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PubMed2001

Gastric wall elasticity assessed by dynamic holographic endoscopy: ex vivo investigations in the porcine stomach.

BACKGROUND: Holographic interferometry is based on the superimposition of the holograms of different motional states of an object on a single holographic storage medium. It has been used to detect structural changes in prosthetic heart valves. The combination of holographic interferometry and endoscopic imaging were applied to assess disturbances of porcine stomach wall elasticity. METHODS: By connecting an electronic speckle pattern interferometry (ESPI) camera system (light source: continuous wave argon-ion laser, lambda = 514.5 nm) to different types of endoscopes, ex vivo experiments were performed on porcine stomachs to detect areas characterized by altered tissue elasticity. With linkage of the endoscopic ESPI camera complex to a fast image processing system, the method of double pulse exposure image subtraction was applied at a video frame rate of 12.5 Hz. RESULTS: The speckle correlation patterns resulting from gentle gastric wall deformation were analyzed in a series of experiments in 16 porcine stomachs. Interferograms of gastric wall areas without structural abnormalities exhibited concentric fringes, whereas fringe patterns corresponding to areas of reduced tissue elasticity were characterized by parallel lines. CONCLUSION: Applying the nondestructive method of dynamic holographic endoscopy, abnormalities of the gastric wall leading to diminished tissue elasticity can be distinguished reliably from surrounding healthy tissue.

Animals↗
PubMed2000

The elasticity and failure of fluid-filled cellular solids: theory and experiment.

We extend and apply theories of filled foam elasticity and failure to recently available data on foods. The predictions of elastic modulus and failure mode dependence on internal pressure and on wall integrity are borne out by photographic evidence of distortion and failure under compressive loading and under the localized stress applied by a knife blade, and by mechanical data on vegetables differing only in their turgor pressure. We calculate the dry modulus of plate-like cellular solids and the cross over between dry-like and fully fluid-filled elastic response. The bulk elastic properties of limp and aging cellular solids are calculated for model systems and compared with our mechanical data, which also show two regimes of response. The mechanics of an aged, limp beam is calculated, thus offering a practical procedure for comparing experiment and theory. This investigation also thereby offers explanations of the connection between turgor pressure and crispness and limpness of cellular materials.

Biomechanical Phenomena↗
PubMed1997

Ionic effects on the elasticity of single DNA molecules.

We used a force-measuring laser tweezers apparatus to determine the elastic properties of lambda-bacteriophage DNA as a function of ionic strength and in the presence of multivalent cations. The electrostatic contribution to the persistence length P varied as the inverse of the ionic strength in monovalent salt, as predicted by the standard worm-like polyelectrolyte model. However, ionic strength is not always the dominant variable in determining the elastic properties of DNA. Monovalent and multivalent ions have quite different effects even when present at the same ionic strength. Multivalent ions lead to P values as low as 250-300 A, well below the high-salt "fully neutralized" value of 450-500 A characteristic of DNA in monovalent salt. The ions Mg2+ and Co(NH3)63+, in which the charge is centrally concentrated, yield lower P values than the polyamines putrescine2+ and spermidine3+, in which the charge is linearly distributed. The elastic stretch modulus, S, and P display opposite trends with ionic strength, in contradiction to predictions of macroscopic elasticity theory. DNA is well described as a worm-like chain at concentrations of trivalent cations capable of inducing condensation, if condensation is prevented by keeping the molecule stretched. A retractile force appears in the presence of multivalent cations at molecular extensions that allow intramolecular contacts, suggesting condensation in stretched DNA occurs by a "thermal ratchet" mechanism.

Cobalt↗
PubMed2005

The elasticity of individual titin PEVK exons measured by single molecule atomic force microscopy.

The I-band region of the giant muscle protein titin contains a large domain enriched for the amino acids proline, glutamate, valine, and lysine and is denoted the PEVK domain. The PEVK domain of titin encodes a random coil shown to be an important factor in the passive elasticity of titin. Muscle-specific splicing of 116 PEVK exons encodes this domain. It has been proposed that proline contents determine the elasticity of the PEVK polypeptide, where the individual exons code for "flexibility cassettes." To test this hypothesis, we have measured the elasticity of three distinct polypeptides encoded by individual PEVK exons (161, 120 and 184) that varied greatly in their proline contents (7, 14, and 37% respectively) and total PEVK contents (55, 70, and 87%). We used single molecule atomic force microscopy techniques to measure the persistence length, p, of the engineered PEVK proteins. Surprisingly, all three exons 161, 120, and 184 coded for proteins with similar values of persistence length, p = 0.92 +/- 0.38, 0.89 +/- 0.42, and 0.98 +/- 0.4 nm, respectively. We conclude that the PEVK exons encode polypeptides of similar elastic properties, unrelated to their total PEVK contents. Hence, alternative splicing solely adjusts the length of the PEVK domain of titin.

