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 1,801 records · Page 100Linked to original sources

PubMed2001

Comparative interaction of alpha-helical and beta-sheet amphiphilic isopeptides with phospholipid monolayers.

The two sequential amphiphilic peptide isomers, (Leu-Lys-Lys-Leu)4 and (Leu-Lys)8, were chosen as models for alpha-helical and beta-sheet peptides, respectively. In order to evaluate the contribution of the secondary structure of a peptide to its penetration into cellular membranes, interactions of these isopeptides with L-alpha-dimyristoyl phosphatidylcholine (DMPC) monolayers were studied. Both isopeptides penetrate into DMPC monolayers up to an exclusion pressure of approximately 27 mN/m, but a discontinuity is observed in the penetration profile of the alpha-helical (LKKL)4. The main parameters extracted from the compression isotherms of the mixed peptide/DMPC monolayers-namely, transition pressure, mean area, elasticity modulus, and energy of mixing-were analyzed. These analyses indicate that the alpha-helical isomer interacts strongly with DMPC by forming a 1:32 (LKKL)4-DMPC complex. When engaged in this complex, (LKKL)(4) behaves as an hydrophobic helix and has a tendency to become vertically oriented in the course of the compression process. The beta-sheet (LK)8 interacts more weakly with DMPC and no complex can be detected.

Dimyristoylphosphatidylcholine↗

PubMed2000

An evaluation of mechanical property and microstructural development in HAP-Ca polycarboxylate biocomposites prepared by hot pressing.

A hot-pressing technique was used to prepare composites anticipated to be biocompatible. Ca(4)(PO(4))(2)O (TetCP) was reacted with an acrylic-itaconic copolymer (CoP) in the absence of a solvent to form composites comprised of Ca(10)(PO(4))(6)(OH)(2') (hydroxyapatite, or HAp) and the Ca polyalkenoate salt. The effect of temperature, pressure, and hot-pressing time on the mechanical properties and microstructure of the composites were studied. Results showed that both tensile strength and elastic modulus increased when temperature and time were increased. When the compaction pressure was increased, these properties initially increased but decreased at high pressures. These variations in the mechanical properties were correlated with the microstructure of these composites. The mechanism of the reaction was also studied. Reaction starts when the copolymer is heated to above its T(g) permitting it to flow and react with the TetCP grains. The COOH groups on the polymer are neutralized by Ca(2+) ions liberated from the TetCP. At the end of reaction, a network of the Ca polyalkenoate salt is formed in which HAp crystals are embedded.

Biocompatible Materials↗

PubMed2000

Reinforcement of a self-setting calcium phosphate cement with different fibers.

A water-based calcium phosphate cement (CPC) has been used in a number of medical and dental procedures due to its excellent osteoconductivity and bone replacement capability. However, the low tensile strength of CPC prohibits its use in many unsupported defects and stress-bearing locations. Little investigation has been carried out on the fiber reinforcement of CPC. The aims of the present study, therefore, were to examine whether fibers would strengthen CPC, and to investigate the effects of fiber type, fiber length, and volume fraction. Four different fibers were used: aramid, carbon, E-glass, and polyglactin. Fiber length ranged from 3-200 mm, and fiber volume fraction ranged from 1.9-9.5%. The fibers were mixed with CPC paste and placed into molds of 3 x 4 x 25 mm. A flexural test was used to fracture the set specimens and to measure the ultimate strength, work-of-fracture, and elastic modulus. Scanning electron microscopy was used to examine specimen fracture surfaces. Fiber type had significant effects on composite properties. The composite ultimate strength in MPa (mean +/- SD; n = 6) was (62+/-16) for aramid, (59+/-11) for carbon, (29+/-8) for E-glass, and (24+/-4) for polyglactin, with 5.7% volume fraction and 75 mm fiber length. In comparison, the strength of unreinforced CPC was (13+/-3). Fiber length also played an important role. For composites containing 5.7% aramid fibers, the ultimate strength was (24+/-3) for 3 mm fibers, (36+/-13) for 8 mm fibers, (48 +/-14) for 25 mm fibers, and (62+/-16) for 75 mm fibers. At 25 mm fiber length, the ultimate strength of CPC composite was found to be linearly proportional to fiber strength. In conclusion, a self-setting calcium phosphate cement was substantially strengthened via fiber reinforcement. Fiber length, fiber volume fraction, and fiber strength were found to be key microstructural parameters that controlled the mechanical properties of CPC composites.

