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Results for “Elastic Modulus”

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At least 595 records · Page 33Linked to original sources

PubMed1991

Comparison of viscoelastic properties of suture versus porcine mitral valve chordae tendineae.

Recent reports have advocated the use of polytetrafluoroethylene (PTFE) suture for replacement or reinforcement of ruptured or elongated mitral valve chordae tendineae. The mechanical properties of PTFE (Gore-Tex) and other sutures were determined and compared to those of porcine mitral valve chordae. The results were analyzed to assess how closely chordal mechanical function may be simulated by synthetic suture materials. Chordae tendineae and suture samples were tested in uniaxial tension using an INSTRON Model 1000 at strain rates of 5 and 10 mm/min. The stress (g/mm2) was plotted versus strain, and the elastic modulus determined as the slope of the curve. Chordae tendineae exhibited a nonlinear viscoelastic stress/strain behavior. The elastic modulus of both suture types tested was significantly higher than that of the chordae. However, the PTFE suture did exhibit some viscoelastic characteristics (hysteresis and creep) that begin to approach the chordal behavior. Chordal viscoelastic behavior results from the inherent composite structure (collagen, elastin, endothelium, water, and ground substance). As yet, no synthetic materials are able to imitate this behavior with the appropriate tensile strength and fatigue resistant characteristics. At present, PTFE appears to be the best synthetic alternative for chordal replacement, due to its limited viscoelastic capabilities. Nevertheless, the need to more nearly approximate the mechanical behavior of mitral valve chordae tendineae with synthetic material warrants further investigation.

Animals↗

PubMed2003

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

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

Adult↗

PubMed2005

An orientation distribution function for trabecular bone.

We describe a new method for quantifying the orientation of trabecular bone from three-dimensional images. Trabecular lattices from five human vertebrae were decomposed into individual trabecular elements, and the orientation, mass, and thickness of each element were recorded. Continuous functions that described the total mass (M(phi,theta)) and mean thickness (tau(phi,theta)) of all trabeculae as a function of orientation were derived. The results were compared with experimental measurements of the elastic modulus in three principal anatomic directions. A power law scaling relationship between the anisotropies in mass and elastic modulus was observed; the scaling exponent was 1.41 (R2=0.88). As expected, the preponderance of trabecular mass was oriented along the cranial-caudal direction; on average, there was 3.4 times more mass oriented vertically than horizontally. Moreover, the vertical trabeculae were 30% thicker, on average, than the horizontal trabeculae. The vertical trabecular thickness was inversely related to connectivity (R2=0.70; P=0.07), suggesting a possible organization into either few, thick trabeculae or many thin trabeculae. The method, which accounts for the mechanical connectedness of the lattice, provides a rapid way to both visualize and quantify the three-dimensional organization of trabecular bone.

Aged↗

PubMed1997

Non-destructive characterization of hydrogels.

Hydrogels have been prepared by a freezing-thawing procedure and investigations made of the effect of both number of freezing-thawing cycles and different content of hyaluronic acid (HA) on the mechanical properties of the PVA-HA hydrogels using non-destructive testing. The bulk elastic modulus K of hydrogels has been determined by pulse-echo measurements. It is noted that hydrogel elastic properties improve with the number of the cycles in PVA-HA 100/0; on the other hand samples with a high HA (1,000,000 molecular weight) content, beyond the third cycle, seem to be unaffected by the number of cycles. A bulk elastic modulus fall-off is then observed in samples submitted to an additional overnight freezing between two subsequent cycles. K increases in hydrogels with the highest HA content, when samples undergo pulse-echo measurements soon after their preparation. When hydrogels reach equilibrium, after having been kept in deionized water for 12 h, K values are lower, showing a nearly constant behaviour with different PVA-HA ratios and cycles. Furthermore, by means of scanning laser acoustic microscopy (SLAM) defects have been detected in the hydrogels. In samples which have reached equilibrium, SLAM images show that these defects disappear in PVA-HA hydrogels.

Journal Article↗

PubMed1995

Neuroangiographic assessment of aneurysm stability and impending rupture based on a non-linear biomathematical model.