Alternative Splicing↗
PubMed2003

Raman microscopy and X-ray diffraction, a combined study of fibrillin-rich microfibrillar elasticity.

Fibrillin-rich microfibrils are essential elastic structures contained within the extracellular matrix of a wide variety of connective tissues. Microfibrils are characterized as beaded filamentous structures with a variable axial periodicity (average 56 nm in the untensioned state); however, the basis of their elasticity remains unknown. This study used a combination of small angle x-ray scattering and Raman microscopy to investigate further the packing of microfibrils within the intact tissue and to determine the role of molecular reorganization in the elasticity of these microfibrils. The application of relatively small strains produced no overall change in either molecular or macromolecular microfibrillar structure. In contrast, the application of larger tissue extensions (up to 150%) resulted in a markedly different structure, as observed by both Raman microscopy and small angle x-ray scattering. These changes occurred at different levels of architecture and are interpreted as ranging from alterations in peptide bond conformation to domain rearrangement. This study demonstrates the importance of molecular elasticity in the mechanical properties of fibrillin-rich microfibrils in the intact tissue.

Animals↗
PubMed2006

Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible.

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

Anisotropy↗
PubMed2001

Time dependence of elastic recovery for characterization of tableting materials.

The purpose of this study was to complete information on elastic recovery during a compression cycle by measuring the expansion of the tablet after ejection, and thus, to measure the whole recovery process, which means the time dependency of elastic recovery. Two methods were applied: manual measurement by a micrometer screw, and a continuous measurement by thermomechanical analysis, always at a constant temperature and humidity. Elastic recovery of the tablet continued after ejection from the die, and the amount of expansion was different for the tableting materials used. The results showed that expansion continued for most of the materials over several days, until a steady state of the tablet and its physical properties was reached. The extent and the profiles of the elastic recovery curves were different for the tableting materials dicalcium phosphate dihydrate, carrageenan, microcrystalline cellulose, cellulose acetate, hydroxypropyl methylcellulose and theophylline monohydrate. There were slight differences between both the methods used. The profiles of the materials could be related to some properties of the materials.

Calcium Phosphates↗
PubMed2001

Influence of elastic deformation of particles on Heckel analysis.

The Heckel equation is one of the most useful equations for describing the compaction properties of pharmaceutical powders. Important material properties (e.g., yield strength) of powders can be derived using Heckel analysis. Two types of Heckel analysis are in common use. One is the "out-of-die," or "zero-pressure" method, the other is the "in-die" or "at-pressure" method. Because particles undergo elastic deformation under pressure, which tends to lower the porosity of the powder bed, the "out-of-die" method describes powder consolidation and compaction more accurately than the "in-die" method. However, "in-die" Heckel analysis has been widely used because of the speed and ease of data collection. Using L-lysine monohydrochloride dihydrate as a model compound, this work analyzes quantitatively the effects of elastic deformation on the calculation of porosity of a tablet, and therefore on the Heckel analysis. The effects of a small change in porosity, epsilon, on Heckel analysis are presented mathematically. It is found that a decrease in porosity of 0.001, when the porosity is lower than 0.05, causes a significant increase in the value of -ln epsilon. Therefore, data at epsilon < 0.05 should be interpreted with caution when using Heckel analysis. Elastic deformation causes positive deviations in the Heckel plot, and therefore leads to a yield strength that is lower than the true value. The lower the elastic modulus of the powder, the greater is the deviation from the true value. Therefore, the "in-die" method gives values of yield strength that are significantly lower than the true values for most pharmaceutical powders.

Elasticity↗
PubMed1967

Theoretical series elastic element length in Rana pipiens sartorius muscles.

Assuming a two component system for the muscle, a series elastic element and a contractile component, the analyses of the isotonic and isometric data points were related to obtain the series elastic stiffness, dP/dl(s), from the relation, See PDF for Equation From the isometric data, dP/dt was obtained and shortening velocity, v, was a result of the isotonic experiments. Substituting (P(0) - P)/T for dP/dt and (P(0) - P)/(P + a) times b for v, dP/dl(s) = (P + a) /bT, where P < P(0), and a, b are constants for any lengths l </= l(0) (Matsumoto, 1965). If the isometric tension and the shortening velocity are recorded for a given muscle length, l(0), although the series elastic, l(s), and the contractile component, l(c), are changing, the total muscle length, l(0) remains fixed and therefore the time constant, T. Integrating, See PDF for Equation the stress-strain relation for the series elastic element, See PDF for Equation is obtained; l(sc0) - l(s) + l(c0)where l(co) equals the contractile component length for a muscle exerting a tension of P(0). For a given P/P(0), l(s) is uniquely determined and must be the same whether on the isotonic or isometric length-tension-time curve. In fact, a locus on one surface curve can be associated with the corresponding locus on the other.

