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Results for “Elastic Modulus”

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At least 433 records · Page 24Linked to original sources

PubMed2001

[Strength testing of pins made of human femur cortical bone].

For biomechanical evaluation of cortical bone as a potential source for internal fixation devices, pins of 2 and 3 mm in diameter were made from fresh human femora and subjected to bending loads. Some of the pins were tested without further treatment; others were defatted and dried in acetone solution. Of the acetone-treated pins, some were autoclaved either at 121 degrees C for 20 min or at 134 degrees C for 8 min. Acetone treatment of the pins caused a 5.5% increase in bending strength (p < or = 0.05) and a 6.6% increase in the elastic modulus (p < or = 0.05). The mean bending strength of the acetone-treated pins was 257 +/- 52 N/mm2 and the mean elastic modulus was 18,346 +/- 1292 N/mm2. Autoclaving of the pins at the lower temperature for a longer time led to a decrease in the bending strength of up to 16% and at the higher temperature for a shorter time to a decrease of up to 41%. To compare the strengths of the cortical and synthetic pins, 2-mm Biofix pins were also tested. The Biofix pins showed a 25% higher bending strength than the acetone-treated pins but a 12.5% lower elastic modulus. It should be noted that in animal studies the synthetic Biofix pins showed a 20% loss of strength within 2 days after implantation in situ.

Bioprosthesis↗

PubMed1984

An approach to the noninvasive periodic assessment of arterial elasticity in the young.

The detailed variation of the lumen diameter of common carotid arteries throughout the cardiac cycle was noninvasively measured using a pulse-echo ultrasonic technique in a population of 100 free-living, unrelated, human subjects between the ages of 6 and 25 years. The fractional diameter change (mean +/- SEM) during the cardiac cycle in the 50 male subjects (0.122 +/- 0.004) was found to be significantly (P less than 0.001) greater than the corresponding diameter change in the 50 female subjects (0.106 +/- 0.003). The pressure-strain elastic modulus, Ep, for the carotid arteries was also computed for these subjects by dividing the blood pulse pressure measured in the brachial artery by the fractional diameter change of the carotid. The male elastic modulus (67 +/- 3 kPa) was not significantly (P approximately 0.17) different from the female elastic modulus (62 +/- 2 kPa). Subject age and systolic blood pressure were able to explain approximately one-third of the variability in Ep. Reproductibility studies clearly demonstrated that only a small fraction of the remaining variability could be attributed to experimental technique or intrasubject variability. The results suggest that studies can now be safely performed on young human subjects to assess the effects of a variety of developmental, behavioral, and environmental factors on arterial elasticity. Such results could help to establish an important data base on arterial mechanics which might help in evaluating health promotion recommendations to societies.

Adolescent↗

PubMed2005

Effect of porosity on the fluid flow characteristics and mechanical properties of tantalum scaffolds.

In many cases of traumatic bone injury, bone grafting is required. The primary source of graft material is either autograft or allograft. The use of both material sources are well established, however, both suffer limitations. In response, many grafting alternatives are being explored. This article specifically focuses on a porous tantalum metal grafting material (Trabecular Metaltrade mark) marketed by Zimmer. Twenty-one cylindrical scaffolds were manufactured (66% to 88% porous) and tested for porosity, intrinsic permeability, tangent elastic modulus, and for yield stress and strain behavior. Scaffold microstructural geometries were also measured. Tantalum scaffold intrinsic permeability ranged from 2.1 x 10(-10) to 4.8 x 10(-10) m(2) and tangent elastic modulus ranged from 373 MPa to 2.2 GPa. Both intrinsic permeability and tangent elastic modulus closely matched porosity-matched cancellous bone specimens from a variety of species and anatomic locations. Scaffold yield stress ranged from 4 to 12.7 MPa and was comparable to bovine and human cancellous bone. Yield strain was unaffected by scaffold porosity (average = 0.010 mm/mm). Understanding these structure-function relationships will help complete the basic physical characterization of this new material and will aid in the development of realistic mathematical models, ultimately enhancing future implant designs utilizing this material.