The probability or risk of aneurysm rupture is assessed using conventional angiography by applying the aneurysm radius and systolic blood pressure obtained at examination to a non-linear biomathematical model of an aneurysm. A non-linear biomathematical model was developed based on Laplace's law to represent the viscoelastic relation between the wall tension and the radius. A differential expression of this relation was used to derive the critical radius: Rc = [2Et/P]2At/P where E is the elastic modulus of the aneurysm, t is the wall thickness, P is the pressure, and A is the elastic modulus of collagen. Using average values of E, A, and t, the risk of aneurysm rupture is defined as the area of integration under the curve defined by the minimum value of pressure (50 mmHg) and the patient pressure recorded at examination. This area was normalized by the area of integration defined by the pressure limits: 50 to 300 mmHg. This method of risk assessment was applied to four previously published case studies of patients with documented aneurysm rupture in which both the aneurysm size at rupture and the patient systolic blood pressure were reported. Two additional parameters were calculated to further evaluate aneurysm stability: (1) a ratio given as (Rexp/Rth) where Rexp is the radius of aneurysm rupture measured from angiography and Rth is the critical radius based on the model; and (2) chi 2 analysis defined by chi 2 = (O - E)2/E where O and E are the observed (Rexp) and expected (Rth) variables, respectively. The average systolic blood pressure and radius of aneurysm rupture was 147.2 mmHg and 3.95 mm, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aneurysm, Ruptured↗

PubMed2004

[Effects of post material on stress distribution in dentine].

OBJECTIVE: To investigate stress distribution of different material restored post-cores in dentine and provide a theoretical guidance for clinical use. METHODS: A three-dimensional finite element model of maxillary central incisor restored with post-core and PFM crown was constructed by SCT scan technology. Based on this model, stress distribution in dentine was analyzed before and after post-core restorations with 6 different materials, including cast Ni-Cr alloy, cast titanium alloy, cast gold alloy, glass fiber reinforced composite, polythene fiber reinforced composite, and common composite resin. RESULTS: When the tooth was restored with cast Ni-Cr alloy post and PFM crown, the maximum tensile stress and Von Mises stress in dentin at post apex increased 152% and 162% respectively, compared with a tooth restored only with PFM crown. If polythene fiber reinforced composite was used as post material, the stress distribution did not significantly change. When the other materials were used for the post, the stress distribution changed greatly. The elastic modulus of post-core materials affected the stress distribution pattern in dentine. CONCLUSION: The materials with elastic modulus similar to that of dentin, such as polythene fiber reinforced composite, may be suitable for post restoration.

Chromium Alloys↗

PubMed1978

Mucus rheology and mucociliary clearance: Normal physiologic state.

Tracheal mucociliary clearance studies, mucus collections, and rheologic studies were performed on a weekly basis in 7 adult purebred beagles in an attempt to correlate clearance rate with rheology of mucus. Clearance rates were determined by a percutaneous transtracheal, radioisotope injection technique. Mucus was collected from dogs equipped with a tracheal pouch, and rheologic determinations were performed on a dynamic microrheometer. Individual analysis of data for each dog failed to reveal any significant relationship between clearance rate and any parameter of elasticity or viscosity. However, when data from all 7 dogs were pooled, covering a much wider range of the measured variables, it was seen that as the elastic modulus increased, the rate of clearance decreased. The mucociliary clearance rate was halved by an approximate ten-fold increase in elastic modulus of mucus.

Animals↗

PubMed1997

Regional vascular mechanical properties by 3-D intravascular ultrasound with finite-element analysis.