Animals↗
PubMed2000

Three-dimensional static displacement, stimulated echo NMR elasticity imaging.

This article presents a method for measuring three-dimensional mechanical displacement and strain fields using stimulated echo MRI. Additional gradient pulses encode internal displacements in response to an externally applied deformation. By limiting the mechanical transition to the stimulated echo mixing time, a more accurate static displacement measurement is obtained. A three-dimensional elasticity reconstruction within a region of interest having a uniform shear modulus along its boundary is performed by numerically solving discretized elasticity equilibrium equations. Data acquisition, strain measurements and reconstruction were performed using a silicone gel phantom containing an inclusion of known elastic properties. A comparison between two-dimensional and three-dimensional reconstructions from simulated and experimental displacement data shows higher accuracy from the three-dimensional reconstruction. The long-term objective of this work is to provide a method for remotely palpating and elastically quantitating manually inaccessible tissues.

Echocardiography↗
PubMed2006

Derivation of elastic stiffness from site-matched mineral density and acoustic impedance maps.

200 MHz acoustic impedance maps and site-matched synchrotron radiation micro computed tomography (SR-muCT) maps of tissue degree of mineralization of bone (DMB) were used to derive the elastic coefficient c(33) in cross sections of human cortical bone. To accomplish this goal, a model was developed to relate the DMB accessible with SR-muCT to mass density. The formulation incorporates the volume fractions and densities of the major bone tissue components (collagen, mineral and water), and accounts for tissue porosity. We found that the mass density can be well modelled by a second-order polynomial fit to DMB (R(2) = 0.999) and appears to be consistent with measurements of many different types of mineralized tissues. The derived elastic coefficient c(33) correlated more strongly with the acoustic impedance (R(2) = 0.996) than with mass density (R(2) = 0.310). This finding suggests that estimates of c(33) made from measurements of the acoustic impedance are more reliable than those made from density measurements. Mass density and elastic coefficient were in the range between 1.66 and 2.00 g cm(-3) and 14.8 and 75.4 GPa, respectively. Although SAM inspection is limited to the evaluation of carefully prepared sample surfaces, it provides a two-dimensional quantitative estimate of elastic tissue properties at the tissue level.

Acoustics↗
PubMed2003

Effect of Nd:YAG laser irradiation on the hardness and elastic modulus of human dentin.

OBJECTIVE: The purpose of this study was to investigate the changes of hardness and elastic modulus of human dentin after Nd:YAG laser irradiation. BACKGROUND DATA: The application of Nd:YAG laser in dental hard tissues has been widely studied. However, little information is available about the mechanical properties of teeth after Nd:YAG laser irradiation. METHODS: The human dentin was irradiated by Nd:YAG laser through a 400-microm optic bare fiber. The parameters in laser delivery were 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec. Both the hardness and elastic modulus were obtained using an Instron microhardness tester and Vickers indenter. The indentations were then examined under a scanning electron microscope. RESULTS: The hardness and elastic modulus of irradiated human dentin in the energy of 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec were 44.7 kg/mm(2) and 22.8 GPa, and 46.9 kg/mm(2) and 21.4 GPa, respectively. These values were significantly lower than that of non-irradiated dentin by the Student's t test. CONCLUSION: Our study demonstrated that Nd:YAG laser irradiation would reduce the hardness and elastic modulus of human dentin.

Dentin↗
PubMed1990

Effects of muscarinic and beta-adrenergic blockade on the aortic elastic response to epinephrine induced acute hypertension in conscious dogs.

To determine the effects of parasympathetic blockade and beta-blockade on the elastic response of aortic stiffness to vasopressive interventions, we studied 5 unanesthetised adult mongrel dogs by means of a pressure microtransducer and two ultrasonic crystals positioned at opposing sites in the proximal descending thoracic aorta which were used for diameter measurements. Systolic and diastolic changes in pressure and diameter were used to calculate Peterson and incremental elastic moduli. Acute hypertension was induced using infusions of epinephrine during the control period and later propranolol (1.5 mg/kg) plus atropine (0.2 mg/kg). Percent variations of mean aortic diameter were correlated to percent variations in mean aortic pressure in the control period and after autonomic blockade (P less than .001). The slopes of these correlations in the control group were higher than after autonomic blockade (P less than .05). Correlations were also found between Peterson and incremental elastic moduli and mean pressure in the control group and after autonomic blockade (P less than .001). The slopes of the correlations of incremental elastic modulus and Peterson's modulus versus mean aortic pressure were lower in the control group than after blockade (P less than .001). We conclude that in conscious dogs, autonomic blockade with propranolol and atropine decreased the distension and increased the stiffness of the aortic wall in response to acute hypertension mediated by epinephrine.

