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Results for “Elastic Modulus”

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PubMed2002

[Investigation on culture of rat pulmonary microvascular endothelial cells and their viscoelasticity].

It is the infent of this study to establish a simple method for cultivation of rat pulmonary microvascular endothelial cells(PMVECs) and investigate the viscoelasticity of PMVECs. First, we obtained rat's peripheral pulmonary tissue, which then was cut into small pieces and cultured with 3 ml DMEM containing 20% bovine calf serum, 90 U/ml heparin, 4 mmol L-glutamine, 100 U/ml penicillin and 100 micrograms/ml streptomycin. Next, moved away the pulmonary tissue pieces 60 h later, and started passage 2-4 days after continued culture. Last, digested and separated PMVECs and studied viscoelastic coefficients of PMVECs by using micropipette aspiration technique. The results revealed that the cultured PMVECs showed regular cobblestone morphology and conformed with endothelial cells morphological characterization by phase contrast microscopy. PMVECs elastic modulus K1 was 49.3 +/- 9.2 Pa, K2 was 73.2 +/- 24.8 Pa, and it's viscosity factor mu was 19.2 +/- 7.2 Pa. s. These data demonstrate that it is feasible to cultivate PMVECs with tissue pieces method, and PMVECs is of greater rigidity.

Animals↗

PubMedDate not supplied

[A longitudinal elasticity study of hair from the human head in forensic medicine].

A rapid and sensitive method for assessing hair keratin stretch elasticity modulus has been developed. The technique is based on measuring the oscillation resonance frequency of hair fragments fixed at one end. The first results indicate a high sensitivity of the method and the possibility of its use in forensic medicine.

Adolescent↗

PubMed2003

Stress analysis of interbody fusion--finite element modelling of intervertebral implant and vertebral body.

OBJECTIVE: To investigate stresses in cage type interbody fusion systems during compressive loading.Design. The study uses finite element methods to investigate predicted stresses. Previously published experimental material properties are used as inputs to the numerical simulation. BACKGROUND: Interbody spinal fusion procedures using cage style intervertebral implants often cause subsidence failure of the vertebral endplate, resulting in potential pain and mechanical instability of the fusion system. METHODS: Finite element models were developed to simulate compressive load transfer between interbody implants and adjacent vertebral body. The vertebral body was modelled using separate finite element mesh regions for cancellous core and cortical shell, with the meshes tied together at the core/shell interface. Coulomb friction was implemented to model the contact between implants and vertebral endplate.Results. Simulation results predicted endplate stresses of approximately 12 times the nominal contact pressure due to differing deformation stiffnesses of the implant and endplate structures. Reduction of the cancellous core elastic modulus to simulate severely osteoporotic bone resulted in endplate stresses up to three times higher than the values for an intact cancellous core. CONCLUSIONS: In this study, finite element analysis was used to investigate the stresses in interbody fusion systems. Published vertebral loads corresponding to certain activities were shown to generate endplate stresses which approach and exceed the failure stress for cortical bone. Endplate stresses are strongly dependent on the modulus of the underlying cancellous core. RELEVANCE: Endplate subsidence failure can potentially occur at the corners of existing cage-type interbody implants under physiological compressive loads. Matching material properties between cortical endplate and implant does not guarantee optimal contact conditions, and overall bending stiffness should be assessed.

Compressive Strength↗

PubMed2000

A new imaging technique for measuring the surface strains applied to dentine.

OBJECTIVES: To investigate possible variation in directional material properties of dentine in relationship to tubule orientation using a new optical imaging technique. METHOD: The optical imaging technique records photometrically a grid pattern formed by using a transmission electron microscope grid as a template on the polished surface of the dentine. The grid pattern is silhouetted onto the sample surface using standard techniques. Compression (c) and diametral compression (dc) tests were undertaken using a servo hydraulic testing machine (MTS model 810) acting on rectangular blocks of dentine with dimensions 1.5 x 1.0 x 1.0 mm (for c) and cylindrical samples with dimensions 2.1 mm in diameter and 1-1.5 mm thick (for dc), respectively. The samples were cut using a diamond wheel and miniature lathe and the cut surfaces polished. Images due to a changing load profile were captured and stored as digitised files on a computer for later analysis. The precision is mainly determined by the pixel resolution of the charged-coupled device camera. RESULTS: Preliminary results show the value of elastic modulus of dentine (10.4 +/- 2.9 GPa) to be similar to those previously reported in the literature. Very small localised strains at the surface of a sample can be observed qualitatively and measured quantitatively by reference to the line spacing (approximately 85 microns). Maximum strength varied with tubule orientation and (compressive/tensile) stress. CONCLUSION: Very small samples of dentine may be investigated for strain in more than one direction using the imaging technique described. These results may be more appropriate for finding relative directional change rather than obtaining the elastic properties of the dentine.

