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Results for “Elastic Modulus”

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At least 757 records · Page 42Linked to original sources

PubMed1999

Effects of water immersion on mechanical properties of new esthetic orthodontic wire.

New fiber-reinforced plastic orthodontic wire (FRP wire) was fabricated with polymethyl methacrylate (PMMA) for the matrix and biocompatible CaO-P(2)O(5)-SiO(2)-Al(2)O(3) (CPSA) glass fibers for fibers that have not only high esthetics but also mechanical properties similar to those of metal wires. The purpose of this study was to evaluate the effects of water immersion on the mechanical properties of this new wire. The fiber-reinforced plastic orthodontic wire specimens were 0.5 mm in diameter with 29.1% to 60. 4% volume fraction of fibers that were 20 microm in diameter. A three-point flexural test was performed to obtain the elastic modulus and flexural load at the deflection of 1 mm under dry and wet conditions. Stress relaxation of the wires was tested under dry and wet conditions, and the wire diameters were measured before and at 20 days after immersion. The results showed that there were changes in the elastic modulus up until 10 days and in flexural load up until 20 days after immersion. The values of these two at 30 days after immersion were 93% and 87%, respectively, of those before immersion. Stress relaxation occurred rapidly from the start of immersion until about 60 minutes under dry conditions and about 120 minutes under wet conditions and then approached saturation. The swelling of hydrated fiber-reinforced plastic orthodontic wires affected the wire diameter, although this effect was not significant. The results of this study therefore suggest that the mechanical properties of fiber-reinforced plastic orthodontic wires are reduced by water immersion in the initial stage.

Dental Materials↗

PubMed1994

Estimation of material properties in the equine metacarpus with use of quantitative computed tomography.

The purpose of this study was to investigate the relationships between data obtained from quantitative computed tomography and mechanical properties in the equine metacarpus, as measured in vitro in bone specimens. Three hundred and fifty-five bone specimens from the metacarpi of 10 horses were machined into right cylinders aligned with the long axis of the bone. A computed tomographic scan of the specimens, along with a Cann-Genant K2HPO4 calibration standard, was obtained. The specimens then were compressed to failure, and the elastic modulus, yield stress, yield strain, strain energy density at yield, ultimate stress, ultimate strain, and strain energy density at ultimate failure were calculated. The specimens were dried and ashed. Quantitative computed tomography-derived K2HPO4 equivalent density proved to be an excellent estimator (r2 > 0.9) of elastic modulus, yield stress, ultimate stress, wet density, dry density, and ash density; a moderately good estimator (0.4 < r2 < 0.9) of strain energy density at yield and at ultimate failure; and a poor estimator (r2 < 0.2) of yield strain and ultimate strain. It was concluded that the relationships between quantitative computed tomography data and mechanical properties of the equine metacarpus were strong enough to justify the use of these data in automated finite element modeling.

Animals↗

PubMed1994

Effect of long term treatment with oxitropium bromide on airway secretion in chronic bronchitis and diffuse panbronchiolitis.

BACKGROUND: Anticholinergic bronchodilator drugs improve lung function in chronic bronchitis but less is known of their effects on the volume and physical properties of sputum in conditions associated with excessive airway secretions. This study examines the effects of the regular use of oxitropium bromide in such patients. METHODS: The study was conducted in a parallel, double blind, placebo controlled fashion. Patients were divided into two groups: the first group (n = 17) received oxitropium bromide from a metered dose inhaler (two puffs three times daily; 100 micrograms/puff) for eight weeks, and the second group (n = 16) received placebo. Lung function was measured as forced expiratory volume in one second (FEV1) and vital capacity. In evaluating airway secretion, daily amount of expectorated sputum, percentage solid composition, viscoelastic properties including elastic modulus and dynamic viscosity, and sputum microbiology were determined. RESULTS: Oxitropium bromide increased FEV1 and decreased the mean (SE) sputum production from 61(4) to 42(3) g/day after treatment, whereas placebo had no effect. Bacterial density and sputum flora were unchanged, but solid composition and elastic modulus increased from 2.52(0.43)% to 3.12(0.34)%, and 68(12) dyne/cm2, respectively, in the group taking oxitropium bromide. CONCLUSIONS: Regular treatment with oxitropium bromide not only improves airflow limitation but also reduces sputum production, probably through the inhibition of both mucus secretion and water transport, the latter component being predominant.

