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Results for “Elastic Modulus”

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PubMed2001

Micromechanical and structural properties of a pennate diatom investigated by atomic force microscopy.

The mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Bréb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces. Different experimental configurations and evaluation methods were tested. They gave a consistent result of the shell micromechanical properties. The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical properties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences. The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.

Diatoms↗

PubMed1997

Mathematical optimization of elastic properties: application to cementless hip stem design.

The designer of a cementless hip stem in total hip replacement must find a balance between two conflicting demands. On the one hand, a stiff stem shields the surrounding bone from mechanical loading (stress shielding), which may lead to bone loss, particularly around the proximal part of the stem. Reducing the stem stiffness decreases the amount of stress shielding and hence the amount of bone loss. However, this measure inevitably promotes higher proximal interface stresses and thereby increases the risk of proximal interface failure. The designer's task therefore is to optimize the stem stiffness in order to find the best compromise in the conflict. Yet, a better compromise might be found when the stem material was nonhomogeneous, in other words when an arbitrary distribution of the elastic properties inside the stem was allowed. The number of conceivable designs would increase enormously, making the designer's task almost impossible. In the present paper, we develop a numerical design optimization method to determine the optimal stiffness characteristics for a hip stem. A finite element program is coupled with a numerical optimization method, thus producing a design optimization scheme. The scheme minimizes the probability for interface failure while limiting the amount of bone loss, by adapting the parameters describing the nonhomogeneous elastic modulus distribution. As an example, a simplified model of a hip stem is made, whose modulus distribution is optimized. Assuming equal long-term bone loss, the maximum interface stress can be reduced by over 50 percent when compared to a homogeneous flexible stem, thus demonstrating the value of the new approach.

Elasticity↗

PubMed1980

The effect of mucolytic agents on the rheologic and transport properties of canine tracheal mucus.

The effect of several sulfhydryl and other agents on the rheologic and mucociliary transport properties of a model secretion, reconstituted canine tracheal mucus, was investigated. The mucus was obtained via the canine tracheal pouch. Rheologic properties were determined by mirorheometry, and the ciliary transport rate was determined using the frog palate technique. It was found that N-acetyl cysteine decreased the elastic modulus, leading to improved mucociliary transport at concentrations such that the mucin did not precipitate. S-carboxymethyl cysteine had no effect on either mucus properties or mucociliary transport rate, and its reported effectiveness in vivo must be due to some mechanism other than solubilization of mucin. Similar results were found with other blocked sulfhydryl compounds. Urea and potassium iodide to decrease mucus elasticity, but are harmful to cilia at the concentrations needed.

Acetylcysteine↗

PubMed1999

Mechanical design in arteries.

The most important mechanical property of the artery wall is its non-linear elasticity. Over the last century, this has been well-documented in vessels in many animals, from humans to lobsters. Arteries must be distensible to provide capacitance and pulse-smoothing in the circulation, but they must also be stable to inflation over a range of pressure. These mechanical requirements are met by strain-dependent increases in the elastic modulus of the vascular wall, manifest by a J-shaped stress-strain curve, as typically exhibited by other soft biological tissues. All vertebrates and invertebrates with closed circulatory systems have arteries with this non-linear behaviour, but specific tissue properties vary to give correct function for the physiological pressure range of each species. In all cases, the non-linear elasticity is a product of the parallel arrangement of rubbery and stiff connective tissue elements in the artery wall, and differences in composition and tissue architecture can account for the observed variations in mechanical properties. This phenomenon is most pronounced in large whales, in which very high compliance in the aortic arch and exceptionally low compliance in the descending aorta occur, and is correlated with specific modifications in the arterial structure.

Animals↗

PubMed1981

Mechanical factors and tissue stresses in chronic hydronephrosis.

From 21 dogs kidneys removed at 0, 1, 2, and 4 weeks after ureteral blockage we found the expected early increase, than subsequent decrease, in pressure and the expected continuing increase in volume and thinning of the walls. However the calculated wall stress builds up continuously with time as does the elastic modulus of the wall. By the 4th week, the wall material has become approximately 3 times as resistant to stretch as the normal ureter.

