SEARCH · PubMed Health

Results for “Elastic Modulus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources

PubMed1988

Arteriosclerotic change in the human abdominal aorta in vivo in relation to coronary heart disease and risk factors.

In 137 living subjects, arteriosclerotic change in the human abdominal aorta was examined in relation to coronary heart disease (CHD) using a new ultrasonic method. The pressure strain elastic modulus (Ep) was calculated as an index of elastic properties from which arteriosclerotic change in the aorta was estimated. Thirty-one patients with CHD and 36 subjects with hypertension showed progression of the arteriosclerotic change in the abdominal aorta compared with 70 normal controls with the same age distribution (40-60 yrs). The Ep values were 1.03 +/- 0.27 X 10(6) dyne/cm2 in the normal group, and were elevated significantly (P less than 0.001) to 1.81 +/- 0.55 X 10(6) dyne/cm2 in the CHD group, and 1.95 +/- 1.31 X 10(6) dyne/cm2 in the hypertensive group. A significant correlation (r = 0.49, P less than 0.01) between the Ep values of the abdominal aorta and serum total cholesterol was observed in the CHD group. It was shown in living human subjects that the progression of arteriosclerotic change in the abdominal aorta was associated with coronary heart disease, and that some coronary risk factors, such as hypertension and serum total cholesterol, also affected arteriosclerotic change in the abdominal aorta.

Aorta, Abdominal↗

PubMed2004

Enhancement of growth and cellulose accumulation by overexpression of xyloglucanase in poplar.

Because the loosening of xyloglucan in the cell wall promotes plant growth (Takeda et al. (2002) Proc. Natl. Acad. Sci. USA 99, 9055-9060; Park et al. (2003) Plant J. 33, 1099-1106), we expressed Aspergillus xyloglucanase constitutively in Populus alba. The expression increased the length of stem even in the presence of sucrose. Increased stem growth was accompanied by a decrease in Young's elastic modulus in the growth zone but an increased elasticity in mature tissue. The increased internode length corresponded to an increase in cellulose content as well as specific gravity, showing that the removal of xyloglucan might cause an increase in cellulose density in the secondary xylem.

Biomechanical Phenomena↗

PubMed1976

Effects of hypertension on the static mechanical properties and chemical composition of the rat aorta.

The contributions of the relative radius, relative wall thickness, incremental strain, incremental elastic modulus, and medial scleroprotein content to the static elastic properties of the rat aortic wall have been examined in three groups of rats. Controls, rats made hypertensive at four weeks of age, and rats whose blood pressure was lowered after 6 weeks hypertension, were studied. The results show evidence of adaptive changes in the aorta of hypertensive animals, and that irreversible alterations in the mechanical properties of the wall may be induced by a brief period of hypertension. A direct relationship between aortic medial scleroprotein content and the elastic properties of the wall is demonstrated.

Age Factors↗

PubMed1979

The effects of geometry, elasticity, and external pressures on the diastolic pressure-volume and stiffness-stress relations. How important is the pericardium?

The concept of an incremental elastic modulus is applied in the quantification of passive elastic stiffness-stress relations of intact heart muscle, and a transmural pressure-volume relation for the left ventricle is subsequently derived in terms of geometry, muscle elasticity, and external pressures to assess their importance. Physiological and clinical applications of this method indicate that: (1) stiffness-stress relations obtained on the basis of pressure-volume data from dog hearts are not significantly different from those obtained from muscle strips excised from these same hearts; (2) shape and the presence of right ventricular, pericardial, or pleural pressures are of secondary importance in an assessment of passive elastic stiffness; and (3) dramatic shifts in the left ventricular intracavity pressure-volume relations following drug interventions are primarily due to the presence of substantial pericardial pressures; however, the transmural pressure-volume relations are not markedly altered, implying no alteration in the intrinsic ventricular compliance.

Animals↗

PubMed2004

Vascular intramural strain imaging using arterial pressure equalization.

