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Results for “Elastic Modulus”

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PubMed1983

Left ventricular pressure-volume relations shift to the left after long-term loss of pericardial restraint.

The short-term effect of pericardiectomy is to shift the in vivo left ventricular (LV) pressure-volume curve to the right. We studied nine weight-matched pairs of male guinea pigs 28 to 39 days (mean 35) after complete pericardiectomy or sham thoracotomy to determine the long-term effects of pericardiectomy on LV pressure-volume relations. Hemodynamic and in vitro LV pressure-volume data were collected in matched pairs on the same day, 2 to 3 hr after catheter placement and recovery from anesthesia. Cardiac output was measured by the microsphere reference sample method. Postsurgical weight gain was similar in both groups: 823 +/- 6 (mean +/- SD) to 925 +/- 6 g in the pericardiectomy group and 829 +/- 7 to 927 +/- 7 g in the sham thoracotomy group. We found no difference in LV weight: 1.555 +/- 0.145 g in the pericardiectomy group vs 1.564 +/- 0.148 g in the sham thoracotomy group, nor any difference in heart rate, mean arterial, right atrial, or left ventricular end-diastolic pressures, cardiac outputs, or stroke volumes (p = NS). LV pressure-volume relations, however, were shifted to the left in the pericardiectomy group (p less than .005). At 10 mm Hg, LV volume in the pericardiectomy group (0.85 +/- 0.22 cc) was less than that in the sham thoracotomy group (1.02 +/- 0.15 cc; p less than .025). The LV stress-elastic modulus relationship was not different between groups (p greater than .30). One month after pericardiectomy, LV pressure-volume relations in vitro were shifted to the left without a change in LV weight, LV elastic modulus, or hemodynamics. We speculate that this shift compensates for the lack of pericardial restraint and returns LV volume and hemodynamics to normal in vivo.

Animals↗

PubMed1989

[Relationship among the composition and the physical and chemical properties of photo-cured composites for crown and bridge].

In this study, the relationship among the chemical composition and the physical and chemical properties of four photo-cured composites and one heat curing composite for crown and bridge were investigated. Five composites were composed of the base monomer, UDMA, TriEGDMA, 1, 3-BDMA, 1, 4-BDMA, 1, 10-DDMA, 1, 12-DDDMA or those mixture, and the composite-filler consist of the resin (TMPTMA, UDMA, 1, 10-DDMA or 1, 12-DDDMA) and micro-silica particles. Four photo-curing composites had a high elastic modulus and Vickers hardness and a low thermal expansion coefficient and water sorption compared with the heat-cured composite (Is). The effects of filler contents in the composites examined were positively on the elastic modulus and the hardness, and were inversely on the bending strength and the thermal expansion coefficient of the cured products. While the organic phase in the composite fillers had effect on the abrasive resistance of the composites. But no significant correlation between the abrasive resistance and the filler contents and the physical properties of the materials tested was noted.

Composite Resins↗

PubMed2002

Stiff and strong compressive properties are associated with brittle post-yield behavior in equine compact bone material.

Our hypothesis was that post-yield mechanical behavior of compact bone material in compression, defined as the stress, strain, or energy absorbed between 0.2% strain-offset and the point of maximum stress, is correlated with material density, modulus, strength, histomorphometric evidence of remodeling, and post-failure gross specimen morphology. Post-yield behavior of compact bone material from the third metacarpal bone of 10 horses, ages 5 months to 20 years, was investigated using single-load compression-to-failure. The post-yield stress, strain, and absorbed energy were compared with the compressive elastic modulus, yield stress, ash density. post-failure macroscopic appearance of the specimen, and histologic evidence of remodeling. High values of elastic modulus, yield stress, and ash density were associated with low values of post-yield mechanical properties (stress, strain, and absorbed energy). Macroscopic post-failure morphology was associated with post-yield mechanical behavior, in that specimens displaying fractures were associated with lower post-yield mechanical properties, and that those without evidence of frank fracture were associated with higher post-yield mechanical properties. Microscopic evidence of remodeling activity was associated with high post-yield mechanical properties, but not with gross post-failure morphology. There was an abrupt change from relatively high values to extremely low values of post-yield mechanical properties at intermediate levels of ash density. This feature may serve as a functional tipper limit to the maximization of bone material stiffness and strength.