Bone Cements↗

PubMed2001

Correlations between osteocalcin content, degree of mineralization, and mechanical properties of C. carpio rib bone.

Osteocalcin is one of the most abundant noncollagenous proteins in bone. It is strongly associated with the mineral phase of bone, and has long been associated as a marker of bone turnover. However, its relationship to bone composition, strength, and structure is unclear. Carp rib bone is an excellent model for the study, because osteocalcin represents almost 60% of the total extractable noncollagenous proteins found in it. Because of the abundance of osteocalcin relative to other extractable proteins, any changes in the properties of carp rib bone would be more likely influenced by the osteocalcin concentration. To test the hypotheses that the concentration of osteocalcin is reflected in other properties of bone, the correlations between the osteocalcin concentration and the mineral content, microstructural properties, and physical characteristics of the bone mineral crystals were determined utilizing radioimmunoassay (RIA), spectrophotometry, nanoindentation, and small-angle X-ray scattering (SAXS) techniques, respectively. Osteocalcin concentration was found to be correlated to the molar Ca/P ratio and inversely correlated to the elastic modulus and hardness in the longitudinal plane. This study provides evidence for a putative relationship between the concentration of osteocalcin and the microstructural mechanical properties of bone. Correlations were also found between the mechanical properties in the longitudinal plane and both the phosphate content and the molar Ca/P ratio. However, no relationships could be identified between osteocalcin concentration and several parameters of bone crystals, as determined by SAXS.

Animals↗

PubMed2001

Strain rate dependent orthotropic properties of pristine and impulsively loaded porcine temporomandibular joint disk.

The purpose of this study was to characterize the tensile stress-strain behavior of the porcine temporomandibular joint (TMJ) disk with respect to collagen orientation and strain rate dependency. The apparent elastic modulus, ultimate tensile strength, and strain at maximum stress were measured at three elongation rates (0.5, 50, and 500 mm/min) for dumbbell-shaped samples oriented along either anteroposterior or mediolateral axes of the disks. In order to study the effects of impact-induced fissuring on the mechanical behavior, the same properties were measured along each orientation at an elongation rate of 500 mm/min for disks subjected to impulsive loads of 0.5 N. s. The results suggested a strongly orthotropic nature to the healthy pristine disk. The values for the apparent modulus and ultimate strength were 10-fold higher along the anteroposterior axis (p < or = 0.01), which represented the primary orientation of the collagen fibers. Strain rate dependency was evident for loading along the anteroposterior axis but not along the mediolateral axis. No significant differences in any property were noted between pristine and impulsively loaded disks for either orientation (p > 0.05). The results demonstrated the importance of choosing an orthotropic model for the TMJ disk to conduct finite element modeling, to develop failure criteria, and to construct tissue-engineered replacements. Impact-induced fissuring requires further study to determine if the TMJ disk is orthotropic with respect to fatigue.

Animals↗

PubMed2001

Whisker-reinforced bioactive composites containing calcium phosphate cement fillers: effects of filler ratio and surface treatments on mechanical properties.

Calcium phosphate cement (CPC) sets to form microporous solid hydroxyapatite with excellent osteoconductivity, but its brittleness and low strength prohibit use in stress-bearing locations. The aim of this study was to incorporate prehardened CPC particles and ceramic whiskers in a resin matrix to improve the strength and fracture resistance, and to investigate the effects of key microstructural variables on composite mechanical properties. Two types of whiskers were used: silicon nitride, and silicon carbide. The whiskers were surface-treated by fusing with silica and by silanization. The CPC particle fillers were either silanized or not silanized. Seven mass ratios of whisker-silica/CPC were mixed: 0:1 (no whisker-silica), 1:5, 1:2, 1:1, 2:1, 5:1, and 1:0 (no CPC). Each powder was blended with a bisphenol-a-glycidyl methacrylate-based resin to harden in 2 x 2 x 25 mm molds by two-part chemical curing. The specimens were tested in three-point flexure to measure strength, work-of-fracture (toughness), and elastic modulus. Two-way analysis of variance was used to analyze the data, and scanning electron microscopy was used to examine specimen fracture surfaces. The whisker-silica/CPC ratio had significant effects on composite properties (p < 0.001). When this ratio was increased from 0:1 to 1:0, the strength was increased by about three times, work-of-fracture by five times, and modulus by two times. Whisker surface treatments and CPC filler silanization also had significant effects (p < 0.001) on composite properties. Scanning electron microscopy revealed rough fracture surfaces for the whisker composites with steps and whisker pullout. Resin remnants were observed on the surfaces of the pulled-out whiskers, indicating strong whisker-matrix bonding. In conclusion, incorporating highly osteoconductive CPC fillers and ceramic whiskers yielded composites with substantially improved mechanical properties compared with composites filled with CPC particles without whiskers. The composite properties were determined by whisker-to-CPC ratio and filler surface treatments.