Adult↗

PubMed1994

Relationship between body mass and biomechanical properties of limb tendons in adult mammals.

We investigated the allometric relationship between the mechanical properties of various limb tendons and body mass. The elastic modulus (i.e., stiffness) and hysteresis (i.e., energy dissipation) of digital flexor, ankle extensor, and digital extensor tendons from 18 species of adult quadrupedal mammals ranging in body mass from 0.5 to 545 kg were determined by cyclic tensile testing in vitro. The results show that these elastic properties do not vary significantly among tendons from animals of different body mass, nor do they differ between the digital flexor and ankle extensor tendons (those situated to act as springs during locomotion) and the digital extensor tendons (those not likely to function as springs during locomotion). Consequently, the inherent capability of different limb tendons to store elastic energy, based on their material properties, is the same for large and small animals. The relationship between tendon elastic modulus (E; in GPa) and body mass (Mb; in kg) is described by the allometric equation E = 1.22Mb0.00. The hysteresis (H), as a percentage of total strain energy, is related to body mass as H = 8.89Mb-0.03.

Animals↗

PubMed1979

[Visco-elastic characteristics of the rat aorta].

In order to estimate wave propagation "in vitro", aortic compliance has been studied by means of rings and stripes from 6 adult male Wistar rats. Lengthening and shortening maneuvres have been performed; the pulse transmission rate was evaluated by calculating the elastic modulus during the maneuvres. A Norepinephrine infusion has been done. Results obtained show that transmission rate is higher in shortening than in lengthening phases. Norepinephrine did not significantly affect the values. The rate values were not greatly different whether "in vitro" or "in vivo". By increasing specimen stress, the rate too was increased, but the amount was lower than "in vivo" values. Hence it was assumable that rate variations "in vivo", should be partially influenced by elastic modulus, and a vegetative intervention should be implied.

Animals↗

PubMed2007

Microindentation test for assessing the mechanical properties of cartilaginous tissues.

Mechanical properties of the fresh control, frozen, and vitrified cartilaginous (cartilage and meniscus) samples were measured by microindentation. Indentation depth, elastic modulus, and indentation yield strength were obtained from the microindentation loading curves. Indentation deformation behavior was studied using Hertz contact model. The stress distribution of cartilaginous tissues under indentation loading was analyzed by finite element technique. It was found that fresh tissue shows the lowest indentation depth and the highest elastic modulus and indentation yield strength, followed by vitrified and frozen tissues. The vitrified tissue shows slightly lower but comparable mechanical properties with control tissue. The vitrification technique used in this study can preserve live cells with superior mechanical properties that make it an ideal technique for use in orthopedic and other biomedical applications. The microindentation tests and corresponding analysis methods used in this study offer a simple way to evaluate the mechanical properties of cartilaginous tissues. It suits small sample sizes and it may be used for other biological tissues.

Animals↗

PubMed2005

Micro/nanoscale mechanical and tribological characterization of SiC for orthopedic applications.

Micro/nanomechanical and tribological characterization of SiC has been carried out. For comparison, measurements on SiC, CoCrMo, Ti-6Al-4V, and stainless steel have also been made. Hardness and elastic modulus of these materials were measured by nanoindentation using a nanoindenter. The nanoindentation impressions were imaged using an atomic force microscope (AFM). Scratch, friction, and wear properties were measured using an accelerated microtribometer. Scratch and wear damages were studied using a scanning electron microscope (SEM). It is found that SiC exhibits higher hardness, elastic modulus, scratch resistance as well as lower friction with fewer and smaller debris particles compared to other materials. These results show that SiC possesses superior mechanical and tribological properties that make it an ideal material for use in orthopedic and other biomedical applications.