Animals↗

PubMed2005

Mechanical properties, proteolytic degradability and biological modifications affect angiogenic process extension into native and modified fibrin matrices in vitro.

During initial stages of wound healing, fibrin clots provide a three-dimensional scaffold that induces cell infiltration and regeneration. Here, L1Ig6, a ligand for alphavbeta3 integrin was covalently incorporated within fibrin matrices to explore it as a matrix-immobilized angiogenic factor. Incorporation at concentrations greater than 1 microg/ml reduced the fibrin crosslink density, as reflected by measurements of elastic modulus and swelling. The influence of crosslink density on endothelial cell process extension was characterized by modulating factor XIII concentrations in the coagulation mixture. At low incorporated concentrations of L1Ig6, it was possible to compensate gel elastic modulus via increased factor XIII, but not at high concentrations of L1Ig6. Similar findings were found when matrix swelling was analyzed. Fibrin crosslink density strongly influenced endothelial cell process extension, fewer and shorter processes were observed at high crosslink density. Matrix metalloproteinases (MMPs) were required for process extension and zymography and Western blots identified MMP-2 but not MMP-9. The amount of active MMP-2 increased for endothelial cells cultured in native and L1Ig6-modified matrices or when stimulated with VEGF-A165. The data indicate that distinct matrix properties can be tailored such that they become biologically stimulating and respond to cellular proteolytic activities, being a prerequisite for potential use of such matrices in biomedical applications.

Absorbable Implants↗

PubMed1991

Histological and biomechanical studies of hydroxylapatite implant.

Bony defects measuring 12x12x12 millimeters in size were created bilaterally over the proximal end of the femurs of 10 Macaca cyclopis monkeys and implanted with particulate hydroxylapatite. The animals were sacrificed according to a predetermined sequence of post-operative 1, 2, 3, 6, and 8 months. The specimens taken from the implant sites in the two femurs of each animal were chosen randomly either for histological observation or for compressive strength tests under vertical loads. Histological pictures showed only loose fibrous tissue over the interparticular space of the implant site at the first month after surgery. Woven bone could be observed over the basal part of the implant site at the second month. New bone formed over the central part of the implant site at the third month after surgery. Continuing maturation of the bone tissue could be observed over the interparticular space of the implant site until the late stages at the 6th and 8th month after surgery. The results of compressive strength tests were compatible with the histological observations. The value of the elastic modulus was low initially at the first month, but increased gradually with time due to organization of fibrous tissue, condensation of HA particles, and ossification as well as maturation of bone tissue. The value of elastic modulus at the third month was equal to that of cortical bone tissue and even two-fold higher than that of the cortical bone at the eighth month after surgery. These results provide valuable information about the compressive strength of the HA implant in host tissue.

Animals↗

PubMed1995

[Effects of age in the correction of isthmus stenosis on postoperative stiffness of the aorta].

Operative surgery for coarctation aims to eliminate the narrowed segment of the aorta and to restore a normal function of the aortic Windkessel, which depends on normal elastic properties of the aorta. To evaluate the effect of age at coarctectomy on the postoperative aortic elasticity, parameters of regional wall stiffness within the aortic arch were determined in 24 children after coarctectomy by means of echocardiography and blood pressure measurements. Actual data were compared with reference data (mean value normalized to body weight: mn +/- SD) obtained from n = 43 children, adolescents and young adults (age 1 month to 28 years; mean 12.6 years): elastic modulus Epn = 0.20 +/- 0.07 Mdyn/cm2/kg0.11; stiffness index beta = 3.45 +/- 1.3; diameter Dn = 0.52 +/- 0.08 cm/kg0.37. The results revealed that 4.9 years (mean) after coarctation repair within the first year of life (mean 3.2 months, n = 10) the parameters of elasticity and the diameter did not differ from normal. In those n = 5 children operated on in the age of 4.7 years there was a tendency towards increased aortic stiffness and reduced diameter 8.9 years later. In n = 9 children with a mean age of 9.2 years at operation the elastic modulus was increased 7.6 years later: Epn = 0.28 +/- 0.11 Mdyn/cm2/kg0.11; (p < 0.01). The diameter of the proximal aortic arch was significantly reduced (DN =0.42 +/- 0.08 cm/kg0.37., P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1996

The mechanical properties of fin whale arteries are explained by novel connective tissue designs.

