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Results for “Elastic Modulus”

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PubMed1980

The effect of smooth muscle activation on the mechanical properties of pig carotid arteries.

The contractile properties and the effect of contraction on the mechanical properties of noradrenaline (0.5 micrograms/ml) activated smooth muscle of cylindrical segments of porcine carotid arteries were studied in vitro under quasi-static pressure loading. Maximum tangential isometric stress developing in the vessel wall was 4.4 +/- 0.6 X 10(5) dyn/cm2. Incremental elastic modules of activated smooth muscle, calculated for total wall cross sectional area, was 4.6 +/- 2.7 X 10(6) dyn/cm2, whereas the value computed for estimated smooth muscle thickness was 9.8 +/- 14.8 X 10(6) dyn/cm2. During smooth muscle activation maximum increase of strain-energy density of the vessel wall was 6.8 +/- 1.2 X 10(4) dyn/cm2 under isometric conditions and 25 +/- 3% increase occurred under isobaric conditions. Isobaric diameter response was only 2--4% in the physiological pressure range (100--150 mmHg) while the incremental elastic modulus decreased by 40 +/- 3% and distensibility increased by 80 +/- 10% under isobaric conditions. Smooth muscle activation induced a 19 +/- 2% maximum decrease of characteristic impedance, and a rather a uniform 14--15% decrease in the impedance was observed in the 100--150 mmHg pressure range. The obtained results show that the control of distensibility and elastic modulus in smooth muscle is most efficient in the physiological pressure range under in vitro conditions. It is assumed that in vivo in addition to vascular diameter the most important controlled parameters are the distensibility and characteristic impedance of the large arteries.

Animals↗

PubMed2007

Effects of wall calcifications in patient-specific wall stress analyses of abdominal aortic aneurysms.

It is generally acknowledged that rupture of an abdominal aortic aneurysm (AAA) occurs when the stress acting on the wall over the cardiac cycle exceeds the strength of the wall. Peak wall stress computations appear to give a more accurate rupture risk assessment than AAA diameter, which is currently used for a diagnosis. Despite the numerous studies utilizing patient-specific wall stress modeling of AAAs, none investigated the effect of wall calcifications on wall stress. The objective of this study was to evaluate the influence of calcifications on patient-specific finite element stress computations. In addition, we assessed whether the effect of calcifications could be predicted directly from the CT-scans by relating the effect to the amount of calcification present in the AAA wall. For 6 AAAs, the location and extent of calcification was identified from CT-scans. A finite element model was created for each AAA and the areas of calcification were defined node-wise in the mesh of the model. Comparisons are made between maximum principal stress distributions, computed without calcifications and with calcifications with varying material properties. Peak stresses are determined from the stress results and related to a calcification index (CI), a quantification of the amount of calcification in the AAA wall. At calcification sites, local stresses increased, leading to a peak stress increase of 22% in the most severe case. Our results displayed a weak correlation between the CI and the increase in peak stress. Additionally, the results showed a marked influence of the calcification elastic modulus on computed stresses. Inclusion of calcifications in finite element analysis of AAAs resulted in a marked alteration of the stress distributions and should therefore be included in rupture risk assessment. The results also suggest that the location and shape of the calcified regions--not only the relative amount--are considerations that influence the effect on AAA wall stress. The dependency of the effect of the wall stress on the calcification elastic modulus points out the importance of determination of the material properties of calcified AAA wall.

Aorta, Abdominal↗

PubMed2002

Mechanical properties of light-cured composite resins cured through filters that simulate enamel.

The light-attenuating effects of enamel on the mechanical properties of light-cured composite resins were evaluated using simple experimental filters. Three filters were designed to simulate the light transmittance characteristics of 0.5, 1.0, and 1.5 mm thick human enamel. The Knoop hardness numbers (KHN) and the elastic modulus in transverse tests for twelve shades of three light-cured composite resins were examined. These resins were cured either using direct irradiation with a light source, or indirect irradiation through one of the filters. The attenuations of light by 0.5, 1.0, and 1.5 mm thick enamel filter were 45%, 67% and 81% in the 430 nm-550 nm wavelength region, respectively. For all materials, KHN and the elastic modulus of specimens irradiated through filters were significantly lower than those irradiated directly. The results suggest that the light-attenuating effect of enamel reduces the mechanical properties of light-cured resin, and may cause poor clinical longevity of restorations.

Algorithms↗

PubMed2001

Influence of adsorbed plasma proteins on erythrocyte rheological properties: in vitro and ex vivo studies.