Compressive Strength↗

PubMed1992

Alteration of Components of Leaf Water Potential and Water Content in Velvetleaf under the Effects of Long-Term Humidity Difference.

Velvetleaf (Abutilon theophrasti Medik.) was grown in growth chambers set at 45 or 85% relative humidity at 30 degrees C, CO(2) 350 microliters per liter and 1000 micromoles per square meter per second of photosynthetically active radiation. Soil water potential was maintained at -0.05 megapascal by subirrigation with half strength Hoagland solution. The third, fourth, and fifth leaves from the base of 21- and 25-day-old plants were used for pressure-volume measurements. Components of leaf water status including water potential (osmotic and potential associated with the apoplast), leaf water content (apoplasmic and symplasmic water), and elastic modulus of leaf tissue were determined. Results indicate: (a) persistent dry air generated leaves with lower water potential at a given relative water content than did humid air; (b) the higher total leaf water content in plants grown in dry air was related to an increase in apoplasmic water, whereas symplasmic water remained similar in both humidity treatments; (c) difference in leaf water potential between low and high humidity treatments was related to decreased potential associated with the apoplast but not to a change in cell wall elasticity.

Journal Article↗

PubMed1999

Analysis of indentation: implications for measuring mechanical properties with atomic force microscopy.

Indentation using the atomic force microscope (AFM) has potential to measure detailed micromechanical properties of soft biological samples. However, interpretation of the results is complicated by the tapered shape of the AFM probe tip, and its small size relative to the depth of indentation. Finite element models (FEMs) were used to examine effects of indentation depth, tip geometry, and material nonlinearity and heterogeneity on the finite indentation response. Widely applied infinitesimal strain models agreed with FEM results for linear elastic materials, but yielded substantial errors in the estimated properties for nonlinear elastic materials. By accounting for the indenter geometry to compute an apparent elastic modulus as a function of indentation depth, nonlinearity and heterogeneity of material properties may be identified. Furthermore, combined finite indentation and biaxial stretch may reveal the specific functional form of the constitutive law--a requirement for quantitative estimates of material constants to be extracted from AFM indentation data.

Biomechanical Phenomena↗

PubMed2000

Time-dependent mechanical behaviour of the periodontal ligament.

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.

Animals↗

PubMed2003

Dependence of the mechanical properties of a pullulan film on the preparation temperature.

The mechanical properties of pullulan films prepared at various temperatures were investigated. The films prepared at high temperatures (40 degrees C and 60 degrees C; H-films) did not show any clear plastic deformation in tensile test, indicating that they were brittle. In contrast, those prepared at low temperatures (4 degrees C, 13 degrees C, and 25 degrees C; L-films) showed such deformation. The latter films had higher values for both tensile strength and elastic modulus than the former, indicating that the L-films were stiffer and more flexible than the H-films. Stretching the L-films clearly showed a shear deformation band inclined at 45 degrees to the stretching direction, indicating that they were amorphous.

Elasticity↗

PubMed2001

Dynamic behaviour of the common femoral artery: age and gender of minor importance.

The distensibility of elastic arteries has been extensively studied, while studies of muscular arteries are sparse. The influences of age and gender on the mechanical properties of the common femoral artery (CFA) were studied. The pulsatile diameter changes of the CFA were noninvasively measured using echo-tracking sonography in 173 healthy volunteers (95 females, 78 males, range 7-81 years). In combination with blood pressure measurements, stiffness (beta) and pressure strain elastic modulus (Ep) were calculated. Neither beta nor Ep was related to age or gender and a considerable interindividual variation was present. The CFA diameter increased with age. In conclusion, the distensibility of this muscular artery is not clearly affected by age or gender, although the diameter increases with age. This indicates remodelling of the arterial wall and an impact of vascular smooth muscles on long-term wall mechanics. Thus, there appear to be fundamental differences in the dynamic behaviour of the common femoral artery when compared to elastic arteries, such as the aorta and the common carotid artery.

Adolescent↗

PubMed2001

Viscoelasticity of dilute solutions of semiflexible polymers.