Biocompatible Materials↗

PubMed2025

Granular Hydrogels as Brittle Yield Stress Fluids.

While granular hydrogels are increasingly used in biomedical applications, methods to capture their rheological behavior generally consider shear-thinning and self-healing properties or produce ensemble metrics (e.g., dynamic moduli) while neglecting transient yielding and unyielding processes. Combining oscillatory shear testing with Brittility (Bt) via the Kamani-Donley-Rogers (KDR) model, this work shows that granular hydrogels behave as brittle yield stress fluids. This work quantifies steady and transient rheology as a function of microgel properties and granular composition for polyethylene glycol and gelatin microgels. The KDR model with Bt captures granular hydrogel behavior for a wide range of design parameters, reducing the complex rheology to a determination of model parameters. In granular mixtures, this work observes monotonic dependencies of the elastic modulus, structural viscosity, and brittility upon granular composition, while the yield stress is lower for mixtures. Microgel size distribution and polymer fraction are the most influential parameters in monolithic granular hydrogels, while microgel size and packing density are less impactful. The model robustly captures self-healing behavior and reveals that granular hydrogel relaxation accelerates with an increased small-amplitude strain rate. This quantitative framework is an important step toward rational design of granular hydrogels for applications ranging from injection and in situ stabilization to 3D bioprinting.

brittility↗

PubMedDate not supplied

Influence of solvent composition on the mechanical properties of arterial elastin.

We have investigated the effects of changes in solution composition on the mechanical properties of rings of arterial elastin. The time course of force equilibration at constant strain following a change in the composition of the bathing solution was measured. Both the force developed during slow extension and force relaxation following rapid straining were also measured in each of the test solutions. The results are difficult to summarize because all of the primitive quantities measured--sample dimension, slope of the force-extension curve, force overshoot and time of relaxation--as well as the derived quantities such as elastic modulus changed in different and apparently uncorrelated ways. Changes in pH and ionic composition of the bathing solution had small effects consistent with the low fixed charge density of elastin. Solutions of glucose, sucrose, and ethylene glycol had larger effects consistent with changes in hydrophobic interactions. The viscosity of the solution that penetrated the intrafibrillar space of the elastin appeared to be a major determinant of the dynamic response.

Animals↗

PubMed1995

The distribution of water in arterial elastin: effects of mechanical stress, osmotic pressure, and temperature.

Using gravimetric and radiotracer techniques, we investigated the effects of mechanical stress, osmotic pressure, and temperature on the volumes of the intra- and extrafibrillar water spaces in arterial elastin. We also investigated the effects of temperature on water flow through elastin membranes and on dynamic mechanical properties of elastin rings. Compression by mechanical or osmotic loading reduced the hydration of the elastin in an identical manner. Two distinct stages were evident; at low loads there was extensive water removal from the extrafibrillar space while high loads were required to remove water from the intrafibrillar space. Conversely, dehydration caused by mechanical extension of the matrix was associated with a much smaller loss from the extrafibrillar compartment and a large fractional decrease in the intrafibrillar space. Contraction of the matrix as a result of increased temperature had similar effects on hydration to those produced by extension. Water flux across elastin membranes, corrected for changes in viscosity, and specific hydraulic conductivity both increased as a result of temperature-induced contraction. This effect was attributed to increases in both the fractional volume of the extrafibrillar space and the fiber radius. The elastic modulus decreased with increasing temperature, but there was an increase in viscoelasticity. Previous studies have determined that viscoelasticity depends on the rate of redistribution of intrafibrillar water, so this finding provides additional evidence that heating affects primarily the volume of the intrafibrillar space.

