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Results for “Elastic Modulus”

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PubMed1991

[An experimental study on transmission of hand-arm vibration on the body of users].

Vibration forced into the hand-arm system was observed on the body surface during work with chain saw and under loading experiments by electrodynamic shaker in the laboratory, and factors related to transmission over joints were investigated using pig elbow joints constructed with ulna, radius and humerus. Vibration was measured according to IS 5349 and JIS C1511 between 8 and 1,000 Hz in vibration frequency. Vibration on the bone of pig foreleg conducted without attenuating its amplitude from the peripheral side to the central side between 8 and 1,000 Hz. On the other hand, vibration transmitted over joints damped its amplitude in higher frequency components rather than in lower frequency between 8 and 1,000 Hz. The decreasing ratio of transmitted vibration over joint was changed by the resonance of the soft tissues between the bones constructing the joint. The attenuation changed with the elastic modulus of the soft tissues. The peak frequency was considered to be the resonance because of the physical mass and elasticity. The harder the joint was tied, the stronger became the transmission, because the resonance moved to higher frequencies with increase in elastic modulus. In the loading test from the electrodynamic shaker to the hand-arm system of man, vibration on the soft tissues was transmitted on its surface as wave motion, when the vibration was observed over the skin on the soft tissues. Vibration reduced its amplitude at every joints especially above 100 Hz. The shape of the vibration attenuation curves varied according to the frequency and components of the chain saws.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

The effects of adding chlorhexidine and polyhexamethylene bisguanide to a light-cured periodontal dressing material.

The effect of adding two bisguanide antimicrobial agents (chlorhexidine and PHMB) on some physical properties of the light-cured periodontal dressing material Barricaid are reported. The physical properties tested were elastic modulus, initial and 10 min recovery strains, and tear stress. The addition of both chlorhexidine and PHMB solutions reduced the elastic modulus as did water. The addition of PHMB to Barricaid produced greater initial recovery in the strain test than either the addition of chlorhexidine or water, but there were no differences between the treatments after 10 min. Tear stress was also reduced by the addition of water and the chlorhexidine and PHMB solutions. These results suggest that as far as the physical properties of Barricaid are concerned the addition of the antimicrobial agent PHMB had no long-term advantages over chlorhexidine.

Anti-Infective Agents, Local↗

PubMed1988

In vivo creep behavior of the normal and degenerated porcine intervertebral disk: a preliminary report.

The viscoelastic properties of normal and surgically altered lumbar intervertebral disks from eight immature swine were examined in vivo. Rheological models were used to mathematically characterize the compressive creep-relation behavior of the disks before and after alteration by either chemonucleolysis [chymopapain (Chymodyactin) injection] or denucleation. In the normal disks, a significant modulating effect of respiration was observed that tended to increase the creep deformation response in comparison to that observed during similar in vitro and in situ studies. These results suggest that, in terms of assessing the absolute magnitude of the viscoelastic properties of lumbar disks, the influence of normal physiological function on adjacent vertebrae and surrounding tissues cannot be neglected. Preliminary results obtained from the experimentally altered disks indicated that partial denucleation primarily affected the initial stiffness behavior of the disk (24% decrease in elastic modulus), whereas chemonucleolysis caused changes in both the time-dependent (15% increase in creep rate) and instantaneous (23% decrease in elastic modulus) properties of the disk. Both partial denucleation and acute chemonucleolysis produced biomechanical changes that were comparable to grade II or slightly degenerative, age-related changes found in human lumbar intervertebral disks.

Animals↗

PubMed2003

Oscillations of plants' stems and their damping: theory and experimentation.

