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Results for “Elastic Modulus”

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At least 451 records · Page 25Linked to original sources

PubMed1996

The effects of irradiation dose on the stiffness of cartilage grafts.

Various centers report irradiated cartilage graft absorption rates that differ quite widely. We postulated that a major factor governing this phenomenon might be irradiation dose. Irradiation produces collagen cross-binding and increased resistance to absorption of such material when implanted. Since cross-binding produces stiffening of collagen, cartilage grafts were exposed to increasing doses of irradiation and their elastic modulus was measured. The postulate was that increasing radiation doses will produce grafts of increasing stiffness. Sternal cartilage, harvested from horses, was cut into blocks of a standard size and irradiated to 4, 6, 8, and 10 megarads. The elastic modulus of each specimen and matched control were measured on an Instron flexural testing machine (Instron Corp, Canton, MA). Irradiation at all four doses reduced the elastic modulus of the cartilage grafts, with the lowest dose producing a reduction of 50% and the highest dose one of 90%. High-dose irradiation appears to lessen greatly the stiffness of cartilage grafts and may be responsible for increasing absorption of grafts in centers in which high doses are used.

Absorption↗

PubMed2000

Properties of growing trabecular ovine bone. Part I: mechanical and physical properties.

Our aim was to determine the relationship between age and the mechanical and physical properties of trabecular bone, to describe the patterns in which the variations in these properties take place, and to investigate the influence of the physical properties on the mechanical characteristics of trabecular bone during growth. We used 30 lambs in three age groups and 20 sheep in two age groups. Cubes of subchondral bone were cut from the proximal tibia according to a standardised protocol. We performed non-destructive compression tests of the specimens in three orthogonal directions and compression tests to failure in the axial direction. The physical properties of the specimens were also determined. The data were correlated with age and compared in skeletally immature and mature animals. Multiple regression analyses were performed between the mechanical and the physical properties. Age correlated positively with elastic modulus, bone strength, energy absorption to failure, elastic energy, mechanical anisotropy ratio, tissue density, apparent density, apparent ash density, and bone mineral content, and inversely with ultimate strain, viscoelastic energy absorption, relative energy loss, the collagen content of bone and the percentage porosity. The values of all variables were significantly different in the skeletally mature and immature groups. The apparent density of trabecular bone tissue was found to be the major predictor of its compressive mechanical properties. Together with the content of bone muscle and bone collagen, the apparent density could explain 84% of the variation in the elastic modulus, whereas only a small portion of the variation in ultimate strain could be explained by the variation in apparent density.

Age Factors↗

PubMed2000

Indentation modulus and hardness of whisker-reinforced heat-cured dental resin composites.

OBJECTIVES: Recent studies showed that ceramic whisker reinforcement imparted a two-fold increase in the strength of dental composites. The aim of this study was to investigate the indentation response and measure the elastic modulus, hardness, and brittleness of whisker-reinforced heat-cured resin composites as a function of filler level, heat-cure temperature, and heat-cure duration. METHODS: Silica particles were fused onto silicon nitride whiskers to facilitate silanization and to roughen the whiskers for improved retention in matrix. Whisker filler mass fractions of 0, 20, 40, 60, 70, 74 and 79% were tested. Heat-cure temperature ranged from 100 to 180 degrees C, and duration from 10 min to 24 h. A nano-indentation system enabled the measurement of elastic modulus. Fracture toughness was measured and composite brittleness index was calculated. An inlay/onlay composite and a prosthetic composite were tested as controls. RESULTS: Whisker filler level and heat-cure duration had significant effects on composite properties, while heat-cure temperature had non-significant effects. The whisker composite with 79% filler level had a modulus in GPa (mean (SD); n = 6) of 26.9 (1.0), significantly higher than 15.1 (0.2) of an inlay/onlay control, and 16.1 (0.3) of a prosthetic control (Tukey's multiple comparison test; family confidence coefficient = 0.95). The fracture toughness in MPa.m1/2 was 2.22 (0.26) for the whisker composite, higher than 0.95 (0.11) for inlay/onlay control, and (1.13 +/- 0.19) for prosthetic control. The brittleness index was (0.49 +/- 0.07) for whisker composite, lower than (1.02 +/- 0.12) for inlay/onlay control and (0.63 +/- 0.13) for prosthetic control. SIGNIFICANCE: Whisker filler level had a profound influence, heat-cure duration had significant effects, while temperature did not have significant effects, on the properties of whisker composite. The whisker composite had significantly higher elastic modulus and fracture toughness, and lower brittleness than the inlay/onlay and prosthetic controls.

