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Results for “Elastic Modulus”

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PubMed1996

Measuring the viscoelastic properties of human platelets with the atomic force microscope.

We have measured force curves as a function of the lateral position on top of human platelets with the atomic force microscope. These force curves show the indentation of the cell as the tip loads the sample. By analyzing these force curves we were able to determine the elastic modulus of the platelet with a lateral resolution of approximately 100 nm. The elastic moduli were in a range of 1-50 kPa measured in the frequency range of 1-50 Hz. Loading forces could be controlled with a resolution of 80 pN and indentations of the platelet could be determined with a resolution of 20 nm.

Biophysical Phenomena↗

PubMed2006

Smad3 deficiency alters key structural elements of the extracellular matrix and mechanotransduction of wound closure.

The loss of TGFbeta or its downstream mediator, Smad3, key players in tissue repair, accelerates closure of incisional wounds in mice. In contrast, we now report that excisional ear wounds in mice lacking Smad3 enlarge compared with wild-type controls resulting from changes in extracellular matrix molecules, which alter the mechanotransduction properties of these wounds. Specifically, levels of elastin and glycosoaminoglycans are increased, collagen fibers are more compactly organized, and matrix modulators like integrins, TGFbeta1, and matrix metalloproteinases (MMPs) are altered both basally and after wounding in Smad3 knockout mice. Mechanical testing of dorsal skin correlates these changes in matrix composition with functional parameters, specifically an increased elastic modulus, suggesting an imbalance of tissue forces. We propose that the altered mechanical elastic properties translate into a persistent retractile force that is opposed by decreased wound contractile forces contributing to the enlarging ear wound in Smad3 knockout mice. These studies highlight a previously undescribed role for Smad3 in the mechanotransduction of matrix unsupported ear wound closure.

Animals↗

PubMedDate not supplied

AAPM/RSNA physics tutorial for residents: topics in US: beyond the basics: elasticity imaging with US.

A new mode of imaging with ultrasonography (US) is under development in several laboratories around the world. This technique allows estimation of some measure of the viscoelastic properties of tissue. The information displayed in the images is a surrogate for that obtained with manual palpation. Fundamental concepts in elasticity imaging include stress, strain, and the elastic modulus; strain imaging has received the most attention from researchers. A system for elasticity imaging is under development that produces images of mechanical strain in real time by means of a freehand scanning technique. This system is integrated into a clinical US system without any external equipment and involves software changes only. Data obtained with this system demonstrate that the relative stiffness of many fibroadenomas changes as they and the surrounding tissue are deformed. At elasticity imaging of in vivo breast lesions, invasive ductal carcinomas appear, on average, more than twice as large on the elasticity image than on the B-mode image, but fibroadenomas and cysts are nearly equal in size on the two image types. The usefulness of this technology and the new information it provides suggest that it might soon be available on commercial US systems.

Algorithms↗

PubMed2006

Transposition of great arteries is associated with increased carotid artery stiffness.

Transposition of great arteries is the consequence of abnormal aorticopulmonary septation. Animal embryonic data indicate that septation and elastogenesis are related events, but human and clinical data are not available. We tested the hypothesis that large artery elastic function was impaired in patients with transposition of great arteries. We studied 34 patients aged 9 to 19 years, 12+/-3 years after atrial switch operation; 14 patients aged 7 to 9 years, 8+/-1 years after arterial switch operation; and 108 healthy control subjects matched for age. Carotid artery diastolic diameter and pulsatile distension were determined by echo wall-tracking; carotid blood pressure was measured by tonometry. Systolic pressure was higher and diastolic pressure was lower in patients than in controls. Patients with atrial and arterial switch repair were compared with their respective controls by 2-factor ANOVA. For patients with atrial switch repair versus control, stiffness index beta was 4.9+/-1.5 versus 3.1+/-1.0 (P<0.001); for patients witch arterial switch versus control, stiffness index beta was 3.8+/-1.1 versus 2.1+/-0.6 (P<0.001). Similar differences were observed for carotid compliance, distensibility, and incremental elastic modulus as well. The interaction term was not significant for any of the elastic variables, indicating that carotid stiffening was a characteristic of the condition and not the consequence of different hemodynamics. Carotid artery is markedly stiffer in patients, suggesting that impaired elastogenesis may constitute part of the congenital abnormality. Since carotid artery stiffness has been established as an independent cardiovascular risk factor, this condition may have consequences in the clinical management of these patients.