The aortic arch and the descending aorta in the fin whale (Balaenoptera physalus) are structurally and mechanically very different from comparable vessels in other mammals. Although the external diameter of the whale's descending thoracic aorta (approximately 12 cm) is similar to that predicted by scaling relationships for terrestrial mammals, the wall thickness:diameter ratio in the whale (0.015) is much smaller than the characteristic value for other mammals (0.05). In addition, the elastic modulus of the thoracic aorta (12 MPa at 13 kPa blood pressure) is about 30 times higher than in other mammals. In contrast, the whale's aortic arch has a wall thickness/diameter ratio (0.055) and an elastic modulus (0.4 MPa) that are essentially identical to those for other mammals. However, the aortic arch is unusual in that it can be deformed biaxially to very large strains without entering a region of high stiffness caused by the recruitment of fully extended collagen fibres. Chemical composition studies indicate that the elastin:collagen ratio is high in the aortic arch (approximately 2:1) and that this ratio falls in the thoracic (approximately 1:2) and abdominal (approximately 1:3) aortas, but the magnitude of the change in composition does not account for the dramatic difference in mechanical properties. This suggests that there are differences in the elastin and collagen fibre architecture of these vessels. The descending aorta contains dense bands of tendon-like, wavy collagen fibres that run in the plane of the arterial wall, forming a fibre-lattice that runs in parallel to the elastin lamellae and reinforces the wall, making it very stiff. The aortic arch contains a very different collagen fibre-lattice in which fibres appear to have a component of orientation that runs through the thickness of the artery wall. This suggests that the collagen fibres may be arranged in series with elastin-containing elements, a difference in tissue architecture that could account for both the lower stiffness and the extreme extensibility of the whale's aortic arch. Thus, both the structure and the mechanical behaviour of the lamellar units in the aortic arch and aorta of the whale have presumably been modified to produce the unusual mechanical and haemodynamic properties of the whale circulation.

Animals↗

PubMed1979

A correlation between abrasion resistance and other properties of some acrylic resins used in dentistry.

This investigation studies the relationship of hardness, elastic modulus and scratch width as dependent variables to the abrasion resistance of twenty-three dental acrylic resins. The multiple correlation R, when all three variables are used as predictors, is 0.727. Because of the significant intercorrelations between the variables themselves a stepwise multiple regression analysis showed hardness as a redundant variable. Abrasive wear can be estimated from the following equation Abrasive wear = 806.1 - 0.1498 modulus + 0.681 scratch width (R = 0.725; standard deviation of estimate +/- 50.8) The deletion of scratch width does not appreciably reduce the standard deviation of the estimate: Abrasive wear = 1063.4 - 0.2055 modulus (r = 0.683; standard deviation of estimate +/- 50.3) The method of curing the specimens conformed to the respective manufacturers' instructions. Abrasion and scratch tests were performed using methods developed by the authors and previously described in the literature, whereas the hardness and elastic modulus results were devised from standard test procedures. Further research is currently in progress to improve the predictive power of abrasion resistance with additional new variables.

Acrylic Resins↗

PubMed1997

Effect of Cross-Linking on the Dewetting of an Elastomeric Surface

It has been shown over the last few years how the wetting (or dewetting) of a soft, elastomeric substrate can be markedly affected by local deformation of the solid near the triple line, due to the component of liquid surface tension acting perpendicularly to the (undeformed) solid surface, i.e., the "wetting ridge." Since the degree of cross-linking of an elastomer affects its mechanical properties, we have undertaken a study of the influence of cross-linking on (de)wetting behavior. Using a silicone rubber in four states of cross-linking, we have observed that triple-line motion of tricresyl phosphate increases in speed with degree of cross-linking. Two principal factors influence this behavior, both being directly linked to average intercross-link molecular weight, M c . A decrease in M c increases elastic modulus and therefore decreases the importance of the wetting ridge, whilst also lowering the dissipative properties of the polymer. The combined effects lead, in the case studied, to a linear relationship between dewetting speed and elastomeric elastic modulus to the power 10/3.

Journal Article↗

PubMed1999

Variations in the individual thick lamellar properties within osteons by nanoindentation.