Biocompatible Materials↗

PubMed2004

X-ray scattering study of pike olfactory nerve: elastic, thermodynamic and physiological properties of the axonal membrane.

The effects of several agents, sugars, isotonic KCl, and a variety of drugs, on the structure of the axonal membranes of unmyelinated pike olfactory nerve have been studied by synchrotron radiation X-ray scattering experiments. The main effects of the sugars are: (i) to increase the electron density of the extra-axonal space and thereby yield the absolute scale of the electron density profile; (ii) to osmotically stress the membrane and thus yield its elastic modulus of area compressibility, since the related strain, thickness dilation, is directly determined by the X-ray scattering experiments. Exposure to isotonic KCl, a depolarizing agent, induces membrane thickness to increase. The energy liberated in this process is a function of the amplitude of the dilation and of the elastic modulus of the membrane. This energy turns out to be close to the thermal energy liberated by the pike olfactory nerve during the initial phase of action potential that has previously been measured by others. Electrical depolarization thus seems to be accompanied by a thickness dilation of the axonal membrane. Another effect of isotonic KCl is to induce a large fraction of the membranes to pair by tight apposition of their extra-axonal faces. Local anaesthetics and some drugs have the effect of altering membrane thickness. All these observations are interpreted in terms of a modulation of the conformational disorder of the hydrocarbon chains of the lipid molecules.

Anesthetics, Local↗

PubMed2004

Physical characterization of coupled poly(lactic acid)/starch/maleic anhydride blends plasticized by acetyl triethyl citrate.

Acetyl triethyl citrate (ATC) was used as a plasticizer for poly(lactic acid) (PLA)/starch blends coupled with maleic anhydride and an initiator of 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (L101). Elongation of the blend at break was markedly increased when the ATC content was above the 8% loading level, which is referred to as the percolation threshold. The extended elongation was achieved at the expense of tensile strength and elastic modulus. Thermal transitions of the blend, including the glass transition temperature (T(g)), cold crystallization temperature (T(c)) and melting temperature (T(m)), decreased with ATC content. Thermally induced ATC migration affected the thermal behavior of the plasticized blends and reduced elongation and tensile strength, whereas the elasticity modulus increased. ATC migration increased with ambient temperature, which was controlled by the activation energy of the blend system. Leaching of ATC was slow at room temperature in distilled water, but significant in boiling water. Additionally, the leaching rate was also directly proportional to the ATC content of the blend. Glass transition temperatures of PLA/starch/MA/L101 blends with various acetryl triethyl citrate contents.

Citrates↗

PubMed1994

[Effect of hardness and surface quality of metal cones on fracture load of ceramic ball heads of hip endoprostheses].

The safety of ceramic ball heads attached to hip endoprostheses by means of a conical fitting requires that the connection be designed with the ceramic material in mind. The ISO 7206-5 standard describes a static testing protocol to measure the maximal loading limit of the conical connection. In order to achieve high fracture loads in this test, it is necessary to optimize the load-bearing parts of the connection to prevent stress concentrations, to which the ceramic ball is sensitive. For this reason, manufacturers of ceramic balls give their customers specifications for the design of the metal taper, specifying tolerances for angle, roughness, roundness and straightness. In order to investigate which parameters of the metal taper have an influence on the fracture load achievable according to ISO 7206-5, fracture load tests were conducted with zircon oxide (ZIOLOX) heads in combination with test tapers from various manufacturers. The test tapers were made of Ti- or CoCr-based alloys. Before the tests the tapers were completely measured and characterized according to geometric parameters of roughness, roundness, straightness, profile and angle, and physical parameters such as hardness and elastic modulus. Subsequent measurements after the fracture tests characterized changes that occurred in the metal tapers. The fracture loads achieved depended on the potential for deformation of the taper surface. This potential can be described by a factor computed as hardness/roughness. A dependence of the fracture load on elastic modulus, form deviations or taper angle could not be established within the Cerasiv specifications.

