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Results for “Elastic Modulus”

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PubMed2002

An automated approach for direct measurement of two-dimensional strain distributions within articular cartilage under unconfined compression.

An automated approachfor measuring in situ two-dimensional strain fields was developed and validated for its application to cartilage mechanics. This approach combines video microscopy, optimized digital image correlation (DIC), thin-plate spline smoothing (TPSS) and generalized cross-validation (GCV) techniques to achieve the desired efficiency and accuracy. Results demonstrate that sub-pixel accuracies can be achieved for measuring tissue displacements with this methodology with a measurement uncertainty ranging from 0.25 to 0.30 pixels. The deformational gradients (from which the strains are determined) can be evaluated directly using the optimized DIC, with a measurement uncertainty of 0.017 to approximately 0.032. In actual measurements of strain in cartilage, TPSS and differentiation can be used to achieve a more accurate measurement of the gradients from the displacement data. Using this automated approach, the two-dimensional strain fields inside immature bovine carpometacarpal joint cartilage specimens under unconfined compression were characterized (n=21). The depth-dependent apparent elastic modulus and Poisson's ratio were also determined and found to be smallest at the articular surface and increasing with depth. The apparent Poisson's ratio is found to decrease with increasing compressive strain, with values as low as 0.01 observed near the articular surface at 25% compression. The variation of the apparent Poisson's ratio with depth is found to be consistent with a theoretical model of cartilage which accounts for the disparity in its tensile and compressive moduli.

Animals↗

PubMed1985

[Non-invasive measurement of the elastic properties of the abdominal aorta and the analysis of aging change--changes of elasticity of the aorta by aging].

For the purpose of the non-invasive measurement of the elastic properties of human abdominal aorta, we developed high sensitive measurement system of small displacement of tissue. This system consists of phase locked echo tracking loop combined with conventional B-mode imaging. The sensitivity to displacement in the model experiment was in the order of micro meter. Pressure strain elastic modulus (Ep) and stiffness parameter (beta) of abdominal aorta were calculated by our equipment in 61 persons, which were subdivided into 3 age groups, the young group (20 persons less than 35 yrs.), the middle aged group (21 persons between 35 yrs. and 60 yrs.), and the old group (20 persons more than 60 yrs.). Ep in the young group was 0.99 +/- 0.34 X 10(6) dynes/cm2, the middle aged group 1.55 +/- 0.68 X 10(6) dynes/cm2, the old group 3.80 +/- 2.05 X 10(6) dynes/cm2. Beta in the young group was 9.3 +/- 3.3, the middle aged group 12.0 +/- 4.5, the old group 27.6 +/- 14.0. The values of Ep and beta in the old group were significantly different from those in the young group and the middle group. Moreover large deviation of the both values was showed within the old group. The influence of aging on the elastic properties of abdominal aorta was found with large individual variation in relation to the progression of the sclerotic change.

Adult↗

PubMedDate not supplied

Constitutive modelling of brain tissue: experiment and theory.

Recent developments in computer-integrated and robot-aided surgery--in particular, the emergence of automatic surgical tools and robots--as well as advances in virtual reality techniques, call for closer examination of the mechanical properties of very soft tissues (such as brain, liver, kidney, etc.). The ultimate goal of our research into the biomechanics of these tissues is the development of corresponding, realistic mathematical models. This paper contains experimental results of in vitro, uniaxial, unconfined compression of swine brain tissue and discusses a single-phase, non-linear, viscoelastic tissue model. The experimental results obtained for three loading velocities, ranging over five orders of magnitude, are presented. The applied strain rates have been much lower than those applied in previous studies, focused on injury modelling. The stress-strain curves are concave upward for all compression rates containing no linear portion from which a meaningful elastic modulus might be determined. The tissue response stiffened as the loading speed increased, indicating a strong stress-strain rate dependence. The use of the single-phase model is recommended for applications in registration, surgical operation planning and training systems as well as a control system of an image-guided surgical robot. The material constants for the brain tissue are evaluated. Agreement between the proposed theoretical model and experiment is good for compression levels reaching 30% and for loading velocities varying over five orders of magnitude.