The nanoindentation method was used to examine variations in the individual thick lamellar properties within completed secondary osteons as a function of distance from the osteonal center (haversian canal). In general, there is a decline in both elastic modulus and hardness from the center of the osteon outward. Because some of the osteons may have a different general trend than others, an analysis of covariance was also carried out. The overall analysis was highly significant for both elastic modulus and hardness. Also, osteon number was significant as a factor, indicating that there was some difference in the overall thick lamellar properties of the different osteons. An unpaired t-test showed statistically significant differences (p = 0.0005 and 0.0004, respectively) between thick lamellar properties obtained from most of the inner two osteonal lamellae (E = 20.8 +/- 1.3 GPa and H = 0.65 +/- 0.06 GPa) and those from outermost two osteonal lamellae (E = 18.8 +/- 1.0 GPa and H = 0.55 +/- 0.05 GPa). In general, lamellar properties from near to the center of the osteon were greater than those from the outermost osteonal lamella. The mechanical properties of osteons are also significantly lower than those of the interstitial bone (p < 0.0001). The ratio (E1/E2) of the elastic moduli of the outermost osteonal lamella (E1) (considered to be the soft part of the osteons) and that of interstitial bone (E2) was approximately 0.7. These results may have important implications for the mechanical contribution of individual osteons to bone biomechanics.

Elasticity↗

PubMed1995

Effect of clarithromycin on sputum production and its rheological properties in chronic respiratory tract infections.

Macrolide antibiotics possess a variety of actions other than antimicrobial activities. To determine the effects of long-term administration of clarithromycin (CAM) on the amount and physical properties of sputum in patients with clinical conditions associated with excessive airway secretions, we conducted the present study in a parallel, double-blind, placebo-controlled fashion. Patients were divided into two groups: the first group (n = 16) received CAM (100 mg, twice a day) for 8 weeks, and the second group (n = 15) received placebo. In evaluating airway secretion, the daily amount of expectorated sputum, solid composition, viscoelastic properties (including elastic modulus and dynamic viscosity), and sputum microbiology were assessed. CAM decreased sputum production from 51 +/- 6 to 24 +/- 3 g/day after treatment, whereas placebo had no effect. The bacterial density and sputum flora were unaltered. In the group receiving CAM, the percent solid composition and elastic modulus increased from 2.44% +/- 0.29% to 3.01% +/- 0.20% and 66 +/- 7 to 87 +/- 8 dyne/cm2 (P < 0.05), respectively, but the dynamic viscosity remained unchanged. These results suggest that long-term treatment with CAM reduces the amount of sputum production, probably by inhibiting airway secretions, and increases sputum elasticity.

Adult↗

PubMed2005

Heat-induced soy-whey proteins interactions: formation of soluble and insoluble protein complexes.

The aggregation behavior during heating of a solution containing soy protein and whey protein isolate (WPI) was studied using rheology, confocal microscopy, gel filtration, and electrophoresis. Soy/WPI mixtures formed gels at 6% total protein concentration with a high elastic modulus (G') and no apparent phase separation. The ratio of soy to WPI was fundamental in determining the type of network formed. Systems containing a high soy to WPI ratio (>70% soy protein) showed a different evolution of the elastic modulus during heat treatment, with two apparent stages of network development. Whey proteins formed disulfide bridges with soy proteins during heating, and at low ratios of soy/WPI, the aggregates seemed to be predominantly formed by 7S, the basic subunits of 11S and beta-lactoglobulin. Size exclusion chromatography indicated the presence of high molecular weight soluble complexes in mixtures containing high soy/WPI ratios. Results presented are the first evidence of interactions between soy proteins and whey proteins and show the potential for the creation of a new group of functional ingredients.

Chromatography, Gel↗

PubMedDate not supplied

Effects of aging and spinal degeneration on mechanical properties of lumbar supraspinous and interspinous ligaments.