The influence of plasma protein adsorption on the mechanical properties characterizing erythrocyte behaviour under flow was studied in human and rats. The deformability index, elastic modulus and surface viscosity were measured by laser diffractometry. In in vitro studies, human and rat erythrocytes were washed to remove their original protein coating, and then incubated in saline-diluted plasma media. For erythrocytes incubated in the most diluted solutions (plasma/saline 1:3, v/v), the deformability index increased 30% for both species (human, P<0.01 and rat, P<0.2); the elastic modulus decreased 20% (human, P<0.05) and 60% (rat, P<0.01); and surface viscosity decreased 20% (human, P<0.05) and 40% (rat, P<0.01), relative to values for erythrocytes incubated in pure plasma. Ex vivo experiments were performed using rats. Plasma proteins were diluted replacing 15% volemic plasma by saline in three consecutive plasmapheresis steps. The rheological properties of erythrocytes, tested after each step, followed the general trends of the in vitro pattern. These results suggest that the decrease in plasma protein concentration affects blood rheology in two ways. The first is the well known decrease in plasma viscosity, and the second is an improvement of erythrocyte deformability, as has been shown in this work. Thus, a new argument supporting the benefits of normovolemic hemodilution in patients with poor peripheral perfusion is provided.

Adsorption↗

PubMed1977

Right and left ventricular compliance in the hereditary cardiomyopathy of the Syrian hamster.

Ventricular pressure-volume curves were examined in 10 pre-oedematous cardiomyopathic Syrian hamsters, aged 120 d, and 10 oedematous cardiomyopathic hamsters, aged 210 d, and compared with 10 and 8 age-matched controls, respectively. Previous studies had shown filling pressures and cardiac output to be normal in the pre-oedematous stage. In contrast, the oedematous stage was characterised by elevated filling pressures and increased cardiac output, raising the question whether this stage represents true myocardial failure or circulatory congestion associated with decreased ventricular compliance. Compliance, defined as dV/dP, was derived simulataneously for both ventricles from post-mortem pressure-volume curves from 0 to 2.66 kPa (0 to 20 mmHg). Left ventricular tissue elastic modulus, E, defined as dsigma/depsilon or the incremental stress (sigma) for an increment of strain (epsilon), was derived from the compliance curves and certain linear dimensions of the heart. At isobaric intervals, compliance did not differ between control and myopathic ventricles. At pressures corresponding to previously measured, naturally prevailing end-diastolic pressures, the myopathic ventricles were significantly dilated in both stages; end-diastolic compliance was normal in pre-oedematous hamsters, but was significantly decreased in the oedematous animals. Left ventricular elastic modulus was elevated at all values of sigma in both groups of myopathic animals.

Animals↗

PubMed2005

Evaluation of polydimethylsiloxane scaffolds with physiologically-relevant elastic moduli: interplay of substrate mechanics and surface chemistry effects on vascular smooth muscle cell response.

Polydimethylsiloxane (PDMS) is used extensively to study cell-substrate interactions because its mechanical properties are easily tuned in physiologically relevant ranges. However, changes in mechanical properties also modulate surface chemistry and cell response. Here, we correlate the mechanical and surface properties of PDMS to vascular smooth muscle cell (VSMC) behavior. We find that a 5-fold increase in base:crosslinker ratio leads to approximately 40-fold decrease in elastic modulus but no significant differences in surface wettability. However, when polyelectrolyte multilayers are adsorbed to promote cell adhesion, wettability varies inversely with substrate stiffness. Despite these differences in hydrophobicity, the amount of adsorbed protein remains the same. In the absence of serum, there is a 39% decrease in cell attachment and a 42% decrease in spreading as the elastic modulus decreases from 1.79 to 0.05 MPa. In the presence of serum or adsorbed fibronectin, the differences in attachment and spreading are diminished. This is not the case for the rate of serum-stimulated cell proliferation, which remains inversely dependent on crosslinker concentration. We conclude that for the range of crosslinker concentrations investigated, the surface properties dominate the initial cell attachment and spreading, whereas the mechanical properties influence the long-term cell growth.

Adsorption↗

PubMed2004

Polymerization and gelation of whey protein isolates at low pH using transglutaminase enzyme.