Analysis of Variance↗

PubMed1993

Evaluation of segmental elastic properties of the aorta in normotensive and medically treated hypertensive patients by intravascular ultrasound.

DESIGN AND METHODS: Local elastic properties of the descending aorta at different levels were evaluated by means of intravascular ultrasound images and pressure measurements. For this purpose, 30 normotensive patients and 30 age-matched medically treated patients with essential hypertension, all undergoing diagnostic cardiac catheterization, were studied. RESULTS: Hypertension was well controlled in the essential hypertensives (137.1 +/- 6.79/74.5 +/- 2.65 mmHg). Systolic but not diastolic blood pressure in the hypertensive patients was significantly different from that of the normotensives (118.8 +/- 4.38/69.7 +/- 1.65 mmHg). The continuous loss of volume compliance with increasing distance from the heart was significantly higher in the hypertensives than in the normotensive patients [normotensives (1.45 +/- 0.19) x 10(-10) m5/N at the thoracic aorta, (0.08 +/- 0.05) x 10(-10) m5/N at the external iliac artery; hypertensives (0.81 +/- 0.09) x 10(-10) and (0.05 +/- 0.01) x 10(-10) m5/N at the corresponding sites]. Similarly, the hypertensives had an elevated elastic modulus proximal to the aortic bifurcation compared with the normotensives (244.47 +/- 44.06 versus 108.10 +/- 17.76 m/s, respectively). The decrease in buffering function of the vessel at this site is presumably caused by a turbulent flow pattern. Compared with the normotensives, the treated hypertensives had a significantly higher elastic modulus at each site where this was measured, whereas volume compliance and sectional compliance were lower. CONCLUSION: The differences in elastic modulus and compliance between hypertensive and normotensive patients seem disproportionate to the difference in systolic blood pressure (within the normal range in both the treated hypertensives and the normotensives). Therefore, normalization of high blood pressure by long-term antihypertensive treatment may not fully reverse changes, caused by arterial hypertension, in the viscoelastic properties of the arterial wall.

Adult↗

PubMed2007

Development and characterization of a porous poly(methyl methacrylate) scaffold with controllable modulus and permeability.

Functional restoration following extensive bone injury often requires bone grafting. The primary source of graft material is either autograft or allograft. The use of both material sources is well established, however both suffer limitations. In response, grafting alternatives are being investigated. This manuscript presents the development of a highly porous scaffold with controllable elastic modulus and permeability for use in tissue grafting and tissue engineering applications that is manufactured from FDA approved poly(methyl methacrylate) (PMMA). Fifteen protocol variations based on the commonly used porogen leaching technique for porous scaffold fabrication were employed to control scaffold pore size, pore interconnectivity, and structural strength. Scaffolds were tested for porosity, permeability, elastic modulus, cell culture compatibility, and fatigue tested in compression. Scaffold permeability ranged from 6.6 x 10(-16) m(2) to 1.4 x 10(-10) m(2), and elastic modulus was adjustable between 14 and 322 MPa; data similar to cancellous bone specimens from a variety of species and anatomic locations. Fatigue evaluations revealed 65% strength maintenance after 80,000 loading cycles, and in vitro culture with marrow-derived stromal cells show no cytotoxic effects based on Live/Dead assay. The scaffolds detailed herein will help broaden the spectrum of available orthopaedic tissue scaffolds for research in this evolving field. , 2007.