Peripheral vascular strain imaging has limited strain dynamic range because arterial wall deformations only exhibit small strains under physiologic pressures. A noninvasive freehand ultrasound (US) scanning procedure was performed to apply external force, comparable to the force generated in measuring a subject's blood pressure, to achieve higher strains by equalizing the internal arterial baseline pressure. When the applied pressure matched the internal baseline diastolic pressure, intramural strain and strain rate increased by a factor of 10 over a cardiac cycle. Radial arterial strain was assessed within the vessel wall over the entire deformation procedure using a phase-sensitive 2-D speckle-tracking algorithm. The feasibility of this technique to assess vascular nonlinear elastic properties is demonstrated in an ex vivo experiment and further supported by in vivo measurements. With some uncertainty associated with the elastic properties of surrounding tissue, an elastic modulus reconstruction procedure was developed to estimate the nonlinear elastic properties of the vascular wall.

Adult↗

PubMed2001

A constrained modulus reconstruction technique for breast cancer assessment.

A reconstruction technique for breast tissue elasticity modulus is described. This technique assumes that the geometry of normal and suspicious tissues is available from a contrast-enhanced magnetic resonance image. Furthermore, it is assumed that the modulus is constant throughout each tissue volume. The technique, which uses quasi-static strain data, is iterative where each iteration involves modulus updating followed by stress calculation. Breast mechanical stimulation is assumed to be done by two compressional rigid plates. As a result, stress is calculated using the finite element method based on the well-controlled boundary conditions of the compression plates. Using the calculated stress and the measured strain, modulus updating is done element-by-element based on Hooke's law. Breast tissue modulus reconstruction using simulated data and phantom modulus reconstruction using experimental data indicate that the technique is robust.

Breast Neoplasms↗

PubMed2001

Influence of shade and storage time on the flexural strength, flexural modulus, and hardness of composites used for indirect restorations.

STATEMENT OF PROBLEM: Fracture resistance, elastic modulus, and hydrolytic degradation resistance are important properties of indirect composite restorations. Composite systems developed specifically for indirect application are said to have enhanced mechanical properties due to their elevated monomer conversion. PURPOSE: This study evaluated the influence of shade and the effect of 30-day water storage on the flexural strength, flexural modulus, and hardness of 4 commercially available indirect composite systems and 1 composite used with the direct technique. MATERIAL AND METHODS: A variety of commercially available indirect resin composites (Artglass, Belleglass, Sculpture, and Targis) and 1 directly placed composite (Z100, control) were used. Specimens made with either incisal or dentin shade (n = 10) were fractured with a 3-point bending test. Pre-failure loads corresponding to specific displacements of the crosshead were used for flexural modulus calculation. Knoop hardness was measured on fragments (n = 3) obtained after the flexural test. Tests were performed after 24 hours and after a 30-day water storage at 37 degrees C. Flexural strength data were analyzed with the Weibull distribution. Flexural modulus and Knoop hardness data were analyzed with 3-way ANOVA and Tukey's post-hoc test (alpha=0.05). RESULTS: In general, the directly placed composite (Z100) demonstrated flexural strength similar to that of Artglass, Targis, and Sculpture. Belleglass presented the highest flexural strength (221.7 MPa for incisal shade after 24 hours storage; 95% confidence interval: 208.3-235.4). Z100 demonstrated the highest flexural modulus (range: 10.9 +/- 0.6 to 12.0 +/- 0.9 GPa) and Targis the lowest (range: 5.1 +/- 0.5 to 5.9 +/- 0.9 GPa). Sculpture was the only material that showed differences in flexural strength with respect to shade (incisal-24 hours: 149.8 MPa; incisal-30 days: 148.7 MPa; dentin-24 hours: 200.0 MPa; dentin-30 days: 177.9 MPa). The flexural modulus and hardness of the dentin shade of Sculpture were higher than those of the incisal shade after 30 days. Belleglass also showed a significant difference in flexural modulus (dentin-24 hours: 11.1 GPa; incisal-24 hours: 9.6 GPa). The effect of water storage was more evident on hardness since all composite systems softened after 30 days. Prolonged water storage decreased flexural strength only for Artglass-dentin and Z100, both incisal and dentin shades. Water aging did not affect the flexural modulus of any composite tested. CONCLUSION: In general, indirect composites did not show enhanced mechanical properties compared to the directly placed composite. Property differences due to shade were more evident for Sculpture. Prolonged water storage had a deleterious effect on the hardness of all composites tested. However, water storage did not affect the flexural strength of most of the indirect composites or the flexural modulus of any composite tested.

