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PubMed1995

Intravenous olpadronate restores ovariectomy-affected bone strength. A mechanical, densitometric and tomographic (pQCT) study.

Female Wistar rats aged 3 months were ovariectomized (OX, n = 27). Three months later they were given i.v. doses of 150 (6), 300 (7), or 600 (6) ug/kg 2/wk of olpadronate during 12 weeks or left as OX controls (OXc). Bending fracture load of femur diaphyses, reduced in OXc, was recovered by olpadronate. This effect was paralleled by changes in material quality indicators as DEXA-BMD, tomographic (volumetric) BMD, elastic modulus, and maximum elastic stress of cortical bone. No changes were induced by any of the treatments on cross-sectional area or moment of inertia. Diaphyseal stiffness, not reduced by OX, was enhanced to overnormal values by olpadronate at any dose. None of the treatments affected the normal mechanostatic interrelationships between cross-sectional architecture and bone material quality indicators. The positive effects described point out important differences in bisphosphonate action on bone biomechanics according to the experimental conditions assayed.

Absorptiometry, Photon↗

PubMed2001

High-pressure elastic properties of solid argon to 70 GPa.

The acoustic velocities, adiabatic elastic constants, bulk modulus, elastic anisotropy, Cauchy violation, and density in an ideal solid argon (Ar) have been determined at high pressures up to 70 GPa in a diamond anvil cell by making new approaches of Brillouin spectroscopy. These results place the first complete study for elastic properties of dense Ar and provide an improved basis for making the theoretical calculations of rare-gas solids over a wide range of compression.

Journal Article↗

PubMed2006

In vitro and in vivo studies on blends of isotactic and atactic poly (3-hydroxybutyrate) for development of a dura substitute material.

Blends of semicrystalline isotactic poly(3-hydroxybutyrate) (PHB) with amorphous atactic PHB (at-PHB) were prepared by solution-casting using 30%, 50% and 70% at-PHB, and were studied for medical applications. The mechanical properties of the blends including the elastic modulus and elongation at break are strongly affected by the blend composition. The elastic modulus decreases with increasing fraction of at-PHB in the blend from 3350 MPa in the case of PHB to 170 MPa of PHB/at-PHB (30/70). In contrast, the elongation at break increases from 2% in pure PHB up to 50% in the case of the blend with 70% at-PHB. The in vitro degradation is changed as well. The molecular weight of PHB/at-PHB (30/70) is reduced to 5% after 2 years storage in phosphate buffer compared to 35% for pure PHB stored at identical conditions. The in vitro cell vitality is slightly reduced depending on the composition. PHB/at-PHB blends with 30% and 50% at-PHB were selected as dura substitute in minipigs based on the results of the in vitro investigation and the mechanical testing. Patch films with a structured surface on one side were fabricated by a dipping-leaching method. Dura defects were clinically and histologically examined 3, 6, and 9 months after implantation, confirming defect closure, prevention of adhesions to brain tissue, and no signs of inflammation or malignant degeneration. The PHB-based patch materials fulfill the requirements which are necessary for a dura substitute.

3-Hydroxybutyric Acid↗

PubMed2006

[Investigation in the dependency of stiffness of cancellous bone on apparent density--based on the combination model of rod-rod structure and perforated plate structure].

The structure of cancellous bone is cellular. There are two basic models of cancellous bone structure namely the model of rod-rod structure and the model of framework of perforated plate. This paper presents several models of structure developed from the model of rod-rod structure to the model of framework of perforated plate. We computed the elastic modulus of cancellous bone based on these modes using homogenization. The relationship between the elastic modulus(E) of cancellous bone and the apparent density(p) was determined to be E = 1.78rho1.88.

Biomechanical Phenomena↗

PubMed1980

Mucociliary transport in vivo and in vitro. Relations to sputum properties in chronic bronchitis.