Animals↗

PubMed1990

Wall extensibility and cell hydraulic conductivity decrease in enlarging stem tissues at low water potentials.

Measurements with a guillotine psychrometer (H Nonami, JS Boyer [1990] Plant Physiol 94: 1601-1609) indicate that the inhibition of stem growth at low water potentials (low psi(w)) is accompanied by decreases in cell wall extensibility and tissue hydraulic conductance to water that eventually limit growth rate in soybean (Glycine max L. Merr.). To check this conclusion, we measured cell wall properties and cell hydraulic conductivities with independent techniques in soybean seedlings grown and treated the same way, i.e. grown in the dark and exposed to low psi(w) by transplanting dark grown seedlings to vermiculite of low water content. Wall properties were measured with an extensiometer modified for intact plants, and conductances were measured with a cell pressure probe in intact plants. Theory was developed to relate the wall measurements to those with the psychrometer. In the elongation zone, the plastic deformability of the walls decreased when measured with the extensiometer while growth was inhibited at low psi(w). It increased during a modest growth recovery. This behavior was the same as that for the wall extensibility observed previously with the psychrometer. Tissue that was killed before measurement with the extensiometer also showed a similar response, indicating that changes in wall extensibility represented changes in wall physical properties and not rates of wall biosynthesis. The elastic compliance (reciprocal of bulk elastic modulus) did not change in the elongating or mature tissue. The hydraulic conductivity of cortical cells decreased in the elongating tissue and increased slightly during growth recovery in a response similar to that observed with the psychrometer. We conclude that the plastic properties of the cell walls and the conductance of the cells to water were decreased at low psi(w) but that the elastic properties of the walls were of little consequence in this response.

Journal Article↗

PubMed2000

Estrogen-dependent tensile properties of the rabbit knee medial collateral ligament.

The influence of oophorectomy or continuous administration of estradiol on the tensile properties of the rabbit knee medial collateral ligament was investigated. Young postpubertal female New Zealand white rabbits were either oophorectomized or underwent a sham operation. The sham-operated animals received in addition a daily dosage of 4 mg 17beta-estradiol. After 5 months the animals were killed, and the material properties of the bone-ligament-bone complex in one knee were determined using a material testing machine and video system, and compared to non-treated control animals. There was no difference in elastic modulus between the groups. However, the ligaments from low-dose estrogen-treated animals had a smaller cross-sectional area and a higher ultimate tensile strength than those from controls or oophorectomized rabbits (P<0.04-0.0003).

Animals↗

PubMed2004

Measurements of mouse pulmonary artery biomechanics.

BACKGROUND: Robust techniques for characterizing the biomechanical properties of mouse pulmonary arteries will permit exciting gene-level hypotheses regarding pulmonary vascular disease to be tested in genetically engineered animals. In this paper, we present the first measurements of the biomechanical properties of mouse pulmonary arteries. METHOD OF APPROACH: In an isolated vessel perfusion system, transmural pressure, internal diameter and wall thickness were measured during inflation and deflation of mouse pulmonary arteries over low (5-40 mmHg) and high (10-120 mmHg) pressure ranges representing physiological pressures in the pulmonary and systemic circulations, respectively. RESULTS: During inflation, circumferential stress versus strain showed the nonlinear "J"-shape typical of arteries. Hudetz's incremental elastic modulus ranged from 27 +/- 13 kPa (n = 7) during low-pressure inflation to 2,700 +/- 1,700 kPa (n = 9) during high-pressure inflation. The low and high-pressure testing protocols yielded quantitatively indistinguishable stress-strain and modulus-strain results. Histology performed to assess the state of the tissue after mechanical testing showed intact medial and adventitial architecture with some loss of endothelium, suggesting that smooth muscle cell contractile strength could also be measured with these techniques. CONCLUSIONS: The measurement techniques described demonstrate the feasibility of quantifying mouse pulmonary artery biomechanical properties. Stress-strain behavior and incremental modulus values are presented for normal, healthy arteries over a wide pressure range. These techniques will be useful for investigations into biomechanical abnormalities in pulmonary vascular disease.