Analysis of Variance↗

PubMed1994

Preparation of a new nerve guide from a poly(L-lactide-co-6-caprolactone).

A copolymer of L-lactide and 6-caprolactone (50:50, w/w) was synthesized and characterized. The thermal behaviour of this material did not show any crystallinity for several months; only after more than 1 yr of aging at room temperature and, particularly, in the in vitro degradation tests did it partially crystallize. The values of tensile strength, percent elongation at break and elastic modulus were, respectively, 25 MPa, 490% and 3 MPa. Transparent, elastic nerve guides having inner diameter of 1.3 mm and wall thickness of 175 microns were prepared.

Animals↗

PubMed2004

Rheological, mucoadhesive and release properties of Carbopol gels in hydrophilic cosolvents.

Carbopol is one of the most common thickening agent for water phases. It is used after neutralisation and its rheological properties in the aqueous medium are well known. The aim of this work was to investigate the gelation properties of Carbopol 971 e 974 polymeric systems in water-miscible cosolvents such as glycerine and PEG 400. Since in these cosolvents, carboxypolymethylene precipitates after neutralisation with a base, then the attention was pointed out of the gelation properties of the different systems at increasing temperature, in order to obtain Carbopols gels avoiding neutralisation and, at the same time, making possible the dissolution in these gels of insoluble or poorly soluble water drugs. Rheological properties of PEG 400 and glycerine samples were compared with similar systems in water by performing oscillatory analyses and measuring the main rheological parameters, G', G" and delta. The results obtained showed that Carbopol 971 and 974 in PEG 400 gave rise after heating to gels that show a satisfactory rheological behaviour. The elastic modulus is greater than the viscous one showing a remarkable elastic character of these samples and the performed frequency sweeps show a typical spectrum of a "gel-like" structure. Being Carbopols well-known mucoadhesive polymers, gels adhesive properties were studied using the ex vivo method. Then, the possible cutaneous irritation were also tested using the in vivo method (Draize test). No signs of cutaneous irritation and good mucoadhesive properties were obtained for the PEG 400 and water gels of Carbopol 974 prepared by heating. After rheological and mucoadhesive properties were set, paracetamol as a model drug was then inserted in the composition of the gels and the release characteristics were defined. Dissolution tests pointed out the greater release control properties of PEG 400-Carbopol 971 samples. These studies showed PEG 400-Carbopol systems as a first-rate alternative to traditional water gels.

Acetaminophen↗

PubMed2005

Rheological, adhesive and release characterisation of semisolid Carbopol/tetraglycol systems.

