years in age, were measured using bubble-based acoustic radiation force. Bubble displacements decrease closer to the porcine lens center, suggesting that the nucleus is stiffer than the cortex. Bubble displacements decrease with increasing lens age, suggesting that porcine lenses become stiffer with age. Bubble-based acoustic radiation force may be well-suited as a potential in vivo technique to spatially map elastic properties of the lens and guide therapeutic procedures aimed at restoring accommodation.

Aging↗
PubMed2006

Quantitative analysis of the elastic fibres in the human temporomandibular articular disc and its attachments.

A quantitative study of the elastic fibres found in the human temporomandibular disc and its attachments was performed. Seven left discs from 57- to 82-year-old subjects, without macroscopic evidence of a TMJ disorder, were analysed and prepared in parasagittal sections. The surface amount was measured, thresholded and expressed from 0 to 1, using microscopic digitized views after Weigert's resorcin-fuchsin staining of elastic fibres. Fibre density rates ranged from 0 to 0.687. The mean density was 0.1532 (sigma=0.1150) in the upper bilaminary zone, 0.1097 (sigma=0.1159) in the lower bilaminary zone, 0.0474 (sigma=0.0782) in the anterior band, 0.0180 (sigma=0.0603) in the posterior band and null in the intermediate zone. The difference in density rate between the structures was significant, except for the posterior band and the intermediate zone. The elastic fibre density rates in central and medial locations of the upper and lower bilaminary zones were twice as big as in the lateral locations. In the anterior band, the elastic fibre density was less abundant medially than in its lateral part. These quantitative results support the current elastic fibre distribution scheme, and confirm the necessity of studying their orientation, taking into account age and temporomandibular joint health parameters.

Age Factors↗
PubMed2005

Determination of subject-specific model parameters for visco-elastic elements.

The determination of subject-specific model parameter values is necessary in order for a computer simulation model of human motion to be evaluated quantitatively. This study used an optimisation procedure along with a kinematically driven simulation model of the contact phase in running jumps to determine the elastic parameters of segmental wobbling masses and the foot-ground interface. Kinetic and kinematic data were obtained on running jumps for height and distance performed by an elite male high jumper. Stiffness and damping coefficients of the visco-elastic elements in the model were varied until the difference between simulation and performance was minimised. Percentage differences of 6% and 9% between the simulated and recorded performances were obtained in the jumps for height and distance, respectively. When the parameters obtained from the jump for height were used in a simulation of the jump for distance (and vice versa), there was poor agreement with the recorded jump. On the other hand, a common set of visco-elastic parameters were obtained using the data from both recorded jumps resulting in a mean difference of only 8% (made up of 7% and 10%) between simulation and performance that was almost as good as the individual matches. Simulations were not overly sensitive to perturbations of the common set of visco-elastic parameters. It is concluded that subject-specific elastic parameters should be calculated from more than a single jump in order to provide a robust set of values that can be used in different simulations.

Biomechanical Phenomena↗
PubMed2005

Dermal elastic fibres in the inherited hypermobile disorders.

BACKGROUND: Elastic fibres in the inherited hypermobile disorders are probably abnormal on the inherited grounds. The abnormality may contribute for diagnosis and investigation of connective tissue biology. OBJECTIVE: The abnormality will be specific for every disorders and disclosed in the age-dependent change when exposure-dependent change was excluded. MATERIALS AND METHODS: Skin specimens from Ehlers-Danlos syndrome and hypermobile syndrome, Marfan syndrome, Osteogenesis imperfecta type I, homocysteinuria and normal controls are studied by routine electron microscopy. Age-dependent ultrastructural change of broad elastic fibres was evaluated in reticular dermis. RESULTS: Age-dependent change was categorized in infantile, adolescent, adult and senile pattern. Infantile pattern showed normal ultrastructure. Degeneration was first found in adolescent pattern by disarrayed microfibrils and degenerate matrix. Degeneration proceeded in adult pattern and ended in senile pattern. Typical abnormality developed in adult pattern. Ehlers-Danlos syndrome and hypermobile syndrome showed no specific abnormality but the degeneration began earlier and was severer than the control. Marfan syndrome showed defects of microfibrils and matrix surface. Moth-eaten figure was characteristic. Osteogenesis imperfecta showed abnormal matrix and revealed homogenous bulges of matrix. Homocysteinuria was specified by numerous microfibrils on the matrix surface in infantile pattern. CONCLUSION: Abnormality of elastic fibre was recognized in the reticular dermis of elbow. Ehlers-Danlos syndrome and hypermobile syndrome showed no specific abnormality but the degeneration was more intensive than the control. Abnormality of Marfan syndrome was degeneration of elastic microfibrils and matrix surface, Osteogenesis imperfecta was characterized by excess amount of matrix. Homocysteinuria revealed numerous microfibrils. Ultrastructural abnormality provided grounds for studies on histopathology and biology of elastic fibre.

