Local Stiffness Measurement Research Articles

Hamstrings load bearing in different contraction types and intensities: A shear-wave and B-mode ultrasonographic study

The main aim was to examine the load bearing of individual hamstring muscles in different contraction types and intensities, through local stiffness measurement by shear wave elastography (SWE). A secondary aim was to examine the relationship between the SWE stiffness measure and hamstrings morphology. Ten healthy males (age 22.1±4.1 years; height 173.7±5.9 cm; body mass 68.6±12.4 kg; mean ± SD) performed knee flexions on an isokinetic dynamometer at different intensities (20–70%MVC, random order) in three separate, randomized conditions: isometric (ISO), concentric (CON) and eccentric (ECC). SWE was used to measure muscle shear wave velocity (SWV) in biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) during contraction. Muscle anatomical cross-sectional area (ACSA) was measured with magnetic resonance imaging and muscle architecture with B-mode ultrasonography. Muscle SWV increased linearly with contraction intensity, but at a varying rate among muscles and contraction types. ST exhibited greater SWV than BFlh and SM in all contraction types, however, there was an upward shift in the SM SWV–torque relationship in ECC compared to ISO and CON. Strong negative correlations were found between peak ISO SWV and ST ACSA (r = -0.81, p = 0.005) and BFlh pennation angle (r = -0.75, p = 0.012). These results suggest that ST has a primary role in hamstrings load bearing in all contraction types, likely due to its morphology; however, there is evidence of increased contribution from SM in eccentric muscle actions.

Body composition is a strong predictor of local carotid stiffness in Swedish, young adults \u2013 the cross sectional Lifestyle, biomarkers, and atherosclerosis study

BackgroundObesity has nearly tripled worldwide during the last four decades, especially in young adults, and is of growing concern since it is a risk factor for cardiovascular diseases (CVD). We explored how different body composition measurements are associated with intima media thickness (cIMT) and local stiffness in the common carotid artery, in a subsample of healthy, young women and men, from the Swedish Lifestyle, Biomarkers, and Atherosclerosis (LBA) Study.MethodsFrom the LBA study, a subsample of 220 randomly selected, self-reported healthy individuals, 18–25 years old, were collected for the automatized local stiffness measurements; arterial distensibility, Young’s elastic modulus, and β stiffness index. Blood pressure and mean arterial pressure (MAP) was measured using automatic blood pressure equipment. Body mass index (BMI) was calculated, waist circumference was measured, and percentage of body fat assessed using an impedance body composition analyzer. The carotid artery was scanned by ultrasound and analyzed using B-mode edge wall tracking. cIMT was measured and local stiffness measurements were calculated with carotid blood pressure, measured with applanation tonometry.ResultsNo association was found between cIMT and body composition. Local carotid stiffness was associated with body composition, and women had less stiff arteries than men (p < 0.001). Of the local stiffness measurements, arterial distensibility had the strongest associations with body composition measurements in both women and men (p < 0.05). Multiple regression analyses showed that BMI in women and BMI and percentage of body fat in men had the highest impact on arterial distensibility (p < 0.01 in both women and men).ConclusionsArterial distensibility was the local stiffness measurement with the strongest associations to different body composition measurements, in both women and men. In this age group, body composition measurements seem to be stronger predictors of common carotid arterial stiffness than MAP, and is a convenient way of detecting young adults who need cardiovascular risk follow-up and lifestyle counseling.

Water jet indentation for local elasticity measurements of soft materials.

We present a novel elastography method for soft materials (100Pa-100kPa) based on indentation by a μm-sized water jet. We show that the jet creates a localized deformation ("cavity") of the material that can be easily visualized. We study experimentally how cavity width and depth depend on jet speed, height, incidence angle and sample elasticity. We describe how to calibrate the indenter using gels of known stiffness. We then demonstrate that the indenter yields quantitative elasticity values within 10% of those measured by shear rheometry. We corroborate our experimental findings with fluid-solid finite-element simulations that quantitatively predict the cavity profile and fluid flow lines. The water jet indenter permits in situ local stiffness measurements of 2D or 3D gels used for cell culture in physiological buffer, is able to assess stiffness heterogeneities with a lateral resolution in the range 50-500μm (at the tissue scale) and can be assembled at low cost with standard material from a biology laboratory. We therefore believe it will become a valuable method to measure the stiffness of a wide range of soft, synthetic or biological materials.

CO-19: Measurement of arterial stiffness by ultrafast echo: comparison with echotracking in normotensive subjects and hypertensive patients

Background Because measurement of arterial stiffness is highly dependent on blood pressure (BP), methods independent of BP are required. Ultrafast echography (UFE, Supersonic Imagine, Aix-en-Provence, France) makes use of very fast sampling rate (up to 10kHz), so transient events such as pressure wave arrival can be tracked. This method has never been tested against classical echotracking (Artlab, Esaote, Maastricht, NL) and carotid-femoral pulse wave velocity (cf-PWV, Sphygmocor, AtCor, Sydney, Australia). Methods We included 56 subjects, 27 normotensives (NT) and 29 essential hypertensives (HT), matched for age and sex. We optimized UFE algorithms for pressure wave detection and tracking, for both foot of the wave (FW) and dicrotic notch (DN) PWV. Results Feasibility appears good (FW: 78%, DN: 96%). The relations of arterial stiffness with age and blood pressure were stronger for echotracking and cf-PWV than for UFE. DN wave fronts appeared better associated with cf-PWV (r = 0.32, p Conclusions After optimizing algorithms for wave front identification and tracking, UFE appears as a promising technique for assessing arterial stiffness. DN showed the best associations with echotracking, whereas FW did not provide meaningful data. As previously shown by Hermeling et al (J Hypertens 2008 and 2009), FW is not appropriate for local stiffness measurement likely because of very early wave reflections.