Gels dosage forms are successfully used as drug delivery systems considering their ability to control drug release and to protect medicaments from an hostile environment. This study deals with the gelation properties of Carbopol 971 e 974 polymeric systems in tetraglycol, a water-miscible cosolvent. In this paper, the attention was noted of the thickening properties of the different Carbopol in tetraglycol solvent at increasing temperatures, in order to obtain gels avoiding neutralisation and, at the same time, to make possible the dissolution in these gels of insoluble or poorly soluble water drugs. Samples were prepared by simply dispersing different Carbopols amount (0.5-4%) were added to tetraglycol and different systems were prepared at room temperature and by heating at 70 degrees C. All these systems were then characterised rheologically. Frequency sweep, creep-recovery, temperature sweep and time sweep analyses outlined that Carbopol 971 and 974 in tetraglycol gave rise after heating to gels with satisfactory rheological behaviour: the elastic modulus was greater than the viscous one and a remarkable elastic character was found to be present. Systems obtained by heating procedure were examined also from a mechanical point of view using a texture profile analysis. Besides, being Carbopols well known mucoadhesive polymers, gels adhesive properties were also studied using the ex vivo method. Texture and adhesion characterisation confirmed rheological results pointing out a certain greater elasticity and adhesiveness of Carbopol 974 systems. Then, the possible cutaneous irritation was also tested using the in vivo method (Draize test). No signs of cutaneous irritation were obtained for all the samples that were analysed. After rheological and mucoadhesive properties were set, paracetamol as a model drug was inserted in the composition of the gels and the release characteristics were defined. Dissolution tests pointed out the greater release control properties of tetraglycol/Carbopol 971 samples. These studies showed tetraglycol/Carbopol systems as a first-rate alternative to traditional water gels when low water-soluble drugs have to be added.

Acetaminophen↗

PubMed2000

Alterations of biochemical and two-dimensional biomechanical properties of human skin in diabetes mellitus as compared to effects of in vitro non-enzymatic glycation.

OBJECTIVE: The aim of this study was to evaluate whether multiaxial analysis of diabetes-specific biomechanical changes generated in vitro by non-enzymatic glycation of human skin samples from healthy subjects reflect the changes seen in skin from subjects with diabetes mellitus. DESIGN: Descriptive study. BACKGROUND: Non-enzymatic glycation of skin in vitro causes an increased stiffness comparable to in vivo changes seen in diabetic patients. These changes are probably due to increased cross-linking of collagen molecules. METHODS: Skin specimens from 7 subjects with diabetes mellitus and 7 controls (age range: 74-90) were analyzed for biomechanical changes using a multiaxial tensile testing device. Control skins from healthy individuals in the age range of 50-65 yr were artificially glycated. One part of these samples was coincubated with the glycation inhibitor aminoguanidine. Glycation of tissues was determined by measuring fluorescence of solubilized samples. Multiaxial biomechanical analysis allows the determination of maximum (a(I)) and minimum elastic modulus (a(II)). These parameters describe the amplitude of the elastic stress response, which is exponentially related to strain. RESULTS: Principal stresses, both maximum and minimum, were increased in skins from diabetic subjects as compared to controls. The increases of the principal stresses were comparable to those obtained by in vitro glycation of normal skins. CONCLUSION: These results, which can be detected unequivocally with the multiaxial test mode, show that our in vitro model closely reflects changes in skin samples from individuals with diabetes mellitus. Aminoguanidine partially inhibited these as well as biochemical changes. RELEVANCE: Multiaxial testing of in vitro glycated skin samples can be used as a model for in vivo changes caused by diabetes mellitus. In addition, therapeutical effects of aminoguanidine, an inhibitor of non-enzymatic glycation, can be monitored in this model.

Aged↗

PubMed2006

Laser diffractometry technique: clinical applications to vascular pathologies.

Hypertension (HTA) and dyslipidemia (DLP) represent major risk factors for cardiovascular and cerebral-vascular ischemic disease. The mechanisms through which they can induce vascular damage are both metabolic and mechanical. Hemorheological alterations in HTA are result of changes affecting both red cell intrinsic structure and their interactions with the plasmatic components. Several hemorheological determinants (biochemical, ionic, metabolic and rheologic) could influence and produce an impaired erythrocyte deformability determining an increased flow resistance in the microcirculation. The "Erythrodeformeter" allows obtaining the stationary and dynamical linear parameters of erythrocyte membrane by laser diffractometry. Stationary and oscillatory shear-induced elongation of cells leads to an elliptical diffraction pattern, its geometric characteristics being directly related to those of deformed RBC. Erythrocyte stationary parameters (Deformability Index, surface viscosity and elastic modulus) were obtained in stationary regime. Complex viscoelastic parameters (dynamic elasticity, dynamic loss, viscous and elastic components of the complex viscosity) were obtained when operating in oscillating mode. The diffractometric method is sensitive to detect pathological or induced alterations on RBC membrane, which can affect blood flow in vivo. The rheological parameters obtained give important information about the erythrocyte membrane and allow to detect and characterize erythrocyte alterations in vascular pathologies.