Adolescent↗
PubMed2004

Elastic energy storage in unmineralized and mineralized extracellular matrices (ECMs): a comparison between molecular modeling and experimental measurements.

In order to facilitate locomotion and limb movement many animals store energy elastically in their tendons. In the turkey, much of the force generated by the gastrocnemius muscle is stored as elastic energy during tendon deformation and not within the muscle. As limbs move, the tendons are strained causing the collagen fibers in the extracellular matrices to be strained. During growth, avian tendons mineralize in the portions distal to the muscle and show increased tensile strength, modulus, and energy stored per unit strain as a result. In this study the energy stored in unmineralized and mineralized collagen fibers was measured and compared to the amount of energy stored in molecular models. Elastic energy storage values calculated using the molecular model were slightly higher than those obtained from collagen fibers, but display the same increases in slope as the fiber data. We hypothesize that these increases in slope are due to a change from the stretching of flexible regions of the collagen molecule to the stretching of less flexible regions. The elastic modulus obtained from the unmineralized molecular model correlates well with elastic moduli of unmineralized collagen from other studies. This study demonstrates the potential importance of molecular modeling in the design of new biomaterials.

Animals↗
PubMed2004

Quo vadis elasticity imaging?

In the past decade, an important field that has emerged as complementary to ultrasonic imaging is that of elasticity imaging. The term encompasses a variety of techniques that can depict a mechanical response or property of tissues. In ultrasound, its premise is built on two important facts: (a) that significant differences between mechanical properties of several tissue components exist and (b) that the information contained in the coherent scattering, or speckle, is sufficient to depict these differences following an external or internal mechanical stimulus. Parameters, such as velocity of vibration, displacement, strain, strain rate, velocity of wave propagation and elastic modulus, have all been demonstrated feasible in their estimation and have resulted in the accurate depiction of stiffer tissue masses, such as tumors, high-intensity focused ultrasound (HIFU) lesions and atherosclerotic plaques. More recently, through the development of ultrafast algorithms tailored to suitable hardware as well as the familiarity of the physician with the sensitivity of the methods used, one elasticity imaging technique in particular, elastography, has been shown applicable in a typical clinical ultrasound setting. In other words, elastograms can currently be obtained at quasi real-time (approximately at a frame rate of 8 frames/s) and with the use of a hand-held transducer (as opposed to the previously used frame-suspended setup) during and simultaneously with an ultrasound exam of, e.g., the breast or the prostate. The higher frame rate available with certain clinical ultrasound scanners has also resulted in the successful application of elasticity imaging techniques on the myocardium and monitoring its deformation over several cardiac cycles for the detection of ischemic regions. As a result, elasticity imaging with its ever increasing number of applications and demonstrated applicability in a typical, clinical ultrasound setting promises to make an important contribution to the ultrasound practice as we know it.

Elasticity↗
PubMed2000

Diet high in monounsaturated fat does not have a different effect on arterial elasticity than a low-fat, high-carbohydrate diet.

