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Results for “Elastic Modulus”

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PubMed2004

Zone-specific micromechanical properties of the extracellular matrices of growth plate cartilage.

Growth plate cartilage demonstrates a unique capacity for cell proliferation and matrix synthesis while sustaining mechanical stresses. To test the hypothesis that the extracellular matrices along various depth of growth plate cartilage have different elastic properties, microindentation by atomic force microscopy was applied to en bloc dissected rabbit cranial base growth plate samples from the reserve zone to mineralizing zone in 50-microm increments. The average elastic modulus upon transverse indentation orthogonal to the long axis of the growth plate showed a gradient distribution, increasing significantly from the reserve zone (0.57 +/- 0.05 MPa) to mineralizing zone (1.41 +/- 0.19 MPa). Longitudinal indentation of the reserve zone along the long axis of the growth plate revealed an average elastic modulus of 0.77 +/- 0.12 MPa, significantly different from the same zone upon transverse indentation. Thus, the extracellular matrix of growth plate cartilage seems to be inhomogenous in its capacity to withstand mechanical stresses.

Animals↗

PubMed2006

Pamidronate does not adversely affect bone intrinsic material properties in children with osteogenesis imperfecta.

Cyclical intravenous pamidronate therapy increases bone mass in children with osteogenesis imperfecta (OI), but the effect on the intrinsic material properties of bone is unknown at present. Thus, a possible influence of pamidronate treatment on bone quality at the material level might negate the beneficial effects of the gain in bone mass and lead to bone fragility in the long term. In the present study, we used transiliac bone biopsy samples and assessed the intrinsic material properties of the bone tissue at the micron-level by combined backscattered electron imaging and nanoindentation. Paired iliac bone samples from 14 patients (age 3 to 17 years) with severe OI before and after 2.5 +/- 0.5 years (mean +/- SD) of pamidronate treatment as well as age-matched controls were examined. Bone histomorphometry was performed in all samples and confirmed an increase of bone mass in treated patients. Backscattered electron imaging was used to measure the weighted mean calcium content (Ca(Mean)), the most frequent calcium content (Ca(Peak)), the variation in mineralization (Ca(Width)) and the amount of lowly mineralized areas (Ca(Low)) that correspond to sites of primary mineralization. Nanoindentation was performed in a subgroup of 6 patients and 6 controls to determine hardness and elastic modulus. Compared to controls, untreated OI patients had a significantly higher degree of bone matrix mineralization (Ca(Peak) +7%, P < 0.001) and a strong reduction of Ca(Low) (-38%, P < 0.001) despite enhanced bone formation, as well as increased hardness (+21%, P < 0.01) and elastic modulus (+13%, P < 0.01). However, none of these parameters was significantly altered by the subsequent pamidronate treatment. This shows that OI bone is stiffer and more mineralized and that, despite the enhanced bone formation rate in these patients, areas of primary mineralization are hardly visible. We also conclude that pamidronate treatment in children with OI does not have an adverse effect on the intrinsic material properties of bone and, as a consequence, that a long-term administration of the drug might not increase brittleness and fragility of the bone matrix. The antifracture effectiveness of pamidronate treatment in OI, as shown in previous clinical studies, has to be explained by the increase of mainly cortical bone volume.

Adolescent↗

PubMed2004

New evidence of red blood cell rheological disorders in beta-thalassaemia minor.

Haemorheological parameters, such as red blood cell deformability, membrane elastic modulus and membrane surface viscosity in twenty one thalassaemia heterozygous patients (14 beta0/beta and 7 beta+/beta) were compared with normal individuals (n = 15). Parameters were measured applying a laser diffractometric method (ektacytometry). Thalassaemia erythrocytes showed statistically significant lower deformability and higher elastic modulus. Surface viscosity showed no significant differences in thalassaemia. Creep and recovery curves were registered by diffractometry. The normal recovery curve was fitted by a first order exponential decay function, expressing the fitting degree by the chi2 coefficient. The shape of the recovery curve in beta-thalassaemia patients (beta0/beta or beta+/beta) was significantly different from the control group. The possible mechanism of red blood cells abnormal rheological behaviour in beta-thalassaemia minor could be explained by a surface charge reduction. Our results enable us to conclude that the shape of the recovery curve (chi2 coefficient) could be considered as a marker that might be useful in beta-thalassaemia diagnosis.