Biocompatible Materials↗

PubMed1980

[Studies on the biomechanics of the human clavicle (author's transl)].

64 non preserved and 35 preserved clavicles were fractured in three defined positions in a bending test by a tension testing machine with electronic measurement of force. 30 non preserved bones were fractured in an axial infraction test. Force-deflection-diagrams were registered, and the values of maximum load, breaking load, ultimate deflection and energy were correlated to cross section and thickness of compacta. The significantly greater non preserved male clavicles are loadable at a higher level (medium breaking load about 1200 N) than female bones (medium breaking load abut 800 N). The breaking energy of the more flexible female clavicles is about 30% lower than those of males whereas elastic modulus of female clavicles is significant greater. Preservation has a significant influence on biomechanical properties of bones: ultimate deflection decreases; breaking energy, ultimate stress and elastic modulus increase. Breaking load is greatest in the middle portion of the clavicle, while deflection is greatest in the sternal portion. Removal of periosteum causes lower breaking load, deflection, ultimate stress and elastic modulus as well. With axial load clavicle fractures occur most frequently between middle and sternal third.

Age Factors↗

PubMed1994

Resistance and elasticity of the suture threads employed in cardiac bioprostheses.

The mechanoelastic features of five types of sutures were studied. The breaking stress for each was determined by means of tensile tests in which a constant strain rate was applied, and a tensile test with graduated stress and relaxation defined the elastic limit, i.e. the point beyond which deformation becomes irreversible. The study of the stress-strain curve during this elastic period enabled us to obtain the mathematical function that governs these reversible deformations, which shows excellence of fit (R2 > 0.98). The prime derivative at each point of the resulting functions is the elastic modulus, the best parameter for comparing the elasticities of the suture threads. Since breaking stress alone does not suitably define the mechanical quality of a suture, we propose the use of other parameters during the elastic period, such as percentage of elongation at a point 10 times lower than the elastic limit (safety coefficient of 10), and tensile stress and elastic modulus at the said point, which are more reliable in the assessment of the resistance and elasticity of these threads.

Animals↗

PubMedDate not supplied

Effect of re-using nickel-chromium alloy on its ultimate tensile strength, yield strength and modulus of elasticity.

In order to bring down the cost of the castings used in fixed partial denture prosthesis, a study was conducted by reusing the nickel chromium alloy without adding any new material. We studied the effect on the ultimate tensile strength, yield strength and modulus of elasticity after reusing the nickel-chromium alloys. Results showed degenerative changes in the properties evaluated after recasting. These changes were statistically significant, suggesting that it can not be reused.

Chromium Alloys↗

PubMed2006

Modulus of elasticity and dry-matter content of bovine claw horn affected by the changes of chronic laminitis.

The mechanical properties of horn samples from 22 hind claws with chronic laminitis were determined in adult Austrian Fleckvieh cows. The resistance to deformation was quantified as the modulus of elasticity (E). Tension tests revealed mean E values of 520MPa for the dorsal wall, 243MPa for the abaxial wall, 339MPa for the axial wall and 97MPa for the sole. E tended to be lower in laminitic horn than in sound horn in all segments tested, with the difference being largest in the abaxial wall. The mean dry-matter content (DMC) of the laminitic claws was 75.8% in the dorsal wall, 75.86% in the abaxial wall, 71.15% in the axial wall and 69.28% in the sole. These values are generally comparable to those for sound claws except in the axial wall. Further, E and DMC were only correlated in the axial wall. Chronic laminitis leads to a low resistance of claw horn to mechanical insults in the dorsal wall, abaxial wall and sole, and to the loss of a correlation between the E and DMC in these segments. The reason for these alterations is therefore not increased ingress of moisture, but must be due to changes in the microstructure, biochemical components and/or horn formation by the diseased dermis.

Animals↗

PubMed1980

[Stress/strain ratio of the left ventricle in systole. Influence of age and of some drugs (author's transl)].