A method employing intravascular ultrasound (IVUS) and simultaneous hemodynamic measurements, with resultant finite element analysis (FEA) of accurate three-dimensional IVUS reconstructions (3-DR), was developed to estimate the regional distribution of arterial elasticity. Human peripheral arterial specimens (iliac and femoral, n = 7) were collected postmortem and perfused at three static transmural pressures: 80, 120, and 160 mmHg. At each pressure, IVUS data were collected at 2.0-mm increments through a 20.0-mm segment and used to create an accurate 3-DR. Mechanical properties were determined over normotensive and hypertensive ranges. An FEA and optimization procedure was implemented in which the elemental elastic modulus was scaled to minimize the displacement error between the computer-predicted and actual deformations. The "optimized" elastic modulus (Eopt) represents an estimate of the component element material stiffness. A dimensionless variable (beta), quantifying structural stiffness, was computed. Eopt of nodiseased tissue regions (n = 80) was greater than atherosclerotic regions (n = 88) for both normotensive (Norm) and hypertensive (Hyp) pressurization: Norm, 9.3 +/- 0.98 vs. 3.5 +/- 0.30; Hyp, 11.3 +/- 0.72 vs. 8.5 +/- 0.47, respectively (mean +/- SE x 10(6) dyn/cm2; P < 0.01 vs. nondiseased). No differences in beta between nondiseased and atherosclerotic tissue were noted at Norm pressurization. With Hyp pressurization, beta of atherosclerotic regions were greater than nondiseased regions: 21.5 +/- 2.21 vs. 14.0 +/- 2.11, respectively (P < 0.03). This method provides a means to identify regional in vivo variations in mechanical properties of arterial tissue.

Arteriosclerosis↗

PubMed1994

Aortic walls in atherosclerotic rabbits--mechanical study.

Mechanical properties of the descending thoracic aortae harvested from endothelial cell-denuded and/or cholesterol diet-fed rabbits were studied primarily with their pressure-diameter relationships. Male Japanese white rabbits having 3.1 to 3.5 kg initial body weight were divided into 4 groups. The rabbits in Groups A and C were fed a regular chow, while those in Groups B and D were given 1 percent cholesterol diet; the luminal surfaces of the descending thoracic aortae in the rabbits of Groups C and D were injured by drawing catheter-tip balloons. These animals were sacrificed after keeping for 4, 8, 16 or 32 weeks and, then, their descending thoracic aortae were excised for the studies of pressure-diameter relationships. Stiffness parameter (beta") and incremental elastic modulus (H theta theta were used to quantitatively represent the structural stiffness of the aortic wall and the elastic modulus of the wall material, respectively. Denudation of endothelial cells thickened the aortic walls in Group C, but induced no significant changes in beta" and H theta theta. Shape of the pressure-diameter curve changed gradually with time in Group D, and beta", H theta theta, and thickness to wall radius ratio increased significantly, while those in Group B showed no significant changes with a few exceptions. Averaged percent fraction of the luminal surface area stained with Sudan IV (As) was around 50 percent in Group B and 100 percent in Group D at 32 weeks. Even if As is over 80 percent in Group D, 50 percent (7/14) of the walls gave significantly higher beta"- and H theta theta-values at 100 mm Hg than the others. Significantly increased calcification and intimal hyperplasia were observed in the walls with high beta"- and H theta theta-values.

Animals↗

PubMed2002

Material properties of interstitial lamellae reflect local strain environments.

The objective of this study was to determine if the material properties of bone at the lamellar level are related to the predominant mode and magnitude of mechanical strain experienced in situ. The tibia and first metatarsal bones of five unpaired cadaveric lower extremities were instrumented with strain gauge rosettes and subjected to repeated loading trials in an apparatus that replicates the muscle forces and external loads experienced by the foot and shank while walking. The spatial distributions of axial strain within diaphyseal cross-sections taken from each bone were subsequently determined. Nanoindentation measurements were then performed on the same cross-sections to determine the compressive elastic moduli of individual lamellae located within osteonal, interstitial, and outer circumferential microstructures. Twenty percent of the variance in interstitial elastic modulus within cross-sections of diaphyseal bone was explained by local strain magnitude. Lamellae residing in regions of compressive strain displayed significantly higher compressive elastic modulus values than those located in predominantly tensile regions (19.9 +/- 1.6 GPa compared to 17.9 +/- 1.7 GPa, p < 0.05). Elastic moduli of interstitial lamellae were 11% greater than those of osteonal or outer circumferential lamellae, irrespective of strain or anatomical location (p < 0.001). Differences exist in the material properties of individual bone lamellae located within different anatomical regions and different microstructures, and these differences are related to the distribution of axial strain. These findings suggest that mechanical strain, or another closely related variable, may influence the design and ultimate mechanical behavior of the extra-cellular matrix found in lamellar bone. This tissue heterogeneity is of potential importance in bone fragility and adaptation.

Aged↗

PubMed2004

Shear modulus of elasticity of the esophagus.