Animals↗

PubMed2000

Are there systemic changes in the arterial biomechanics of intracranial aneurysm patients?

Current theories on the development of intracranial aneurysm suggest that there is a general weakness of vascular connective tissue. Potential systemic alterations in arterial wall biomechanics were tested in the present study. A three-dimensional in vitro stress-strain analysis was made in the 0-200-0 mmHg pressure range on cylindrical segments excised from the anterior cerebral artery, the radial artery and from the arteria dorsalis pedis of aneurysm patients and of control cadavers. In the anterior cerebral artery from aneurysm patients (intracranial artery segments directly not affected by the aneurysm or by the subarachnoid bleeding), we found the wall thickness to be larger (0.1480+/-.019 versus 0.091+/-0.004 mm), the radius/wall thickness ratio smaller (9.7+/-1.4 versus 14.1+/-1.2), and the tangential wall stress lower [(0.122+/-0.019)x10(6) versus (0.181+/-0.016)x10(6) N/m2 at 100 mmHg] than in control subjects. Reduced radius was found in the extremity arteries studied. Elastic parameters, as incremental distensibility and elastic modulus, were remarkable similar. Our study demonstrates changes in the geometry of walls of arteries not directly affected by aneurysm formation, and it thus confirms systemic vascular pathology in this disease. At the same time, these data show that the molecular and morphological defects of arterial connective tissue formation generally thought to induce intracranial aneurysms will probably not affect the components responsible for the passive elastic properties of the vascular wall.

Adult↗

PubMed2002

Communicating hydrocephalus: the biomechanics of progressive ventricular enlargement revisited.

BACKGROUND: This article investigates the physical mechanisms involved in the chronic ventricular enlargement that accompanies communicating hydrocephalus (CH)--including its normal and low-pressure forms. In particular, it proposes that this phenomenon can be explained by the combined effect of: (a) a reversal of interstitial fluid flow in the parenchyma, and (b) a reduction in the elastic modulus of the cerebral mantle. METHOD: To investigate this hypothesis, these changes have been incorporated into a finite element computer simulation of CH, in which brain tissue is idealized as a sponge-like material. The fluid pressure in the lateral ventricles and the subarachnoid space has been set to 10 mmHg, while the fluid pressure inside the parenchyma has been set to 7.5 mmHg. The elastic moduli of white and gray matter have been set to the reduced values of 1 and 5 kPa, respectively. FINDINGS: The simulation revealed a substantial ventricular distension (6.5 mm mean outward displacement), which was accompanied by the appearance of stress concentrations in the cerebral mantle. INTERPRETATION: These results support the notion that a relative reduction in intraparenchymal fluid pressure coupled with low tissue elasticity can produce both a significant ventricular enlargement and periventricular solid stress concentrations.

Biomechanical Phenomena↗

PubMed2002

Magnesium supplementation and deoxycorticosterone acetate--salt hypertension: effect on arterial mechanical properties and on activity of endothelin-1.

The aim of this study was to show whether the decrease in blood pressure induced by Mg supplementation in deoxycorticosterone acetate - salt (DOCA-salt) hypertensive rats is associated with mechanical modifications of blood vessels and (or) changes in tissular production and (or) vasoconstrictor activity to endothelin-1. DOCA-salt treatment increased blood pressure, media thickness, cross-sectional area, and lumen diameter of carotid arteries. Distensibility and incremental elastic modulus versus stress were not altered in carotid arteries, suggesting that the DOCA-salt vessel wall adapts structurally to preserve its blood pressure buffering capacity. Magnesium supplementation attenuated DOCA-salt hypertension. In comparison with normotensive rats, systolic, mean, and pulse pressures were higher whereas diastolic pressure was not different in Mg-supplemented DOCA-salt rats. Magnesium supplementation did not significantly modify the elastic parameters of carotid arteries. In resistance mesenteric arteries, DOCA-salt hypertension induces an inward hypertrophic remodeling. Magnesium supplementation attenuates wall hypertrophy and increases lumen diameter to the normotensive diameter, suggesting a decrease in peripheral resistance. Magnesium supplementation normalizes the altered vasoconstrictor activity of endothelin-1 in mesenteric arteries and attenuates endothelin-1 overproduction in kidney, left ventricle, and aorta of DOCA-salt rats. These findings suggest that Mg supplementation prevents blood pressure elevation by attenuating peripheral resistance and by decreasing hypertrophic effect of endothelin-1 via inhibition of endothelin-1 production.