Dynamic and steady shear rheology is used to examine the synthesis of low-pH (approximately 4) whey protein gels obtained through a two-step process. The first step involves cross-linking of whey proteins at pH 8 and 50 degrees C using transglutaminase enzyme, while the second step entails cold-set acidification of the resulting solution using glucono-delta-lactone (GDL) acid. During the first step, the sample undergoes enzyme-catalyzed epsilon-(gamma-glutamyl)lysine bond formation with a substantial increase in viscosity. Acidification in the second step using GDL acid leads to a rapid decrease in pH with a concomitant increase in the elastic (G') and viscous (G' ') moduli and formation of a gelled network. We examine the large strain behavior of the gel samples using a relatively new approach that entails plotting the product of elastic modulus and strain (G'gamma) as a function of increasing dynamic strain and looking for a maximum, which corresponds to the yield or fracture point. We find the enzyme-catalyzed gels to have significantly higher yield/fracture stress and strain compared to cold-set gels prepared without enzyme or conventional heat-set gels. In addition, the elastic modulus of the enzyme-catalyzed gel is also higher than its non-enzyme-treated counterpart. These results are discussed in terms of the gel microstructure and the role played by the enzyme-induced cross-links.

Cold Temperature↗

PubMedDate not supplied

Mechanical properties of trabecular bone from the proximal femur: a quantitative CT study.

We have investigated the relationships between trabecular bone compressive strength and elastic modulus and the directly measured apparent density and noninvasively measured CT equivalent mineral density for 49 cylindrical specimens harvested from fresh human proximal femora. Compressive strength demonstrated a high positive correlation with both densities, being proportional to the apparent density raised to the 1.8 power (R2 = 0.93) and equivalent mineral density to the 1.5 power (R2 = 0.89). Similarly, the compressive modulus demonstrated a high correlation with both density measures, being proportional to the apparent density raised to the 1.4 power (R2 = 0.91) and CT equivalent mineral density to the 1.2 power (R2 = 0.90). Though variations in architecture and bone marrow fat were observed to influence trabecular properties, the data presented here demonstrate that apparent density, compressive strength, and elastic modulus can be determined accurately using single energy quantitative CT. We expect that the use of these noninvasive data will result in improved estimates of that component of hip fracture risk that is attributable to bone strength.

Biomechanical Phenomena↗

PubMedDate not supplied

Quantitative ultrasound pulsation study in human carotid artery disease.

Pulsation in the human carotid artery during two complete cardiac cycles was studied by using computer digitized video-frames from B-mode ultrasound images. Eight patients with identifiable atherosclerotic lesions in the common carotid immediately proximal to the bulb area were studied. Diameter, strain, and elastic modulus were compared between lesion site and an adjacent reference segment 1 or 2 cm proximal to the bulb. As controls, nine patients without identifiable lesions were analyzed. The results indicate a significantly wider diameter (p less than 0.01) at the proximal reference site in patients with lesions as compared to comparable segments in control patients. The strain was significantly lower (p less than 0.05), whereas the elastic modulus was significantly higher (p less than 0.05), at the lesion site as compared to the proximal reference sites in patients with lesions. These results may indicate that an initial dilation of the carotid artery followed by loss of wall flexibility may be associated with atherosclerotic lesion formation.

Blood Flow Velocity↗

PubMed1994

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy.

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Acrylic Resins↗

PubMed2002

Influence of plasticizer type and coat level on Surelease film properties.

Two commercially available formulations of aqueous ethylcellulose dispersion differing in their plasticizer, i.e., Surelease/E-7-7050 containing dibutyl sebacate (DBS) and Surelease/E-7-7060 containing glyceryl tricaprylate/caprate (GTC), were evaluated and compared for their film properties as a function of polymeric coat level. Ibuprofen tablets were coated at 1, 2, 3, and 5% w/w levels using each Surelease formulation, and the coated tablets were evaluated for their drug release characteristics, coat reflectivity (gloss), surface texture, Brinell hardness, and elastic modulus. The drug release was dependent on the coat level and followed Hixson-Crowell cube-root model at 1% coat level. However, at > or = 2% coat levels, the release from tablets coated with GTC plasticized formulation appeared to be best described by non-Fickian release mechanism and that from tablets coated with DBS plasticized formulation appeared to follow apparent zero-order release mechanism. At equal coat levels, tablets coated with GTC plasticized Surelease yielded lower drug release rates, higher reflectivity (gloss), lower surface roughness, higher Brinell hardness, and lower elastic modulus than those coated with DBS plasticized formulation. A good correlation was observed between the drug release rates and the reflectivity and surface texture of the coated tablets. The film-coats of GTC plasticized formulation were harder and more elastic than those of DBS plasticized formulation indicating better mechanical integrity.

Cellulose↗

PubMed2004

Preclinical changes in the mechanical properties of abdominal aorta in obese children.