OBJECTIVE: To compare the effects of a modified-fat diet high in monounsaturated fat, and a low-fat/high-carbohydrate diet on arterial elasticity. DESIGN: Randomized crossover design; each diet period was 1 month and a 2-week wash out period occurred in between. SUBJECTS/SETTING: Thirty healthy, free-living, nonsmoking men and women were recruited from the Melbourne, Australia, metropolitan region of Australia. Men were aged 35 to 55 years and postmenopausal women were aged 50 to 60 years and were not taking hormone replacement therapy. Twenty-eight subjects completed the study. INTERVENTION: Two diets of equal energy value: a modified-fat diet and a low-fat/high-carbohydrate diet; the modified-fat diet had 3 times more energy from monounsaturated fat. MAIN OUTCOME MEASURES: Arterial elasticity and serum lipoprotein concentrations. STATISTICAL ANALYSIS: The general linear model was used to investigate overall effect and any carryover or order effects. Paired t test and the general linear model were used to compare the results from the 2 diet periods. RESULTS: High-density lipoprotein cholesterol concentration was significantly higher on the modified-fat diet than on the low-fat/low-carbohydrate diet. Arterial elasticity and concentrations of total cholesterol, low-density lipoprotein cholesterol, and triglycerides were not significantly different on the 2 diets. APPLICATIONS/CONCLUSIONS: There is no evidence to favor a diet high in monounsaturated fat over a low-fat/high-carbohydrate diet because of an effect on arterial elasticity. Other changes in diet may be needed to cause a beneficial effect on arterial elasticity.

Adult↗
PubMed2003

Comparison of aortic elasticity determined by cardiovascular magnetic resonance imaging in obese versus lean adults.

The vascular properties of large vessels in the obese have not been adequately studied. We used cardiovascular magnetic resonance imaging to quantify the cross-sectional area and elastic properties of the ascending thoracic and abdominal aorta in 21 clinically healthy obese young adult men and 25 men who were age-matched lean controls. Obese subjects had greater maximal cross-sectional area of the ascending thoracic aorta (984 +/- 252 vs 786 +/- 109 mm(2), p <0.01) and of the abdominal aorta (415 +/- 71 vs 374 +/- 51 mm(2), p <0.05). When indexed for height the differences persisted, but when indexed for body surface area, a significant difference between groups was found only for the maximal abdominal aortic cross-sectional area. The obese subjects also had decreased abdominal aortic elasticity, characterized by 24% lower compliance (0.0017 +/- 0.0004 vs 0.0021 +/- 0.0005 mm(2)/kPa/mm, p <0.01), 22% higher stiffness index beta (6.0 +/- 1.5 vs 4.9 +/- 0.7, p <0.005), and 41% greater pressure-strain elastic modulus (72 +/- 25 vs 51 +/- 9, p <0.005). At the ascending thoracic aorta, only the pressure-strain elastic modulus was different between obese and lean subjects (85 +/- 42 vs 65 +/- 26 kPa, respectively; p <0.05), corresponding to a 31% difference-but arterial compliance and stiffness index were not significantly different between groups. In clinically healthy young adult obese men, obesity is associated with increased cross-sectional aortic area and decreased aortic elasticity.

Adult↗
PubMed1988

Elastic properties of relaxed, activated, and rigor muscle fibers measured with microsecond resolution.

Tension responses due to small and rapid length changes (completed within 40 microseconds) were obtained from skinned single-fiber segments (4- to 7-mm length) of the iliofibularis muscle of the frog incubated in relaxing, rigor, and activating solution. The fibers were skinned by freeze-drying. The first 500 microseconds of the responses for all three conditions could be described with a linear model, in which the fiber is regarded as a rod composed of infinitesimally small identical segments, containing an undamped elastic element, two damped elastic elements and a mass in series. An additional damped elastic element was needed to describe tension responses of activated fibers up to the first 5 ms. Consequently phase 1 and phase 2 of activated fibers can be described with four apparent elastic constants and three time constants. The results indicate that fully activated fibers and fibers in rigor have similar elastic properties within the first 500 microseconds of tension responses. This points either to an equal number of attached cross-bridges in rigor and activated fibers or to a different number of attached cross-bridges in rigor and activated fibers and nonlinear characteristics in rigor cross-bridges. Mass-shift measurements obtained from equatorial x-ray diffraction patterns support the latter possibility.

Animals↗
PubMed1988

Clots of beta-fibrin. Viscoelastic properties, temperature dependence of elasticity, and interaction with fibrinogen-binding tetrapeptides.