Animals↗

PubMed2001

Strength of mid-logarithmic and stationary phase Saccharopolyspora erythraea hyphae during a batch fermentation in defined nitrate-limited medium.

A method for measuring mechanical properties of Saccharopolyspora erythraea is reported with data from a batch fermentation. Briefly, hyphae were glued to the end of a tungsten filament mounted horizontally on a sensitive force transducer. Free ends of hyphae were trapped against a flat surface by a second probe. The force transducer and tungsten filament were then moved at a fixed rate, the hypha were strained, and the force resisting motion recorded. From these data the maximum force resisting motion is taken as the force at which breakage occurs. Hyphae from the mid-logarithmic phase of a simple batch fermentation on defined medium were found to have a breaking force of 890 +/- 160 nN (95% confidence), while stationary phase hyphae were weaker at 580 +/- 150 nN. Video recordings of the experiments allowed an approximation of breaking strain, which did not differ significantly between samples at 0.18 +/- 0.03. Electron microscopy was used to measure cell wall thickness, cell diameter, and hence cell wall cross-sectional area. The ultimate tensile strength was estimated to be 24 +/- 3 MPa with no difference between the two samples, the lower breaking force of the stationary phase hyphae being attributed to a thinner cell wall. Assuming a linear relationship between stress and strain, the elastic modulus was estimated to be 140 +/- 30 MPa. These values are comparable with other structural biological materials such as yeast cell walls and collagen.

Anti-Bacterial Agents↗

PubMed1993

Influence of type III collagen genotype on aortic diameter and disease.

Type III collagen contributes to the tensile strength of the aortic wall, and mutations in the type III collagen gene have been suggested as the basis for the familial tendency to abdominal aortic aneurysm (AAA). Variation in this gene was investigated in 153 patients with AAA, 87 with aortoiliac stenosis and 98 age-matched controls. The rare mutation at amino acid 619 of Gly-->Arg, previously associated with AAA in a single family, was not found in any of the patients with aneurysm. For the Ala-->Thr variation at amino acid 531, the frequency of the threonine allele was 0.25 in patients with AAA and stenosis, compared with 0.35 in controls. The frequency of the rare allele in the region 3' to the gene demonstrated by Ava II digestion (0.27 in the general population) was found to be 0.29 in the AAA group and 0.19 in the stenosis group (P = 0.023). In the AAA group the presence of the Ava II rare allele was associated with a significant increase in aneurysm diameter (P = 0.044). Non-invasive assessment of aortic distensibility was available in 25 patients: those carrying the Ava II rare allele had less distensible aortas than those not carrying this allele (median pressure-strain elastic modulus 42.0 and 23.9 N/cm2 respectively, P = 0.008). Variation in the type III collagen gene may influence the mechanical properties of the ageing aorta and hence its susceptibility to disease and dilatation. In contrast, there is no evidence for a single common founder mutation in type III collagen predisposing to AAA.

Aged↗

PubMed1991

Diastolic pressure-volume relationship during handgrip exercise in patients with coronary artery disease.

There is some controversy regarding the mechanisms of an upward shift in the left ventricular diastolic pressure-volume curve during ischemia. The effects of handgrip exercise on the pressure-volume curve were examined in 21 patients with coronary artery disease and in 6 control subjects. Pressure-volume curves were constructed from digitized left ventricular pressure and volume derived from biplane left ventriculogram. Diastolic pressure-volume curve shifted upward in 12 patients with coronary artery disease during handgrip exercise (Group 1), but not in the other 9 patients who were similarly afflicted (Group 2). The upward shift did not occur in any control subject. No difference was observed in rate-pressure product gain during exercise. In Group 1, left ventricular end-diastolic pressure increased (p less than 0.01) and ejection fraction was reduced (p less than 0.01), although it did not change in Group 2. In Group 1, the time constant was prolonged (p less than 0.01) with no change in the coefficient for elastic modulus. In Group 2, these parameters remained unchanged. Group 1 was accompanied by more extensive asynergy than Group 2. Thus, isometric handgrip exercise resulted in an upward shift in the diastolic pressure-volume curve in patients with coronary artery disease. Incomplete relaxation and/or the viscoelastic properties of the left ventricle associated with ischemia could be responsible for this phenomenon.

