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Results for “Elastic Modulus”

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PubMed2001

Endothelium-derived nitric oxide regulates arterial elasticity in human arteries in vivo.

Arterial elasticity is determined by structural characteristics of the artery wall and by vascular smooth muscle tone. The identity of endogenous vasoactive substances that regulate elasticity has not been defined in humans. We hypothesized that NO, a vasodilator released constitutively by the endothelium, augments arterial elasticity. Seven healthy young men were studied. A 20-MHz intravascular ultrasound catheter was introduced through an arterial sheath to measure brachial artery cross-sectional area, wall thickness, and intra-arterial pressure. After control was established, indices of elasticity (pressure-area relationship, instantaneous compliance, and stress-strain, pressure-incremental elastic modulus (E(inc)), and pressure-pulse wave velocity relationships) were examined over 0 to 100 mm Hg transmural pressure obtained by inflation of an external cuff. Thereafter, the basal production of endothelium-derived NO was inhibited by N(G)-monomethyl-L-arginine (L-NMMA) (4 and 8 mg/min). Finally, nitroglycerin (2.5 and 12.5 microgram/min), an exogenous donor of NO, was given to relax the vascular smooth muscle. Elasticity was measured under all of these conditions. L-NMMA (8 mg/min) decreased brachial artery area (P=0.016) and compliance (P<0.0001) and increased E(inc) (P<0.01) and pulse wave velocity (P<0.0001). Nitroglycerin (12.5 microgram/min) increased brachial artery area (P<0.001) and compliance (P<0.001) and decreased pulse wave velocity (P=0.02). NO, an endothelium-derived vasodilator, augments arterial elasticity in the human brachial artery. Loss of constitutively released NO associated with cardiovascular risk factors may adversely affect arterial elasticity in humans.

Adult↗

PubMed2004

Dynamic properties of composite cemented clay.

In this work, the dynamic properties of composite cemented clay under a wide range of strains were studied considering the effect of different mixing ratio and the change of confining pressures through dynamic triaxial test. A simple and practical method to estimate the dynamic elastic modulus and damping ratio is proposed in this paper and a related empirical normalized formula is also presented. The results provide useful guidelines for preliminary estimation of cement requirements to improve the dynamic properties of clays.

Adhesives↗

PubMed2004

Nitric oxide synthase gene polymorphism (G894T) influences arterial stiffness in adults: The Bogalusa Heart Study.

The endothelial nitric oxide synthase (eNOS) gene is known to influence the regulation of blood pressure (BP) levels. However, whether the eNOS gene locus influences arterial stiffness independently of BP is unknown. This study examines the independent effect of the eNOS gene polymorphism (G894T) on arterial stiffness in 118 African American and 285 white young adults, aged 25 to 37 years. Arterial stiffness was measured from M-mode ultrasounds of common carotid artery using Peterson's (Ep) and Young's (YEM) elastic modulus. African Americans displayed a lower frequency of the T allele than did whites (0.131 v 0.321, P <.001). The T allele was associated with lower systolic BP in African Americans (P =.04) but not in whites. African Americans showed significantly higher values of Ep (that is, increased stiffness) than did whites (49.9 kPa vs 45.5 kPa, P =.003), whereas no such difference in ethnicity was found for YEM, a measure of elasticity adjusted for relative wall thickness. After controlling for sex, age, body mass index, insulin, heart rate, and mean arterial pressure, the T allele was associated with significantly lower values of Ep (P =.037) and YEM (P =.068) in African Americans. Although the genotype effect on Ep and YEM was not significant in whites, trends were similar to those in African Americans. In the total sample, including ethnicity as an additional covariate, the G894T genotype was significantly associated with Ep (P =.046) and YEM (P =.035). These results suggest that the allelic variation (G894T) of the eNOS gene or a locus closely linked to it is associated with lower arterial wall stiffness, adjusting for BP levels, in young adults.

Adult↗

PubMed2004

Relationship between the minute structure and the lodging resistance of rice stems.

The aim of this experiment is to measure the morphological and mechanical properties, and to analyze the relationship between the morphology and lodging resistance of several different kinds of rice stem. Choose the typical species of tall, mid and short stem and hybrid rice, ten individual plants each species (all should be caulis), and when paddies are full heading, intercept the third internode above the ground. The minute structure characteristics include the size of outer diameter, Culm wall thickness, and the number of big and small vascular bundles. Mechanical properties include the tensile breaking point and the tensile elastic modulus. Based on the above characteristics it is concluded that the middle stem has the highest lodging resistance. Thus when we select the high-yield and lodging resistance species, the middle and rigid stem should be considered.

