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PubMed2002

Elastic modulus measurements of human liver and correlation with pathology.

Viral hepatitis causes fibrosis in the liver and may change mechanical properties of the liver. To evaluate the impact of fibrosis on elastic properties of human liver and to investigate potential benefits of ultrasonic elasticity imaging, 19 fresh human liver samples and 1 hepatic tumor (focal nodular hyperplasia) sample obtained during operations were studied. Simple 1-D estimates based on the cyclic compression-relaxation method were performed. Elastic modulus values were derived from the predetermined strain (controlled by a step motor system) and the stress values (measured by an electronic balance). Each specimen subsequently received histologic examination and a grade of liver fibrosis was scored from 0 to 5. Results show that the elastic modulus values were on the order of several hundreds to thousands of Pascals. The elastic modulus generally increased with the fibrosis grade, although some discrepancies existed at the middle grades of fibrosis (scores 1 to 3). The correlation between the fibrosis score and the elastic modulus was significant (p < 0.01) based on the statistical analysis using the Pearson correlation method. In addition, the relation between the elastic modulus and the fibrosis grade generally exhibited a quadratic trend. It was concluded that severity of fibrosis had a good correlation with stiffness of the liver. Results also indicated that the elasticity imaging of the liver may provide significant clinical values if the elastic modulus can be accurately measured.

Elasticity↗

PubMed2001

Dynamic elastic modulus of 'packable' composites.

OBJECTIVE: A new type of so-called 'packable', 'condensable' or 'mouldable' composite has been developed and aims at replacing amalgam for posterior restorations. The purpose of the present investigation was to study the dynamic elastic modulus of 12 packable composites, and to follow the evolution of this property following prolonged water absorption. METHODS: Of each material ten rectangular samples (1.5x5x35 mm) were prepared. The elastic modulus (GPa) of each sample was determined with a non-destructive dynamic method using a Grindo-Sonic after 24 h of dry storage at room temperature, and after 24h, 1, 3 and 6 months of wet storage at 37 degrees C. All data were analyzed using two-way ANOVA, Bonferroni/Dunn's test for multiple comparisons and paired t-test with a significance level of p<0.05. In addition, inorganic filler volume percentages were derived from the phenomenological model introduced by Braem et al. [11]. RESULTS: The studied materials varied widely in terms of elastic modulus, ranging between composites classified as Compact-Filled Densified (elastic modulus of 23.4+/-2.4 GPa) and as Microfine (elastic modulus of 8.5+/-2.1 GPa). SIGNIFICANCE: The great diversity observed in the elastic modulus of this type of composites necessitates clear specifications with regard to 'first' the definition of marketing terms such as packable and so on, and 'second' the justified use in posterior teeth.

Analysis of Variance↗

PubMed1999

Application of dynamic computed tomography for measurements of local aortic elastic modulus.

A novel computed tomographic (CT) technique used for the instantaneous measurement of the dynamic elastic modulus of intact excised porcine aortic vessels subjected to physiological pressure waveforms is described. This system was comprised of a high resolution X-ray image intensifier based computed tomographic system with limiting spatial resolution of 3.2 mm-1 (for a 40 mm field of view) and a computer-controlled flow simulator. Utilising cardiac gating and computer control, a time-resolved sequence of 1 mm thick axial tomographic slices was obtained for porcine aortic specimens during one simulated cardiac cycle. With an image acquisition sampling interval of 16.5 ms, the time sequences of CT slices were able to quantify the expansion and contraction of the aortic wall during each phase of the cardiac cycle. Through superficial tagging of the adventitial surface of the specimens with wire markers, measurement of wall strain in specific circumferential sectors and subsequent calculations of localised dynamic elastic modulus were possible. The precision of circumferential measurements made from the CT images utilising a cluster-growing segmentation technique was approximately +/- 0.25 mm and allowed determination of the dynamic elastic modulus E(dyn) with a precision of +/- 8 kPa. Dynamic elastic modulus was resolved as a function of the harmonics of the physiological pressure waveform and as a function of the angular position around the vessel circumference. Application of this dynamic CT (DCT) technique to seven porcine thoracic aortic specimens produced a circumferential average (over all frequency components) E(dyn) of 373 +/- 29 kPa. This value was not statistically different (p < 0.05) from the values of 430 +/- 77 and 390 +/- 47 kPa obtained by uniaxial tensile testing and volumetric measurements respectively.