Free oscillations of upright plants' stems, or in technical terms slender tapered rods with one end free, can be modelled by considering the equilibrium between bending moments and moments resulting from inertia. For stems with apical loads and negligible mass of the stem and for stems with finite mass but without top loading, analytical solutions of the differential equations with appropriate boundary conditions are available for a finite number of cases. For other cases approximations leading to an upper and a lower estimate of the frequency of oscillation omega can be derived. For the limiting case of omega = 0, the differential equations are identical with Greenhill's equations for the stability against Euler buckling of slender poles. To illustrate, the oscillation frequencies of 25 spruce trees (Picea sitchensis (Bong.) Carr.) were compared with those calculated on the basis of their morphology, their density and their static elasticity modulus. For Arundo donax L. and Cyperus alternifolius L. the observed oscillation frequency was used in turn to calculate the dynamic elasticity modulus, which was compared with that determined in three-point bending. Oscillation damping was observed for A. donax and C. alternifolius for plants' stems with and without leaves or inflorescence. In C. alternifolius the difference can be attributed to the aerodynamic resistance of the leaves, whereas in A. donax structural damping in addition plays a major role.

Biomechanical Phenomena↗

PubMed2003

Glucocorticoid-treated sheep as a model for osteopenic trabecular bone in biomaterials research.

The purpose of this study was to determine the alterations in ovine trabecular bone induced by a combination of ovariectomy and steroid treatment. Twenty-four female skeletally mature Merino sheep were randomly assigned to ovariectomy alone (OVX), ovariectomy combined with glucocorticoid treatment for 6 months (OVX + GC), or no treatment (control). Biopsies of trabecular bone were harvested 6 and 12 months after the beginning of the study from the proximal tibia. The biopsies were scanned for apparent bone mineral density by quantitative computed tomography and were mechanically tested. Three-dimensional bone reconstructions were obtained by micro-computed tomography. Trabecular bone from the OVX + GC animals had a markedly reduced apparent bone mineral density (27% less than control), bone volume (34%), and elastic modulus (36%) at 6 months. At 12 months, the reductions in apparent bone mineral density (33%), bone volume (37%), and elastic modulus (62%) appeared to be even more pronounced. Ovariectomy alone did not result in a perceptible reduction in any parameter. The combination of ovariectomy and glucocorticoid treatment in sheep resulted in a successful induction of substantial loss of trabecular bone and thus may serve as a large-animal model for osteopenic trabecular bone for the development and testing of orthopedic implants and techniques under osteoporotic conditions.

Animals↗

PubMed2005

Novel experimental effects on bone material properties and the pre- and postyield behavior of bones may be independent of bone mineralization.

In this article, we summarize the results of six different tomographic/biomechanical rat studies involving hypophysectomy (Hx), ovariectomy, treatment with rhGH, olpadronate, alendronate, and toxic doses of aluminum and the development of a genetic diabetes in the eSS strain. All these conditions induced some interesting and rarely reported effects on postyield bone strength. These effects were generally related neither to the degree of mineralization or the elastic modulus of the bone tissue nor to the preyield behavior of the bones. In two particular cases (Hx, eSS), the elastic modulus of bone tissue varied independently of its degree of mineralization. These results suggest the involvement of some microstructural factor(s) of bone tissue resistance to crack progression (a postyield feature of bone behavior), rather than to crack initiation (the yield-determining factor) in the corresponding mechanism. Changes in collagen or crystal structure may play that role. These changes are relevant to the mechanism of fracture production during plastic deformation, a feature of bone strength that might be independent from mineralization. Therefore, these changes might help to explain some effects of novel treatments on bone strength unrelated to bone mineralization. This questions the belief that the remaining bone mass in metabolic osteopenias is biologically and mechanically normal.

Animals↗

PubMed1993

Tensile properties of free films cast from aqueous ethylcellulose dispersions.

Free films of two commercially available formulations of aqueous ethylcellulose dispersion differing only in plasticizer content (Sure-lease/E-7-7050 without silica and E-7-7060 containing dibutyl sebacate and glyceryl tricaprylate/caprate as plasticizers, respectively) were cast and coalesced at temperatures ranging between 30 and 70 degrees C. Mechanical properties of these films were measured using tensile stress analysis. Three mechanical parameters, namely, tensile strength, work of failure, and elastic modulus, were computed from the load-time profiles of these films. The results showed that the tensile strength and elastic modulus values of the films cast from both formulations increased with the corresponding increase in coalescence temperature up to 60 degrees C, beyond which no significant differences were observed. In the case of work of failure, however, the difference between the two formulations was observed above 60 degrees C. The films cast from Surelease/E-7-7050 formulation without silica (dibutyl sebacate as the plasticizer) were relatively softer than those from Surelease/E-7-7060 formulation (glyceryl tricaprylate/caprate as the plasticizer). At coalescence temperatures above 50 degrees C, the films cast from both formulations exhibited temperature-dependent plastic deformation.