Experimental and diagnostic procedures like distension of a balloon catheter, bougie, and esophagogastroduodenoscopy can induce shear deformation in the esophageal wall. However, the shear modulus of the esophagus is yet unknown. The aim of this study was to determine the esophageal shear modulus and its dependence on the circumferential and longitudinal stresses and strains in the rat. The constitutive equation including the shear deformation based on a pseudo-strain-energy function was generated. Results were obtained using a new triaxial instrument to perform simultaneous torsion, inflation, and longitudinal stretching tests. The shear modulus varied with the inflation pressure and the longitudinal stretch ratio. The shear modulus at the longitudinal stretch ratio of 1.5 and between inflation pressures of 0 and 2.0 kPa ranged from 5.43 to 185.01 kPa. The mechanical constant of the esophagus showed that the esophageal wall was anisotropic with different stiffness in the circumferential, longitudinal, and the shear directions. The stiffness in the longitudinal direction was higher than in the circumferential direction (P < 0.001). This test can be extended for further mechanical remodeling experiments and for other tubular organs such as the small intestine or blood vessels.

Animals↗

PubMed2003

Hydroxyapatite whiskers provide improved mechanical properties in reinforced polymer composites.

Synthetic hydroxyapatite (HA) whiskers have been utilized as a new, biocompatible reinforcement for orthopedic biomaterials. High-density polyethylene (HDPE) was reinforced with either the synthesized HA whiskers or a commercially available spherical HA powder using a novel powder processing technique that facilitated uniform dispersion of the reinforcements in the matrix prior to compression molding. Composites were processed for up to 60 vol % HA whiskers and up to 50 vol % spherical HA. The mechanical properties of the new composite biomaterials were examined by uniaxial tensile tests. As expected, increased volume fraction of either reinforcement type over 0-50 vol % resulted in increased elastic modulus, a maximum in ultimate tensile stress, and decreased work to failure. Composites reinforced with HA whiskers had higher elastic modulus, ultimate tensile strength, and work to failure relative to composites reinforced with spherical HA. Thus, HA whisker-reinforced HDPE composites possessed improved mechanical properties over those reinforced with spherical HA. HA whisker-reinforced composites were anisotropic due to alignment of the whiskers in the matrix during processing.

Biocompatible Materials↗

PubMed2003

Acousto-optical characterization of the viscoelastic nature of a nuchal elastin tissue scaffold.

A nondestructive, acousto-optical method for characterizing the mechanical loss factor of biological tissues and tissue scaffolds is presented and applied to the characterization of an elastin tissue scaffold derived from bovine nuchal ligament. The method relies on launching guided surface acoustic waves into the tissue scaffold with a small speaker and simultaneously illuminating a small region of the scaffold distant from the speaker with a low-power HeNe laser. The phase lag between the driving acoustic wave and the shift in the backscattered laser speckle pattern is determined as a measure of the mechanical loss factor of the scaffold, tan delta. Measurements of tan delta and elastic modulus were also made by traditional dynamic mechanical loading techniques. Through the central portion of the loading cycle, the elastic modulus of the elastin scaffold was 1.2 x 10(6) +/- 1 x 10(5) N x m(-2) (parallel to fiber orientation). The estimated value of tan delta in the direction parallel to the elastin fibers was 0.03 +/- 0.017 by traditional methods and 0.029 +/- 0.03 when using the acousto-optical method. In the direction perpendicular to fiber orientation, tan delta was measured as 0.14 +/- 0.056 by the acousto-optical method. Because of a lack of mechanical integrity, it was not possible to measure tan delta in the direction perpendicular to fiber orientation by traditional methods. The acousto-optical method may prove to be useful in the mechanical characterization of developing engineered tissues.

Acoustics↗

PubMed1991

Biomechanical study of the bile duct system outside the liver.

Diseases of the bile duct system in the digestive system after surgery are common. In order to clarify the cause of these diseases, research on the diseases from a biomechanical perspective is increasing; however, the same cannot be said of biochemical research. In this paper, by using a new, well-devised testing apparatus, specimens extracted from the bile duct system of canine body are tested. The test data are analyzed using the finite deformation theory, and mechanical properties of the bile duct system outside the liver are investigated. The conclusions show that the viscoelasticity of the bile duct system is very small. In its normal physiological condition, the bile duct wall has an almost uniform distribution of circumferential and longitudinal stress. However, when the diseases of the bile duct system cause high pressure at the bile duct, the circumferential stress and longitudinal stress at the bile inside wall suddenly increase and are much larger than those stresses at the outside wall. The elastic modulus gradually becomes small from the common bile duct and the common hepatic duct to hepatic duct, and the value of elastic modulus for the cystic duct is almost equal to that of the hepatic duct.