Algorithms↗

PubMedDate not supplied

Finite element analysis study of the effect of superstructure material on stress distribution in an implant-supported fixed prosthesis.

This study used three-dimensional finite element analysis to investigate the effect of three different occlusal surface materials (resin, resin composite, and porcelain) and four different framework materials (gold, silver-palladium, cobalt-chromium, titanium alloys) on the stress distribution in a six-implant-supported mandibular fixed prosthesis and surrounding bone. A total of 172 N vertical load was distributed over the entire occlusal surface of the finite element model. Generated stress values were calculated in the occlusal surface material, framework, prosthesis retaining screws, implants, and surrounding cortical and spongy bones. The results obtained demonstrated that using a prosthesis superstructure material with a lower elastic modulus (1) did not lead to substantial differences in stress patterns nor in values at the cortical and spongy bones surrounding the implants; and (2) concentrated stresses in the retaining screws for the prosthesis and thus increased the potential risk of prosthesis failure. For the single loading condition investigated, the optimal combination of materials was found to be cobalt-chromium for the framework and porcelain for the occlusal surface.

Acrylic Resins↗

PubMed1998

Chondrocytes in culture produce a mechanically functional tissue.

A mechanically testable tissue was grown in vitro from rabbit chondrocytes that were initially plated at high density (approximately 80,000 cells/cm2). The DNA, collagen, and proteoglycan content, as well as the tissue thickness, tensile stiffness, and synthesis rates, were measured at 4, 6, and 8 weeks. The biochemical properties were similar to those for immature cartilage, with predominantly type-II collagen produced; this indicated that the cells retained their chondrocytic phenotype. The tissue formed a coherent mechanical layer with testable tensile stiffness as early as 4 weeks. The tensile elastic modulus reached 1.3 MPa at 8 weeks, which is in the range of values for native cartilage from the midzone. Collagen density was approximately 24 mg/ml at 8 weeks, which is about one-half the value for native cartilage, and the collagen fibril diameters were smaller. Chondrocytes in culture responded to culture conditions and were stimulated by cytokine interleukin-1beta. When culture conditions were varied to RPMI nutrient medium with lower fetal bovine serum and higher ascorbic acid concentrations, the thickness decreased and the modulus increased significantly. Interleukin-1beta, added to the 8-week culture for 2 weeks, caused a decrease of 60% in thickness, a decrease of 81% in proteoglycan content, and a decrease of 31% in collagen content; this is similar to the response of cartilage explants to interleukin-1beta. This cartilage analog may be useful as a model system to study structure-function relationships in cartilage or as cartilage-replacement tissue.

Animals↗

PubMed1989

Effect of temperature and ageing on the mechanical properties of dental polymeric composite materials.

Evaluation of the mechanical properties of some dental composite materials, Compact, Finesse and Prisma-Fil based on bisphenol glycidyl methacrylate resin was undertaken by applying compression, tension and hardness tests. The effects of temperature and ageing times on these properties were studied. There was a marked increase in the mechanical properties (compressive strength, diametral tensile strength, compressive elastic modulus and hardness) for all the investigated composites with increase of both temperature and time. This was explained in terms of the influence of temperature on the polymerization rate of the materials. The improvement in the mechanical properties of the samples, kept at 37 degrees C, was attributed to further and continued polymerization of the polymer content of their resin system. Such mechanical improvement was verified by the regression equation of linearity versus both temperature and time.

Chemical Phenomena↗

PubMed2003

Elastohydrodynamic separation of pleural surfaces during breathing.

To examine effects of lung motion on the separation of pleural surfaces during breathing, we modeled the pleural space in two dimensions as a thin layer of fluid separating a stationary elastic solid and a sliding flat solid surface. The undeformed elastic solid contained a series of bumps, to represent tissue surface features, introducing unevenness in fluid layer thickness. We computed the extent of deformation of the solid as a function of sliding velocity, solid elastic modulus, and bump geometry (wavelength and amplitude). For physiological values of the parameters, significant deformation occurs (i.e. bumps are 'flattened') promoting less variation in fluid thickness and decreased fluid shear stress. In addition, deformation is persistent; bumps of sufficient wavelength, once deformed, require a recovery time longer than a typical breath-to-breath interval to return near their undeformed configuration. These results suggest that in the pleural space during normal breathing, separation of pleural surfaces is promoted by the reciprocating sliding of lung and chest wall.