By testing with echocardiographic techniques on healthy hearted human subjects, it is shown that the myocardium elastic modulus, defined as the ratio between the equatorial stress in the left ventricular wall and the strain of the left ventricular cavity, results to be independent from the age of subjects at rest. In healthy subjects the treatment with vasoxine, a vessel-constrictor drug, causes an increase in the elastic modulus, the treatment with isoproterenol, an inotropic agent, makes the elastic modulus decrease, whereas the treatment with peritrate, a nitroderivative, does not modify this modulus. In conclusion this parameter, though it cannot be considered a cardiac contractility index, yet it may be utilized to characterize the left ventricular functional state. The alterations caused by the use of vasoxine and isoproterenol in cardiac frequency, left ventricular geometry and arterial pressure, in the examined subjects, are comparable with the alterations reported in the recent literature.

Adult↗

PubMedDate not supplied

[Electrostriction of plane lipid membranes and elasticity moduli].

A comparative analysis is given of the data on measuring the deformation of bilayer lipid membranes (BLM) by the optical (reflexometry) and capacity methods with regard to both the electrostatic forces compressing the bilayer and the changes in bilayer tension. The essential difficulties in interpreting (in terms of elastic modulus) the data on electrostriction changes in BLM integral capacity are shown. Based on the optical data it is shown that most "soft" BLM formed from lipid solution in short-chain (below n-decane) alkanes have a cross-section elasticity modulus E no less than 10(-7) Pa even at zero frequency. The elasticity modulus in the membrane plane upon isotropic tension (E) is about two times as much as E. At a voltage jump, the time of establishing a new value of the contact angle theta between the volumic phase (torus) and the bilayer and, respectively, of a new value of bilayer tension does not exceed 0.25 ms.

Elasticity↗

PubMed1999

Mechanics and composition of human subcutaneous resistance arteries in essential hypertension.

Mechanical properties of arteries are altered in some rat models of hypertension, and this may influence peripheral resistance and blood pressure as well as some of the complications of hypertension. It has usually been assumed that arterial wall stiffness is increased in hypertension, although recent studies suggest that this may not necessarily be the case in large arteries. We determined whether the mechanics of human resistance arteries are altered in hypertension. Subcutaneous resistance arteries (lumen diameter<300 microm) were isolated from hypertensive and normotensive subjects of similar ages (46+/-3 and 43+/-4 years, respectively). Vessels were mounted in a pressurized myograph, deactivated, and exposed to intraluminal pressures ranging from 3 to 140 mm Hg. At each pressure, lumen and media dimensions were measured. Media-to-lumen ratio and media width were greater in hypertensive vessels, reducing wall stress (P<0.01), whereas media cross section was similar in vessels from both groups. Isobaric elastic modulus (which is influenced by vessel geometry and by wall component stiffness) was lower in hypertensive vessels (P<0. 01). Stiffness of wall components (slope of incremental elastic modulus versus stress, which is geometry-independent) was significantly lower in hypertensive vessels (8.2+/-0.7) versus normotensive vessels (11.0+/-1.0, P<0.05), whereas distensibility was unchanged. Electron microscopic analysis of the media of the small arteries showed a greater collagen to elastin ratio (P<0.05) in the media of vessels from hypertensive patients. In conclusion, the stiffness of wall components (slope of elastic modulus versus stress) is not increased but is in fact decreased in subcutaneous resistance arteries from patients with mild essential hypertension. Reduced stiffness of resistance arteries from hypertensive patients does not appear to relate to changes in volume density of extracellular matrix components but may be the result of changes in extracellular matrix architecture or cell-matrix attachment, which remains to be established.

Adult↗

PubMed1995

Aortic wall properties in normotensive and hypertensive rats of various ages in vivo.