Ceramics↗

PubMedDate not supplied

Increased arterial wall stiffness and thickness in medium-sized arteries in patients with insulin-dependent diabetes mellitus.

By means of ultrasonography, arterial wall stiffness, arterial wall thickness, and the elastic modulus of the common femoral artery were estimated in a group of 19 young insulin-dependent diabetics. The ultrasound technique for determination of these parameters is described as well as the echo-anatomy of the arterial wall. In accordance with a previous investigation a significant rise in arterial wall stiffness was found. Furthermore, there was a highly significant correlation between the stiffness and the thickness of the arterial wall. The elastic modulus also correlated to the stiffness. It is concluded that the diabetic macroangiopathy is characterized by an increased stiffness of the arterial wall caused by increased thickness as well as by progressive alterations of the elastic characteristics of the wall tissue. Possible pathogenetic reasons are discussed.

Adult↗

PubMed1994

A nonlinear mathematical model for the development and rupture of intracranial saccular aneurysms.

Mathematical models of aneurysms are typically based on Laplace's law which defines a linear relation between the circumferential tension and the radius. However, since the aneurysm wall is viscoelastic, a nonlinear model was developed to characterize the development and rupture of intracranial spherical aneurysms within an arterial bifurcation and describes the aneurysm in terms of biophysical and geometric variables at static equilibrium. A comparison is made between mathematical models of a spherical aneurysm based on linear and nonlinear forms of Laplace's law. The first form is the standard Laplace's law which states that a linear relation exists between the circumferential tension, T, and the radius, R, of the aneurysm given by T = PR/2t where P is the systolic pressure. The second is a 'modified' Laplace's law which describes a nonlinear power relation between the tension and the radius defined by T = ARP/2At where A is the elastic modulus for collagen and t is the wall thickness. Differential expressions of these two relations were used to describe the critical radius or the radius prior to aneurysm rupture. Using the standard Laplace's law, the critical radius was derived to be Rc = 2Et/P where E is the elastic modulus of the aneurysm. The critical radius from the modified Laplace's law was R = [2Et/P]2At/P. Substituting typical values of E = 1.0 MPa, t = 40 microns, P = 150 mmHg, and A = 2.8 MPa, the critical radius is 4.0 mm using the standard Laplace's law and 4.8 mm for the modified Laplace's law.(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm, Ruptured↗

PubMed2006

Effect of cigarette smoking on nitric oxide, structural, and mechanical properties of mouse arteries.

Cigarette smoking (CS) is a major risk factor for vascular disease. The aim of this study was to quantitatively assess the influence of CS on mouse arteries. We studied the effect of short-term (6 wk) and long-term (16 wk) CS exposure on structural and mechanical properties of coronary arteries compared with that of control mice. We also examined the reversibility of the deleterious effects of CS on structural [e.g., wall thickness (WT)], mechanical (e.g., stiffness), and biochemical [e.g., nitric oxide (NO) by-products] properties with the cessation of CS. The left and right coronary arteries were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and WT of coronary arteries were determined. Western blot analysis was used to analyze endothelial NO synthase (eNOS) in the femoral and carotid arteries of the same mice, and NO by-products were determined by measuring the levels of nitrite. Our results show that the mean arterial pressure was increased by CS. Furthermore, CS significantly increased the elastic modulus, decreased stress and strain, and increased the WT and WT-to-radius ratio compared with those of control mice. The reduction of eNOS protein expression was found only after long-term CS exposure. Moreover, the NO metabolite was markedly decreased in CS mice after short- and long-term exposure of CS. These findings suggest that 16 wk of CS exposure can cause an irreversible deterioration of structural and elastic properties of mouse coronary arteries. The decrease in endothelium-derived NO in CS mice was seen to significantly correlate with the remodeling of arterial wall.

Animals↗

PubMed2026

Fused Deposition Modeling (FDM) of polyether-ether-ketone (PEEK) dental implants: A systematic review of the effect of printing parameters on mechanical behaviour and surface quality.