Obesity in childhood has been associated with the development of early cardiovascular abnormalities. The aim of the present study was to investigate whether preclinical functional changes are detectable in the abdominal aorta of obese children. One hundred consecutively seen obese children and 50 healthy controls were studied. The groups were matched in terms of age and gender. The pulsatile wall-motion of the abdominal aorta was determined using a B-mode ultrasound technique. The following mechanical property parameters were measured or computed: lumen diastolic and systolic diameters, relative aortic strain, elastic modulus, and stiffness. Compared to controls, obese children had higher blood pressure values and higher concentrations of total cholesterol, triglycerides, insulin, and C-reactive protein. Homeostasis model assessment (HOMA) score, a parameter of insulin resistance, was significantly higher in obese children than in controls (3.2 +/- 1.9 v 1.4 +/- 0.5, P <.001). Aortic mechanical parameters were significantly different in obese children as compared to controls: stiffness was higher (3.00 +/- 1.45 v 2.22 +/- 0.87, P <.001) as was elastic modulus (0.38 +/- 0.18 v 0.24 +/- 0.10 N/m(2), P <.001). Obese girls with insulin resistance (ie, in the highest tertile of HOMA, >3.7) had increased aortic stiffness (3.79 +/- 2.25) compared to obese girls in the lowest tertiles of HOMA (2.67 +/- 1.09, P =.045), even after adjustment for traditional cardiovascular risk factors (P =.031). The present findings suggest that preclinical changes in the aortic elastic properties are detectable in obese children. Insulin resistance seems to play an important role in the increased rigidity of the aortic wall in obese girls.

Aorta, Abdominal↗

PubMed1999

Effects of drying on the mechanical properties of bovine femur measured by nanoindentation.

Effects of drying on the measurement of mechanical properties of bone by nanoindentation methods have been examined. Tests were conducted to measure the elastic modulus and hardness of two cross-sectional cortical specimens obtained from adjacent areas of bovine femur. One specimen was thoroughly dried in air prior to testing while the other was stored in deionized water. The properties of osteons and interstitial lamellae showed statistically significant differences (p<0.0001) and were therefore investigated separately. Drying was found to increase the elastic modulus by 9.7% for interstitial lamellae and 15.4% for osteons. The hardness was also found to increase by 12.2% for interstitial lamellae and 17.6% for osteons.

Journal Article↗

PubMed1989

Analysis of the bending behaviour of porcine xenograft leaflets and of natural aortic valve material: bending stiffness, neutral axis and shear measurements.

Flexibility of the materials used in the construction of bioprosthetic heart valves is essential for proper valve operation. We therefore examined the bending behaviour of glutaraldehyde treated porcine aortic valve cusps in comparison with fresh aortic valve tissue. We repeatedly bent a total of 35 strips of fresh and treated tissue to curvatures ranging from 0.2 to 2.2 mm-1. We compared the stiffness of the two materials between circumferential and radial bending, natural and reverse curvatures and constant or variable tensile stress (0.8-40 kPa). Our results showed a weak positive relationship between bending stiffness and applied tensile stress and a strong positive dependance of stiffness on tissue thickness (t). For the fresh tissue, the bending stiffness increased in proportion to t1.14 while for the glutaraldehyde treated tissue it increased with t2.18. Fourteen strips of fresh and treated tissue were also histologically processed, sectioned and examined with polarized light microscopy. Collagen fiber wavelengths and shear deformations were measured utilizing the tissue banding patterns produced by polarized light microscopy. The neutral axis of bending was found to lie very close to the outer surface of the tissue, suggesting that aortic leaflets have a very low compressive elastic modulus. The shear strains measured in fresh tissue were 10 +/- 2.7% vs 3 +/- 4.4% for the treated, indicating a stiffening of the tissue following glutaraldehyde fixation. We conclude that both natural and bioprosthetic valve cusps have a complex flexural behaviour that cannot be modeled using simple bending principles, although the bioprosthetic material more closely approximates the simple beam than does the fresh. The non-linear elastic modulus, high compressibility and shearing between fiber layers are likely responsible for the observed behaviour of the fresh tissue, while the cross-linking and dehydrating effects of glutaraldehyde are believed to be responsible for the alteration in bending properties observed in the treated tissue. Our study suggests that bioprosthetic valve material does not adequately mimic the mechanics of the natural valve tissue, and that the current glutaraldehyde fixation process eliminates many of the beneficial, stress-reducing properties of the aortic leaflet.

Animals↗

PubMed1989

Abnormal structure and increased stiffness of the femoral arterial wall in young patients with sustained essential hypertension.