Elasticity↗

PubMed1975

Pressure dependence of the mechanical properties of arteries in vivo.

Simultaneously measurements of intra-arterial pressure and external diameter were recorded from the thoracic and abdominal aortas, the carotid, brachiocephalic, left subclavian, and femoral arteries of anesthetized dogs. Data were recorded under control conditions and during efferent vagal stimulation, and were used to compute values of wall geometry, mechanical properties, phase velocity, and characteristic impedance. Values of these parameters computed for both control and vagal stimulation were used to represent their dependence on mean arterial pressure. Both the dynamic elastic modulus and the phase velocity increased with mean pressure at each arterial site. Values of computed characteristic impedance were constant and independent of mean arterial pressure between 80--150 mmHg. The tropical application of norepinephrine (100 mug/ml) to the femoral artery produced no change in mean pressure, while external diameter and dynamic modulus were decreased, and characteristic impedance was increased. These results provide direct support for the conclusion of previous studies on vascular impedance spectra which suggested a constancy of characteristic impedance with changes in mean arterial pressure.

Acetylcholine↗

PubMedDate not supplied

Mechanical analysis of elasticity and flexibility of virgin and polymer-treated hair fiber assemblies.

The elasticity and flexibility of virgin and polymer-treated hair fiber assemblies were investigated by employing straight hair tresses or hair shaped into omega loops. Polymer treatment was accomplished by saturating fibers with polymeric solutions, resulting in a deposition of 10-90 mg of polymer per gram of hair. The mechanical testing procedure consisted of subjecting omega-loop-shaped hair or straight hair tresses to multiple bending deformations at 25% strain in a texture analyzer. A total of ten deformations were typically carried out, and elasticity or flexibility parameters were evaluated from data such as (a). the force at 8% deformation, i.e., within the elastic region of bending deformation for hair shaped into an omega loop, (b). maximum force in the first (F(1)) and tenth (F(10)) deformation cycles, (c). elastic modulus in the first (E(1)) and tenth (E(10)) deformation cycles, and (d). the change in hair sample dimensions between the first (H(1)) and tenth (H(10)) deformation cycles. Parameters such as stiffness ratio (1), F(10)/F(1), E(10)/E(1), and H(10)/H(1) were employed to characterize hair tress rigidity, flexibility or resistance to breakage, and plasticity. Untreated hair was found to be almost perfectly elastic and flexible at 50% RH, evident by the linear dependence of force vs deformation. Flexibility parameters F(10)/F(1), E(10)/E(1), and H(10)/H(1) were in the range of 0.95 to 1.0 at low humidity, while the parameters F(10)/F(1) and E(10)/E(1) and were 10% lower at 90% RH. Examination of polymer-modified hair allowed for classification of treatments into categories termed brittle, quite flexible and nonplastic, flexible and plastic, very flexible and very plastic, and very flexible and nonplastic. Poly(vinyl pyrrolidone) is shown as an example of a quite flexible and nonplastic material, with its flexibility and stiffness dependent upon its molecular weight. The effect of plasticizers on polymer behavior is also discussed.

Animals↗

PubMed1989

[Mechanical analysis of the denture bases, using the photoelastic-coating method. 1. Influence of the coating on mechanical properties of the test denture].

The anterior palatal area may be related with the flexural rigidity and bending strength of the upper complete dentures. Therefore, the deformation of this area should be measured widely and continuously when new materials were applied to the dentures. The influence of the photoelastic coating on the mechanical properties of the upper complete dentures was investigated, prior to the measurement of surface strains on the denture bases by the photoelastic coatings. In this experiment, the uniform-moment bending method was employed simulating the occlusal situation. The flexural rigidity of the denture bases depended on the palatal materials in spite of the presence of the coating. The strains concentrated on the anterior palatal area were slightly decreased when the coating was bonded to the polished surface of the palate. The reinforcing effect was significant when the resin dentures of low elastic modulus were coated. The photoelastic-coating method was suitable for the qualitative analysis of the strain distribution of the denture base and selecting the test points to make strain measurement accurate.