In vivo and in vitro mucociliary clearance have been investigated in 27 patients with chronic bronchitis with relation to the rheological, cytobacteriological and biochemical characteristics of sputum. In normal subjects, the mean percentage of bronchial radioactivity cleared (PBRC) by mucociliary clearance was 30.1 +/- SD: 12.5. The patients studied were differentiated into two groups: 1) 10 patients showing a PBRC similar to that of the normal subjects (30.6 +/- SD: 14.3), 2) 17 patients with a markedly decreased mucociliary clearance (PBRC: 4.1 +/- SD: 4.2). In the healthy subjects, PBRC by coughing was significantly lower than by mucociliary clearance, while no consistent difference was observed in the patients. A weak but significant positive correlation (r = 0.53, P less than 0.01) was observed between in vivo mucociliary clearance and the relative transport rate of the sputum measured on the ciliated frog palate mucosa. The optimal rheological conditions for mucociliary transport were characterized by an apparent viscosity (eta 0) ranging from 25 to 180 poise, a strain recovery (SR) ranging from 4 to 12 units and an elastic modulus (G) ranging from 4 to 8 dyn/cm-2. The apparent viscosity and the elastic modulus G respectively, were significantly correlated with the concentration of serum albumin and of secretory IgA. Patients with a sputum leukocyte count higher than 3500/mm3 had a significantly decreased mucociliary clearance in comparison with non-purulent sputum patients.

Bronchi↗

PubMed1988

Elasticity of fibrin and protofibrin gels is differentially modulated by calcium and zinc.

The mechanical properties of fibrin and protofibrin gels in the presence of physiologic levels of Ca(II) and Zn(II) are described. As monitored with a thrombelastograph, Ca(II) (0.5-2 mM) increases the rate of development and the maximum level of gel elastic modulus (G) of fibrin and protofibrin gels. Zn(II) (10-50 microM) decreases the elastic modulus of those gels, even in the presence of a large excess of Ca(II). This contrasts with the ability of both divalent cations to increase fibrin and protofibrin gel turbidity. Unlike the turbidity or fibre thickness of fibrin and protofibrin gels, both of which are increased by these cations, gel elasticity is increased by Ca(II) but decreased by Zn(II). It is demonstrated that Ca(II) and Zn(II) modulate fibrin and protofibrin gels independently of one another, and that they have opposing effects on the mechanical properties of the gels. The disparity between the visual (turbidity, TEM) and the mechanical (elasticity) properties of (proto)fibrin gels indicates the need for new conceptual and analytic paradigms.

Calcium↗

PubMed2005

In vivo mechanical properties of thoracic aortic aneurysmal wall estimated from in vitro biaxial tensile test.

To investigate the mechanism of aneurysm rupture, it is necessary to examine the mechanical properties of aneurysm tissues in vivo. A new approach to evaluate in vivo mechanical properties of aortic aneurysmal tissues has been proposed in this study. The shape of the aneurysm was modeled as a sphere, and equi-biaxial stress in the in vivo state was estimated from the diameter and the wall thickness of each aneurysm and mean blood pressure of each patient. The mechanical properties of the aneurysm at the in vivo stress were estimated from its in vitro biaxial tensile properties. There were no significant correlations among maximum diameter D, wall thickness t, and mean infinitesimal strain in the in vivo state epsilon(m). This indicates the wall deformation during aneurysm development was not elastic but plastic. The mean incremental elastic modulus H(m), an index of tissue stiffness, had a significant positive correlation with elastic modulus anisotropy index K(H). This indicates the aneurysmal wall got more anisotropic in vivo as it becomes stiffer.

Anisotropy↗

PubMed1978

Early arterial lesions in maturity onset diabetes mellitus detected by an ultrasonic technique.

Using an ultrasonic technique preclinical atheroma was studied in maturity onset diabetics. The elasticity of the leg arteries was measured as the elastic modulus in 32 patients and a normal range was established in 13 controls. The elastic modulus was higher (i.e. the arteries were stiffer) in diabetics than controls and this was associated with a higher mean blood pressure in the diabetics. Nine phenformin and 10 chlorpropamide treated diabetics had evidence of more severe arterial disease than 13 diet treated patients. This could not be accounted for by other factors known to influence arterial disease.

Arteriosclerosis↗

PubMed1977

Elasticity of the spinal cord dura in the dog.