PURPOSE: This systematic review evaluated how FDM printing parameters influence mechanical behaviour and surface characteristics of 3D-printed PEEK and identified parameter combinations linked to the most favourable mechanical performance and surface quality. MATERIALS AND METHODS: An electronic search was conducted in: MEDLINE (Ovid), PubMed, Embase, Web of Science, Scopus, and Compendex (last update: January 2025). Studies that evaluated the effect of FDM printing parameters on mechanical and surface properties of PEEK were included. Outcomes comprised compressive, tensile, and flexural strengths, elastic modulus, fracture toughness, surface hardness, roughness, and wettability. RESULTS: Of 4005 reports screened, 54 manuscripts were included. 92.6% (n = 50) of articles showed low risk-of-bias, while 7.4% (n = 4) showed medium risk-of-bias. Tensile strength was the most investigated mechanical parameter (78%), followed by elastic modulus (41%), flexural strength (30%), compressive strength (20%), and fracture toughness (6%). Surface roughness was the most evaluated surface property (30%), followed by hardness (17%) and wettability (6%). Across studies, higher printing temperatures, lower printing speed, thinner layer thickness, and maximum infill ratio in a horizontal printing orientation were associated with higher strengths, less warpage, increased accuracy, and improved surface quality. CONCLUSION: Specific combinations of FDM printing parameters can significantly improve the mechanical and surface properties of PEEK. However, it is difficult to meet all the optimal conditions simultaneously. Thus, balancing between different parameters must be considered in practical production.

Benzophenones↗

PubMed1996

Relationship between mechanical properties of the carotid artery wall and baroreflex function in acutely treated hypertensive patients.

OBJECTIVE: To evaluate the relationship between the mechanical properties of the carotid artery wall and baroreflex function after acute reduction of blood pressure with lacidipine in essential hypertension. DESIGN: After 15 days of placebo washout, the hypertensive patients underwent a single-blind haemodynamic study before and 90 min after administration of 4 mg lacidipine (a dihydropyridine calcium antagonist). METHODS: Brachial intra-arterial blood pressure was recorded in eight mild-to-moderate essential hypertensive patients aged 40-53 years (mean +/- SEM 46.8 +/- 4.7 years). The carotid pulse diameter was recorded simultaneously by an echo-tracking technique. The mechanical properties of the carotid artery wall were evaluated by calculating Peterson's incremental elastic modulus (Ep) both as an averaged value of 10 heart cycles with stable blood pressure and was the dynamic correlation, on a beat-to-beat basis, of Ep and the systolic blood pressure during a 20 mmHg increase in blood pressure following a bolus injection of phenylephrine. The elastic properties of the carotid artery were investigated further by determining the correlation between the systolic pressure and systolic diameter, beat by beat, during a ramped increase of blood pressure after phenylephrine administration. The baroreceptor reflex sensitivity was measured simultaneously by the Oxford method and by correlating Ep and the electrocardiographic R-R' interval on a beat-to-beat basis during phenylephrine injections. RESULTS: After lacidipine administration Peterson's elastic modulus, measured under resting steady-state conditions, was reduced (18.7 +/- 7.4 versus 16.4 +/- 6 x 10(5) dyne/cm2), whereas the baroreflex sensitivity was unchanged (6.6 +/- 3.3 versus 6.3 +/- 0.2 ms/mmHg) and resetting of the baroreflex had occurred. At the same time, the correlations between the systolic blood pressure and Ep and between the systolic blood pressure and carotid systolic diameter over a 20 mmHg increase in blood pressure were unchanged. Moreover, the correlations between the systolic blood pressure and the R-R' interval and between Ep and R-R' interval during the phenylephrine-induced blood pressure increase did not differ statistically. CONCLUSIONS: The results suggest that the resetting of the baroreflex after the acute reduction in blood pressure caused by lacidipine is dissociated from mechanical changes in the carotid artery wall.

Adult↗

PubMed2000

The effects of stress enhancement on the extracellular matrix and fibroblasts in the patellar tendon.