Dental Stress Analysis↗

PubMed1979

Effect of acute ischaemia on active and passive large deformation mechanics of canine carotid arteries.

Large deformation mechanical properties of dog carotid arteries excised following 1 hour of ischaemia and 1 hour of reperfusion were compared to those of contralaterial normal arteries in vitro. Vascular smooth muscle was invariably activated by 0.5 microgram/ml noradrenaline. Relative reduction in the diameter of postischaemia arteries following noradrenaline administration was twice as large (max.: 13.2 +/- 2.0%) as that of normal controls (max.: 5.7 +/- 1.5%) in the pressure range of 0--220 mmHg. If the smooth muscle was totally relaxed there were no differences between the geometrical (wall-thickness, radius) and mechanical properties (stress, incremental elastic modulus, incremental distensibility, strain-energy density) of the arteries in the two series. It is concluded that the increased reactivity of postischaemic arteries is not caused by changes in geometric or mechanical properties of their passive wall elements.

Animals↗

PubMed2006

Stress distribution in a post-restored tooth using the three-dimensional finite element method.

Clinicians are opting ever more frequently for restorative materials which have an elastic modulus similar to that of dentin when reconstructing endodontically treated teeth. Metallic posts, which are capable of causing dangerous and non-homogenous stresses in root dentin, are slowly being abandoned. Ideal posts may be those made of various types of fibre (carbon, mineral and glass) and which are adhesively luted into the canal. Among the different methods for evaluating the mechanical behaviour of posts in root canals (progressive loads and photo-elastic technique) the finite element method (FEM) presents many advantages. The aim of this paper is to evaluate, utilizing three-dimensional analysis of the finite elements, what the effect of material rigidity, depth of insertion and post diameter could be on the stress distribution in the different components of the single tooth-post-core reconstruction unit. The results of the FEM analyses, expressed as the distribution of Von Mises stress values, has allowed us to conclude that (i) fibreglass-reinforced composite distributes stress better than titanium alloy or stainless steel; (ii) fibreglass-reinforced composite posts should be inserted as deeply as possible (but maintaining 5-6 mm of gutta-percha apical seal); (iii) fibreglass-reinforced composite post diameter does not affect stress distribution, therefore, as much radicular dentin as possible should be preserved.

Compressive Strength↗

PubMed1996

Intervertebral disc response to cyclic loading--an animal model.

The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.

Animals↗

PubMedDate not supplied

Block copolypeptides. 2. Viscoelastic properties.

The solid state structure of block copolypeptides of gamma-benzyl L-glutamate (G) and L-leucine (L) case from preferential solvents for G has been investigated by dynamic mechanical and wide angle x-ray diffraction techniques. The WAXD patterns show overlapping reflections characteristic of the individual homopolymers. Further evidence for a phase separated morphology is provided by the viscoelastic behavior. Representation of the dynamic elastic modulus in terms of the equivalent mechanical model suggests that phase separation of GLG-type polymers occurs with G as the matrix phase. In the reverse case, LGL-type polymers, it appears that some phase inversion has taken place.

Elasticity↗

PubMed2000

Two-dimensional MR elastography with linear inversion reconstruction: methodology and noise analysis.

A methodology for imposing approximate plane strain conditions in magnetic resonance elastography through physical constraint is described. Under plane strain conditions, data acquisition and analysis may be conducted in two dimensions, which reduces imaging and reconstruction time significantly compared with three-dimensional analysis. Simulations and experiments are performed to illustrate the constraint concept. A signal/noise analysis of a two-dimensional linear inversion technique for relative elastic modulus is undertaken, and modifications to the numerical method are described which can reduce the SNR requirements by a factor of two to four. Experimentally measured data are reconstructed to illustrate the performance of the method.

Breast Neoplasms↗

PubMed2002

Synthesis of organic-inorganic hybrid fillers at the molecular level and their application to composite resin.