Animals↗

PubMed2006

Quantitative optical coherence tomographic elastography: method for assessing arterial mechanical properties.

Optical coherence tomography elastography represents a potentially attractive new technique for measuring elastic properties of tissues on a micron scale. In this study, the feasibility of optical coherence tomography (OCT) to study the mechanical properties of phantoms and atherosclerotic arterial samples is reported. The elastic modulus of tissue-mimicking phantoms was measured using OCT and correlated with mechanical measurements. The results indicate that elastography based on OCT represents an attractive technique for evaluating the mechanical properties of tissues.

Aorta↗

PubMed1987

Effect of glucose and galactose on red blood cell membrane deformability.

The effect of glucose and galactose on the membrane deformability of red blood cells (RBC) suspended in isotonic solution was determined using micropipette aspiration technique. In this method, a negative pressure was applied to the RBC membrane via a micropipette and the resulting deformation was analyzed using a Kelvin model to yield a membrane elastic modulus E. When glucose concentration was increased from 0 to 0.3 M/dm3 in the extracellular media, E increased seven-fold (p less than 0.0001) with most increase occurring in the 0-0.05 M/dm3 range. The increase in E due to glucose was not completely reversible. The time constant of increase in E was about 14 minutes. Whereas, galactose had no significant effect on the membrane elasticity up to a concentration of 0.3 M/dm3. Increase in the RBC membrane rigidity in the presence of glucose may be due to binding of glucose to the membrane and intracellular proteins. The results obtained may be important for explanation of decrease in tumor blood flow during hyperglycemia.

Animals↗

PubMed2003

Micromechanical studies of mitotic chromosomes.

We review micromechanical experiments studying mechanoelastic properties of mitotic chromosomes. We discuss the history of this field, starting from the classic in vivo experiments of Nicklas (1983). We then focus on experiments where chromosomes were extracted from prometaphase cells and then studied by micromanipulation and microfluidic biochemical techniques. These experiments reveal that chromosomes have a well-behaved elastic response over a fivefold range of stretching, with an elastic modulus similar to that of a loosely tethered polymer network. Perturbation by microfluidic "spraying" of various ions reveals that the mitotic chromosome can be rapidly and reversibly decondensed or overcondensed, i.e., that the native state is not maximally compacted. We compare our results for chromosomes from cells to results of experiments by Houchmandzadeh and Dimitrov (1999) on chromatids reconstituted using Xenopus egg extracts. Remarkably, while the stretching elastic response of reconstituted chromosomes is similar to that observed for chromosomes from cells, reconstituted chromosomes are far more easily bent. This result suggests that reconstituted chromatids have a large-scale structure that is quite different from chromosomes in somatic cells. Finally, we discuss microspraying experiments of DNA-cutting enzymes, which reveal that the element that gives mitotic chromosomes their mechanical integrity is DNA itself. These experiments indicate that chromatin-condensing proteins are not organized into a mechanically contiguous "scaffold," but instead that the mitotic chromosome is best thought of as a cross-linked network of chromatin. Preliminary results from restriction enzyme digestion experiments indicate a spacing between chromatin "cross-links" of roughly 15 kb, a size similar to that inferred from classical chromatin loop isolation studies. These results suggest a general strategy for the use of micromanipulation methods for the study of chromosome structure.

Animals↗

PubMed1998

Titanium alloys in total joint replacement--a materials science perspective.