Adolescent↗

PubMed1995

Estimation of shear modulus distribution in soft tissue from strain distribution.

In order to obtain noninvasively quantitative static mechanical properties of living tissue, we propose a new type of inverse problem by which the spatial distribution of the relative elastic modulus of the tissue can be estimated only from the deformation or strain measurement. The living tissue is modeled as a linear isotropic incompressible elastic medium which has the spatial distribution of the shear modulus, and the deformation or strain is supposedly measured ultrasonically. Assuming that there is no mechanical source in the region of interest, we derive a set of linear equations in which unknowns are the spatial derivatives of the relative shear modulus, and the coefficients are the strain and its spatial derivatives. By solving these equations, the spatial derivatives of the relative shear modulus are determined throughout the region, from which the spatial distribution of the relative shear modulus is obtained by spatial integration. The feasibility of this method was demonstrated using the simulated deformation data of the simple inclusion problem. The proposed method seems promising for the quantitative differential diagnosis on the lesion in the tissue in vivo.

Algorithms↗

PubMed1996

Bilateral symmetry of biomechanical properties in rat femora.

In many studies, bone healing and remodeling have been examined in various animal models using one femur as a control for the contralateral femur based on the assumption that they are bilaterally symmetrical. Symmetry studies have been limited mainly to geometrical properties. The purpose of this study was to determine whether or not there is symmetry in the mechanical properties of rat femora. Two strain gauges were attached to the anterior surface parallel to the long axis of explanted femora of retired female breeder and 120-day-old male Sprague Dawley rats. Femora were mechanically tested in cantilever bending and the strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Female femora showed a bilateral strain difference of less than 2.2% and an elastic modulus difference of less than 8.7%. Males had less than 2.0% and 7.9% differences for strain and elastic moduli, respectively. Statistical analysis showed no significant difference between left and right femoral strain values for the females, but modulus differences were significant different at the p = 0.05 level. There was no significant difference in strain and modulus values for the males, indicating mechanical and geometrical symmetry of their femora.

Analysis of Variance↗

PubMed2003

Rheological study on mucoadhesivity of some nasal powder formulations.

Various powder mixtures were used to administer insulin via the nasal route: a co-spray dried mixture of Amioca starch and Carbopol 974 P (1/3), drum dried waxy maize starch and Carbopol 974 P (9/1), maltodextrin DE38/Carbopol 974 P (9/1) and pure drum dried waxy maize starch. Oscillatory rheology is performed to study and compare the viscosity, elasticity and mucoadhesivity of these powder formulations. There was no rheological synergism detectable with the co-spray dried mixture of Amioca starch and Carbopol 974 P (1/3), drum dried waxy maize starch and Carbopol 974 P (9/1) and maltodextrin DE38/Carbopol 974 P (9/1). Interaction due to entanglements was seen with drum dried waxy maize starch (100%). The differences in nasal bioavailability between the different carriers could be explained by differences in G' (storage modulus, elasticity) and G" (loss modulus, viscosity) values. The formulation giving the highest bioavailability, provided also the highest G' and G" values.

Adhesives↗

PubMed2006

Non-Hertzian approach to analyzing mechanical properties of endothelial cells probed by atomic force microscopy.

Detailed measurements of cell material properties are required for understanding how cells respond to their mechanical environment. Atomic force microscopy (AFM) is an increasingly popular measurement technique that uniquely combines subcellular mechanical testing with high-resolution imaging. However, the standard method of analyzing AFM indentation data is based on a simplified "Hertz" theory that requires unrealistic assumptions about cell indentation experiments. The objective of this study was to utilize an alternative "pointwise modulus" approach, that relaxes several of these assumptions, to examine subcellular mechanics of cultured human aortic endothelial cells (HAECs). Data from indentations in 2- to 5-microm square regions of cytoplasm reveal at least two mechanically distinct populations of cellular material. Indentations colocalized with prominent linear structures in AFM images exhibited depth-dependent variation of the apparent pointwise elastic modulus that was not observed at adjacent locations devoid of such structures. The average pointwise modulus at an arbitrary indentation depth of 200 nm was 5.6+/-3.5 kPa and 1.5+/-0.76 kPa (mean+/-SD, n=7) for these two material populations, respectively. The linear structures in AFM images were identified by fluorescence microscopy as bundles of f-actin, or stress fibers. After treatment with 4 microM cytochalasin B, HAECs behaved like a homogeneous linear elastic material with an apparent modulus of 0.89+/-0.46 kPa. These findings reveal complex mechanical behavior specifically associated with actin stress fibers that is not accurately described using the standard Hertz analysis, and may impact how HAECs interact with their mechanical environment.