Body Fluids↗

PubMedDate not supplied

Viscoelastic properties and dynamics of porcine gastric mucin.

Gastric mucin is a glycoprotein known to undergo a pH-dependent sol-gel transition that is crucial to the protective function of the gastric mucus layer in mammalian stomachs. We present microscope-based dynamic light scattering data on porcine gastric mucin at pH 6 (solution) and pH 2 (gel) with and without the presence of tracer particles. The data provide a measurement of the microscale viscosity and the shear elastic modulus as well as an estimate of the mesh size of the gel formed at pH 2. We observe that the microscale viscosity in the gel is about 100-fold lower than its macroscopic viscosity, suggesting that large pores open up in the gel reducing frictional effects. The data presented here help to characterize physiologically relevant viscoelastic properties of an important biological macromolecule and may also serve to shed light on diffusive motion of small particles in the complex heterogeneous environment of a polymer gel network.

Animals↗

PubMed2004

The impact of factor XIII on coagulation kinetics and clot strength determined by thrombelastography.

Fibrinogen has been shown to be responsible for most protein-mediated clot strength via thrombelastography. However, factor XIII (FXIII) activity also plays a prominent role in the development of clot strength. Thus, we hypothesized that changes in FXIII activity would significantly increase clot strength. FXIII (0%, 1%, 6.25%, 12.5%, 25%, 50%, and 100% normal activity) was placed in a fixed volume of citrated FXIII-deficient plasma with 1% tissue factor and calcium chloride and underwent thrombelastography for 10 min. We measured the variables reaction time (R; a measurement of clot initiation), alpha (a measure of the rate of clot formation), amplitude (A; a measure of clot strength), and shear elastic modulus (G; a measure of clot strength). FXIII activity significantly decreased R in a pattern of exponential decay (R2 = 0.77; P < 0.001). FXIII activity significantly increased alpha, following a sigmoidal pattern (R2 = 0.88; P < 0.001). Finally, increases in FXIII activity significantly increased A and G in a sigmoidal pattern (R = 0.89; P < 0.001). We concluded that FXHI significantly affects R, alpha, A, and G. Thus, transfusion decision making with protein-mediated thrombelastographic patterns must account for the contribution of both fibrinogen and FXIII.

Blood Coagulation↗

PubMed1979

Human cervical mucus. V. Oral contraceptives and mucus rheologic properties.

Mucus viscoelasticity on individual samples obtained from patients using combination oral contraceptives was quantitated by microrheometry. These results, in conjunction with mucus chemical characterization, indicate that combination oral contraceptive use eliminates the cyclic variations in mucus chemical, physicochemical, and rheologic properties associated with the ovulatory menstrual cycle. A correlation was demonstrated between the mucus elastic modulus and mucus nondialyzable dry weight, and the mucins produced during oral contraceptive therapy were shown to be similar to those recovered from ovulatory donors. Differences in mucus properties were noted when donors using estrogenic contraceptives were contrasted with those using androgenic contraceptives. On the basis of established relationships between sperm penetrability and mucus solids content, it was concluded that the use of contraceptives, as examined in this study, provided a secondary degree of fertility control at the cervical level.

Cervix Mucus↗

PubMed1986

Non-invasive ultrasonic measurement of the elastic properties of the human abdominal aorta.