Adult↗

PubMed1995

Microscopic analysis of the elastic properties of nebulin in skeletal myofibrils.

The elastic properties of nebulin were studied by measuring the elasticity of single skeletal myofibrils, from which the portion of the thin filament located at the I band had been selectively removed by treatment with plasma gelsolin under rigor conditions. In this myofibril model, a portion of each nebulin molecule at the I band was expected to be free of actin filaments and exposed. The length of the exposed portion of the nebulin molecule was controlled by performing the gelsolin treatment at various sarcomere lengths. The relation between the passive tension and extension of the exposed portion of the nebulin showed a convex curve starting from a slack length, apparently in a fashion similar to that of wool. The slack sarcomere length shifted depending on the length of the exposed portion of the nebulin, however, the relation being represented by a single master curve. The elastic modulus of nebulin was estimated to be two to three orders of magnitude smaller than that of an actin filament. Based on these results, we conclude that nebulin attaches to an actin filament in a side-by-side fashion and that it does not significantly contribute to the elastic modulus of thin filaments. The relation between the passive tension and extension of connectin (titin) was obtained for a myofibril from which thin filaments had been completely removed with gelsolin under contracting conditions; this showed a concave curve, consistent with the previous results obtained in single fibers.

Actins↗

PubMed2001

A composite polymer/tricalcium phosphate membrane for guided bone regeneration in maxillofacial surgery.

The aim of the study was the development of a resorbable membrane for guided bone regeneration (GBR) with improved biocompatibility, which should be stiff enough to avoid membrane collapse during bone healing. Combining a bioactive ceramic with a resorbable polymer may improve the biocompatibility and osteoconductivity of resorbable devices. The present article describes the preparation, the mechanical properties, and the in vitro degradation characteristic of a composite membrane made of poly(L, DL-lactide) and alpha-tricalcium phosphate in comparison to a membrane made of pure poly(L, DL-lactide). The tensile strength and the elastic modulus as well as the molecular weight of the membranes were measured after in vitro degradation in buffer at 37 degrees C up to 28 weeks. The initial tensile strength of the composite and the polymer membrane was 37.3 +/- 2.4 MPa and 27.7 +/- 2.3 MPa and the elastic modulus 3106 +/- 108 MPa and 3101 +/- 104 MPa, respectively. The mechanical properties remained constant up to 8 weeks and then decreased slowly until week 28. The molecular weight of both membranes decreased steadily from 170,000 D to 30,000 D. It was concluded that the mechanical requirements for a membrane for GBR were fulfilled by the composite membrane.

Absorbable Implants↗

PubMed1999

Electrically measuring viscoelastic parameters of adherent cell layers under controlled magnetic forces.