Algorithms↗

PubMed2002

Disruption of the elastin gene in adult Williams syndrome is accompanied by a paradoxical reduction in arterial stiffness.

Although the aetiology of Williams syndrome (WS) is related to elastin gene disruption, its pathogenesis remains unknown, particularly that of vascular lesions. The aim of the present study was to compare the elastic properties of three WS patients with age- and gender-matched normotensive and hypertensive controls. Common carotid arteries of WS patients had a higher distensibility, a thicker intima-media and a lower elastic modulus. Electron microscopy studies of one WS renal artery showed major abnormalities of the elastic fibres, which displayed a reticular structure and a thickening of the internal elastic lamina, whereas the ultrastructure of elastic fibres was normal in a control subadventitial muscular fibrodysplasia. In this WS arterial stenosis, we studied the expression patterns of several major smooth muscle (SM) phenotypic markers using immunofluorescence and used a normal renal artery as a control. In WS, SM-alpha-actin- and myosin-heavy-chain-positive cells contained low amounts of heavy caldesmon, and laminin-beta1 chain was expressed into the basement membranes, indicating a less differentiated phenotype. In conclusion, in WS patients, the carotid artery wall was abnormally distensible and thick, and major ultrastructural abnormalities of elastic fibres were observed in association with smooth muscle cell de-differentiation. These results indicate that the haplo-insufficiency of the elastin gene in WS patients leads to abnormal elastic fibre assembly within the media. Arterial wall hypertrophy found with a primary defect in elastin may represent a major factor responsible for increased distensibility. We suggest that, in WS, the increased proliferative response and the associated de-differentiation process represent two important mechanisms underlying the matrix accumulation and the development of arterial stenosis.

Adult↗

PubMed1987

A new method for determination of drug effects on the arterial distensibility on conscious dogs.

We developed a method for recording drug effects on the distensibility of the arterial system on conscious catheterized beagle dogs. Assuming a pressure-dependent volumic flow from the large arteries into the peripheral vessels, the volume-elasticity of the arterial windkessel is computed by the time-course of the diastolic pressure decline and the total peripheral resistance. A continuous recording of this parameter shows a rapid decrease during each diastolic relaxation, which was in agreement with studies on isolated arteries. An elevation of the mean pressure by an infusion of angiotensin I causes an increase of the elasticity. However, nitroglycerin administration (5 micrograms/kg/min) reduced this parameter significantly. Simultaneous recording of the pulse-wave velocity, which is a measure of the elastic modulus of the arterial wall suggests that nitroglycerin-induced enhancement of the arterial elasticity is caused by a reduced stiffness of the arterial walls as well as by an increased volume of the windkessel. The effects of the nitroglycerin infusion on the venous system and the pulmonary artery showed a faster onset than the decrease of the arterial elasticity. However, the venous effect showed a significant drug tolerance, whereas enhancement of the arterial distensibility remained constant.

Animals↗

PubMed2006

Validation of the small-punch test as a technique for characterizing the mechanical properties of acrylic bone cement.

This paper examines the validity of using the small-punch test technique as a means of quantifying the mechanical properties of acrylic bone cement under different test conditions. The elastic moduli calculated using the small-punch test method were compared with data measured using the international standard for acrylic bone resin, ISO 5833. Conclusions from the study indicate that the small-punch test is a reproducible miniature specimen test method that can be used to characterize the mechanical properties of retrieved acrylic bone cement as used in total joint replacement surgery. Moreover, the test conditions were found to influence the elastic modulus of acrylic bone cement. The test temperature had a greater effect on the elastic behaviour of the bone cement than the test medium.

Bone Cements↗

PubMed1999

Interaction between fatty acid salts and elastin: kinetics, absorption equilibrium, and consequences for elasticity.