Cellulose↗

PubMed1990

Correlation between fracture properties and clinical performance of composite resins in Class IV cavities.

One hundred and two Class IV cavities were restored randomly with four composite resins. The restorations were assessed at six months, one year, two years and three years for surface chipping, bulk fracture and incisal wear. The data were correlated with various mechanical properties of the materials. A significant correlation was found between surface chipping/bulk fracture and fracture toughness (P = 0.002), elastic modulus (P = 0.006) and tensile strength (P = 0.045). There was a trend towards an association between incisal wear and both elastic modulus and inherent flaw size. Fracture toughness may be a useful indicator of the clinical performance of composites in Class IV cavities.

Color↗

PubMed1997

Finite elasticity formulations for evaluation of ligamentous tissue.

The variety of techniques used to measure the cross-sectional area of soft connective tissues during mechanical testing lead to inconsistencies in elastic descriptions. This study compares the numerical differences between finite elasticity (Eularian and Lagrangian formulations) and infinitesimal elasticity when considering stress, strain and elastic modulus of ligamentous tissue. Our results found stress differences (Cauchy versus Kirchhoff) of 22.4%, strain differences (engineering versus Green versus Almansi) as large as 14% and elastic modulus differences (Eularian versus Lagrangian) of 44% from ligament tissue sampled from rats. It is therefore critical to maintain consistent (energy conjugate) elastic formulations for reporting mechanical evaluation of soft hydrated tissue.

Algorithms↗

PubMed1980

Surface elastic properties of surfactant from the lungs of neonatal pigs.

The elasticity of surfactant films from the lungs of neonatal pigs was measured using a torsion elastometer. It was found that the elastic modulus of the films increased markedly as the surfactant concentration was raised. Increasing the temperature stepwise over the range 25--41 degrees C produced a decrease in the elastic modulus. In contrast, altering the pH of the subphase over the range 7.1--7.7 had no significant effect on film elasticity. The influence of surfactant films on pulmonary compliance is discussed.

Animals↗

PubMed1977

Excisional wound biomechanics, skin tension lines, and elastic contraction.

Confusion surrounding the concept of Langer's lines can be reduced by careful distinction among the operational definitions of the phenomenon, the empirical descriptions, and the theoretical explanations. An experimental analysis of the mechanical parameters of excisional wounds in pigskin shows that the marginal retraction, the elastic modulus at the wound midline, and the closing tension are higher for wounds oriented at right angles to tension lines--but the elastic modulus of the terminal segment of the force displacement curve is independent of orientation. The regional distribution of these values shows two patterns. The modulus parameters and the closing tension share a common distribution related to the steepness of regional force-displacement curves, while retraction has a qualitatively different distribution. On the basis of similarities in the behavior of retracting wound margins and in the distortion of punch holes which define tension lines, we hypothesize that the same mechanism may be responsible in both cases.

Animals↗

PubMed1996

Leaf water relations of Eucalyptus globulus ssp. globulus and E. nitens: seasonal, drought and species effects.