Electrical cell-substrate impedance sensing (ECIS) was used to measure the time-dependence and frequency-dependence of impedance for current flowing underneath and between cells. Osteosarcoma cells with a topology similar to a short cylinder (coin-like) surmounted by a dome were used in this study. Application of a small step increase in net vertical stress to the cells (4 and 7 dyn/cm2), via magnetic beads bound to the dorsal (upper) surface, causes an increase in cell body height and an increase in cell-cell separation, as well as stretching of the cell-substrate adhesion bonds. This results in a fast drop in measured resistance (less than 2 s), followed by a slower change with a time constant of 60-150 s. This time constant is about 1.5 times longer at 22 degrees C than that at 37 degrees C; it also increases with applied stress. Our frequency scan data, as well as our data for the time course of resistance and capacitance, show that the fast change is associated with both the under-the-cells and between-the-cells resistance. The slower change in resistance mainly reflects the between-the-cells resistance. To obtain viscoelastic parameters from our data we use a simple viscoelastic model comprising viscous and elastic elements (i.e., dashpot and two springs) for the cell body, and an elastic element (a spring) for the cell-substrate adhesion system. Our results show that the spring constants and the viscosity of the cell body components of this viscoelastic model decrease as the temperature increases, whereas the elastic modulus of cell-substrate adhesion increases with temperature. At 37 degrees C, for the cell body we obtain a value of about 10(5) P for the viscous element of the viscoelastic model, and a spring constant expressed in units of an elastic modulus of about 10(4) dyn/cm2 for the spring in series with the viscous element, with another spring with a modulus of about 2 x 10(3) dyn/cm2 in parallel with these. In comparable units, we have a modulus for the cell-substrate adhesion system of about 3 x 10(3) dyn/cm2.

Animals↗

PubMed2005

Property variations in the prism and the organic sheath within enamel by nanoindentation.

Atomic force microscopy (AFM) combined with nanoindentation technique was used to definitely, site-specifically, test the nanomechanical properties, including nanohardness and elastic modulus, of the isolated domains within single enamel, the prisms and the surrounding sheaths, of mature human maxillary third molars. In this way, it is for the first time that evident differences of nanomechanical properties were revealed between these domains. The nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms, respectively. Measuring the residual impressions with AFM supported the similar conclusion. The variations of mechanical properties in these domains are considered to be mainly relative to their different component and fibrils arrangement.

Biomechanical Phenomena↗

PubMed2003

Enamel dissolution as a function of solution degree of saturation with respect to hydroxyapatite: a nanoindentation study.

The objective of this study was to investigate human enamel dissolution as a function of degree of saturation (DS) of the surrounding solution with respect to hydroxyapatite. Nanoindentation was used to compare changes in enamel nanomechanical properties due to dissolution by two solutions. Citric acid solution (DS=0.000, pH 3.30) and citric acid solution containing calcium (299 mg/l) and phosphate (54.0 mg/l) (DS=0.032, pH 3.30) were compared with a control mineral water (DS=0.673, pH 7.48). Exposure times were 0, 120, 300, 600, 900, and 1200 s. Compared to untreated enamel, there was a statistically significant change in enamel hardness after 120 s exposure to both citric acid solutions, and in elastic modulus after 300 s exposure. The rate of change of both variables decreased with exposure time. This suggests that dissolution rate is diffusion-limited under these conditions, in agreement with previous studies. There was no statistically significant difference between the hardness or elastic modulus of enamel exposed to the two citric acid solutions at any time. This may be due to a change in solution composition during contact with the enamel.

Journal Article↗

PubMed1997

Vessel wall and flow characteristics after carotid endarterectomy: eversion endarterectomy compared with Dacron patch plasty.

OBJECTIVES: Experimental studies have demonstrated that decreases in vessel wall compliance and increases in turbulence may contribute to (re)stenosis. We studied vessel wall and flow characteristics after endarterectomy with Dacron patch plasty and after eversion endarterectomy, and compared those findings with the characteristics of non-stenotic, unoperated carotid arteries (controls). METHODS: Seventy-four patients who underwent 84 carotid endarterectomies were studied postoperatively by ultrasonography (2-24 months) Recorded variables included the diameter of the bulb, strain, elastic modulus (stiffness), and presence of turbulent flow. RESULTS: The vessel wall and flow characteristics of the two groups differed significantly. The diameter was higher and the strain lower in Dacron patch plasty than in controls; eversion endarterectomy did not differ from controls. The elastic modulus was higher (stiffer) in Dacron patch plasty than in eversion endarterectomy; neither Dacron patch plasty nor eversion endarterectomy differed significantly from controls. The stiffness index was not significantly different between the groups. Turbulence was present in Dacron patch plasty and eversion endarterectomy when compared with controls. CONCLUSION: In diameter, strain and stiffness, the operated carotid artery resembles the non-stenotic, unoperated artery more closely after eversion endarterectomy than after Dacron patch plasty.