Elastin from bovine ligamentum nuchae is incubated in aqueous solutions of sodium salts of fatty acids (FAS). The FAS are laurate, myristate, and palmitate. Absorption of FAS in the elastin network is studied as a function of time, FAS concentration, and ionic strength. The consequences of this uptake for the elasticity of the elastin are studied by static and dynamic stress-strain measurements. Generally, distinction must be made between the initial time-dependent stage (I) and the final equilibrium stage (II). In I the initial rate of absorption follows a second-order binding mechanism, with the rate constant increasing with decreasing length of the FAS. In this regime, the elasticity modulus remains more or less unaffected. Especially in regime II the absorption of FAS is enhanced by a reduction in the cross-link density in the elastin network. This is ascribed to an osmotic pressure primarily caused by the concomitant uptake of low molecular weight ions in the elastin. The absorption equilibrium can be described by Langmuir theory. The absorption affinity increases with increasing hydrocarbon chain length of the FAS, indicating the contribution of hydrophobic interaction. Although the elasticity is not lost, the modulus is now reduced and a concomitant viscous component is developed.

Animals↗

PubMed2001

Simultaneous measurements of arterial diameter and blood pressure to determine the arterial compliance, wall mechanics and stresses in vivo.

BACKGROUND: to develop a periarterial dimensional clip-probe which, associated with endovascular pressure measurement, real-time digital signal processing/data treatment systems, enables characterisation of the basic wall mechanics in given arterial sites. DESIGN: experimental study. MATERIAL: a facing pair of ultrasonic crystals was incorporated in periarterial highlight probes, made of sterilisable silicone and manufactured from computer-designed stainless steel casts. The A/D converted diameter and pressure (from an endovascular micro-tip probe) signals, triggered by the ECG, were on-line processed to provide their respective profiles during an averaged cardiac cycle, and subsequently the arterial wall physics. The technique was tested in the iliac and renal arteries in eight pigs. RESULTS: the technique was found to indicate adequately that arterial responses to distending blood pressure, as given by Petersons modulus and relative pulsatility, were identical in renals and iliacs. In contrast, the compliance, circumferential incremental elastic modulus and midwall circumferential stress were higher in iliacs than in renals, whereas arterial stiffness of the renals surpassed that of the iliacs. DISCUSSION: the technique with sterilisable probes produces in vivo pressure-diameter relationships, arterial compliance, and wall mechanics and stresses, whatever the arterial size. The porcine iliacs and renals are elastic and viscorigid arteries, respectively.

Analysis of Variance↗

PubMed1985

Crossbridge kinetics in chemically skinned rabbit psoas fibres when the actin-myosin lattice spacing is altered by dextran T-500.

The actin-myosin lattice spacing of chemically skinned rabbit psoas fibres was osmotically altered by dextran T500, and the transient kinetic response of tension arising from maximally cycling cross-bridges was measured by sinusoidal length perturbations. The lattice spacing was estimated from the width of the fibres measured under a light microscope. As the dextran concentration was increased, the widths during both relaxation and Ca-activation decreased monotonically. The tension increased to a maximum at 7% dextran, and decreased again at further increases in dextran. Dynamic modulus (stiffness) increased monotonically with compression by dextran; this increase is primarily due to the elastic modulus. The rate constants slightly decreased between 0% and 4% dextran, then decreased rapidly at higher concentrations. The rate of oscillatory work output stayed approximately constant between 0% and 4% dextran, and sharply decreased at higher concentrations. Apparently, two independent effects occur as the lattice is compressed by dextran: (1) a compensation for the spacing change through an increase in tension and a decrease in the rate constants (this takes place at low dextran concentrations); and (2) an alteration of the crossbridge kinetics by grossly decreasing both the tension and the rate constants (at high dextran concentrations). The first effect is interpreted as a decrease in the detachment rate, while the second effect is interpreted as a decrease in the rate of the 'power stroke' reaction.

Actins↗

PubMed1998

Mechanical properties of resin composites with filler particles aligned by an electric field.

OBJECTIVES: To explore possible enhancement of the mechanical properties of resin composites by aligning the filler particles. METHODS: The resin for the composites consisted of urethane dimethacrylate (UDMA) and 1,6-hexanediol dimethacrylate (HDDMA) mixed in the ratio of 90 to 10; the filler was silica-zirconia in two particle sizes, 1.7 microns (P50), which was mixed with the resin in the volume fractions of 29 and 48 vol%, and 0.7 micron (Z100), which was mixed with the resin in the volume fractions of 37 and 57 vol%. Particle alignment was obtained by applying a 60 Hz AC electric field across the composite before the resin was photopolymerized. The stress-strain behavior and the elastic modulus of the hardened composite were measured along the alignment axis in compression. RESULTS: The elastic moduli of the aligned composites increased by as much as 20%, and the maximum stress sustainable in compression before significant deformation occurred was elevated. An electric field strength of the order of 1 kV mm-1 was required to obtain sufficient alignment. SIGNIFICANCE: Besides conferring a structure to resin composites that is more like that of the natural tooth, particle alignment increased some of the mechanical properties and may have improved durability.