Dyslipidemias↗

PubMed1976

Elastic area compressibility modulus of red cell membrane.

Micropipette measurements of isotropic tension vs. area expansion in pre-swollen single human red cells gave a value of 288 +/- 50 SD dyn/cm for the elastic, area compressibility modulus of the total membrane at 25 degrees C. This elastic constant, characterizing the resistance to area expansion or compression, is about 4 X 10(4) times greater than the elastic modulus for shear rigidity; therefore, in situations where deformation of the membrane does not require large isotropic tensions (e.g., in passage through normal capillaries), the membrane can be treated by a simple constitutive relation for a two-dimensionally, incompressible material (i.e. fixed area). The tension was found to be linear and reversible for the range of area changes observed (within the experimental system resolution of 10%). The maximum fractional area expansion required to produce lysis was uniformly distributed between 2 and 4% with 3% average and 0.7% SD. By heating the cells to 50 degrees C, it appears that the structural matrix (responsible for the shear rigidity and most of the strength in isotropic tension) is disrupted and primarily the lipid bilayer resists lysis. Therefore, the relative contributions of the structural matrix and lipid bilayer to the elastic, area compressibility could be estimated. The maximum isotropic tension at 25 degrees C is 10-12 dyn/cm and at 50 degrees C is between 3 and 4 dyn/cm. From this data, the respective compressibilities are estimated at 193 dyn/cm and 95 dyn/cm for structural network and bilayer. The latter value correlates well with data on in vitro, monolayer surface pressure versus area curves at oil-water interfaces.

Cell Membrane↗

PubMed2006

Flexural properties of endodontic posts and human root dentin.

OBJECTIVES: To evaluate the flexural modulus and flexural strength of different types of endodontic post in comparison with human root dentin. METHODS: Three different types of fiber-reinforced composite (FRC) posts and three metal posts each comprising 10 specimens (n=10) and 20 dentin bars were loaded to failure in a three-point bending test to determine the flexural modulus (GPa) and the flexural strength (MPa). Three randomly selected fiber posts of each group were evaluated using a scanning electron microscope (SEM) to illustrate the differences in mode of fracture. Data were subjected to a one-way ANOVA to determine significant differences between groups and the Bonferroni t-test multiple comparison was applied to investigate which mean values differed from one another with significance levels of P<0.05. RESULTS: The flexural modulus recorded for the dentin bars was 17.5+/-3.8 GPa. The values for posts ranged from 24.4+/-3.8 GPa for silica fiber posts to 108.6+/-10.7 GPa for stainless steel posts. The flexural strength for dentin was 212.9+/-41.9 MPa, while the posts ranged from 879.1+/-66.2 MPa for silica fiber posts to 1545.3+/-135.9 MPa for cast gold posts. The ANOVA test analysis revealed significant differences between groups (P<0.05) for flexural modulus and flexural strength mean values. SIGNIFICANCE: FRC posts have an elastic modulus that more closely approaches that of dentin while that for metal posts was much higher. The flexural strength of fiber and metal posts was respectively four and seven times higher than root dentin.

Carbon↗

PubMed2003

Mutations that affect flightin expression in Drosophila alter the viscoelastic properties of flight muscle fibers.