Thickness, elastic modulus, and stiffness of the common femoral arterial wall were estimated in 11 patients with essential hypertension and in 11 age-matched normotensive control subjects by use of an in vivo, non-invasive, ultrasound time-motion display technique (M-mode). Hypertensive patients had significantly higher levels than normotensive subjects with regard to arterial wall thickness (0.23 cm vs. 0.18 cm, medians; P less than 0.01), elastic modulus (10.6 x 10(7) Pa vs. 6.18 x 10(7) Pa, medians; P less than 0.05) and arterial wall stiffness (3.80 x 10(7) Pa vs. 2.07 +/- 10(7) Pa, medians; P less than 0.01). It is concluded that structural changes in the wall of the large arteries contribute to the increase in arterial wall stiffness in young patients with sustained essential hypertension.

Adult↗

PubMed1990

[Visible light cured resin. Chronological change in mechanical properties of matrix resin immersed in MeOH].

Monomer composition was examined to improve durability of matrix resin of visible light cured composite resin. As a monomer, five kinds of cyclophosphazene monomers, two kinds of commercial monomers and a mixture of commercial monomers were prepared to the visible light cured resins. The mechanical properties of these set products were examined with time after immersion in MeOH, an aging accelerating solvent. Compressive strength of the resins using cyclophosphazene monomers tended to decrease with time, but it increased in accordance with the increase of the number of polymerization group. Compressive strength of the resins using commercial monomers tended to decrease, but that using the BMPEPP monomer tended to increase with time. Yield point of the resins with the cyclophosphazene monomer 4 PN-(EMA)8 tended to increase with the time but that of the resins with other cases monomers decreased. The yield point of all three resins made using commercial monomers tended to decrease with time, but the rate of decrease was small for BMPEPP monomer. Compressive elastic modulus of the resins using cyclophosphazene monomers tended to increase with time when the number of polymerization group was 6-8, while it decreased when the number was 4-5. When commercial monomers were used, it tended to decrease with time, but the rate of decrease was small for the BMPEPP monomer. Transverse strength of the resins using cyclophosphazene monomers showed a tendency to decrease with time. When a commercial monomer was used, cracks appeared in the Bis-GMA+Tri-EDMA monomer after 7 days, and with the other two monomers, the transverse strength tended to decrease with time, though the rate of decrease was small for the BMPEPP monomer. Transverse elastic modulus tended to decrease with time, but the rate of decrease was small for the BMPEPP monomer.

Composite Resins↗

PubMed1982

Correlation between strength of bonding to enamel and mechanical properties of dental composites.

The strength of bonding of dental composites to enamel was measured in shear. The compressive strength, proportional limit, elastic modulus, and tensile strength of the composites were measured for correlation with the bond strength. Conventional and microfilled composites with a range of filler concentrations were studied. The densities of the composites and their fillers and the concentrations of the fillers were determined. The mechanical properties that were most highly correlated with bond strength to enamel were proportional limit and elastic modulus. Tensile strength and filler concentration had lower correlation coefficients, and compressive strength was not correlated with bond strength. Using unfilled resins as bonding agents between the composites and enamel resulted in increased bond strength with half of the composites.

Composite Resins↗

PubMed2001

A biophysical analysis of stem and root diameter variations in woody plants.

A comprehensive model of stem and root diameter variation was developed. The stem (or root) was represented using two coaxial cylinders corresponding with the mature xylem and the extensible tissues. The extensible tissues were assumed to behave as a single cell separated from the mature xylem by a virtual membrane. The mature xylem and the extensible tissues are able to dilate with temperature and grow. Moreover, the extensible tissues are able to shrink and swell according to water flow intensity. The model is mainly based on the calculation of water volume flows in the "single cell" that are described using the principles of irreversible thermodynamics. The elastic response to storage volume and plastic extension accompanying growth are described. The model simulates diameter variation due to temperature, solute accumulation, and xylem, water potential. The model was applied to the peach (Prunus persica) stem and to the plum (Prunus domestica x Prunus spinosa) root. The simulation outputs corresponded well with the diameter variation observed. The model predicts that variations of turgor pressure and osmotic potential are smaller than the variations of xylem water potential. It also demonstrates correlations between the xylem water potential, the turgor pressure, the elastic modulus, and the osmotic potential. The relationship between the diameter and the xylem water potential exhibits a substantial hysteresis, as observed in field data. A sensitivity analysis using the model parameters showed that growth and shrinkage were highly sensitive to the initial values of the turgor pressure and to the reflection coefficient of solutes. Shrinkage and growth were sensitive to elastic modulus and wall-yielding threshold pressure, respectively. The model was not sensitive to changes in temperature.

Biophysical Phenomena↗