Animals↗

PubMed1996

The stiffness of the crossbridge is a function of the intrinsic protein osmotic pressure generated by the crossbridge itself.

A model is presented that makes it possible to determine the stiffness of the crossbridge from protein osmotic stress experiments. The model was elaborated while studying the osmotic properties of F-actin and of myosin subfragment-1 F-actin. These studies showed that the elastic modulus by bending of the monomer is directly related to the intrinsic protein osmotic pressure of the system. At a protein osmotic pressure of 1.8 x 10(5) dynes/cm2, the physiological protein osmotic pressure of frog skeletal muscle, it was found that the elastic moduli by bending of the monomer in F-actin and in the myosin subfragment-1 decorated F-actin are 6.5 X 10(7) and 3.3 X 10(8) dynes/cm2, respectively. The value of the elastic modulus by bending of the monomer in the myosin subfragment-1 decorated F-actin compares favorably with the values of the elastic modulus by stretching determined in skeletal muscle fibres.

Actins↗

PubMed1980

The influence of design parameters on calcar stresses following femoral head arthroplasty.

A two-dimensional finite element model (FEM) was used to investigate the effect of various prosthesis design parameters on stresses along the proximal medial aspect of the femur. Strain calculations were compared to reported experimentally measured strains for an intact femur and femur containing a prosthesis in an effort to verify the FEM results. The results of the study indicated that stress levels in the medial aspect of the femur approaching those of the intact femur are possible with a device having an elastic modulus similar to bone. It was found that acrylic bone cement had little effect on stress profiles in the medial aspect when compared to stresses for devices utilizing a direct bone to implant attachment mechanism. It was also found that reduction in implant stem length and elastic modulus of tissue present at the prosthesis--bone interface could be used to increase stresses in the medial aspect; however, their effects were not as dramatic as reducing the elastic modulus of the stem material.

Arthroplasty↗

PubMedDate not supplied

Elastic properties of the cell wall of Aspergillus nidulans studied with atomic force microscopy.

Currently, little is known about the mechanical properties of filamentous fungal hyphae. To study this topic, atomic force microscopy (AFM) was used to measure cell wall mechanical properties of the model fungus Aspergillus nidulans. Wild type and a mutant strain (deltacsmA), lacking one of the chitin synthase genes, were grown in shake flasks. Hyphae were immobilized on polylysine-coated coverslips and AFM force--displacement curves were collected. When grown in complete medium, wild-type hyphae had a cell wall spring constant of 0.29 +/- 0.02 N/m. When wild-type and mutant hyphae were grown in the same medium with added KCl (0.6 M), hyphae were significantly less rigid with spring constants of 0.17 +/- 0.01 and 0.18 +/- 0.02 N/m, respectively. Electron microscopy was used to measure the cell wall thickness and hyphal radius. By use of finite element analysis (FEMLAB v 3.0, Burlington, MA) to simulate AFM indentation, the elastic modulus of wild-type hyphae grown in complete medium was determined to be 110 +/- 10 MPa. This decreased to 64 +/- 4 MPa for hyphae grown in 0.6 M KCl, implying growth medium osmotic conditions have significant effects on cell wall elasticity. Mutant hyphae grown in KCl-supplemented medium were found to have an elastic modulus of 67 +/- 6 MPa. These values are comparable with other microbial systems (e.g., yeast and bacteria). It was also found that under these growth conditions axial variation in elastic modulus along fungal hyphae was small. To determine the relationship between composition and mechanical properties, cell wall composition was measured by anion-exchange liquid chromatography and pulsed electrochemical detection. Results show similar composition between wild-type and mutant strains. Together, these data imply differences in mechanical properties may be dependent on varying molecular structure of hyphal cell walls as opposed to wall composition.

Aspergillus nidulans↗

PubMed2005

Elastic property of vertically aligned nanowires.