Aged↗

PubMed1984

Left ventricular size, output, and structure during guinea pig pregnancy.

We investigated left ventricular (LV) hemodynamics, pressure-volume relations, and morphometry to determine what cardiac changes characterize pregnancy in the guinea pig. Time-bred virgin guinea pigs were paired by weight with unbred controls. Hemodynamic studies and LV pressure-volume relations were obtained on days 59-68 of the 68-day gestation. Weight of control sows increased from 817 to 902 g (P less than 0.01) and pregnant sows from 810 to 1,251 g (P less than 0.01). LV weights were not different. When indexed for maternal weight minus uterus and contents, pregnancy produced increases in O2 consumption, +48% (P less than 0.01); cardiac output, +32% (P less than 0.05); and stroke volume, +46% (P less than 0.025). Passive LV pressure-volume curves (dP/dV) were shifted to the right (P less than 0.025), but dP/dV at constant pressure was unchanged. Using a thin-walled spherical model, elastic modulus at constant stress was not different. The percent LV inter- and intracellular volumes and myocyte myofibril and organelle volumes were unchanged during pregnancy. In the guinea pig, pregnancy increases LV output, stroke volume, and size without changes in LV mass, morphometry, or elastic modulus.

Animals↗

PubMed1998

Viscoelastic properties of demineralized human dentin measured in water with atomic force microscope (AFM)-based indentation.

Using an atomic force microscope (AFM) with an attachment specifically designed for indentation, we measured the mechanical properties of demineralized human dentin under three conditions: in water, in air after desiccation, and in water after rehydration. The static elastic modulus (E(h)r = 134 kPa) and viscoelastic responses (tau(epsilon) = 5.1 s and tau(sigma) = 6.6 s) of the hydrated, demineralized collagen scaffolding were determined from the standard linear solid model of viscoelasticity. No significant variation of these properties was observed with location. On desiccation, the samples showed considerably larger elastic moduli (2 GPa), and a hardness value of 0.2 GPa was measured. Upon rehydration the elastic modulus decreased but did not fully recover to the value prior to dehydration (381 kPa).

Analysis of Variance↗

PubMed2005

Alteration of proximal aorta biophysical properties in patients with end stage renal disease.

OBJECTIVE: To present a novel, non-invasive echocardiographic application to assess the structural and functional properties of the complex composition of the proximal aorta in patients with end stage renal disease (ESRD). METHODS: 71 haemodialysis patients (mean (SD) age 61.3 (9.3) years, dialysis duration 79.2 (51.6) months) and 62 age matched controls were studied. From the suprasternal view, the distance between ascending and descending aorta was measured with two dimensional ultrasound. The aortic flow wave transit time was measured with pulsed wave Doppler. M mode echocardiography, with simultaneous blood pressure estimates, was used to assess the diameters of the aortic annulus and of the ascending aorta. Pulse pressure, pulse wave velocity (PWV), pressure strain elastic modulus, characteristic impedance, and beta index were calculated. RESULTS: Patients had increased pulse pressure (68.0 (7.2) v 51.4 (5.0) mm Hg, p < 0.001), PWV (6.1 (1.1) v 3.9 (0.6) m/s, p < 0.001), characteristic impedance (174 (58) v 111 (31) m/s.cm2, p < 0.001), pressure strain elastic modulus (872 (254) v 541 (140) mm Hg, p < 0.001), and beta index (8.9 (3.4) v 5.5 (1.4), p < 0.001) compared with controls. In patients PWV was correlated with age and time on haemodialysis (r = 0.44, p < 0.001, and r = 0.51, p < 0.001, respectively). CONCLUSION: A novel application of duplex ultrasound of the proximal aorta showed that patients with ESRD have impaired proximal aortic function compared with controls. The data indicate that these non-invasive measurements can be used to describe status and change in aortic biophysical properties and may be used as a marker for cardiovascular disease risk.