Animals↗

PubMed1996

[The effect of rehydration on the elasticity modulus and strength of lyophilised and irradiated femur bone in the human].

The influence of rehydration on elasticity modulus and strength of lyophilized and irradiated cortical bone of human femur was studied by means of balance rheometer. The measurements were taken in 20(C and at sample deformation frequency of 12.5 Hz. The bone samples were taken from 40 individuals aged 35-45 who died suddenly. It was found, that after 24 hours rehydration the elasticity modulus of lyophilized and irradiated cortical bone decreased about 11% and strength increased about 18%. The greatest changes of elasticity modulus were observed during first 10 hours of rehydration. Strong negative correlation (r = -0.8, p < 0.001) between changes of elasticity modulus and degree of the bone rehydration was confirmed.

Adult↗

PubMed1995

Venous tone evaluation by elastic modulus and therapeutic implications.

The venous system plays an important role in the determination of cardiac output and venous return. Venous tone is a property of the venous system which reflects the venous resistance and pressure. An increased venous tone caused by venoconstriction leads to an increased net capillary filtration by increasing the venous resistance and venous pressure. Use of a phlebotonic agent to increase the venous tone would prove useful in treating venodilation associated with worsening venous insufficiency. Various methods have been used to investigate the venous tone and these include: 1. isolated vein segment technique; 2. determination of the mean circulatory filling pressure; 3. constant cardiac output-reservoir techniques; 4. venous occlusion plethysmography to assess pressure-volume relationship. These methods have their inherent limitations and their suitability for determining the effects of drugs on the venous tone is sometimes in doubt. Venous occlusion plethysmography using strain gauge plethysmography and measurement of venous pressures with the aid of a needle inserted into a vein on the dorsum of the foot have been used to assess the function of the vein wall by quantifying the elastic modulus < >. The elastic modulus is calculated from the change in pressure and the corresponding change in volume which are measured from the linear high pressure part of the pressure volume curve. Results obtained using this method show a clear difference in elasticity between normal limbs (K = 17.24) and limbs with varicose veins (K = 1.26) and deep venous incompetence (K = 1.21). The limbs of normal individuals that are at a high risk of developing varicose veins have an abnormal K(K = 1.33). This method is however invasive and we have developed a non-invasive method of calculating the elastic modulus < > using air plethysmography. This method has shown a good reproducibility in 3 healthy volunteers examined and this technique can be used to study the effect of a phlebotonic agent on the venous tone in patients at high risk of developing venous insufficiency.

Adult↗

PubMed2004

Determination of elastic modulus of the components at dentin-resin interface using the ultrasonic device.

The purpose of this study was to determine the elastic moduli of the components at resin-dentin interface with the use of an ultrasonic device. Dentin plates were obtained from freshly extracted bovine incisors with a shape in rectangular form. Resin composites and bonding agents were polymerized and trimmed in the same shape as the dentin specimens. The ultrasonic equipment employed in this study was comprised of a Pulser-Receiver, transducers, and an oscilloscope. Each elastic modulus was determined by measuring the longitudinal and shear wave sound velocities. The mean elastic modulus of mineralized dentin was 17.4 GPa, while that of demineralized dentin was 1.4 GPa. When the demineralized dentin was immersed in bonding agents, the elastic modulus changed to 3.7-4.7 GPa, and these values were significantly higher than those of demineralized dentin. A gradient in elastic modulus was detected as the analysis shifted from the dentin side to the resin composite.

Analysis of Variance↗

PubMed1995

Elastic modulus of orbicularis oculi muscle in normal humans, humans with Graves' eye disease, and cynomolgus monkeys.