The distensibility of the arterial system, which is partly determined by arterial wall structure, smooth muscle tone, and actual pressure level, decreases with aging and hypertension. Our aim was to compare aortic wall properties in 3- and 6-month-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at comparable blood pressures in vivo. During ketamine/xylazine anesthesia in rats we performed ultrasound arterial wall tracking and invasive pressure measurements to determine, at the level of the thoracic aorta, diastolic pressure, diastolic lumen area, changes in pressure and lumen area during the cardiac cycle, and indexes of compliance and distensibility. These observations were combined with histological measurements for determination of media cross-sectional area and thickness and the incremental elastic modulus under conditions as expected in situ. Anesthesia abolished the difference in diastolic pressure between SHR and WKY. Between 3 and 6 months of age in WKY, diastolic area and incremental elastic modulus increased significantly, distensibility decreased, and all other recorded variables were not modified. Between 3 and 6 months of age in SHR, diastolic area and incremental elastic modulus increased, distensibility of the aortic wall decreased, and all other mechanical and structural properties did not change significantly. At both ages, diastolic area and compliance were significantly smaller in SHR than WKY. The other mechanical and structural properties measured or calculated at comparable pressure did not differ between strains. Differences between the aorta of 3- and 6-month-old rats and between strains observed in vivo at comparable pressures can largely be attributed to differences in lumen caliber.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1994

Effects of two low-osmolar contrast media, ioxaglate and iopamidol, on erythrocyte membrane elasticity.

RATIONALE AND OBJECTIVES: The effect of ioxaglate and iopamidol, two recently developed low-osmolality contrast media, on the shear elasticity of erythrocyte membranes was studied at an iodine concentration of 300 mg/mL and at a 20% volume concentration and compared with that obtained for control solutions matched in osmolality. METHODS: The authors used a micromanipulation technique, which consists of visualizing deformations of individual erythrocytes when gently aspirated into the tip of a glass micropipette by an accurately controlled pressure. An erythrocyte membrane shear elasticity modulus mu was then deduced. An increase in mu corresponded to an increase in erythrocyte membrane rigidity. RESULTS: In all cases, the erythrocytes remained discocytic. The shear elasticity modulus of the erythrocyte membrane is found to be (1) in the presence of ioxaglate (4.3 +/- 0.9 microN/m) lower (P < .001) than in the presence of hyperosmolar saline (6.2 +/- 1.3 microN/m) and lower (P < .02) than in the presence of iso-osmolar control (4.7 +/- 0.7 microN/m); (2) in the presence of iopamidol (5.4 +/- 0.7 microN/m) lower (P < .001) than in the presence of hyperosmolar sucrose (6.4 +/- 1.2 microN/m) and higher (P < .001) than in the presence of iso-osmolar control (4.7 +/- 0.7 microN/m); and (3) lower (P < .001) in the presence of ioxaglate (4.3 +/- 0.9 microN/m) than in the presence of iopamidol (5.4 +/- 0.7 microN/m). CONCLUSIONS: Under the experimental conditions used, both contrast media (ioxaglate and iopamidol) modify the erythrocyte membrane shear elasticity modulus less than do the matched hyperosmolar controls. Moreover, ioxaglate makes the erythrocyte membrane less rigid, and iopamidol makes the erythrocyte membrane more rigid than does the iso-osmolar control.

Elasticity↗

PubMed1981

Biomechanical properties of normal and fibrosclerotic human cerebral arteries.

Quasi-static passive mechanical properties of histologically fibrosclerotic and normal groups of human anterior cerebral arteries (ACA) and internal carotid arteries (ICA) were studied in vivo. Cylindrical arterial segments were subjected to slow, cyclic inflation by air in the range of 5-250 mm Hg intraluminal pressure at axial isometry. To characterize mechanical properties, incremental elastic modulus, incremental distensibility and strain energy density were computed from the continuously recorded pressure-external diameter curves. Compared to normal arteries, at identical intraluminal pressures, the elastic modulus of fibrosclerotic arteries was found to be 34-45% lower in ACA and 40-56% lower in ICA, and the radius to wall thickness ratio was 25-30% smaller in ACA and 37-38% smaller in ICA. Distensibility of fibrosclerotic arteries was not smaller than that of the normal vessels. There were no significant differences in internal radius and in strain energy density between the fibrosclerotic and normal groups. Results of mathematical modelling suggests that the observed decrease in the elastic modulus of fibrosclerotic arteries was accompanied by different types of structural reorganization in the case of ACA and ICA. It is supposed that changes in mechanical properties of the passive wall elements have a compensatory character to restore some hemodynamically important properties of fibrosclerotic arteries, namely tangential stress, incremental distensibility or characteristic impedance.