Aorta↗

PubMedDate not supplied

Mechanical characterization of micro/nanoscale structures for MEMS/NEMS applications using nanoindentation techniques.

Mechanical properties of micro/nanoscale structures are needed to design reliable micro/nanoelectromechanical systems (MEMS/NEMS). Micro/nanomechanical characterization of bulk materials of undoped single-crystal silicon and thin films of undoped polysilicon, SiO(2), SiC, Ni-P, and Au have been carried out. Hardness, elastic modulus and scratch resistance of these materials were measured by nanoindentation and microscratching using a nanoindenter. Fracture toughness was measured by indentation using a Vickers indenter. Bending tests were performed on the nanoscale silicon beams, microscale Ni-P and Au beams using a depth-sensing nanoindenter. It is found that the SiC film exhibits higher hardness, elastic modulus and scratch resistance as compared to other materials. In the bending tests, the nanoscale Si beams failed in a brittle manner with a flat fracture surface. The notched Ni-P beam showed linear deformation behavior followed by abrupt failure. The Au beam showed elastic-plastic deformation behavior. FEM simulation can well predict the stress distribution in the beams studied. The nanoindentation, scratch and bending tests used in this study can be satisfactorily used to evaluate the mechanical properties of micro/nanoscale structures for use in MEMS/NEMS.

Journal Article↗

PubMed1977

Mechanical behavior of tooth, periodontal membrane, and mandibular bone by the finite element method.

Simulation of the human tooth, periodontal membrane, and mandibular bone was attempted basing on the anatomical form and dimension, and the experimental data of each component were examined by the two-dimensional finite element method. Following problems were investigated: (1) Which of two factors, elastic modulus or Poisson's rate, in periodontal membrane played an important role for supporting the tooth, and (2) Characteristics of tooth and alveolar bone displacement, and stress distribution in periodontal membrane and mandibular bone were investigated under a definite condition. It is clarified that Poisson's ratio plays a much important role than the elastic modulus and this method is more suitable for simulating the model equivalent to human body and for examining the internal stress and it's displacement than the strain gauge and photoelastic method.

Dental Stress Analysis↗

PubMed2002

Microstructural elasticity and regional heterogeneity in human femoral bone of various ages examined by nano-indentation.

The elastic modulus and hardness of secondary osteonal and interstitial bone was examined through the thickness of the cortex of human femora of various ages by nano-indentation. There was a clear difference between the stiffness and hardness of secondary osteonal and interstitial bone, the latter being stiffer (F(1,48)=56.0, P<0.001). There were some differences between the bones of different subjects; however, there were no differences that could be reliably associated with the chronological age of the subject, or with differences in location through the thickness of the cortex (F(2,48)=0.21, P=0.810). Previous studies have been equivocal in relating changes in the macroscopic 'composite' material stiffness of bone to the age of the individual. By combining the results of the nano-tests with histological measures, we were able to produce a good relationship of the microstructural properties at the matrix level with the bending modulus of whole bone (R(2)=0.88, P<0.001) and this improved further by taking into account the age of the individual (R(2)=0.94, P<0.001). Our results suggest that using differences in the volumetric proportions of secondary osteons versus interstitial bone, and the properties of these elements/structures in isolation may be a more accurate method of determining differences in elastic modulus of whole bone between individuals of various ages.

Adult↗

PubMed2000

Mechanical properties of the common carotid artery in Williams syndrome.