We built an experimental apparatus to investigate the passive elastic characteristics of orbicularis oculi muscle and examined specimens from normal humans, humans with stable Graves' eye disease, and cynomolgus monkeys. Stress-strain curves were determined and found to be exponential. The elastic modulus (Young's modulus), analogous to the stiffness of the material, was calculated as a function of strain. Elastic modulus as a function of instantaneous stress was linear. Monkey elastic modulus values were determined, but did not allow meaningful interspecies comparison because of the small sample size. No significant difference was found between normal humans and humans with Graves' eye disease with respect to elastic modulus values.

Animals↗

PubMed2003

Effect of Nd:YAG laser irradiation on the hardness and elastic modulus of human dentin.

OBJECTIVE: The purpose of this study was to investigate the changes of hardness and elastic modulus of human dentin after Nd:YAG laser irradiation. BACKGROUND DATA: The application of Nd:YAG laser in dental hard tissues has been widely studied. However, little information is available about the mechanical properties of teeth after Nd:YAG laser irradiation. METHODS: The human dentin was irradiated by Nd:YAG laser through a 400-microm optic bare fiber. The parameters in laser delivery were 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec. Both the hardness and elastic modulus were obtained using an Instron microhardness tester and Vickers indenter. The indentations were then examined under a scanning electron microscope. RESULTS: The hardness and elastic modulus of irradiated human dentin in the energy of 100 mJ/pulse--10 pps--4 sec and 150 mJ/pulse--10 pps--4 sec were 44.7 kg/mm(2) and 22.8 GPa, and 46.9 kg/mm(2) and 21.4 GPa, respectively. These values were significantly lower than that of non-irradiated dentin by the Student's t test. CONCLUSION: Our study demonstrated that Nd:YAG laser irradiation would reduce the hardness and elastic modulus of human dentin.

Dentin↗

PubMed2002

Use of an ultrasonic device for the determination of elastic modulus of dentin.

The mechanical properties of dentin substrate are one of the important factors in determining bond strength of dentin bonding systems. The purpose of this study was to determine the elastic modulus of dentin substrate with the use of an ultrasonic device. The dentin disks of about 1 mm thickness were obtaining from freshly extracted human third molars, and the dentin disk was shaped in a rectangular form with a line diamond point. The size and weight of each specimen was measured to calculate the density of the specimen. The ultrasonic equipment employed in this study was composed of a Pulser-Receiver (Model 5900PR, Panametrics), transducers (V155, V156, Panametrics) and an oscilloscope. The measured two-way transit time through the dentin disk was divided by two to account for the down-and-back travel path, and then multiplied by the velocity of sound in the test material. Measuring the longitudinal and share wave sound velocity determine elastic modulus. The mean elastic modulus of horizontally sectioned specimens was 21.8 GPa and 18.5 GPa for the vertically sectioned specimens, and a significant difference was found between the two groups. The ultrasonic method used in this study shows considerable promise for determination of the elastic modulus of the tooth substrate.

Acoustics↗

PubMed1989

Pulsatile diameter and elastic modulus of the aortic arch in essential hypertension: a noninvasive study.

A noninvasive evaluation of the aortic arch diameter was performed in 16 subjects with sustained essential hypertension and in 15 normal subjects of similar age, gender and body surface area. In all subjects, measurements were obtained of brachial mean arterial pressure and pulse pressure, cardiac mass (judged on echocardiography) and carotid-femoral pulse wave velocity together with ultrasound determinations of aortic arch diastolic and systolic diameter (suprasternal window). For each subject, pulsatile change in aortic diameter, strain and aortic arch elastic modulus were calculated. Compared with normal subjects, the hypertensive subjects showed an increase in aortic arch diameter (diastolic diameter 29.6 +/- 1.0 versus 25.4 +/- 1.0 mm, p less than 0.01), in elastic modulus (1.071 +/- 0.131 versus 0.526 +/- 0.045 10(5) N.m-2, p less than 0.001) and pulse wave velocity (11.8 +/- 0.5 versus 8.9 +/- 0.3 m/s, p less than 0.001). In the study group, a positive correlation was observed between diastolic aortic arch diameter and mean arterial pressure (r = 0.54, p less than 0.01) and between elastic modulus and cardiac mass (r = 0.60, p less than 0.01). Elastic modulus and age were positively correlated (r = 0.73, p less than 0.01) in hypertensive but not in normal subjects (r = 0.08, NS). This study is the first to demonstrate noninvasively that both the aortic arch diameter and the elastic modulus are increased in patients with sustained uncomplicated essential hypertension. These findings suggest that the increase in elastic modulus could influence the development of cardiac hypertrophy, and that both age and blood pressure act independently as factors that alter the arterial wall of subjects with sustained essential hypertension.