The purpose of the present study is to determine the effect of the stress enhancement and intrinsic fibroblasts on the extracellular matrix of the patellar tendon. Thirty-two female Japanese White rabbits were divided into four groups. In Group 1, the patellar tendon underwent the in situ freeze-thaw treatment to kill intrinsic fibroblasts of the patellar tendon and the patellar tendon underwent the wrapping treatment with nylon membrane filters to inhibit extrinsic cell infiltration. In Group 2, the medial and the lateral portions of the frozen-thawed patellar tendon were resected to enhance the stress, and then the central two-thirds of the patellar tendon underwent the wrapping treatment. In Group 3, the patellar tendon without the freeze/thaw treatment underwent the wrapping treatment. In Group 4, the patellar tendon was narrowed and wrapped in the same manner. All rabbits were killed 6 weeks after surgery. While the elastic modulus and the tensile strength of the patellar tendon in Group 2 were significantly less than those in Group 1, we could not find any significant differences in these parameters between Groups 3 and 4. Histologically, while no fibroblasts were observed in Groups 1 and 2, fibroblasts were found in Groups 3 and 4. This study revealed that stress enhancement decreases the elastic modulus and the tensile strength of the extracellular matrix of the patellar tendon and that intrinsic fibroblasts prevent the detrimental effect of stress enhancement on mechanical properties of the patellar tendon.

Analysis of Variance↗

PubMed1997

Role of nitric oxide in the regulation of the mechanical properties of peripheral conduit arteries in humans.

Whether nitric oxide (NO) contributes to the regulation of the mechanical properties of large arteries in humans is not known. We measured the effect of local administration of the inhibitor of NO synthesis N(G)-monomethyl-L-arginine (L-NMMA; 1 and 4 micromol x L[-1] x min[-1] for 5 minutes) and acetylcholine (3 and 30 nmol x L[-1] x min[-1] for 3 minutes) on radial artery diameter and wall thickness in 11 healthy volunteers using an echo-tracking system coupled to a measurement of radial blood flow (Doppler) and arterial pressure. At the highest dose, L-NMMA reduced radial blood flow but surprisingly decreased incremental elastic modulus (from 1.36+/-0.22 to 1.00+/-0.22 kPa x 10[3]; P<.05) and increased arterial compliance (from 3.20+/-0.46 to 4.07+/-0.45 m2 x kPa x 10(-8), P<.05), without affecting radial artery internal diameter, wall thickness or midwall stress, thus reflecting a decrease in vascular tone. Acetylcholine decreased incremental elastic modulus (from 1.27+/-0.08 to 0.88+/-0.07 kPa x 10[3]; P<.05) and increased arterial diameter, radial blood flow, and compliance (from 2.82+/-0.16 to 5.30+/-0.62m2 x kPa x 10[-8]; P<.05). These results demonstrate in vivo that NO is involved in the regulation of the mechanical properties of large arteries in humans. However, the effects of L-NMMA, ie, a decrease in arterial wall rigidity and an increase in arterial compliance, which occur in the absence of any changes in blood pressure or arterial geometry, suggest that inhibition of NO synthesis is associated in humans with a paradoxical isometric smooth muscle relaxation. This effect could be due to the development of compensatory vasodilating mechanisms after NO synthesis inhibition.

Acetylcholine↗

PubMed2003

Effects of viscoelasticity and time-dependent plasticity on nanoindentation measurements of human cortical bone.

The viscoelastic and time-dependent plastic effects on the nanoindentation measurement of osteonal lamella in a human cortical bone were investigated. The elastic modulus of osteonal lamella obtained from the quasi-static technique was strongly affected by the indentation rate and time-dependent plasticity. The effects of time-dependent plasticity can be diminished by multiple loading-unloading cycles and a long holding period at maximal load. After minimizing the contribution of time-dependent plasticity to unloading data, it was surprisingly found that the elastic modulus was proportional to indentation strain rate raised to the 0.06 power, which is similar to conventional test results.

Analysis of Variance↗