An atomic force microscopy (AFM) based technique is demonstrated for measuring the elastic modulus of individual nanowires/nanotubes aligned on a solid substrate without destructing or manipulating the sample. By simultaneously acquiring the topography and lateral force image of the aligned nanowires in the AFM contacting mode, the elastic modulus of the individual nanowires in the image has been derived. The measurement is based on quantifying the lateral force required to induce the maximal deflection of the nanowire where the AFM tip was scanning over the surface in contact mode. For the [0001] ZnO nanowires/nanorods grown on a sapphire surface with an average diameter of 45 nm, the elastic modulus is measured to be 29 +/- 8 GPa.

Journal Article↗

PubMed2005

Viscoelastic properties of single attached cells under compression.

The viscoelastic properties of single, attached C2C12 myoblasts were measured using a recently developed cell loading device. The device allows global compression of an attached cell, while simultaneously measuring the associated forces. The viscoelastic properties were examined by performing a series of dynamic experiments over two frequency decades (0.1-10 Hz) and at a range of axial strains (approximately 10-40%). Confocal laser scanning microscopy was used to visualize the cell during these experiments. To analyze the experimentally obtained force-deformation curves, a nonlinear viscoelastic model was developed. The nonlinear viscoelastic model was able to describe the complete series of dynamic experiments using only a single set of parameters, yielding an elastic modulus of 2120 +/- 900 Pa for the elastic spring, an elastic modulus of 1960 +/- 1350 for the nonlinear spring, and a relaxation time constant of 0.3 +/- 0.12 s. To our knowledge, it is the first time that the global viscoelastic properties of attached cells have been quantified over such a wide range of strains. Furthermore, the experiments were performed under optimal environmental conditions and the results are, therefore, believed to reflect the viscoelastic mechanical behavior of cells, such as would be present in vivo.

Animals↗

PubMed2007

Biomechanical remodeling of the chronically obstructed Guinea pig small intestine.

Small intestinal obstruction is a frequently encountered clinical problem. To understand the mechanisms behind obstruction and the clinical consequences, data are needed on the relation between the morphologic and biomechanical remodeling that takes place in the intestinal wall during chronic obstruction. We sought to determine the effect of partial obstruction on mechanical and morphologic properties of the guinea pig small intestine. Partial obstruction was created surgically in 2 groups of animals living for 2 and 4 weeks. Controls were sham operated and lived for 4 weeks. A combined impedance planimetry-high-frequency ultrasound system was designed to measure the luminal cross-sectional area and wall thickness. These measures were used to compute the circumferential stress and strain of the excised intestinal segments. The incremental elastic modulus was obtained by using nonlinear fitting of the stress-strain curve. Histologic analysis and the measurements of total wall collagen were also performed. The luminal cross-sectional area, wall thickness, and elastic modulus in circumferential direction increased in a time-dependent manner proximal to the obstruction site (P < 0.01), whereas no differences in these parameters were found distal to the obstruction site (P > 0.25). The circumferential stress-strain curves of the proximal segments in 2- and 4-week groups shifted to the left, indicating the intestinal wall became stiffer. Histologic examination revealed a massive increase in the thickness of the muscle layer especially the circular smooth muscle layer (P < 0.05). The collagen content proximal to the obstruction site was significantly larger in the partially obstructed animals compared to controls (P < 0.05). No difference was found distal to the obstruction site. Strong correlation was found between the collagen content and the elastic modulus at stress levels of 70 kPa stress (P < 0.01) and 10 kPa (P < 0.05) proximal to the obstruction site suggesting that the alteration of collagen has great impact on the mechanical remodeling. The morphologic and biomechanical remodeling likely influence the function of the intestine affected by partial obstructed intestine.

Animals↗

PubMed1998

Analysis of contact mechanics for composite cushion knee joint replacements.