In August 1990, a 2-ha plantation was established in an area where rainfall (about 515 mm year(-1)) was insufficient to meet evaporative demand. On nine occasions between September 1991 and April 1993, pressure-volume curves were constructed for irrigated and rainfed Eucalyptus globulus ssp. globulus Labill. and E. nitens (Deane and Maiden) Maiden trees. During the experiment, rainfed trees experienced six periods when predawn water potential was significantly lower than that of irrigated trees. In early spring of 1991 and 1992, osmotic potentials at full turgor and turgor loss point in the irrigated E. nitens were significantly lower than at other times of the year, probably because of winter hardening. Water stress reduced osmotic potential and increased bulk elastic modulus in E. nitens, whereas the reverse occurred in E. globulus. However, treatment differences with respect to changes in osmotic and elastic properties were commonly overshadowed by interspecific differences. These were most apparent at the end of the sixth period of water stress when osmotic potentials at full and zero turgor were significantly higher and bulk elastic modulus and relative water content at turgor loss point were significantly lower in E. globulus than in E. nitens. We conclude that the drought-tolerance responses of E. globulus make it a more suitable species than E. nitens for establishment on sites where moderate water stress is experienced.

Journal Article↗

PubMed2006

Experimental investigation of interfaces in hydroxyapatite/polyacrylic acid/polycaprolactone composites using photoacoustic FTIR spectroscopy.

Molecular interactions in hydroxyapatite (HAP) polymer composites have been studied using photoacoustic spectroscopy. HAP is mineralized by wet precipitation under two conditions: first is in the absence of polyacrylic acid (PAAc) (ex-situ HAP) and second in the presence of PAAc (in-situ HAP). Porous and solid composites of ex-situ and in-situ HAP with polycaprolactone (PCL) have also been made to evaluate their applicability as bone scaffolds. Photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy studies indicate that both in-situ and ex-situ HAP have HPO4 (2-) in their structure, which leads to Ca2+ deficiency. During crystallization of in-situ HAP, PAAc dissociates to form carboxylate ions, which binds to calcium ions and act as suitable site for nucleation for HAP crystallization. PA-FTIR spectra of porous and solid composites indicate that porous composites adsorb more water, which is hydrogen bonded with carbonyl of PCL. Mechanical tests on solid samples indicate that ex-situ HAP/PCL composites have higher elastic modulus than in-situ HAP/PCL composites. However, in case of porous composites, in-situ HAP/PCL composites are found to have higher elastic modulus. In-situ HAP is chemically and structurally different from ex-situ HAP. This modified HAP causes variation in microstructure of porous composite and hence alteration of its load transfer mechanisms and hence mechanical properties.

Acrylic Resins↗

PubMed1999

Effects of oxidative damage of membrane protein thiol groups on erythrocyte membrane viscoelasticities.

In three oxidative damaging systems: the diamide-mercaptoethanol redox modification system (DM), the pyrogallol oxygen free radicals system (PG) and the hypoxanthine-xanthine oxidase oxygen free radical system (HXO), the effect of erythrocyte membrane oxidative damage on membrane viscoelasticities was investigated with micropipette aspiration method. The experimental results indicated that erythrocyte membrane oxidative damage has a great influence upon the membrane mechanical properties. The oxidative damage led to decrease of contents of membrane protein thiol radical. The scanning of SDS-PAGE presented that membrane proteins form the higher molecular weight component (HMP) by the cross-linking of membrane protein thiol radicals that might hinder the conformational change of membrane protein. This might be the reason for the increased membrane elastic modulus and viscous coefficient upon treating erythrocytes with the oxidative damaging systems. A significant negative logarithm regression relation was found between the membrane elastic modulus, mu, or viscoefficient, eta, and the contents of membrane protein thiol radicals. These experimental results suggested that thiol radicals oxidative damage reaction due to the superoxides anions (*O2-) may be an important molecular mechanism inducing changes of membrane viscoelasticities or whole cell deformability of erythrocyte under physiological and pathological oxidative stress.

Blood Viscosity↗

PubMed2002

Linear poroelastic cancellous bone anisotropy: trabecular solid elastic and fluid transport properties.