BACKGROUND CONTEXT: The effects of aging and spinal degeneration on the mechanical properties of spinal ligaments are still unknown, although there have been several studies demonstrating those of normal spinal ligaments. PURPOSE: To investigate the mechanical properties of the human posterior spinal ligaments in human lumbar spine, and their relation to age and spinal degeneration parameters. STUDY DESIGN/SETTING: Destructive uniaxial tensile tests were performed on the human supraspinous and interspinous ligaments at L4-5 level. Their mechanical properties were compared with age and spinal degeneration using several imaging modalities. PATIENT SAMPLE: Twenty-four patients with lumbar degenerative diseases on whom posterior surgeries were performed, with the age ranging from 18 to 85 years. OUTCOME MEASURES: The ultimate load and elastic stiffness as structural properties, the degree of disc degeneration, range of segmental motion, the disc height, disc space narrowing ratio and degree of facet degeneration as the parameters of spinal degeneration. METHODS: Twenty-four supraspinous and interspinous ligaments at the L4-5 level were obtained from posterior surgeries of patients with lumbar degenerative disease. The mechanical tests of bone-ligament-bone complexes were performed in a uniaxial tensile fashion with a specially designed clamp device. The ultimate load and elastic stiffness were calculated as structural properties. The degree of disc degeneration, range of segmental motion, the disc height, disc space narrowing ratio and degree of facet degeneration were examined by using radiographs, computed tomography and magnetic resonance imaging. RESULTS: The average and SD value of ultimate load, elastic stiffness, tensile strength and elastic modulus were 203+/-102.9 N, 60.6+/-36.7 N/mm, 1.2+/-0.6 Mpa and 3.3+/-2.1 Mpa, respectively. A significant negative correlation was found between age and tensile strength (p= 0.02). The specimens with facet degeneration showed lower values in tensile strength and elastic modulus than those without facet degeneration (p<0.04). However, no correlation was found between disc-related parameters and tensile strength. CONCLUSIONS: The mechanical strength of human lumbar posterior spinal ligaments decreases with age and facet degeneration, particularly in the ligament substance.

Adolescent↗

PubMed2004

Effect of age on mechanical properties of rat mesenteric small arteries.

With aging, large arteries become stiffer and systolic blood pressure consequently increases. Less is known, however, about the age-related change in mechanics of small resistance arteries. The aim of this study was to determine whether aging plays a role in the stiffening of the small mesenteric arteries of rats. Intra-arterial systolic, diastolic, mean and pulse pressures were measured in male Wistar rats aged 2, 4, 15 and 26 months. The passive mechanical properties of the wall of isolated perfused and pressurized arterial segments of mesenteric small arteries were also investigated. Intra-arterial systolic, diastolic and mean blood pressures tended to decrease with age and were significantly lower in the oldest rats (26-month-old group). Pulse pressure was significantly higher in the 15- and 26-month-old groups than in the two younger groups. Under isobaric conditions, increasing age is associated with an outward hypertrophic remodeling of the mesenteric arteries. Under relaxed conditions, incremental distensibility in response to increasing intravascular pressure did not change with aging. As a function of strain (under isometric conditions), stress shifted to the left as age increased, indicating an age-related vascular stiffening. Under isobaric conditions or in relation to wall stress, the elastic modulus was greater in the adult 15-month-old rats than in the younger rats. These findings suggest that distensibility seems to be preserved with aging, despite stiffness of the wall components, probably by arterial wall geometric adaptation, which limits the pulse pressure damage. It is interesting to note that elastic modulus in mesenteric arteries from the oldest rats (26-month-old), examined in relation to wall stress and intravascular pressure, did not differ from that of the youngest rats, thus suggesting that elasticity of wall components had been restored.

Aging↗

PubMed2001

The distribution of osteocalcin, degree of mineralization, and mechanical properties along the length of Cyprinus carpio rib bone.

This study examined the spatial distribution of selected biochemical and mechanical properties along the length of carp rib bone. Carp rib bone was chosen because of its unusually high osteocalcin content relative to other extractable proteins. The amount of osteocalcin was significantly lower (p<0.01) at the most distal section, relative to all other sections. The amount of phosphate (p<0.05) and the elastic modulus in the longitudinal plane (p<0.0001) were found to be significantly higher in the most distal section, relative to the most proximal section. There was no significant difference in the calcium distribution, molar Ca/P ratio, or elastic modulus in the transverse plane. It was speculated that the distal section contains less mature bone. The methods illustrate the potential usefulness of nanoindentation to characterize the mechanical properties of bone, relative to its biochemical composition.