Recent research in the area of cushion form bearings for total joint replacements has primarily used thin, soft, elastomeric layers with similar elastic modulus to articular cartilage, bonded to rigid substrates. These are designed to promote the body's natural lubricants to separate the articulating surfaces and prevent wear. Applications to joint replacements have revealed that the abrupt change in stiffness between the soft layer and the rigid substrate and the relatively low strength of the interface resulted in high shear stresses and debonding of the soft layer from the substrate. The approach adopted in this study is to use components with a graded modulus or composite construction. The composite construction consists of a soft compliant layer of polyurethane and a second stiffer polyurethane layer thought to be rigid enough to mechanically interlock to a metallic tibial tray. In this composite structure the deformation of the more rigid polyurethane underlay may generally influence the stress distribution and deformation in the softer upper layer and at the interface between the two materials. A simple analysis technique is presented in the present study where the composite double layer was approximated as an equivalent modulus single layer. Single layer theory, which is readily available in the literature, can then be used to determine the contact parameters, including the maximum contact pressure and the contact radius, for the composite structure. By varying the layer thicknesses and material properties of both the soft surface layer and the stiffer structural support layer, the magnitudes and locations of stresses can be controlled. Results of a parametric stress analysis are presented to assist in the selection of the most appropriate composite layers for cushion knee designs. A 4 mm thick surface layer with an elastic modulus of 20 MPa and a 4 mm thick structural support layer with an elastic modulus of 1000 MPa were considered suitable for this application.

Biomechanical Phenomena↗

PubMed2000

Head-neck finite element model for motor vehicle inertial impact: material sensitivity analysis.

The aim of this study was to conduct a material sensitivity analysis using a head-neck finite element model (FEM). The model included the skull, C1-T1 vertebrae, intervertebral discs, facet joints, and biomechanically relevant ligaments. Poisson's ratio and elastic modulus of the head-neck components were varied. The loading condition included the impact load applied to the first thoracic vertebra. Commercially available software (LS-DYNA) was used for the analysis. Head angle versus time, head center of gravity trajectory, and head center of gravity angular acceleration responses were computed. In general, the variation of elastic modulus had a higher effect on the response compared to variation of Poisson's ratio. As the elastic modulus was increased, the head angle and angular acceleration increased. The present findings form a first step in the study of computational biomechanics of vehicular-related trauma.

Acceleration↗

PubMed1992

Effect of fluoride dosage on bone density, sonic velocity, and longitudinal modulus of rabbit femurs.

Relationships between the fluoride dosage administered to weanling New Zealand white male rabbits and some mechanical properties of the compact bone were investigated for a wide range of dosages. The measured quantities were density, longitudinal sonic velocity in the radial direction, and fluoride ion concentration in compact bone. The longitudinal elastic modulus was estimated from the product of the density and the square of the sonic velocity. The relative static load stress was estimated from the ratio of the final body weight to the cross-sectional area of the femur. These measurements and derived quantities provide quantitative measures of bone quality. A slight peak (2% greater than reference) was determined for the density and a slightly larger peak (5% above reference) for the longitudinal sonic velocity at a dosage of approximately 20 mg/kg/day. The longitudinal elastic modulus exhibited a substantial peak, 14% greater than reference. The relative static load stress showed a very slight peak as a function of dosage and also as a function of fluoride concentration in the bone. When plotted against the elastic modulus, a nonlinear monotonic increase was observed with modulus, showing that the cross-sectional area of the bone is responsive to the stiffness of the tissue. Stiffer tissue produces a smaller cross section, whereas a more compliant tissue requires a marked increase in the area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

Plastic and elastic properties of the systems interstratified clay-water-electrolyte-xanthan.

The present study concerns the rheological behavior of the Jebel Shemsi clay dispersions (Shp). Shp is an interstratified illite/smectite clay from southern Tunisia. The influences of clay concentration, NaCl, and xanthan-a semirigid polymer-on the yield stress, the elastic modulus, and the xanthan adsorption were investigated. The sol-gel transition and the scale laws of rheometric properties are established. Progressive addition of NaCl to the clay dispersions decreases the thickness of the diffuse double layer, which makes the system rigid, increasing the yield and the elastic modulus. In the presence of xanthan, the negative surface charges become higher and the repulsive interparticle interactions increase; consequently the yield and the elastic modulus increase. The xanthan adsorption on the clay particle surface increases slightly with the NaCl concentration. The particle aggregation due to the salt and the particle dispersion due to the polymer are observed. The behavior of this interstratified clay is compared to that found for pure smectite. The 15% illite stratified with smectite in the Shp clay does not change the gels' rheological properties significantly. Meanwhile the amount of Shp clay needed to obtain a gel is more important than in the case of a pure smectite.