The elasticity of the spinal cord dura in the dog has been investigated histologically, in situ, and by measurement. The dura was composed of collagenous and elastic connective tissue fibers. The collagenous fibers were arranged in longitudinal bundles, straight when stretched and wavy when unstretched, with a delicate network of fine elastic fibers coursing in all directions. Transecting the cord and dura at T-5 caused a separation of 25 to 30 mm of the dura and a 15- to 20-mm gap in the cord. By means of an appropriate sequence of transections of nerve roots and denticulate ligaments within the dura, and transections of the dural sheaths and nerves outside the dura, the strain on the dura was found to be imposed by the attachments of the dural nerve sheaths from T-6 to S-7. The filum terminale was not appreciably strained. By adding weights to a suspended dura, two components of elasticity were found. For loads of 0 to 50 gm, the incremental displacements in the length were large. The elastic modulus was about 4 X 10(6) dynes/sq cm, which was comparable to that of elastic fibers. For loads of 50 to 150 gm the displacements in length were small. The elastic modulus was about 5 X 10(8) dynes/sq cm, which was comparable to that of collagenous fibers.

Animals↗

PubMed2002

Effect of adhesive layer properties on stress distribution in composite restorations--a 3D finite element analysis.

OBJECTIVES: Teeth, adhesively restored with resin-based materials, were modeled by 3D-finite elements analysis that showed a premature failure during polymerization shrinkage and occlusal loading. METHODS: Simulation of Class II MOD composite restorations with a resin bonding system revealed a complex biomechanical behavior arising from the simultaneous effects of polymerization shrinkage, composite stiffness and adhesive interface strain. Due to a polymerization contraction, shrinkage stress increases with the rigidity of the composites utilised in the restoration, while the cusp movements under occlusal loading are inversely proportional to the rigidity of the composites. The adhesive layer's strain also plays a relevant role in the attenuation of the polymerization and occlusal loading stresses. RESULTS: The choice of an appropriately compliant adhesive layer, able to partially absorb the composite deformation, limits the intensity of the stress transmitted to the remaining natural tooth tissues. For adhesives and composites of different rigidities, FEM analysis allows the determination of the optimal adhesive layer thickness leading to maximum stress release while preserving the interface integrity. Application of a thin layer of a more flexible adhesive (lower elastic modulus) leads to the same stress relief as thick layers of less flexible adhesive (higher elastic modulus).

Composite Resins↗

PubMed1998

Effect of vasopressin antagonism on structure and mechanics of small arteries and vascular expression of endothelin-1 in deoxycorticosterone acetate salt hypertensive rats.

The structural and mechanical properties of small arteries are altered in rat models of hypertension. The precise role of humoral factors in these changes has not been determined. In deoxycorticosterone acetate (DOCA) salt hypertension, endothelin-1 (ET-1) peptide content and gene expression are enhanced in mesenteric resistance arteries. These vessels also present augmented vasoconstrictor responsiveness to vasopressin versus control uninephrectomized rats. To determine whether an interaction exists between vasopressin and ET-1 in the pathogenesis of small-artery structural alterations in DOCA-salt rats, we examined the effect of chronic V1 vasopressin receptor antagonism (OPC-21268, 30 mg/kg BID) on the structure and mechanical properties of mesenteric resistance arteries using a pressure myograph and the effect on preproendothelin-1 (preproET-1) gene expression, determined by Northern blot analysis of preproET-1 mRNA. Tail-cuff systolic pressures were elevated in DOCA-salt (200+/-11 mm Hg) versus uninephrectomized rats (109+/-4 mm Hg) and decreased slightly but significantly by OPC-21268 to 187+/-7 mm Hg (P<0.01). Treatment with DOCA-salt increased vascular media-lumen ratios and media cross-sectional areas and reduced both stress and incremental elastic modulus for a given pressure. However, there was no change in distensibility or incremental elastic modulus versus media stress. OPC-21268 partially attenuated the vascular growth in DOCA-salt rats. PreproET-1 mRNA was increased 2-fold in mesenteric arteries of DOCA-salt rats versus uninephrectomized rats, an effect abrogated by OPC-21268. Thus, DOCA-salt hypertension is associated with altered morphology of the small-arterial wall, without altering stiffness of the arterial wall components. OPC-21268 regressed in part these changes, suggesting the involvement of vasopressin. The concomitant attenuation of enhanced ET-1 expression by OPC-21268 suggests that ET-1 may be involved in mediating in part the vascular effects of vasopressin in DOCA-salt hypertensive rats.