Adult↗

PubMed1989

Experimental method for the measurement of the elastic modulus of trabecular bone tissue.

A procedure has been developed to measure the elastic modulus of small, irregularly shaped specimens without significantly disturbing the specimen's internal or surface structure. This procedure was developed to measure the average elastic modulus of isolated trabeculae from human cancellous bone tissue. The procedure combines direct testing of a cantilever beam-type specimen, along with finite element modeling of the specimen and the testing conditions. Initial estimates for the bone tissue material properties are input into the finite element model; differences between the calculated finite element displacement and the experimentally observed displacement allows the actual material modulus to be determined. Machined aluminum and cortical bone specimens were used to test the accuracy and repeatability of the procedure. Manipulations of the finite element models were performed to examine the effect that mesh construction errors might have on the accuracy of the results. None of the parameters examined resulted in changes in the measured finite element displacements of greater than 8%. In tests on six trabecular bone specimens, an average elastic modulus of 7.8 GPa was calculated. Even taking into account the possible sources of error, this value remains significantly less than the accepted value for cortical bone.

Bone and Bones↗

PubMed2005

[A methodological study on testing the elastic modulus of soft bio-anthropomorphic materials].

It is difficult to test the elastic modulus of the soft bio-anthropomorphic materials by using the general stretch-strain test method. With the equipment for a hardness testing system of bio-anthropomorphic materials and millesimal gauge, we introduce in this paper a compress-strain test method and carry out the related test-data curve-fitness. The test results indicate that this kind of method can be adopted in testing the elastic modulus of the soft bio-anthropomorphic materials and help to compare and distinguish the biomechanics equivalent between the tissues.

Biocompatible Materials↗

PubMed2000

Elastic modulus of polypyrrole nanotubes

The first measurements of the tensile elastic modulus of polypyrrole nanotubes are presented. The nanotubes were mechanically tested in three points bending using atomic force microscopy. The elastic tensile modulus was deduced from force-curve measurements on different nanotubes with outer diameter ranging between 35 and 160 nm. It is shown that the elastic modulus strongly increases when the thickness or outer diameter of polypyrrole nanotubes decreases.

Journal Article↗

PubMed1982

Axial elastic modulus as a function of relative fiber width in relaxed skinned skeletal muscle fibers.

The axial elastic modulus as a function of relative fiber width was measured in relaxed skinned fiber segments from the semitendinosus muscle of the frog. Fiber width was reduced by adding the non- penetrating long-chain polymer Dextran T500 (Mm = 181,800 D) to the fiber bathing solution. The axial elastic modulus increased steeply as relative fiber width was reduced. This relationship is independent of both ionic strength and of the presence of low molecular weight fractions of dextran within the interfilament space. The observed increase in axial elastic modulus with compression may reflect an interaction between crossbridges and thin filaments, an hypothesis which is corroborated by the similarity of responses obtained from compressed fibers and from width fibers in rigor.

Animals↗

PubMed1996

Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc.

STUDY DESIGN: Local elastic moduli of sliced intervertebral disc specimens were studied after establishing the relation between the elastic modulus and indentation behaviors by model tests using polyurethane specimens. OBJECTIVES: This study presents a method to quantify the distribution of compressive elastic moduli in the lumbar intervertebral disc and to clarify the effects of degeneration on the distribution. SUMMARY OF BACKGROUND DATA: No study has been performed to evaluate the distribution of axial compressive elastic moduli, which is supposed to relate previous biomechanical, biological, and biochemical findings regarding the intervertebral disc. METHODS: Local compressive elastic moduli of the intervertebral disc were estimated by indentation tests. To evaluate the distribution of elastic moduli, indentation tests were performed at nodal points of a 10 mm x 10 mm network on a specimen. Nine cadaveric lumbar discs (L3-L4 and L4-L5) with various degrees of degeneration were tested. The age of subjects ranged 39 to 90 years (mean, 58.4 years). RESULTS: The distribution of elastic moduli in normal discs was symmetric about the midsagittal plane. The mean elastic modulus in the nucleus pulposus was 5.8 kPa and those of the anterior and posterior anulus fibrosus were 110.7 and 75.8 kPa, respectively. The elastic moduli in the lateral portions were the lowest in the normal anulus, and were close to the values of the nucleus. Compared to normal discs, degenerated discs showed irregular distributions of elastic moduli. The elastic moduli of the degenerated nucleus were higher than those in normal discs. CONCLUSIONS: The distribution of elastic moduli is much different between discs with and without degeneration.