Algorithms↗

PubMed1999

Elasticity and fracture strain of whole blood clots.

The measurement of clot elasticity and fracture strain is carried out using a rotational rheometer with a controlled stress system. The elasticity is quantified by a shear elastic modulus and fracture strain by a critical strain (deformation) when the clot begins to break up. The results indicate a decrease of elasticity and increase of fracture strain of the clot with increasing hematocrit. Moreover, the elastic modulus of the clot is not constant but increasing with deformation.

Blood Coagulation↗

PubMed2002

Contribution of the nucleus to the mechanical properties of endothelial cells.

The cell nucleus plays a central role in the response of the endothelium to mechanical forces, possibly by deforming during cellular adaptation. The goal of this work was to precisely quantify the mechanical properties of the nucleus. Individual endothelial cells were subjected to compression between glass microplates. This technique allows measurement of the uniaxial force applied to the cell and the resulting deformation. Measurements were made on round and spread cells to rule out the influence of cell morphology on the nucleus mechanical properties. Tests were also carried out with nuclei isolated from cell cultures by a chemical treatment. The non-linear force-deformation curves indicate that round cells deform at lower forces than spread cells and nuclei. Finite-element models were also built with geometries adapted to actual morphometric measurements of round cells, spread cells and isolated nuclei. The nucleus and the cytoplasm were modeled as separate homogeneous hyperelastic materials. The models simulate the compression and yield the force-deformation curve for a given set of elastic moduli. These parameters are varied to obtain a best fit between the theoretical and experimental data. The elastic modulus of the cytoplasm is found to be on the order of 500N/m(2) for spread and round cells. The elastic modulus of the endothelial nucleus is on the order of 5000N/m(2) for nuclei in the cell and on the order of 8000N/m(2) for isolated nuclei. These results represent an unambiguous measurement of the nucleus mechanical properties and will be important in understanding how cells perceive mechanical forces and respond to them.

Animals↗

PubMed2000

Influence of mechanical behavior on the wear of 4 clinically relevant polymeric biomaterials in a hip simulator.

The elastic and large-deformation mechanical behavior of 4 materials with known clinical performance was examined and correlated with the wear behavior in a hip simulator. Acetabular liners of a commercially available design were machined from ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polytetrafluoroethylene (PTFE), and polyacetal and wear tested in a multidirectional hip joint simulator. Elastic and large-deformation mechanical behavior was directly measured from the wear-tested liners using the small punch test. The finite element method was used to compute elastic modulus from the measured small punch test initial stiffness, and the contact stress for the liners was calculated using the theory of elasticity solution. Positive, statistically significant correlations were observed between the hip simulator wear rate and the initial peak load, ultimate load, and work to failure from the small punch test. Negative correlations were observed between the wear rate and the elastic modulus and contact stress. The results of this study support the hypothesis that the large-deformation mechanical behavior of a polymer plays a greater role in the wear mechanisms prevalent in total hip replacements than the elastic behavior.

Biocompatible Materials↗

PubMed1995

Additional heat-curing of light-cured composite resin for inlay restoration.

The purpose of this study was to evaluate the effect of heat application after light curing on some physical properties of composite resin for dental inlay. Specimens each were additionally dry heat-cured at various temperatures for 15 min after initial light curing, and other specimens were not heat-cured as a control. Fracture toughness, bending strength, bending elastic modulus, coefficient of thermal expansion, hygroscopic expansion, microhardness, water absorption and solubility were determined. Fracture toughness, bending strength and bending elastic modulus were significantly higher when heated at 80-120 degrees C than the control. The coefficient of thermal expansion, hygroscopic expansion, microhardness and solubility were significantly improved than those of the control when heated, while water absorption was not significantly altered by dry heat-curing. These results indicate that the physical properties of composite resin, except water absorption, were improved significantly when heated after initial cure.

Absorption↗