Composite Resins↗

PubMed2003

Are the material properties and matrix composition of equine flexor and extensor tendons determined by their functions?

REASONS FOR PERFORMING STUDY: Injury to the superficial digital flexor tendon (SDFT) is common in competition horses. The SDFT contributes to locomotory efficiency by storing energy; such tendons have low safety margins. Tendons which merely position the limb, including the opposing common digital extensor tendon (CDET), are rarely injured. The current failure of strategies to prevent or effectively treat injury to the SDFT indicates the importance of understanding how it differs from tendons which are not injury-prone. HYPOTHESIS: That the structural and material properties and matrix composition of the SDFT and CDET differ, reflecting their specific functional requirements in vivo. METHODS: Forelimb tendons were harvested from 26 mature horses and loaded to failure prior to matrix composition analysis of specimens. RESULTS: The SDFT had a significantly higher cross-sectional area, structural stiffness, failure load and failure strain and a lower elastic modulus than the CDET (P < 0.0001). CONCLUSIONS: The SDFT has conflicting requirements for strength and elasticity; although as a whole it is a stiffer structure than the CDET, differences in the matrix molecular composition including water and total sulphated glycosaminoglycan contents allow it to remain more elastic as a material. POTENTIAL RELEVANCE: Further information on how the two tendons attain these different properties may be of use in the development of prevention and treatment strategies for SDFT rupture.

Animals↗

PubMed2005

Sensitivity of multiple damage parameters to compressive overload in cortical bone.

Damage accumulation plays a key role in weakening bones prior to complete fracture and in stimulating bone remodeling. The goal of this study was to characterize the degradation in the mechanical properties of cortical bone following a compressive overload. Longitudinally oriented, low-aspect ratio specimens (n=24) of bovine cortical bone were mechanically tested using an overload-hold-reload protocol. No modulus reductions greater than 5% were observed following overload magnitudes less than 0.73% strain. For each specimen, changes in strength and Poisson's ratio were greater (p=0.02) than that in modulus by 10.8- and 26.6-fold, respectively, indicating that, for the specimen configuration used in this study, longitudinal elastic modulus is one of the least sensitive properties to a compressive overload. Residual strains were also proportionately greater by 6.4-fold (p=0.01) in the transverse than axial direction. These results suggest that efforts to relate microcrack density and morphology to changes in compressive mechanical properties of cortical bone may benefit from considering alternative parameters to modulus reductions.

Adaptation, Physiological↗

PubMed1994

Evaluation of experimental and finite element models of synthetic and cadaveric femora for pre-clinical design-analysis.

The aim of this study was to determine the validity with which the finite element method could model synthetic bone and thereby determine the appropriateness of such femur analogues for application in pre-clinical tests. The performance of these synthetic femora was compared with cadaveric bone when employing the same geometric and material definition protocols. A four-point bend loading configuration was selected for this analysis. Four synthetic femurs and an embalmed cadaveric bone were tested experimentally to determine the structural bending stiffness (k) for the diaphysis of these bones. A finite element (FE) model was generated and an analysis performed for each bone type to estimate the Young's modulus (E) required to obtain a model stiffness equivalent to that obtained experimentally. The estimated material elastic modulus in the FE model for the synthetic femur was found to be very similar to available data for this bone analogue. The estimated cadaveric bone modulus however was found to differ significantly from documented values for cortical bone. A theoretical analysis demonstrated the great sensitivity of the estimated modulus value to the accuracy of the geometric definition. The very low variability found in the experimental test on the synthetic bones together with their more regular geometry and the possibility of achieving greater accuracy in geometric definition was shown to enable the production of a valid FE model of this bone for an isotropic homogeneous material description. Conversely, the greater irregularity of geometry, together with the less obvious differentiation between the cortical and cancellous bone in the cadaveric specimen makes accurate geometric description of this bone very difficult. This fact, together with the uncertainty concerning the quality of the cadaveric bone and its viscoelastic response during mechanical testing, makes reproduction of its behaviour in a FE model a much more demanding task. It is suggested that this greater capability of reproducing the experimental behaviour of the synthetic bone makes them a very useful model for both experimental and numerical studies which involve in-vitro pre-clinical testing of implant design and stem-bone behaviour.

Artificial Organs↗