Acute Disease↗
PubMed1981

Effect of beta-aminopropionitrile on the static elastic properties and blood pressure of spontaneously hypertensive rats.

The static elastic properties of the aorta ad systolic blood pressure in the caudal artery have been measured in 55 spontaneously hypertensive rats of the AS strain. Animals were divided into five groups and treated from the age of 4 to 12 weeks as follows: (1) 0.25 mm silver clip positioned around the right renal artery; (2) renal artery clipped as group (1) followed by daily injection of beta-aminopropionitrile fumarate (beta-APN); (3) daly injection of beta-APN without clipping; (4) daily injection of 0.09% saline; (5) untreated. Mean systolic blood pressures at 12 weeks of age were Group (1) 21.8; Group (2) 16.2; Group (3) 17.0; Group (4) 18.0; Group (5) 17.5 (units kPa). Thus, administration of beta-APN prevents the development of renal hypertension in clipped animals while producing no significant alteration in animals with intact renal arteries. At pressures within the physiological range the functional distensibility of all the treated animals was greater than that of the controls (pressure strain elastic modulus significantly lower). Similar changes were observed in the variation of structural distensibility (incremental elastic modulus) with pressure. At any level of total strain greater than 0.7 the incremental elastic modulus of both groups of animals treated with beta-APN was significantly less than control values. These observations are consistent with reports in the literature that administration of beta-APN causes a reduction in either the amount of cross-linked or normal scleroprotein in the aorta.

Aminopropionitrile↗
PubMed2000

Age-related changes in pumping mechanical behavior of rat ventricle in terms of systolic elastance and resistance.

Both the maximal systolic elastance (Emax) and the theoretical maximal flow (Qmax) can quantify the systolic mechanical behavior of the ventricular pump. Physically, Emax can reflect the intrinsic contractility of the myocardium as an intact heart. The quantity in (Qmax is inversely related to the internal resistance of the left ventricle. How great the effects of age are on these Emax and Qmax has never been examined, however. This study was to determine the ventricular pumping mechanics in terms of the systolic elastance and resistance in male Fischer rats at 6, 12, 18, and 24 months of age. We measured left ventricular (LV) pressure and ascending aortic flow waves using a high-fidelity pressure sensor and an electromagnetic flow probe, respectively. Those two parameters that characterize the systolic pumping mechanics of the left ventricle are obtained by making use of an elastance-resistance model. The basic hemodynamic condition in those animals with different ages is characterized by (i) no significant change in cardiac output and (ii) a decrease in basal heart rate, LV end-systolic pressure, as well as effective arterial volume elastance. Changes that take place in the left ventricle with age include a decline in Emax and an increase in Qmax especially at 24 months. These results demonstrate that the impaired intrinsic contractility of an aging heart may be compensated to some extent by the diminished ventricular internal resistance. Such compensation in aging rats may maintain normal blood flow essential for the metabolic needs of tissues and/or organs before heart dysfunction and failure occur.

Aging↗
PubMed1987

Elastic properties and beta-sheet structure of connectin threads.

Connectin is a very long and flexible protein of striated muscle, linking myosin filaments to z discs in a sarcomere. Isolated native connectin in solution frequently forms elastic threads upon concentration of the solution, by side-by-side association of molecules. An X-ray diffraction study was performed to examine the presence of beta-sheet structure in artificially prepared threads. The elastic properties of such threads were measured at various temperatures. Negative temperature dependence of the elastic coefficient suggests that the elasticity of connectin threads is due to deformation of the three-dimensional structure and not to rubber-like behavior.

Animals↗
PubMed1976

Connectin, an elastic protein from myofibrils.

The elastic protein isolated from myofibrils of chicken skeletal muscle was compared with extracellular non-collagenous reticulin prepared from chicken liver and skeletal muscle. The amino acid compositions of these proteins were similar except that their contents of Phe, Leu, Cys/2, and Hyp were different. The impregnations of the elastic protein and reticulin with silver were also different. The reticulin was not at all elastic. It also differed from reticulin in solubility and antigenicity. It is proposed to call the intracellular elastic protein connectin.

Amino Acids↗
PubMed1999

Elastic tissue in fibroepithelial polyps.

Fibroepithelial polyps are common cutaneous lesions with an unknown etiology. We attempted to demonstrate that fibroepithelial polyps develop secondary to a focal loss of elastic tissue. Forty-five fibroepithelial polyps were examined. All were stained with Verhoeff-van Gieson stain for elastic tissue and examined. All but one specimen had a normal amount of elastin and none revealed abnormally shaped elastic fibers. Abnormal or decreased elastic tissue is not the cause of fibroepithelial polyps.

Elastic Tissue↗