Animals↗

PubMed2006

Use of hydrodynamic forces to engineer cartilaginous tissues resembling the non-uniform structure and function of meniscus.

The aim of this study was to demonstrate that differences in the local composition of bi-zonal fibrocartilaginous tissues result in different local biomechanical properties in compression and tension. Bovine articular chondrocytes were loaded into hyaluronan-based meshes (HYAFF-11) and cultured for 4 weeks in mixed flask, a rotary Cell Culture System (RCCS), or statically. Resulting tissues were assessed histologically, immunohistochemically, by scanning electron microscopy and mechanically in different regions. Local mechanical analyses in compression and tension were performed by indentation-type scanning force microscopy and by tensile tests on punched out concentric rings, respectively. Tissues cultured in mixed flask or RCCS displayed an outer region positively stained for versican and type I collagen, and an inner region positively stained for glycosaminoglycans and types I and II collagen. The outer fibrocartilaginous capsule included bundles (up to 2 microm diameter) of collagen fibers and was stiffer in tension (up to 3.6-fold higher elastic modulus), whereas the inner region was stiffer in compression (up to 3.8-fold higher elastic modulus). Instead, molecule distribution and mechanical properties were similar in the outer and inner regions of statically grown tissues. In conclusion, exposure of articular chondrocyte-based constructs to hydrodynamic flow generated tissues with locally different composition and mechanical properties, resembling some aspects of the complex structure and function of the outer and inner zones of native meniscus.

Animals↗

PubMed2001

Constitutive equations for an elastic material with anisotropic rigid particles.

In this paper we have derived constitutive equations for an elastic material with anisotropic rigid particles. We have included a dependence on the Finger tensor B and the orientation tensor Q in the expression for the free energy of the system. With this expression for the free energy we have derived an expression for the stress tensor up to second order in both these variables. We have shown that the elastic modulus in this expression depends on Q, and this dependence leads to an effective elastic modulus that depends on the strain. We have calculated the explicit form of the equation for the stress tensor for a deformation in the xy plane with a strain equal to -gamma. For fully isotropic materials with Q=0 this expression reduces to an equation containing only odd powers of gamma. The inclusion of a non-zero value for the orientation tensor leads to an additional set of terms in the equation, all proportional to Qxy (the xy component of the tensor Q), and all proportional to even powers of gamma. We have qualitatively compared these expressions with Fourier transform (FT) rheological measurements of xanthan gels, at concentrations above and below the order-disorder transition. In FT rheometry an oscillatory deformation is applied in the nonlinear regime, and the resulting stress response is analyzed in Fourier space. In the 2% (w/w) xanthan system (disordered state) only odd harmonics were found in the stress response, whereas in the 4% (w/w) xanthan gel (ordered state) even harmonics could be detected. As predicted by our theory, the intensity of these even harmonics first increased with increasing gamma, until a maximum value was reached. Beyond this maximum the intensity decreased continuously with increasing gamma.

Journal Article↗

PubMed2003

Shearing or compressing a soft glass in 2D: time-concentration superposition.

We report surface shear rheological measurements on dense insoluble monolayers of micron sized colloidal spheres at the oil/water interface and of the protein beta-lactoglobulin at the air/water surface. As expected, the elastic modulus shows a changing character in the response, from a viscous liquid towards an elastic solid as the concentration is increased, and a change from elastic to viscous as the shear frequency is increased. Surprisingly, above a critical packing fraction, the complex elastic modulus curves measured at different concentrations can be superposed to form a master curve. This provides a powerful tool for the extrapolation of the material response function outside the experimentally accessible frequency range. The results are discussed in relation to recent experiments on bulk systems, and indicate that these two-dimensional monolayers should be regarded as being close to a soft glass state.

Journal Article↗

PubMed2004

Estimation of material elastic moduli in elastography: a local method, and an investigation of Poisson's ratio sensitivity.