Clots of human beta-fibrin, in which only (or predominantly) the B fibrinopeptide is released, were formed at 14 degrees C by copperhead venom procoagulant enzyme (CVE or venzyme), at pH 8.5, ionic strength 0.45. The shear modulus of elasticity increased slowly and after several days attained a constant value, which was lower than those of alpha-fibrin or alpha beta-fibrin under the same conditions. Before studying the temperature dependence of elasticity, the CVE was then inhibited by introducing phenyl methyl sulfonyl chloride (PMSF) by diffusion. With increasing temperature, the modulus decreased progressively from 5 degrees C to nearly zero at 35 degrees and was essentially reversible with temperature change; recovery of elasticity after change from 34.5 degrees to 14 degrees required approximately 2 d but was considerably faster than the initial buildup of elasticity by CVE at 14 degrees. Creep and creep recovery measurements on unligated clots showed creep rates and irrecoverable deformation that were similar in magnitude to those of alpha-fibrin clots formed with batroxobin and much larger than those of alpha beta-fibrin clots formed with thrombin, under the same conditions. During creep and creep recovery, the differential modulus or compliance remained constant, showing that there was no permanent structural damage, and if network strands are severed in slow flow, they must rejoin in new configurations. Introduction (by diffusion) of the tetrapeptides Gly-His-Arg-Pro (GHRP) and Gly-Pro-Arg-Pro (GPRP), which resemble the B and A binding sites on the E domain of fibrin respectively, reduced the shear modulus and increased the creep rate of beta-fibrin clots to an extent similar to the effect of GPRP on alpha beta-fibrin, much more than that of GHRP on alpha beta-fibrin, but much less than that of GPRP on a-fibrin. A ligated beta-fibrin clot formed with Factor XIIIa (in which the activating thrombin had been neutralized by hirudin) showed essentially perfect elastic behavior, with no creep and with complete recovery after removal of stress, and was inert to GHRP.

Blood Coagulation↗
PubMed1990

Elastic behavior of zymogen granule membranes in response to changes in pH and pCa.

In the process of secretion, the membrane of secretory granules is expected to change its elastic behavior. Elastic modulus of the membrane of zymogen granules, prepared from the rat pancreas acinar cell, was measured by an osmotic swelling method. The elastic modulus of the granule membrane at pCa 8 reduced from the maximal value of 230 dyn/cm at pH 6.0 to almost zero at pH 7.5. In a cytosol of an acinar cell, calcium ions play an important role as a second messenger in secretion. The elastic modulus of the granule membrane reduced in a sigmoidal fashion at pCa between 7.0 and 6.0. This range of pCa corresponds to a physiological rise of free Ca2+ concentrations in the cell cytosol when stimulated by external secretagogues. Reduction of the elastic modulus indicates that the state of the granule membrane switches to a more flexible one in which the granule is easy to appose to the cell plasma membrane and then swell as a final step of exocytosis.

Animals↗
PubMed1990

Effect of solute permeability in determination of elastic modulus using the vesicular swelling method.

The modulus of elasticity of artificial and biological membranes can be determined in membrane vesicles by monitoring the limitation of vesicular swelling during a slow decrease in medium tonicity. The higher the elastic modulus of the membrane, the more effectively the vesicles will resist swelling. This method assumes that the solutes in the system are impermeant, so that the final volume of the vesicles is determined solely by a balance of osmotic and hydrostatic forces. In this paper, we present the results of computer simulation of vesicular swelling in which the solute permeability of the membrane was varied. We find that even a small permeability will lead to a loss of solute from the vesicle that will retard the increase in vesicular volume during dilution of the medium, and thereby cause the apparent modulus of elasticity to be much greater than the true value. For example, if one takes the mannitol permeability in brush border membrane vesicles from small intestine to be 0.004 micron/s (a reasonable estimate), one finds that a vesicular swelling study using mannitol as the principal solute will show the apparent elastic modulus of the vesicles to be greater than 10 times larger than the true value. With higher permeabilities, the effect is even more dramatic. We conclude that determination of impermeance of solutes is a critical prerequisite for making valid determinations of membrane elastic modulus using the vesicular swelling method.

Elasticity↗
PubMed2002

Measurements of wave speed and reflected waves in elastic tubes and bifurcations.