A new echo tracking device linked to real time ultrasonic B mode equipment was developed to measure non-invasively the elastic properties of the human abdominal aorta. Pulsatile diameter change and mean diameter of the abdominal aorta were measured in 61 subjects with this ultrasonic device. Strain and pressure-strain elastic modulus Ep were calculated from pulsatile diameter change, diameter, and pulse pressure obtained by the auscultatory method. Strain significantly decreased with age; 0.076(0.024) (mean(SD)) in group 1 (20 young adults below the age of 35 years); 0.048(0.024) in group 2 (21 middle aged subjects between the ages of 35 and 60 years); and 0.030(0.010) in group 3 (20 elderly subjects over the age of 60 years). Ep values were 0.99(0.34) X 10(5), 1.55(0.68) X 10(5), and 3.80(2.05) X 10(5) N X m-2 in groups 1, 2, and 3 respectively. Ep in group 3 was significantly higher than in groups 1 and 2. The regression equation relating Ep to age was Ep = (-0.72 + 0.058 X age) X 10(5) N X m-2 (r = 0.73). The Ep value and its age related increase agreed with the findings in postmortem arteries. The elastic properties of the abdominal aorta could, therefore, be determined non-invasively by this ultrasonic method.

Aorta, Abdominal↗

PubMed2005

Biocatalytic synthesis of highly ordered degradable dextran-based hydrogels.

We have prepared unique macroporous and ordered dextran-based hydrogels using a single-step biocatalytic transesterification reaction between dextran and divinyladipate in neat dimethylsulfoxide. These hydrogels show a unimodal distribution of interconnected pores with average diameters from 0.4 to 2.0 microm depending on the degree of substitution. In addition, the hydrogels show a higher elastic modulus for a given swelling ratio than chemically synthesized dextran-based hydrogels. In vivo studies in rats show that the hydrogel networks are degradable over a range of time scales from 5 to over 40 days, and possess good biocompatibility, as reflected in only a mild inflammatory reaction and minor fibrous capsule formation during the time-frame of subcutaneous implantation. These combined properties may offer competitive advantages in biomedical applications ranging from tissue engineering to controlled drug delivery.

Absorbable Implants↗

PubMed2005

Changes in the long head of the biceps tendon in rotator cuff tear shoulders.

BACKGROUND: Morphologic changes in the long head of the biceps tendon have been described in association with rotator cuff disease, yet mechanical significance of these changes remains unclear. METHODS: An experiment was designed to test the hypotheses that the cross-sectional area and material properties of the long head of the biceps tendon are different in shoulders with full thickness rotator cuff tears and shoulders with intact rotator cuff tendons. Seven pairs of cadaver shoulders were tested. In each pair one shoulder had a full thickness rotator cuff tear and the other did not. Thus, a matched design was used. Cross sectional areas were measured. Tendon material properties were measured using an optical strain system. FINDINGS: We were unable to detect a statistically significant difference in the long head of the biceps area or material properties between tendons in shoulders with and without rotator cuff tears. An a priori power analysis was conducted indicating the sample size was sufficient to detect a difference of 70 MPa in the elastic modulus measurement. INTERPRETATION: Our data indicate there is no difference in the long head of the biceps cross sectional area or material properties. Therefore, the long head of the biceps tendon appears to retain its material properties in the presence of a rotator cuff tear. The clinical significance of this finding is that the long head of the biceps can be retained in the presence of a rotator cuff tear without concern that mechanical properties have substantially deteriorated.

Anatomy, Cross-Sectional↗

PubMed2004

Molecular-dynamics simulation of amphiphilic bilayer membranes and wormlike micelles: a multi-scale modelling approach to the design of viscoelastic surfactant solutions.

Bilayer membranes and wormlike micelles have been studied using molecular-dynamics simulations. The structure of the worm is analysed in terms of radial density distribution functions, and mechanical properties such as the elastic modulus are calculated. From an analysis of the fluctuation spectra of the tensionless states, we have calculated bending rigidities. Micelles consisting of coarse-grained (CG) model surfactants are studied in order to map the properties of the atomistic micelle. We optimize the CG model with respect to the structure factor of the atomistic micelle. The mechanical properties thus obtained will be used as input for a mesoscopic model of wormlike micelles where the persistence length is the smallest length-scale.

Colloids↗

PubMed2000

Removal of fiber posts from endodontically treated teeth.