Adult↗

PubMed1973

Measurement of the elastic modulus for red cell membrane using a fluid mechanical technique.

Red cells which adhere to a surface in a parallel plate flow channel are stretched when acted on by a fluid shear stress. Three types of stretching are studied: whole cell stretching, the stretching of a red cell evagination, and tether (long, thin membrane process) stretching. In addition, the stretching of a large scale model cell attached to a surface is studied in a Couette flow channel. The results indicate that the uniaxial stretching of red cell membrane can be described by a linear stress-strain relationship. Simple theories developed from free body diagrams permit the calculation of a value for the modulus of elasticity of cell membrane in each of the three experiments. In all cases the value for the modulus is on the order of 10(4) dyn/cm(2) for an assumed membrane thickness of 0.01 mum. It was also observed that red cell tethers steadily increase in length when the fluid shear stress is greater than approximately 1.5 dyn/cm(2) and tether lengths in excess of 200 mum have been achieved. Tethers appear to possess both fluid and elastic properties.

Cell Membrane↗

PubMed1996

Properties of the elastic modulus from buccal compact bone of human mandible.

The aim of this study was to elucidate the elastic modulus of the mandible, which is an important factor in analysis of its physical dynamics. To meet this need, three point bending tests of small bone specimens were performed. The authors concluded that the elastic modulus of the mandible varied with site and orientation. When the specimens were obtained from regions paralleling the mandibular plane, the values in the lower portions were generally higher than those in the upper portions, indicating that these regions are more rigid. The elastic modulus in the marginal portions of the mandible, such as the mandibular plane, had comparatively high values. Relatively lower values were found as the angle to the margin of the mandible increased. In the incisal and premolar regions, anisotropic characteristics approximated those of unidirectional fiber reinforced composite materials. In the molar regions, there was a broad distribution of values, reflecting the complexity of mandibular structure.

Anisotropy↗

PubMed2002

Elastic energy storage in human articular cartilage: estimation of the elastic modulus for type II collagen and changes associated with osteoarthritis.

The viscoelastic mechanical properties of normal and osteoarthritic articular were analyzed based on data reported by Kempson [in: Adult Articular Cartilage (1973)] and Silver et al. (Connect. Tissue Res., 2001b). Results of the analysis of tensile elastic stress-strain curves suggest that the elastic modulus of cartilage from the superficial zone is approximately 7.0 GPa parallel and 2.21 GPa perpendicular to the cleavage line pattern. Collagen fibril lengths in the superficial zone were found to be approximately 1265 microm parallel and 668 microm perpendicular to the cleavage line direction. The values for the elastic modulus and fibril lengths decreased with increased extent of osteoarthritis. The elastic modulus of type II collagen parallel to the cleavage line pattern in the superficial zone approaches that of type I collagen in tendon, suggesting that elastic energy storage occurs in the superficial zone due to the tensile pre-tension that exists in this region. Decreases in the elastic modulus associated with osteoarthritis reflect decreased ability of cartilage to store elastic energy, which leads to cartilage fibrillation and fissure formation. We hypothesize that under normal physiological conditions, collagen fibrils in cartilage function to store elastic energy associated with weight bearing and locomotion. Enzymatic cleavage of cartilage proteoglycans and collagen observed in osteoarthritis may lead to fibrillation and fissure formation as a result of impaired energy storage capability of cartilage.

Aged↗