Arteriosclerosis↗

PubMed1987

Evaluation of a filter aspiration technique to determine membrane deformability.

A filter aspiration technique for the measurement of red cell membrane deformability described by Brailsford et al. (Blood Cells 1977;3:25) was evaluated. Pore diameters of 0.6 and 1.0 micron were used. Portions of red cells were aspirated with various hydrostatic pressures between 1 and 9 mm H2O. After fixation the filter was removed and the length and radius of the pressure-induced tongues measured by scanning electron microscopy. One to several tongues per cell were observed. The number of tongues had no influence on the measurements at pressures less than or equal to 7 mm H2O. The elastic modulus of the red cell membrane was calculated; it yielded 2.9 (+/- 0.4) X 10(-3) dynes/cm. Data obtained with filter aspiration were compared with the results obtained concurrently with the micropipette technique. A good correlation was found for normal red cells (r = 0.74, P less than 0.001). Stomatocytes produced by chlorpromazine in vitro had an increased elastic modulus with both methods. For echinocytes produced by salicylate or adenosine triphosphate depletion, the elastic modulus as determined by filter aspiration was normal, but the modulus as measured by micropipette aspiration was increased. Possible reasons for the difference are discussed. We conclude that the filter aspiration is a valid technique to measure elastic properties of red cell membranes, except when there are surface irregularities, such as those in the echinocytes.

Erythrocyte Deformability↗

PubMed2005

Mechanical properties of the human patellar tendon, in vivo.

BACKGROUND: Mechanical properties of the human patellar tendon are largely based on cadaver studies, which may not necessarily be applicable to the human patellar tendon, in vivo. While ultrasonography is an attractive non-invasive method for studying human, in vivo, muscle-tendon behaviour, it has mostly been used to examine Achilles tendon properties. We examine the accuracy of human patellar tendon elongation, in vivo, and its within-day and between-day reproducibility. METHODS: Subjects performed four maximal 10-s ramp isometric knee extension trials to examine within-day reproducibility, and the procedure was repeated on a separate day to assess between-day reproducibility. Continuous and simultaneous ultrasonography based measurement of both tibial and patellar movement together with patellar tendon force yielded mechanical estimates. RESULTS: Longitudinal tibial displacement corresponded to 45 (SEM 8) % of the overall tibia-patella displacement. For within-day reproducibility there was no difference between trials for stiffness [trial a, 4334 (SEM 562) N/mm; trial b, 4273 (SEM 533) N/mm], strain [trial a, 6.9 (SEM 0.6) %; trial b, 6.8 (SEM 0.7) %] or elastic modulus [trial a, 1.09 (SEM 0.12) GPa; trial b, 1.09 (SEM 0.10) GPa]. The within day correlation coefficient and typical error were 0.95 and 9.9% for stiffness, 0.97 and 5.5% for strain, and 0.94 and 9.4% for elastic modulus. The corresponding values for between days were 0.94 and 8.7% for stiffness, 0.98 and 3.7% for strain, and 0.86 and 9.6% for elastic modulus. INTERPRETATION: The present methodology of assessing human patellar tendon elongation, strain and stiffness, in vivo, is accurate and reproducible which permits its use in future investigations of patellar tendon biomechanics and the potential effects of various interventions.

Adult↗

PubMed1999

Predictive value of bone mineral density and Singh index for the in vitro mechanical properties of cancellous bone in the femoral head.