We show using Brownian dynamics simulations and theory how the shear relaxation modulus G(t) of dilute solutions of relatively stiff semiflexible polymers differs qualitatively from that of rigid rods. For chains shorter than their persistence length, G(t) exhibits three time regimes: At very early times, when the longitudinal deformation is affine, G(t) approximately t(-3/4). Over a broad intermediate regime, during which the chain length relaxes, G(t) approximately t(-5/4). At long times, G(t) mimics that of rigid rods. A model of the polymer as an effectively extensible rod with a frequency dependent elastic modulus B(omega) approximately ((i)omega)(3/4) quantitatively describes G(t) throughout the first two regimes.

Journal Article↗

PubMed1980

Minimum energy analysis of membrane deformation applied to pipet aspiration and surface adhesion of red blood cells.

An experimental procedure is demonstrated which can be used to determine the interfacial free energy density for red cell membrane adhesion and membrane elastic properties. The experiment involves micropipet aspiration of a flaccid red blood cell and manipulation of the cell proximal to a surface where adhesion occurs. A minimum free energy method is developed to model the equilibrium contour of unsupported membrane regions and to evaluate the partial derivatives of the total free energy, which correspond to the micropipet suction force and the interfacial free energy density of adhesion. It is shown that the bending elasticity of the red cell membrane does not contribute significantly to the pressure required to aspirate a flaccid red cell. Based on experimental evidence, the upper bound for the bending or curvature elastic modulus of the red cell membranes is 10-12 ergs (dyn-cm). Analysis of the adhesion experiment shows that interfacial free energy densities for red cell adhesion can be measured from a lower limit of 10-4 ergs/cm2 to an upper limit established by the membrane tension for lysis of 5-10 ergs/cm2.

Cell Adhesion↗

PubMed1999

The effect of monomer-to-powder ratio on the material properties of cranioplastic.

Percutaneous vertebroplasty consists of injecting polymethylmethacrylate cement into the cancellous bone of vertebral bodies for the treatment of various lesions of the spine, including osteoporotic compression fractures. Clinicians practicing vertebroplasty commonly alter the mixture of monomer-to-powder recommended by the manufacturer in an effort to decrease viscosity and increase the working time. The purpose of the current study was to measure the effect that varying the monomer-to-powder ratio has on the compressive material properties of a cement (Cranioplastic) commonly used in vertebroplasty. Cylindrical specimens were prepared varying a monomer-to-polymer ratio of 0.40 to 1.07 ml/g and tested per the American Society for Testing and Materials standard F451. Specimens prepared at 0.53 mL/g, which is near the manufacturer's recommended monomer-to-polymer mixture of 0.57 mL/g, exhibited the greatest mean values for ultimate compressive stress, yield stress, and elastic modulus. Specimens prepared at higher or lower ratios exhibited diminished strength, in some cases by as much as 24%. Although altering the monomer-to-powder ratio affects the cement's material properties, it is as yet unknown if the decrease is clinically significant.

Bone Cements↗

PubMed2002

A novel ultrasound technique to study the biomechanics of the human esophagus in vivo.

The objectives of this study were to validate a novel ultrasound technique and to use it to study the circumferential stress-strain properties of the human esophagus in vivo. A manometric catheter equipped with a high-compliance bag and a high-frequency intraluminal ultrasonography probe was used to record esophageal pressure and images. Validation studies were performed in vitro followed by in vivo studies in healthy human subjects. Esophageal distensions were performed with either an isovolumic (5-20 ml of water) or with an isobaric (10-60 mmHg) technique. Sustained distension was also performed for 3 min in each subject. The circumferential wall stress and strain were calculated. In vitro studies indicate that the ultrasound technique can make measurements of the esophageal wall with an accuracy of 0.01 mm. The in vivo studies provide the necessary data to compute the Kirchhoff's stress, Green's strain, and Young's elastic modulus during esophageal distensions. The stress-strain relationship revealed a linear shape, the slope of which corresponds to the Young's modulus. During sustained distensions, we found dynamic changes of stress and strain during the period of distension. We describe and validate a novel ultrasound technique that allows measurement of biomechanical properties of the esophagus in vivo in humans.

Adolescent↗

PubMed2005

Dilation and reduced distensibility of rat carotid artery with aging.