The local material stiffness of tissues is a well-known indicator of pathology, with locally stiffer tissue related to the possible presence of an abnormal growth in otherwise compliant tissue. Elastography is a non-invasive technique for measuring displacement distributions in loaded tissues within a medical imaging context. From these measured displacement fields, estimated for local strain have been made using well-studied techniques, but the calculation of elastic modulus has been difficult. In this study we show a method for estimating local tissue elastic modulus that gives numerically stable and robust results in test cases, and that is numerically efficient. The method assumes the tissue is isotropic and it requires an independent estimate of tissue Poisson's ratio, but the method reaches a stable result when the estimated Poisson's ratio is in error, and the resulting estimates are not very sensitive to the assumed value.

Algorithms↗

PubMed2007

Microstructure and macroscopic properties of bioactive CaO-SiO2-PDMS hybrids.

CaO-SiO2-PDMS (polydimethylsiloxane) hybrid materials were synthesized as crack-free monoliths presenting in vitro bioactivity, i.e. able to be coated with a calcium phosphate-rich layer after having been soaked in simulated body fluid (SBF). A wide physical-chemical characterization of these materials was carried out to relate their microscopic structure and macroscopic properties. The effect of PDMS and the amounts of water used for the tetraethoxysilane (TEOS) hydrolysis on the mechanical properties of hybrid materials was investigated by three-point bending tests. For a given amount of water, as PDMS content in hybrids increased, the elastic modulus decreased. Furthermore, keeping the PDMS content constant, when the amount of H2O decreased, the elastic modulus increased. Regarding in vitro bioactivity and mechanical properties, the hybrid material obtained with molar ratios H2O/TEOS = 2 and TEOS/PDMS = 3.5 proved to be the best candidate for either soft tissue substitution or metallic implant coating since the hybrid material would promote bond to bone formation, simultaneously dampening the mechanical charges.

Biocompatible Materials↗

PubMed1991

Genetic variants of collagen III and abdominal aortic aneurysm.

Collagens provide the tensile strength of the aortic wall. Variations in collagen structure are recognised in Ehlers Danlos syndrome type IV and could also be associated with a predisposition to aortic aneurysm. The frequency of some minor genetic variants of type III collagen, present in the normal population, can be detected by restriction enzyme digestion of genomic DNA from peripheral leucocytes. The frequency of a minor collagen type III allele demonstrated with the restriction enzyme Ava II was compared in patients with abdominal aortic aneurysm (n = 70) and aortoiliac stenosis (n = 47). The frequency of the minor allele was significantly higher in aneurysm patients (0.30) compared with patients with aortoiliac stenosis (0.17), p less than 0.05. The presence of the minor allele was associated with a less elastic aneurysm wall (median pressure strain elastic modulus 4575, n = 7), compared with patients homozygous for the common allele (median pressure strain elastic modulus 1990, n = 6), p less than 0.05. These results indicate that genetic variants of type III collagen may influence the extensile properties of the aortic wall and that mutations in the type III collagen gene may be associated with aortic aneurysms.

Aged↗

PubMedDate not supplied

A comparison of bicortical and intramedullary screw fixations of Jones' fractures.

Two different fixations for treatment of Jones' fracture were tested in bone models and cadaveric specimens to determine the differences in the stability of the constructs. A bicortical 3.5-mm cannulated cortical screw and an intramedullary 4.0-mm partially threaded cancellous screw were tested using physiologic loads with an Instron 8500 servohydraulic tensiometer (Instron Corporation, Canton, MA). In bone models, the bicortical construct (n = 5, 87+/-23 N) showed superior fixation strength (p = .0009) when compared to the intramedullary screw fixation (n = 5, 25+/-13 N). Cadaveric testing showed similar statistical significance (p = .0124) with the bicortical construct (n = 5, 152+/-71 N) having greater load resistance than the intramedullary screw fixation (n = 4, 29+/-20 N). In bone models, the bicortical constructs (23+/-9 N/mm) showed over twice the elastic modulus than the intramedullary screw fixations (9+/-4 N/mm) with statistical significance (p = .0115). The elastic modulus in the cadaveric group showed a similar pattern between the bicortical (19+/-17 N/mm) and intramedullary (9+/-6 N/mm) screw constructs. Analysis of the bicortical screw failure patterns revealed that screw orientation had a critical impact on fixation stability. The more distal the exit site of the bicortical screw was from the fracture site, the greater the load needed to displace the fixation.

Biomechanical Phenomena↗