Striated muscles across phyla share a highly conserved sarcomere design yet exhibit broad diversity in contractile velocity, force, power output, and efficiency. Insect asynchronous flight muscles are characterized by high-frequency contraction, endurance, and high-power output. These muscles have evolved an enhanced delayed force response to stretch that is largely responsible for their enhanced oscillatory work and power production. In this study we investigated the contribution of flightin to oscillatory work using sinusoidal analysis of fibers from three flightless mutants affecting flightin expression: 1) fln0, a flightin null mutant, 2) Mhc13, a myosin rod point mutant with reduced levels of flightin, and 3) Mhc6, a second myosin rod point mutant with reduced levels of phosphorylated flightin. Fibers from the three mutants show deficits in their passive and dynamic viscoelastic properties that are commensurate with their effect on flightin expression and result in a significant loss of oscillatory work and power. Passive tension and passive stiffness were significantly reduced in fln0 and Mhc13 but not in Mhc6. The dynamic viscous modulus was significantly reduced in the three mutants, whereas the dynamic elastic modulus was reduced in fln0 and Mhc13 but not in Mhc6. Tension generation under isometric conditions was not impaired in fln0. However, when subjected to sinusoidal length perturbations, work-absorbing processes dominated over work-producing processes, resulting in no net positive work output. We propose that flightin is a major contributor to myofilament stiffness and a key determinant of the enhanced delayed force response to stretch in Drosophila flight muscles.

Animals↗

PubMed1999

Linear viscoelastic model of a maturing gelatin solution.

The linear viscoelastic model proposed in this work considers the viscoelastic nature of maturing gelatin solutions through a relaxation modulus that depends on temperature and maturation. This modulus is defined in the conceptual contexts of the classical rubber elasticity theory and the rheometric gel theory. An analysis of the relationship between the equilibrium elastic modulus and the percolation variable around the gel point is also included yielding a percolation exponent close to 1.7 as expected from previous theoretical predictions. Additionally, a simple kinetic model is proposed to follow the microstructural changes obtained as a consequence of the generation of junction zones, the number of which vary with time during the dynamic rheometric tests used in this work. Thus, the storage and loss moduli are measured at different temperatures and frequencies, during the period of gelatin maturation. The theoretical aspects of the rheological model are presented emphasizing the quantitative changes of rheological parameters with the maturation.

Animals↗

PubMed1996

Comparison of elasticities of components of a cardiac bioprosthesis leaflet.

The mechanoelastic behavior of calf pericardium employed in cardiac bioprostheses was compared with that of three types of thread (Nylon, Prolene, and silk) used to suture this biological tissue. The elastic limit (EL) of each material was determined by means of tensile tests and the mathematical functions that govern the stress/strain curves within the EL have been described. The first derivative of these functions for each point to the curves allowed the immediate calculation of the elastic modulus (EM), which was considered the best parameter for comparing the elasticities of the materials being assessed. It was observed that the deformation of the pericardium produced by the working stress of a pericardial leaflet was approximately 1000 times greater than that produced in the surgical threads. When the elasticities were compared on the basis of the EM, that of pericardium was 749.06, 626.95, and 1253.17 times greater than that of the Nylon, Prolene, and silk suture threads, respectively. These results demonstrate that the interaction between these materials (pericardium and the threads) could be generating detrimental forces that can diminish the durability of the leaflets of the bioprostheses constructed of calf pericardium.

Animals↗

PubMed2006

Emulsion-templated fully reversible protein-in-oil gels.

We have developed a new method allowing us to transform low-viscous apolar fluids into elastic solids with a shear elastic modulus of the order of 10(3)-10(5) Pa. The elasticity of the elastic solid is provided by a percolating 3D network of proteins, which are originally adsorbed at the interface of an oil-in-water emulsion template. By cross-linking the protein films at the interface and upon removal of water, the template is driven into a structure resembling a dry foam where the protein interfaces constitute the walls of the foam and the air is replaced by oil confined within polyhedral, closely packed droplets. Depending on the density of the protein network, the final material consists of chemically unmodified oil in a proportion of 95 to 99.9%. The physical properties of the elastic solid obtained can be tuned by changing either the average diameter size of the emulsion template or the cross-linking process of the protein film. However, the original low-viscosity emulsion can be restored by simply rehydrating the solidified fluid. Therefore, the present procedure offers an appealing strategy to build up solid properties for hydrophobic liquids while preserving the low viscosity and ease of manufacturing.

Emulsions↗