The objective of this study was to synthesize a hybrid type filler composed of an organic component with inorganic component at the molecular level and to examine the properties of the filler. The composite resin was prepared by mixing synthesized filler with monomer and its physical properties were also examined. An organic-inorganic hybrid filler was synthesized by using 3-methacryloxypropyltrimethoxysilane (3-MPTS), methyltriethyoxysilane (MTES) and methanol silica sol. Firstly, poly3-methacryloxypropyltrimethoxysilane (poly3-MPTS) was synthesized by polymerization of 3-MPTS. A gelation product was obtained by graft-polymerization of poly3-MPTS with condensed organopolysiloxane after the hydrolysis of 3-MPTS, MTES and methanol silica sol. The gelation product was dried and ground to a filler. From the results of thermogravimetry-differential thermal analysis (TG-DTA), the organic-inorganic hybrid filler was found to be composed of 16.5 wt% organic component, 83.1 wt% inorganic component and 0.4 wt% residual water. A trial composite resin was prepared by mixing 55 wt% dimethacryloxyethyl 2,2,4-trimethylhexamethylene diurethane (UDMA), 15 wt% triethyleneglycol dimethacrylate (TEGDMA), 30 wt% 1-fluoro-1,3,3,5,5-penta (methacryloxyethyleneoxy) cyclotriphosphazene [P3N3(F)1 (EMA)5] as a base monomer and then 32.0 wt% of this monomer was mixed with 68.0 wt % of synthesized filler and a photo initiator, comphorquinone (CQ), was added. Compressive strength of the trial visible-light cured composite resin showed 397.0 MPa, and flexural strength and elastic modulus showed 142.5 MPa and 11.5 GPa, respectively. From the results, it was demonstrated that the present organic-inorganic hybrid filler at the molecular level can be used as a composite resin filler.

Composite Resins↗

PubMed2002

Viscoelastic evaluation of topical creams containing microcrystalline cellulose/sodium carboxymethyl cellulose as stabilizer.

The purpose of this study was to examine the viscoelastic properties of topical creams containing various concentrations of microcrystalline cellulose and sodium carboxymethyl cellulose (Avicel(R) CL-611) as a stabilizer. Avicel CL-611 was used at 4 different levels (1%, 2%, 4%, and 6% dispersion) to prepare topical creams, and hydrocortisone acetate was used as a model drug. The viscoelastic properties such as loss modulus (G"), storage modulus (G'), and loss tangent (tan delta) of these creams were measured using a TA Instruments AR 1000 Rheometer and compared to a commercially available formulation. Continuous flow test to determine the yield stress and thixotropic behavior, and dynamic mechanical tests for determining the linear viscosity time sweep data, were performed. Drug release from the various formulations was studied using an Enhancer TM Cell assembly. Formulations containing 1% and 2% Avicel CL-611 had relative viscosity, yield stress, and thixotropic values that were similar to those of the commercial formulation. The elastic modulus (G') of the 1% and 2% formulation was relatively high and did not cross the loss modulus (G"), indicating that the gels were strong. In the commercial formulation, G' increased after preshearing and broke down after 600 seconds. The strain sweep tests showed that for all formulations containing Avicel CL-611, the G' was above G" with a good distance between them. The gel strength and the predominance of G' can be ranked 6% > 4% > 2%. The strain profiles for the 1% and 2% formulations were similar to those of the commercial formulation. The delta values for the 1% and 2% formulations were similar, and the formulations containing 4% Avicel CL-611 had lower delta values, indicating greater elasticity. Drug release from the commercial preparation was fastest compared to the formulations prepared using Avicel CL-611, a correlation with the viscoelastic properties. It was found that viscoelastic data, especially the strain sweep profiles of products containing Avicel CL-611 1% and 2%, correlated with the commercial formulation. Rheological tests that measure the viscosity, yield stress, thixotropic behavior, other oscillatory parameters such as G' and G" are necessary tools in predicting performance of semisolids.

Administration, Topical↗

PubMed1989

Bone stress distribution for three endosseous implants.

Axisymmetric finite element models of three geometries were evaluated: a serrated solid with a 2-degree taper and a rectangular cross section; a cylindrical screw-type solid; and a finned solid with a 1 degree 9' taper and a circular cross section. Ten moduli of elasticity ranging from 0.348 to 74.96 psi x 10(6) were used for each geometry. Contour plots of the resulting Von Mises stresses were used to study the changing stress distribution patterns within the surrounding cortical bone. The results indicated that the serrated geometry led to high-stress concentrations at the tips of the bony ingrowth and near the neck of the implant. Low moduli of elasticity emphasized these concentrations. The nontapered screw-type geometry had high-stress concentrations at the base of the implant when high moduli were studied and at the neck of the implant when low moduli were studied. The conclusion of this study was that a tapered endosseous implant with a high elastic modulus would be most suitable for dental implantology. However, the design must not cause high-stress concentrations at the implant neck that commonly cause bone resorption.