To better understand the pathogenesis of increased arterial stiffening with aging, the relative contribution of geometry (lumen diameter) and stiffening of wall components (elastic modulus) to reduced distensibility of rat carotid artery in the early stages of aging was investigated. Pressure-volume (distensibility) relationships were measured in excised, in vitro perfused right carotid artery of 7-. 10- and 20-month old, male Sprague-Dawley rats. The left carotid artery of rats was perfusion-fixed in situ at 100 mm Hg and then embedded in epoxy for morphometric measurements. Compared to 7- and 10-month old rats, there was dilation (increased lumen diameter), increased wall thickness, and reduced distensibility and unchanged elastic moduli of carotid artery in 20-month old rats. Dilation (with early recruitment of collagen fibrils during pressure rise) rather than increased stiffness of wall components appears to be the cause of reduced distensibility of rat carotid artery in the early stages of aging.

Aging↗

PubMed1988

Regulation by Ca2+ of membrane elasticity of bovine chromaffin granules.

In a range of [Ca2+] similar to cytosolic transient, a drastic reduction from about 20 dyn/cm to almost zero was observed in the membrane elastic modulus of bovine chromaffin granules, isolated in a solution containing 0.3 M sucrose and 5 mM Hepes at pH 7.0, and measured by combination of osmotic swelling and dynamic light-scattering (DLS) methods. This result suggests that the granule membrane becomes extremely flexible as a prelude to exocytosis.

Animals↗

PubMed2000

Cell mechanics studied by a reconstituted model tissue.

Tissue models reconstituted from cells and extracellular matrix (ECM) simulate natural tissues. Cytoskeletal and matrix proteins govern the force exerted by a tissue and its stiffness. Cells regulate cytoskeletal structure and remodel ECM to produce mechanical changes during tissue development and wound healing. Characterization and control of mechanical properties of reconstituted tissues are essential for tissue engineering applications. We have quantitatively characterized mechanical properties of connective tissue models, fibroblast-populated matrices (FPMs), via uniaxial stretch measurements. FPMs resemble natural tissues in their exponential dependence of stress on strain and linear dependence of stiffness on force at a given strain. Activating cellular contractile forces by calf serum and disrupting F-actin by cytochalasin D yield "active" and "passive" components, which respectively emphasize cellular and matrix mechanical contributions. The strain-dependent stress and elastic modulus of the active component were independent of cell density above a threshold density. The same quantities for the passive component increased with cell number due to compression and reorganization of the matrix by the cells.

Animals↗

PubMed1983

Influence of cholesterol content on red cell membrane viscoelasticity and fluidity.

The purpose of this investigation was to correlate the viscoelastic properties and lipid fluidity of the red blood cell membrane to its lipid composition. The viscoelastic properties of human red cells that had been enriched or depleted in cholesterol were determined by the micropipette technique. The lipid fluidity of the outer and inner leaflets of the erythrocyte membrane was concurrently assessed by steady state fluorescence depolarization. The elastic modulus and the viscosity moduli of the erythrocyte membrane showed no significant differences between the cholesterol-modified and the control cells. Cholesterol enrichment decreased the lipid fluidity of the outer membrane leaflet alone, and cholesterol depletion increased the fluidity mainly of the inner leaflet.

Cholesterol↗

PubMed2001

3D-finite element analyses of cusp movements in a human upper premolar, restored with adhesive resin-based composites.

The combination of diverse materials and complex geometry makes stress distribution analysis in teeth very complicated. Simulation in a computerized model might enable a study of the simultaneous interaction of the many variables. A 3D solid model of a human maxillary premolar was prepared and exported into a 3D-finite element model (FEM). Additionally, a generic class II MOD cavity preparation and restoration was simulated in the FEM model by a proper choice of the mesh volumes. A validation procedure of the FEM model was executed based on a comparison of theoretical calculations and experimental data. Different rigidities were assigned to the adhesive system and restorative materials. Two different stress conditions were simulated: (a) stresses arising from the polymerization shrinkage and (b) stresses resulting from shrinkage stress in combination with vertical occlusal loading. Three different cases were analyzed: a sound tooth, a tooth with a class II MOD cavity, adhesively restored with a high (25 GPa) and one with a low (12.5GPa) elastic modulus composite. The cusp movements induced by polymerization stress and (over)-functional occlusal loading were evaluated. While cusp displacement was higher for the more rigid composites due to the pre-stressing from polymerization shrinkage, cusp movements turned out to be lower for the more flexible composites in case the restored tooth which was stressed by the occlusal loading. This preliminary study by 3D FEA on adhesively restored teeth with a class II MOD cavity indicated that Young's modulus values of the restorative materials play an essential role in the success of the restoration. Premature failure due to stresses arising from polymerization shrinkage and occlusal loading can be prevented by proper selection and combination of materials.

Bicuspid↗