OBJECTIVE: To determine whether arterial wall hypertrophy in elastic arteries was associated with alteration in their mechanical properties in young patients with Williams syndrome. METHODS: Arterial pressure and intima-media thickness, cross sectional compliance, distensibility, circumferential wall stress, and incremental elastic modulus of the common carotid artery were measured non-invasively in 21 Williams patients (mean (SD) age 8.5 (4) years) and 21 children of similar age. RESULTS: Systolic and diastolic blood pressures were higher in Williams patients (125/66 v 113/60 mm Hg, p < 0.05). The mean (SD) intima-media thickness was increased in Williams patients, at 0.6 (0.07) v 0.5 (0.03) mm (p < 0. 001). Normotensive Williams patients had a lower circumferential wall stress (2.1 (0.5) v 3.0 (0.7) mm Hg, p < 0.01), a higher distensibility (1.1 (0.3) v 0.8 (0.3) mm Hg(-1).10(-2), p < 0.01), similar cross sectional compliance (0.14 (0.04) v 0.15 (0.05) mm(2). mm Hg(-1), p > 0.05), and lower incremental elastic modulus (7.4 (2. 0) v 14.0 (5.0) mm Hg.10(2); p < 0.001). CONCLUSIONS: The compliance of the large elastic arteries is not modified in Williams syndrome, even though increased intima-media thickness and lower arterial stiffness are consistent features. Therefore systemic hypertension cannot be attributed to impaired compliance of the arterial tree in this condition.

Adolescent↗

PubMed1999

Determinants of mechanical properties in the developing ovine thoracic aorta.

We previously reported changes in mechanical properties and collagen cross-linking of the ovine thoracic aorta during perinatal development and postnatal maturation, and we now report changes in biochemical composition (elastin, collagen, and DNA contents per mg wet wt) over the same developmental intervals. A comparison of results from the present and previous studies has yielded novel and important observations concerning the relationship between aortic mechanics and composition during maturation. Developmental changes in aortic incremental elastic modulus at low tensile stress (E(low)) closely followed changes in relative elastin content (i.e., per mg wet wt). An 89% increase in E(low) during the perinatal period was associated with a 69% increase in relative elastin content, whereas neither variable changed during postnatal life. Incremental elastic modulus at high tensile stress (E(high)) did not change during the perinatal period but increased 88% during postnatal life. This pattern closely paralleled changes in collagen cross-linking index, which did not change perinatally but almost doubled postnatally. In contrast, relative collagen content (per mg wet wt) increased only slightly from fetal to adult life, a trend that was unrelated to aortic mechanics. Substantial, progressive decreases in measures of wall viscosity (pressure wave attenuation coefficient and viscoelastic phase angle) from fetal to adult life followed the pattern observed for relative DNA (smooth muscle cell) content (per mg wet wt). Our findings suggest that accumulation of elastin per milligram wet weight contributes most to developmental changes in E(low), change in collagen cross-linking is the primary determinant of developmental changes in E(high), and cell accumulation contributes most to developmental changes in wall viscosity.

Aging↗

PubMedDate not supplied

Sintered hydroxyfluorapatites. Part III: sintering and resultant mechanical properties of sintered blends of hydroxyapatite and fluorapatite.

The presence of chemically dissimilar apatites occurs widely in biological systems as a result of exposure to chemically enriched media, but also to optimize the mechanical properties. The use of mechanical blends of apatites can be used to manufacture high temperature processed fluoride containing hydroxyapatites with improved properties. Mechanical blends of fluorapatite and hydroxyapatite were produced with 0%, 20%, 40%, 60%, 80% and 100% fluorapatite. Pellets were sintered at 1150 degrees C, 1200 degrees C and 1250 degrees C and the density determined by the Archimedes method. Mechanical properties including hardness, elastic modulus and fracture toughness were measured using indentation. It was found that mechanical blends of 150 nm sized hydroxyapatite and 300 nm sized fluorapatite lead to solid solutions after sintering. The mechanical blends do not sinter as effectively as homogeneous hydroxyfluorapatite solid solutions and exhibit a minimum density at 80 wt.% fluorapatite. The hardness, elastic modulus and brittleness decreases with a higher flourapatite content, attributed primarily to a decrease in density. The higher fracture toughness for mechanical blends indicates that these materials are more crack resistant and provide a means for improving mechanical properties.

Apatites↗