Electromechanical Properties of Polymer Electrolyte-Based Stretchable Supercapacitors

Aligned carbon nanotube (CNT) forests filled with a dehydrated polymer electrolyte are used to fabricate flexible solid state supercapacitors (SSCs) for multifunctional structural-electronic applications. Local stiffness measurements on the composite electrodes determined through nano­indentation showed an 80% increase over the neat solid polymer electrolyte matrix. Electrochemical properties are monitored as a function of average tensile strain in the SSCs. Galvanostatic charge-discharge tests with in situ microtensile testing on SSCs are used to show a 10% increase in the specific capacitance through the elastic region of the composite. The increase in capacitance is partly attributed to the enhanced double layer interaction that results from the partial alignment of the polymer electrolyte chains at the electrode-electrolyte interface. When soaked in 1 m sulfuric acid, the specific capacitance of the CNT-polymer electrolyte reached approximately 72 F g–1 at 60 °C.

Cellular Force Microscopy for in Vivo Measurements of Plant Tissue Mechanics

Although growth and morphogenesis are controlled by genetics, physical shape change in plant tissue results from a balance between cell wall loosening and intracellular pressure. Despite recent work demonstrating a role for mechanical signals in morphogenesis, precise measurement of mechanical properties at the individual cell level remains a technical challenge. To address this challenge, we have developed cellular force microscopy (CFM), which combines the versatility of classical microindentation techniques with the high automation and resolution approaching that of atomic force microscopy. CFM's large range of forces provides the possibility to map the apparent stiffness of both plasmolyzed and turgid tissue as well as to perform micropuncture of cells using very high stresses. CFM experiments reveal that, within a tissue, local stiffness measurements can vary with the level of turgor pressure in an unexpected way. Altogether, our results highlight the importance of detailed physically based simulations for the interpretation of microindentation results. CFM's ability to be used both to assess and manipulate tissue mechanics makes it a method of choice to unravel the feedbacks between mechanics, genetics, and morphogenesis.

Micromechanical study of corrosion products layers. Part I: Experimental characterization

A micromechanical characterization had been performed on ancient artefacts corrosion products. The proposed experimental approach allies scanning electron microscopy observations, micro-indentation tests which allow the characterization of the local stiffness of elementary constituents, and finally Raman micro-spectroscopy tests which give access to the local crystallised phases of the samples. The experimental campaign contains a large series of tests, which give us the opportunity to interpret the dispersion of local stiffness measurements.

2P1-C20 Local Stiffness Measurement of Single Cell using Nanoprobes through ESEM-Nanomanipulator System

In this paper, the characterization of cellular mechanics of W303 yeast cells was conducted using nanoneedles inside an Environmental-SEM (ESEM). Three types of nanoneedles were used in our experiments, i.e. titanium coated silicon (Si-Ti) and two types of tungsten (W) nanoneedles. The Si-Ti nanoneedle was fabricated using 2 N/m spring constant cantilevers while the W nanoneedles were fabricated using 0.09 N/m and 2 N/m spring constant cantilevers (W_<0.09> and W_2 nanoneedles). The Si-Ti, W_<0.09> and W_2 nanoneedles are suitable to be used for local stiffness characterization of single cells. This capability can be used in future for fast disease detection since disease cells may show different cell mechanics properties compared to the normal cells. The Si-Ti and W_2 nanoneedles can penetrate the cell without cell bursting and this could be important in single cell surgery in future to eliminate cell damage.

Imaging of flexural and torsional resonance modes of atomic force microscopy cantilevers using optical interferometry

Commercial rectangular atomic force microscope cantilever beams made of silicon were set into vibration, using a piezoelectric ultrasonic transducer coupled to the chip of a cantilever. The transducer was excited with continuous rf in the frequency range of 100 kHz to 3 MHz. The vibrations were monitored using an optical Michelson heterodyne-interferometer allowing the surface of the cantilever under examination to be scanned with a lateral resolution of several μm. A number of free torsional and flexural vibration modes of the beams were imaged quantitatively. Comparison of the experimental resonance frequencies and the amplitude and phase distribution of the modes to theoretical models showed that asymmetries in the beam strongly influence the vibrational behavior of the beam. The consequences for quantitative local stiffness measurements are discussed.

312 繰り返し荷重を作用させた家兎大腿骨の局所的スティフネス : 原子間力顕微鏡による計測

312 繰り返し荷重を作用させた家兎大腿骨の局所的スティフネス : 原子間力顕微鏡による計測

The pipette aspiration applied to the local stiffness measurement of soft tissues.

A simple method of identifying the initial slope of the stress-strain curve (i.e., Young's modulus of the soft tissue) by introducing the pipette aspiration technique is presented. The tissue was assumed to be isotropic and macroscopically homogeneous. Numerical simulations by the linear finite element analysis were performed for the axisymmetric model to survey the effects of friction at the tissue-pipette contact boundary, pipette cross-sectional geometry, relative size of the specimen to the pipette, and the layered inhomogeneity of the specimen tissue. The friction at the contact region had little effect on the measurement of Young's modulus. The configuration of the pipette was shown to affect the measurement for small pipette wall thickness. The measurement also depended on the relative size of the specimen to the pipette for relatively small specimens. The extent of the region contributing to the measurement was roughly twice the inside radius of the pipette. In this region, the maximum stress did not exceed the level of the aspiration pressure, with only minor exceptional locations. Calculation of strain energy components indicated that the major contributions to the deformation under pipette aspiration were by the normal extension and shear deformation in pipette axial direction. Experimental verification of the present method for the isotropic, homogeneous artificial material is also presented.