Wave intensity analysis is a time domain method for studying waves in elastic tubes. Testing the ability of the method to extract information from complex pressure and velocity waveforms such as those generated by a wave passing through a mismatched elastic bifurcation is the primary aim of this research. The analysis provides a means for separating forward and backward waves, but the separation requires knowledge of the wave speed. The PU-loop method is a technique for determining the wave speed from measurements of pressure and velocity, and investigating the relative accuracy of this method is another aim of this research. We generated a single semi-sinusoidal wave in long elastic tubes and measured pressure and velocity at the inlet, and pressure at the exit of the tubes. In our experiments, the results of the PU-loop and the traditional foot-to-foot methods for determining the wave speed are comparable and the difference is on the order of 2.9+/-0.8%. A single semi-sinusoidal wave running through a mismatched elastic bifurcation generated complicated pressure and velocity waveforms. By using wave intensity analysis we have decomposed the complex waveforms into simple information of the times and magnitudes of waves passing by the observation site. We conclude that wave intensity analysis and the PU-loop method combined, provide a convenient, time-based technique for analysing waves in elastic tubes.

Arteries↗
PubMed1999

Elastic modulus and hardness of cortical and trabecular bone lamellae measured by nanoindentation in the human femur.

The mechanical properties of bone tissue are determined by composition as well as structural, microstructural and nanostructural organization. The aim of this study was to quantify the elastic properties of bone at the lamellar level and compare these properties among osteonal, interstitial and trabecular microstructures from the diaphysis and the neck of the human femur. A nanoindentation technique with a custom irrigation system was used for simultaneously measuring force and displacement of a diamond tip pressed 500 nm into the moist bone tissue. An isotropic elastic modulus was calculated from the unloading curve with an assumed Poisson ratio of 0.3, while hardness was defined as the maximal force divided by the corresponding contact area. The elastic moduli ranged from 6.9 +/- 4.3 GPa in trabecular tissue from the femoral neck of a 74 yr old female up to 25.0 +/- 4.3 GPa in interstitial tissue from the diaphyseal cortex of a 69 yr old female. The mean elastic modulus was found to be significantly influenced by the type of lamella (p < 10(-6)) and by donor (p < 10(-6)). The interaction between the type of lamella and the donor was also highly significant (p < 10(-6)). Hardness followed a similar distribution as elastic modulus among types of lamellae and donor, but with lower statistical contrast. It is concluded that the nanostructure of bone tissue must differ substantially among lamellar types, anatomical sites and individuals and suggests that tissue heterogeneity is of potential importance in bone fragility and adaptation.

Aged↗
PubMed2003

Elastic friction drive of surface acoustic wave motor.

Importance of elastic deformation control to obtain large output force with a surface acoustic wave (SAW) motor is discussed in this paper. By adding pre-load to slider, stator and slider surfaces are deformed in a few tens nanometer. Appropriate deformation in normal direction against normal vibration displacement amplitude of SAW existed. By moderate deformation, the output force of the SAW motor was enlarged up to about 10 N and no-load speed was 0.7 m/s. To produce this performance, the transducer weight and slider size were only 4.2 g and 4 x 4 mm(2).By traveling wave propagation, surface particles of the SAW device move in elliptical motion. Due to the amplitude of the elliptical motion is 10 or 20 nm order, the contact condition of the slider is very critical. To control the contact condition, namely, the elastic deformation of the slider and stator surface in nanometer order, a lot of projections were fabricated on the slider surface. The projection diameter was 20 micro m. In static condition, the elastic deformation and stress were evaluated with the FEM analysis. From this calculation and the simulation result, it is consider that the wave crest is distorted, hence the elasticity has influence on the friction drive condition. Elastic deformation of the stator surface beneath the projection from the initial position were evaluated. In 4 x 4 mm(2) square area, the sliders had from 1089 to 23,409 projections. Depression was independent to the contact pressure. However, the output force depended on the depression although the projection density were different. From the view point of the output power of the motor, the proper depression was independent to the projection density. Around 25 nm depression, the output force and output power were maximized. This depression value was almost same as the vibration displacement amplitude of the stator transducer.

Acoustics↗