Journal Article↗

PubMed1993

[An experimental study on the replacement of the anterior cruciate ligament of the rabbit's knee using an augmented substitute].

The mechanical properties of a reconstruction of the anterior cruciate ligament (ACL) using an augmented substitute were investigated in rabbits' knees. After total resection of the ACL, 25 knees were reconstructed with a patellar tendon alone (nonaugmented group) and 25 with a patella tendon augmented by a Leeds-Keio artificial ligament (augmented group). The rabbits were sacrificed for biomechanical testing at 0, 4, 8, 12 and 24 weeks, respectively, after operation. In the augmented group, the mean ultimate load was 48.8% of the original ACL load at 4 weeks, and this gradually increased to 65.6% at 8 weeks. That of the twenty-four-week specimens was restored to 71% of the original ACL load. In the nonaugmented group, the mean ultimate load decreased to 9.3% at 8 weeks, but increased to 37.5% at 24 weeks. The mean static stiffness in the augmented group was higher than in the nonaugmented group at all time periods. The differences between the augmented and nonaugmented groups were statistically significant in the 8 to 12 week period (p < 0.01). Tan delta values, exhibiting the magnitude of viscosity in a viscoelastic material, in the augmented group were significantly higher than those in the nonaugmented group at 8 weeks (p < 0.05) and 12 weeks (p < 0.01). The mean tan delta in the augmented group decreased to 0.08 +/- 0.04 at 24 weeks, but the values were higher than those of the original ACL. The mean dynamic elastic modulus in the augmented group was higher than in the nonaugmented group at all time periods. The difference between the augmented and nonaugmented groups was statistically significant in the 8th week (p < 0.05). The values of dynamic elastic modulus in both groups were increased at 24 weeks: 96.4 MPa in the augmented group, and 77.5 MPa in the nonaugmented group. It was demonstrated that the augmented ligaments used for anterior cruciate ligament reconstruction had greater strength and static stiffness than the patellar tendon autograft. As for dynamic properties, the augmented group showed higher viscosity group than ACL.

Animals↗

PubMed1994

Microfracture mechanisms of dental resin composites containing spherically-shaped filler particles.

The effects of spherically-shaped filler particles on bending strength, bending elastic modulus, and fracture toughness of resin composites were studied. The filler content was changed by 0, 20, 40, 60, and 70 wt%. Bending properties and fracture toughnesses were determined on three-point bending specimens. Acoustic Emission (AE), i.e., the elastic wave released from a localized source in the material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Detected acoustic emission signals were analyzed for parameters such as amplitude, events, and locations. The fractured surface was examined by a scanning electron microscope. The bending strength and the fracture toughness showed almost the same trend in their increasing rates by filler content, but the elastic modulus showed a much higher increasing rate. A microfracture mechanism of the dental resin composites containing spherically-shaped filler particles is proposed based on the results obtained from the AE-releasing pattern, two-dimensional AE location, and fracture surface findings. In addition to the toughening effects of crack pinning and crack branching, which are observed in the usual commercial resin composites, crack-deflecting effects are confirmed in this new type of dental resin composites.

Composite Resins↗

PubMed2005

Sol/gel transition of chitosan solutions.

This work studies the occurrence of sol/gel transition and the gel rheology for chitosan solution under various conditions. Experiments were conducted in an oscillatory shear apparatus with small amplitude, using a Rheometrics SR-5 rheometer, with Couette and parallel plate geometries. The experimental results demonstrate that the sol/gel transition concentration and the elastic modulus (G') for CS gel decrease as the pH value and the molecular weight (Mw) increase. However, the sol/gel transition concentration and G' became independent of Mw when Mw exceeded a threshold. The higher ionization constant, Kp, is responsible for the higher sol/gel transition concentration in a formic acid solution than in an acetic acid solution with equivalent molar concentration. The elastic modulus G' of a CS gel increases with temperature, which relationship differs from that for many polysaccharides, and can be understood through classical rubber elastic theory. Finally, a gel whose concentration was barely above the sol/gel point exhibited aging, and its G' and G" declined rather than increase with time, accompanied by a reversal from the sol/gel state back to the sol state. This is an uncommon aging behavior for a polysaccharide and a detailed explanation is provided.

Acetic Acid↗