Adult↗

PubMed1995

Mechanical and histological fixation of hydroxylapatite-coated pyrolytic carbon and titanium alloy implants: a report of short-term results.

Historically, pyrolytic carbon has been a material for cardiovascular applications, but it has several properties suited for orthopedic uses as well. Pyrolytic carbon has an elastic modulus similar to bone and is highly fatigue resistant, but has not been used in orthopedics because of poor fixation to bone. Plasma sprayed hydroxylapatite (HA) has significantly improved the bonding of bone to titanium alloy implants. The effect of plasma-sprayed HA on pyrolytic carbon implants was investigated in this study. Cylindrical samples were implanted through a single cortex in Beagle femurs. The animals were sacrificed after 8 weeks, and a mechanical push-out test was performed on the implants immediately after explantation. Samples were microradiographed, stained for histology, and examined histomorphometrically. Interface strength for each type of implant was calculated. Pyrolytic carbon showed almost no attachment strength with an average strength value of 1.59 MPa. HA-coated pyrolytic carbon (8.71 MPa) yielded the same interfacial strength as HA-coated titanium (8.71 MPa). Histology revealed that bone was in direct apposition to all implants, both HA coated and noncoated. Failures occurred between the core material and the coating, or within the coating, but not at the bone/HA interface. Histomorphometry results confirmed that the two types of HA-coated implants had more bone apposition than the uncoated pyrolytic carbon implants. It was concluded that a plasma sprayed HA coating significantly improves the bone fixation of pyrolytic carbon.

Animals↗

PubMed2002

Characterization of damage modes in dental ceramic bilayer structures.

Results of contact tests using spherical indenters on flat ceramic coating layers bonded to compliant substrates are reported for selected dental ceramics. Critical loads to produce various damage modes, cone cracking, and quasiplasticity at the top surfaces and radial cracking at the lower (inner) surfaces are measured as a function of ceramic-layer thickness. It is proposed that these damage modes, especially radial cracking, are directly relevant to the failure of all-ceramic dental crowns. The critical load data are analyzed with the use of explicit fracture-mechanics relations, expressible in terms of routinely measurable material parameters (elastic modulus, strength, toughness, hardness) and essential geometrical variables (layer thickness, contact radius). The utility of such analyses in the design of ceramic/substrate bilayer systems for optimal resistance to lifetime-threatening damage is discussed.

Ceramics↗

PubMed2002

Self-curing acrylic formulations containing PMMA/PCL composites: properties and antibiotic release behavior.

Partially biodegradable acrylic composites containing poly(methyl methacrylate)-poly(epsilon-caprolactone) (PMMA/PCL) systems were prepared by mixing the corresponding PMMA/PCL beads (89:11, 86:14, 83:17, and 77:23 weight ratio) used as solid phase with methyl methacrylate (MMA) (liquid phase) in a solid/liquid ratio of 1.5:1. The physical and chemical microheterogeneity of these beads influenced significantly the curing parameters, because several aspects involved in the polymerization reaction are closely related to both morphology and size distribution of the particles. In vitro behavior was studied by immersion in simulated body fluid at pH = 7.4 and 37 degrees C for more than 8 weeks and the composition was followed by 1H-nuclear magnetic resonance spectroscopy. Approximately 2% wt/wt weight loss was observed after a period of 8 weeks for the composites richest in PCL. Mechanical properties of the dry and wet specimens were evaluated by compressive and tensile tests. In all cases, the presence of PCL in the composites provided a significant decrease in both compressive strength and elastic modulus compared with plain PMMA. Tensile and compressive strength also decreased significantly after 2 weeks of immersion in simulated body fluid compared with dry specimens. The self-curing composites based on PMMA/PCL beads and loaded with 3% wt/wt vancomycin were evaluated as carriers for local release of antibiotics. The composite prepared with beads of PMMA/PCL ratio 86:14 was the most effective. It eluted 64% of the initial drug within the first 5 h, allowing progressive release of nearly the total amount of the initial drug (90%) in approximately 2 months. The results obtained suggest that the described composites can be suitable for antibiotic release in non-load bearing graft applications.