The mechanical performance of cancellous bone is characterized using experiments which apply linear poroelasticity theory. It is hypothesized that the anisotropic organization of the solid and pore volumes of cancellous bone can be physically characterized separately (no deformable boundary interactive effects) within the same bone sample. Due to its spongy construction, the in vivo mechanical function of cancellous or trabecular bone is dependent upon fluid and solid materials which may interact in a hydraulic, convective fashion during functional loading. This project provides insight into the organization of the tissue, ie., the trabecular connectivity, by defining the separate nature of this biphasic performance. Previous fluid flow experiments [Kohles et al., 2001, Journal of Biomechanics, 34(11), pp. 1197-1202] describe the pore space via orthotropic permeability. Ultrasonic wave propagation through the trabecular network is used to describe the solid component via orthotropic elastic moduli and material stiffness coefficients. The linear poroelastic nature of the tissue is further described by relating transport (fluid flow) and elasticity (trabecular load transmission) during regression analysis. In addition, an empirical relationship between permeability and porosity is applied to the collected data. Mean parameters in the superior-inferior (SI) orientation of cubic samples (n=20) harvested from a single bovine distal femur were the largest (p<0.05) in comparison to medial-lateral (ML) and anterior-posterior (AP) orientations: Apparent elastic modulus (2,139 MPa), permeability (4.65x10(-10) m2), and material stiffness coefficient (13.6 GPa). A negative correlation between permeability as a predictor of structural elastic modulus supported a parametric relationship in the ML (R2=0.4793), AP (R2=0.3018), and SI (R2=0.6445) directions (p<0.05).

Animals↗

PubMed1975

Static mechanical properties of the developing and mature rat aorta.

The static mechanical properties of the aorta have been examined in rats, aged between 4 weeks and 2 years. Internal radius, relative wall thickness, circumferential incremental strain, and circumferential incremental elastic modulus have been measured at pressures between 1.33 and 33.3 kPa (10 and 250 mm Hg). The results show that the value of the incremental elastic modulus does not change after 12 weeks. Changes observed in younger animals are related to alterations in relative wall thickness. The findings correlate with previously observed chemical and morphological changes. Studies of muscle function indicate that the smooth muscle of the media does not contribute significantly to the static elastic properties of the vessel wall.

Age Factors↗

PubMed2003

Characterization of dynamic cellular adhesion of osteoblasts using atomic force microscopy.

BACKGROUND: Atomic force microscopy (AFM) can be used to visualize the cell morphology in an aqueous environment and in real time. It also allows the investigation of mechanical properties such as cell compliance as a function of cell attachment. This study characterized and evaluated osteoblast adhesion by AFM. METHODS: Human bone marrow stromal cells were cultured on two types of surface to induce weak and strong cellular adhesions. RESULTS: Cells were considered as spreading if they had a flattened and lengthened shape and a cytoskeletal organization in the submembrane cytosolic region. Cell detachment demonstrated different adhesion states between adherent cells to be distinguished. The stability of the cytoskeletal fibers indicated that cells were adherent. The elastic modulus was estimated by two complementary approaches. The values deduced were between 3 x 10(2) and 2 x 10(5) Nm(-2) according to the state of cell adhesion and the approaches used to measure this elastic modulus. CONCLUSIONS: Although the results were qualitative, a relation may be deduced between the elasticity of living cells as demonstrated by cytoskeletal organization and the state of cell adhesion. The technique could be used to determine the adhesion state of an adherent osteoblast observed under AFM.

Bone Marrow Cells↗

PubMed1988

A method for fixation of elastin demonstrated by stress/strain characterization.

In the process of examining the effects of oxidants on the mechanical properties of purified ligamentum nuchae elastin, it was found that sodium hypochlorite as constituted in Clorox will fix elastin at any preset extension. The treatments were carried out at a 1 to 5 dilution and at 0, 20 and 40% extensions. In each case, the new resting length was near the preset length and the elastic modulus increased remarkably, for example, from 1 to 5 x 10(7) dynes/cm2 for the sample preset at 20% extension. As reflected in the increased elastic modulus, the fixation was achieved by the formation of irreversible cross-links. Due to the near absence of side chains containing chemically reactive groups suitable for contributing to the formation of additional cross-links required in fixation, this is the first method whereby irreversible fixation of elastin has been achieved. The absence of a suitable fixative for elastic tissues such as lung, arteries, etc. has limited the microscopic characterization of functional extended states of these tissues.

Animals↗