The removal of posts from endodontically treated teeth can be a major obstacle in the retreatment of teeth that have recurrent pathology, often leading to extraction of a tooth that could have been saved with endodontic retreatment. The use of a fiber post offers the advantages of a suitable elastic modulus and good bonding between post and cement, but also the advantage of easy removal, if so indicated by clinical findings. A special removal kit for fiber posts has been developed, and its use is illustrated, and described. The removal procedure can be completed in a very short time, usually less than 5 min. The tooth can then be restored with the same type and size of fiber post as was in the tooth prior to removal. Removal kits are found to be for single use only.

Carbon↗

PubMed2005

[Arterial stiffness: parameters, methods of assessment and methodological difficulties].

Arterial stiffness has been shown to be an independent marker of morbidity and cardiovascular mortality in multiple prospective studies of various populations. The purpose of this review is to present different parameters of arterial stiffness (compliance; distensibility; elastic modulus; pulse wave velocity; wave reflection), and to discuss existing difficulties of their application. Means of evaluation of various types of arterial stiffness and principles of their use are also described. Arterial stiffness is not a static but dynamic characteristic, thus prior to its evaluation it is necessary to standardize both the state of a patient and methodology of measurements. Diagnostic value of noninvasive methods of assessment of arterial stiffness is similar to that of invasive techniques, therefore stress can be made on less traumatic investigation of vascular properties.

Coronary Angiography↗

PubMed2005

Effect of mineral content on the nanoindentation properties and nanoscale deformation mechanisms of bovine tibial cortical bone.

In this paper, a multitechnique experimental and numerical modeling methodology was used to show that mineral content had a significant effect on both nanomechanical properties and ultrastructural deformation mechanisms of samples derived from adult bovine tibial bone. Partial and complete demineralization was carried out using phosphoric and ethylenediamine tetraacetic acid treatments to produce samples with mineral contents that varied between 37 and 0 weight percent (wt%). The undemineralized samples were found to have a mineral content of approximately 58 wt%. Nanoindentation experiments (maximum loads approximately 1000 microN and indentation depths approximately 500 nm) perpendicular to the osteonal axis for the approximately 58 wt% samples were found to have an estimated elastic modulus of approximately 7-12 GPa, which was 4-6x greater than that obtained for the approximately 0 wt% samples. The yield strength of the approximately 58 wt% samples was found to be approximately 0.24 GPa; 3.4x greater than that of the approximately 0 wt% sample. These results are discussed in the context of in situ and post-mortem atomic force microscopy imaging studies which show clear residual deformation after indentation for all samples studied. The partially demineralized samples underwent collagen fibril deformation and kinking without loss of the characteristic banding structure at low maximum loads (approximately 300 microN). At higher maximum loads (approximately 700 microN) mechanical denaturation of collagen fibrils was observed within the indent region, as well as disruption of interfibril interfaces and slicing through the thickness of individual fibrils leading to microcracks along the tip apex lines and outside the indent regions. A finite element elastic-plastic continuum mechanical model was able to predict the nanomechanical behavior of all samples on loading and unloading.

Animals↗

PubMed1998

A waveguide-based acoustic microscope.

A new instrument is presented which is capable of high resolution acoustic imaging at relatively low frequencies. This approach results in increased complexity of the signal processing required and reduced throughput of the instrument. However, these disadvantages are amply compensated by the ability to create velocity scan images of materials with either high attenuation or low material velocities. These measurements are not possible using traditional/acoustic microscopes. The initial performance of the new instrument is demonstrated using thin samples of shim materials to show that acceptable spatial resolution and highly accurate time delay measurements are possible. An application is then shown using the instrument to evaluate subchondral sclerosis in horse bones. It has been hypothesized that changes in the elastic modulus may be associated with fatigue-induced microdamage. The modulus change may further represent bone damage which precedes the development of microcracking. Thin samples are used to allow complementary microradiography to be performed on the bone slices. Because of the low material velocity, surface wave interference methods (so called V(z) curves) are not well suited for use in some bone samples. The thickness of the samples eliminates the potential for the samples to be evaluated using pulse-echo time delay measurements. The new instrument is thus unique in its ability to create velocity scans of these samples.

Animals↗