Alveolar Process↗

PubMed1995

Chemistry and sintering behaviour of thin hydroxyapatite ceramics with controlled porosity.

Hydroxyapatite ceramic tapes (several hundred micrometres thick), have been prepared at different porosity levels, using the tape casting technique. The reactions, which occur during processing and sintering of the tapes, have been characterized by power X-ray diffraction analysis, differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Volume changes have been measured during different stages of heat treatment. These can be attributed to phase transformations of the starting materials, which determine the sintering behaviour and final porosity of the samples. Measurements of the elastic modulus were performed by the resonant frequency method. A cubic dependence on the relative density is found. Finally, some possible improvements for the technique and selection of powders are suggested, based on the reported results.

Ceramics↗

PubMed2006

The cell as a material.

To elucidate the dynamic and functional role of a cell within the tissue it belongs to, it is essential to understand its material properties. The cell is a viscoelastic material with highly unusual properties. Measurements of the mechanical behavior of cells are beginning to probe the contribution of constituent components to cell mechanics. Reconstituted cytoskeletal protein networks have been shown to mimic many aspects of the mechanical properties of cells, providing new insight into the origin of cellular behavior. These networks are highly nonlinear, with an elastic modulus that depends sensitively on applied stress. Theories can account for some of the measured properties, but a complete model remains elusive.

Animals↗

PubMed2006

Intradiscal injections of osteogenic protein-1 restore the viscoelastic properties of degenerated intervertebral discs.

BACKGROUND CONTEXT: Using biochemical, histological, and radiological parameters in a rabbit model of intervertebral disc (IVD) degeneration, the intradiscal injection of a growth factor, such as osteogenic protein-1 (OP-1), has been shown to regenerate the IVD. However, very little is known about how such a biological therapeutic approach affects the biomechanical properties of the degenerated IVD. PURPOSE: To investigate the effects of an intradiscal injection of OP-1 on the biomechanical properties of IVDs in the rabbit annular-puncture disc degeneration model and to determine their relationship to biochemical properties. STUDY DESIGN/SETTING: In vivo study on the effects of intradiscally administered OP-1 on the biomechanical and biochemical properties of IVDs in the rabbit annular-puncture disc degeneration model. METHODS: New Zealand White rabbits (n=16) underwent annulus fibrosus (AF) puncture, using an 18-gauge needle, at L2-L3 and L4-L5 (L3-L4: nonpunctured control). Four weeks later, the punctured discs received an injection of either 5% lactose (10 microL) or OP-1 (100 microg/10 microL of 5% lactose) into the nucleus pulposus (NP). The disc height was radiographically monitored biweekly. After sacrifice and removal of bone-disc-bone complexes 8 weeks postinjection, the dynamic viscoelastic properties of the IVDs were tested by applying a cycle of sinusoidal strain in uniaxial compression at six loading frequencies (0.05 to 2 Hz). The biochemical properties of the dissected IVDs were then analyzed and correlated with the biomechanical properties. RESULTS: A single injection of OP-1 significantly restored disc height when compared with the lactose-injected discs (OP-1 vs. lactose, p<.001). The elastic modulus of the IVDs in the OP-1-injected discs was significantly higher than that in the lactose-injected discs at all frequencies (mean: +43%, p<.001). The viscous modulus in the OP-1-injected discs was significantly higher at 0.05, 0.2, 0.5, and 1 Hz (mean: +55%, p<.001) and showed higher tendencies at other frequencies (p=.08-.09). For both moduli, no significant differences were observed between the OP-1-injected and the nonpunctured control discs. The OP-1 injection significantly increased the proteoglycan (PG) content in the NP and AF, and the collagen content in the NP (p<.001-.05). Both elastic and viscous moduli showed significant positive correlations with PG content in the NP and collagen content in the NP and AF (Rho=.357-.466, p=.010-.047). CONCLUSIONS: We have shown for the first time that an injection of the growth factor, OP-1, restored the biomechanical properties of IVDs in a rabbit model of IVD degeneration. Comparing biomechanical with biochemical data suggests that the OP-1-induced biomechanical restoration was a consequence of increased activities of anabolic pathways that resulted in biochemical changes in the IVD.

Animals↗