OBJECTIVE: The purpose of this study was to assess the validity of two methodically different radiological parameters, bone mineral density and Singh Index, for the prediction of mechanical properties in femoral cancellous bone. DESIGN: Coherence between in vitro evaluation of mechanical properties and bone mineral density on a femoral bone slice, combined with clinical determination of Singh Index on ordinary X-rays. BACKGROUND: It is accepted that bone densitometry yields excellent prediction of mechanical bone quality, but is considered to be an expensive and not widely available method for routine diagnostics in clinical practice. In contrast, determination of Singh Index is an inexpensive and simple technique, but its predictive value for bone mechanics is still controversially discussed. METHODS: We used cortically confined bone slices from 33 femoral heads. Bone mineral density was measured using quantitative computed tomography. Strength and elastic modulus were assessed by mechanical testing in up to 39 circular positions on each slice. Singh Index was evaluated on ordinary X-rays of the hip by two independent readers. RESULTS: Bone mineral density showed strong correlations with strength (r=0.86) and good correlations with elastic modulus (r=0.68). Singh Index correlated well with strength (r=0.70), but only moderately with elastic modulus (r=0.52). CONCLUSIONS: The strong validity of bone mineral density in predicting mechanical bone quality was confirmed. Singh Index assessment permits a rough estimation of mechanical strength in particular and can therefore be used for first estimations of mechanical bone quality, provided that readings were performed by experienced clinicians. RELEVANCE: Reduced mechanical bone quality induces an increase in fracture risk. Whenever performed, bone mineral density measurement allows an excellent evaluation of the mechanical properties of cancellous bone in the hip and can be recommended for screening evaluations. The assessment of Singh Index on ordinary X-rays of the hip is an inexpensive and simple method, and allows a rough estimation of the mechanical quality of the femur. However, due to its subjective character, its predictive value for the mechanical quality of bone in individual patients remains uncertain.

Aged↗

PubMed2002

Investigation of ultrasonic properties of PAG and MAGIC polymer gel dosimeters.

Ultrasonic speed of propagation and attenuation were investigated as a function of absorbed radiation dose in PAG and MAGIC polymer gel dosimeters. Both PAG and MAGIC gel dosimeters displayed a dependence of ultrasonic parameters on absorbed dose with attenuation displaying significant changes in the dose range investigated. The ultrasonic attenuation dose sensitivity at 4 MHz in MAGIC gels was determined to be 4.7 +/- 0.3 dB m(-1) Gy(-1) and for PAG 3.9 +/- 0.3 dB m(-1) Gy(-1). Ultrasonic speed dose sensitivities were 0.178 +/- 0.006 m s(-1) Gy(-1) for MAGIC gel and -0.44 +/- 0.02 m s(-1) Gy(-1) for PAG. Density and compressional elastic modulus were investigated to explain the different sensitivities of ultrasonic speed to radiation for PAG and MAGIC gels. The different sensitivities were found to be due to differences in the compressional elastic modulus as a function of dose for the two formulations. To understand the physical phenomena underlying the increase in ultrasonic attenuation with dose, the viscoelastic properties of the gels were studied. Results suggest that at ultrasonic frequencies, attenuation in polymer gel dosimeters is primarily due to volume viscosity. It is concluded that ultrasonic attenuation significantly increases with absorbed dose. Also, the ultrasonic speed in polymer gel dosimeters is affected by changes in dosimeter elastic modulus that are likely to be a result of polymerization. It is suggested that ultrasound is a sufficiently sensitive technique for polymer gel dosimetry.

Acrylic Resins↗

PubMed2005

Physical properties of human premolar cementum: hardness and elasticity.

AIMS: To determine if the cementum on the maxillary right and left first premolars has identical physical properties. METHODS: Ten normal maxillary first premolar teeth, extracted from five orthodontic patients with a mean age of 14.0 years, were used. The teeth had not been subjected to an orthodontic force. The hardness and elastic modulus of the cementum were measured on the buccal and lingual surfaces of the roots at three locations: cervical third, middle third and apical third. RESULTS: There were no significant side-to-side differences in cementum hardness (Mean side-to-side difference: 0.0063 GPa; SD: 0.0279; p = 0.525) or elastic modulus (Mean side-to-side difference: -0.027 GPa; SD: 0.111; p = 0.814). The hardness and elastic modulus of the cementum decreased from cervical to apical regions on both root surfaces. CONCLUSIONS: Similar physical properties of the cementum on the maxillary right and left first premolars suggest that intra-arch comparisons can be used to investigate root resorption caused by orthodontic forces.

Adolescent↗