Biocompatible Materials↗

PubMed2002

PMMA-based bioactive cement: effect of glass bead filler content and histological change with time.

A new bioactive bone cement (designated GBC), which is a polymethyl methacrylate (PMMA)-based composite consisting of bioactive glass beads as an inorganic filler and high molecular-weight PMMA as an organic matrix, has been developed. The purpose of the present study was to evaluate the effect of the filler content on the mechanical properties and osteoconductivity of GBC, to decide the most suitable filler proportion, and to evaluate the degree of cement degradation with time. The bioactive beads, consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass, were added to the cement in various proportions (40-70 wt %). The bending strength of GBC did not differ among the proportions (approximately 136 MPa), but the elastic modulus of bending of GBC increased as the glass bead filler content increased (approximately 4.1-7.2 GPa). The all types of GBC were packed into the intramedullary canals of rat tibiae to evaluate osteoconductivity, as determined by an affinity index calculated as the length of bone in direct contact with the cement surface expressed as a percentage of the total length of the cement surface. Rats were sacrificed at 4, 8, 25, and 39 weeks after implantation, and the affinity index was calculated for each type of GBC at each time point. Histologically, new bone had formed along the surface of all types of GBC within 4 weeks, even in GBC containing only 40 wt % of glass beads. The affinity indices of GBC tended to increase as the proportion of glass bead filler increased and as the implantation period increased. In GBC containing 60 or 70 wt % of glass beads, significant rapid increases in the affinity indices were found from 4 to 8 weeks, and the high values (approximately 70%) were maintained up to 39 weeks. A sign of glass bead degradation was observed at the bone-cement interface in the rat tibiae at 39 weeks. We conclude that, when mechanical properties and osteoconductivity are both taken into consideration, GBC containing 60 or 70 wt % of glass beads is the most suitable formulation, but that further studies are needed to investigate and overcome the degradation.

Animals↗

PubMed1985

Mechanical stability of elastomeric polymers for blood pump applications.

As a series of studies on the mechanical properties of materials used in cardiac prostheses, static and dynamic characteristics and stability of five kinds of elastomeric polymers have been studied by uniaxial tensile and fatigue tests in air at room temperature and in saline solution at 37 degrees C. Of all materials tested in this study, Texin MD85A, a segmented polyether polyurethane, has the lowest flexibility under static and dynamic conditions, with relatively high strength. Hexsyn, a polyolefin rubber, is highly flexible with little stress relaxation. However, this material has very low tensile strength and short elongation, and shows unstable change in the elastic modulus during cyclic deformation. Avcothane 51, a copolymer of polyurethane and silicon, has unstable mechanical properties and gradually stiffens upon cyclic deformation. On the other hand, Biomer, a segmented polyether polyurethane, has high flexibility and shows the most stable behavior during cyclic deformation regardless of test environment. Toyobo TM5, a similar segmented polyurethane to Biomer, has higher strength and ductility than Biomer, although its static and dynamic flexibility are slightly worse and less stable than those of Biomer. These results indicate that Biomer and Toyobo TM5 are more suitable for flexible components of cardiac prostheses.

Air↗

PubMedDate not supplied

Mechanical properties and biomechanical compatibility of porous titanium for dental implants.

Titanium powder with a granule diameter of 420-500 micron was prepared and porous titanium specimens were made from this powder. The mechanical properties of these specimens were examined. The compressive strength and low cyclic compressive fatigue strength were 182 and 40 MPa, respectively. Fractography was also observed by scanning electron microscopy. Typical fatigue characteristics of the bonding areas of the powder were observed. In addition, porous-titanium-coated dental implants with pure titanium cores were prepared. The compressive strength of the material used was 230 MPa, fatigue strength not being improved. Biomechanical stress calculations using the finite element method were made using a model that employed the use of the material implanted in alveolar bone. Shear stress at the implant-bone interface as well as compressive stress concentrations in the bone was calculated. The most suitable elastic modulus for the dental implant was then estimated from these calculations. Finally, based on these results, the use of porous titanium for dental implants was assessed.

Chemical Phenomena↗

Refine your search to explore more results.