Journal Article↗

PubMed2004

Application of dynamic mechanical analysis (DMA) to the determination of the mechanical properties of coated pellets.

Pellets containing a model drug, paracetamol, and microcrystalline cellulose (MCC) were designed to vary their mechanical properties by the incorporation of lactose, glyceryl monostearate (GMS), ethanol, or glycerol, and were produced by the process of extrusion and spheronization. The pellets were coated with an aqueous dispersion of ethyl cellulose (Surelease) to different levels of weight gain (5, 10, and 20%). The tensile strength, deformability, linear strain, elastic modulus, and shear strength of the coated and uncoated pellets were determined by conventional techniques, which are obtained from diametral compression test of individual pellets and compaction of a bed of pellets. Dynamic Mechanical Analysis (DMA) was performed on single pellets to determine the storage modulus and phase angle of the coated pellets. This work demonstrated that the coating film affected the mechanical properties of the pellets differently depending on the properties of the core pellets. Analysis of variance established a significant increase in the strength of the soft GMS- or glycerol-containing pellets with coating, while the effect of the coating material was not significant with respect to the elastic modulus, storage modulus, and phase angle of such pellets. The effects of the coating material on the elastic modulus, deformability, storage modulus, and phase angle of the rigid lactose-containing pellets were significant. The sinusoidal stress-relaxation cycle of the DMA illustrated the increase in the viscoelasticity of all the pellets after coating. Finally, the work demonstrate the advantages of DMA in determining the reversible or dissipated energy by means of storage modulus or phase angle when compared with the irreversible structural destruction of the pellets by conventional techniques.

Cellulose↗

PubMed2002

Variation of nanomechanical properties of bone by gene mutation in the zebrafish.

Significant variations of nanomechanical properties and fracture morphology between gene-mutated liliput(dtc232) (lil/lil) zebrafish skeletal bone and wild-type bone have been observed. Nanoindentation measurement disclosed that lil/lil bone has 36% lower nanohardness and 32% lower elastic modulus. The standard deviations of hardness and elastic modulus of lil/lil bone were both much higher than those of wild-type bone. SEM morphology of fracture surfaces further revealed that in bones after gene mutation, formative microcracks make the performance reduction and the increasing of brittleness. What is more, the plywood-like structure of the normal bone does not exist in the lil/lil bone.

Animals↗

PubMed1991

Graded stress radiography of injured anterior cruciate ligaments.

Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) were examined by graded stress radiography before arthroscopic verification in an effort to determine the loss of ACL function as a result of ligament tearing. Using a commercially available stress device capable of applying varying pressures to the mid-calf, anterior drawers were measured from lateral radiographs at 0-, 7-, 14-, and 21-kiloPascal pressures and used to calculate the equivalent elastic modulus of the remaining ACL fibers. According to viscoelastic theory, this modulus is proportional to the number of elastically active fibers in the ligament. To verify the validity of this concept, the stress-strain relationship of a freshly excised ACL ligament was examined in a tensile testing machine, and the procedure was repeated after the ligament had been partially transsected with a scalpel. Comparison with the elastic modulus of the (intact) ACL of the opposite knee permits an estimate of the percentage of rupture in cases of partial tears. Overstretched ligaments show essentially normal viscoelastic properties once the slack in the ligament has been taken up. Complete tears, on the other hand, show a complete breakdown in the viscoelastic properties of the ACL. The results show that partial tears can be diagnosed by graded stress radiography with a sensitivity of 20% and specificity of 90%. Diagnosis of overstretched ligaments had sensitivity of 50% and specificity of 94%. Complete tears were detected with sensitivity of 88% and specificity of 75% as diagnosed against all other ACL lesions and including normals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