Increased use of titanium alloys as biomaterials is occurring due to their lower modulus, superior biocompatibility and enhanced corrosion resistance when compared to more conventional stainless steels and cobalt-based alloys. These attractive properties were a driving force for the early introduction of alpha (cpTi) and alpha + beta (Ti-6A1-4V) alloys as well as for the more recent development of new Ti-alloy compositions and orthopaedic metastable beta titanium alloys. The later possess enhanced biocompatibility, reduced elastic modulus, and superior strain-controlled and notch fatigue resistance. However, the poor shear strength and wear resistance of titanium alloys have nevertheless limited their biomedical use. Although the wear resistance of beta-Ti alloys has shown some improvement when compared to alpha + beta alloys, the ultimate utility of orthopaedic titanium alloys as wear components will require a more complete fundamental understanding of the wear mechanisms involved. This review examines current information on the physical and mechanical characteristics of titanium alloys used in artifical joint replacement prostheses, with a special focus on those issues associated with the long-term prosthetic requirements, e.g., fatigue and wear.

Alloys↗

PubMed2003

Spastic muscle cells are shorter and stiffer than normal cells.

The mechanical properties of isolated single muscle fiber segments were measured in muscle cells obtained from patients undergoing surgery for correction of flexion contractures secondary to static perinatal encephalopathy (cerebral palsy). "Normal" muscle cells from patients with intact neuromuscular function were also mechanically tested. Fiber segments taken from subjects with spasticity developed passive tension at significantly shorter sarcomere lengths (1.84 +/- 0.05 microm, n = 15) than fibers taken from normal subjects (2.20 +/- 0.04 microm, n = 35). Elastic modulus of the stress-strain relationship in fibers from patients with spasticity (55.00 +/- 6.61 kPa) was almost double that measured in normal fibers (28.25 +/- 3.31 kPa). The fact that these muscle cells from patients with spasticity have a shorter resting sarcomere length and increased modulus compared with normal muscle cells suggests dramatic remodeling of intracellular or extracellular muscle structural components such as titin and collagen. Such changes in muscles of patients with spasticity may have implications for therapy.

Adult↗

PubMed1992

Micromechanics modeling of Haversian cortical bone properties.

A finite-element micromechanics model for Haversian cortical bone tissue has been developed and studied. The model is an extension of two-dimensional micromechanics techniques for fiber-reinforced composite materials. Haversian systems, or secondary osteons, are considered to be the fiber component, and interstitial lamellar bone the matrix material. The cement line is included as an 'interphase' component along the fiber/matrix interface. The model assumes a regular repeatable spacing of the longitudinally aligned continuous fibers and is, therefore, restricted to approximating Haversian cortical bone in its present form. Haversian porosity is modeled explicitly by incorporating a hollow fiber to represent the Haversian canal. Solutions have been obtained by applying uniform macroscopic stresses to the boundaries of the repeating unit cell model. Macroscopic mechanical property predictions correspond reasonably well with the experimental data for cortical bone, but are necessarily dependent on the input properties for each constituent, which are not well established. The predicted variation in the elastic modulus with porosity is not as sensitive as that observed experimentally. Stresses within the constituents can also be modeled with this method and are demonstrated to deviate from the macroscopic applied stress levels.

Biomechanical Phenomena↗

PubMed2007

Adaptive nanomechanical response of stratified polymer brush structures.

We have fabricated a stratified polymer surface film with tunable thickness (within 17-34 nm) through facile, room-temperature, UV-initiated polymerization with a temperature-sensitive pNIPAAM layer confined beneath a hydrophobic layer. AFM morphology and ellipsometric measurements were measured at each grafting step, along with XPS measurements of the overall layer to verify layer growth. The strong characteristic LCST behavior of pNIPAAM was observed in water, with a 100% change in thickness above and below this transition. The AFM nanomechanical results demonstrate vertical gradients of the elastic response tunable to a desired state by the external temperature. These temperature-sensitive, adaptive polymer structures with the pNIPAAM layer "hidden" beneath the rubbery, hydrophobic PBA topmost layer represent an interesting example of nanoengineering surfaces with properties such as adhesion, elastic modulus, and multi-level structural reorganization responsive to fluidic and temperature variations that can be important for biological purposes such as implant coatings, cell-surface mimicry, and drug delivery vehicles.

Acrylic Resins↗