Elastic modulus of trabecular bone material

An ultrasonic technique was used to measure both the elastic modulus (Young's modulus) of trabecular bone material and the elastic modulus of the cancellous structure. The average trabecular modulus, measured on specimens obtained from three human and one bovine distal femora, was 13.0 GPa (S.D. 1.47) and 10.9 GPa (S.D. 1.57), respectively. On human specimens the structural elastic modulus was found to be related to the structural (apparent) density raised to the 1.88 power. The elastic modulus from the bovine specimens showed a more linear relationship with the density of the cancellous structure (density raised to the 1.57 power).     

Elastic modulus and hydraulic permeability of MDCK monolayers

The critical role of cell mechanics in tissue health has led to the development of many in vitro methods that measure the elasticity of the cytoskeleton and whole cells, yet the connection between these local cell properties and bulk measurements of tissue mechanics remains unclear. To help bridge this gap, we have developed a monolayer indentation technique for measuring multi-cellular mechanics in vitro. Here, we measure the elasticity of cell monolayers and uncover the role of fluid permeability in these multi-cellular systems, finding that the resistance of fluid transport through cells controls their force–response at long times.     

Elastic modulus of tree frog adhesive toe pads

Previous work using an atomic force microscope in nanoindenter mode indicated that the outer, 10- to 15-??m thick, keratinised layer of tree frog toe pads has a modulus of elasticity equivalent to silicone rubber (5?C15?MPa) (Scholz et al. 2009), but gave no information on the physical properties of deeper structures. In this study, micro-indentation is used to measure the stiffness of whole toe pads of the tree frog, Litoria caerulea. We show here that tree frog toe pads are amongst the softest of biological structures (effective elastic modulus 4?C25?kPa), and that they exhibit a gradient of stiffness, being stiffest on the outside. This stiffness gradient results from the presence of a dense network of capillaries lying beneath the pad epidermis, which probably has a shock absorbing function. Additionally, we compare the physical properties (elastic modulus, work of adhesion, pull-off force) of the toe pads of immature and adult frogs.     

Anisotropy in hard dental tissues

The critical angle reflection technique was used to determine longitudinal and shear sonic velocity components in the exposed surface of bovine incisors along the tooth axis and perpendicular to it. By grinding a flat on the tooth surface successive layers were exposed and the velocity components measured. Plots of the velocity variation with depth were prepared which show some variation in the enamel, much less in the dentine and a sharp drop at the dentino-enamel junction. Strong evidence of anisotropy is demonstrated, especially in enamel.

The longitudinal velocity component is larger than previous values for measurements through these hard tissues. Hydroxyapatite and bone models assuming hexagonal symmetry indicate that the surface velocity should be the smaller component. The Katz hexagonally symmetrical bone model shows a significant dip in the velocity along the 45° propagation direction. If it is assumed that prior measurements correspond to the 45° rather than the c-axis direction, a set of elastic constants can be calculated which are an estimate for enamel and dentine. These resemble the Katz bone model.

Enamel C₁₁ 115, C₁₂ 42·4, C₁₃ 30, ₃₃ 125, C₄₄ 22·8

Dentine C₁₁ 37, C₁₂ 16·6, C₁₃ 8·7, C₃₃ 39, C₄₄ 5·7

Katz bone model C₁₁ 31, C₁₂ 14·7, C₁₃ 11·3, C₃₃ 33, C₄₄ 6·2

(all × 10⁹N/m²)

Poisson's ratio for enamel is estimated to be 0·28 and for dentine 0·32.     

Elastic modulus and stress-transfer properties of tunicate cellulose whiskers

Experimental deformation micromechanics of natural cellulose fibers using Raman spectroscopy and X-ray diffraction have been widely reported. However, little has been published on the direct measurements of the mechanical properties, and in particular the elastic modulus, of the highly crystalline material in the native state. Here we report on measurements of the elastic modulus of tunicate cellulose using a Raman spectroscopic technique. A dispersed sample of the material is deformed using a four-point bending test, and a shift in a characteristic Raman band (located at 1095 cm(-1)) is used as an indication of the stress in the material. Relatively little intensity change of the Raman band located at 1095 cm(-1) is shown to occur for samples oriented parallel and perpendicular to the polarization direction of the laser, as compared to a highly oriented flax sample. This indicates that the tunicate sample is a two-dimensional in-plane random network of fibers. By use of this result, the Raman shift, and calibrations with strain from other materials, it is shown that the modulus of the material is very high, at about 143 GPa, and a lack of Raman band broadening is thought to be due to the fact that there is pure crystalline deformation occurring without the effect of crystalline/amorphous fractions. A strain sensitivity of the shift in the 1095-cm(-1) Raman peak for this specimen is shown to be -2.4 +/- 0.2 cm(-1)/%. A molecular mechanics approach, using computer simulation and an empirical force field, was used to predict the modulus of a highly oriented chain of the material, and this is found to be 145 GPa, which is in agreement with the experimental data. However, by use of a normal-mode analysis, it is found that a number of modes have positions close to the central positions of the experimental Raman band. One in particular is found to shift at a rate of 2.5 cm(-1)/%, but due to the complex nature of the structure, it is not entirely conclusive that this band is representative of the experimental findings.     

Elastic area compressibility modulus of red cell membrane.

Micropipette measurements of isotropic tension vs. area expansion in pre-swollen single human red cells gave a value of 288 +/- 50 SD dyn/cm for the elastic, area compressibility modulus of the total membrane at 25 degrees C. This elastic constant, characterizing the resistance to area expansion or compression, is about 4 X 10(4) times greater than the elastic modulus for shear rigidity; therefore, in situations where deformation of the membrane does not require large isotropic tensions (e.g., in passage through normal capillaries), the membrane can be treated by a simple constitutive relation for a two-dimensionally, incompressible material (i.e. fixed area). The tension was found to be linear and reversible for the range of area changes observed (within the experimental system resolution of 10%). The maximum fractional area expansion required to produce lysis was uniformly distributed between 2 and 4% with 3% average and 0.7% SD. By heating the cells to 50 degrees C, it appears that the structural matrix (responsible for the shear rigidity and most of the strength in isotropic tension) is disrupted and primarily the lipid bilayer resists lysis. Therefore, the relative contributions of the structural matrix and lipid bilayer to the elastic, area compressibility could be estimated. The maximum isotropic tension at 25 degrees C is 10-12 dyn/cm and at 50 degrees C is between 3 and 4 dyn/cm. From this data, the respective compressibilities are estimated at 193 dyn/cm and 95 dyn/cm for structural network and bilayer. The latter value correlates well with data on in vitro, monolayer surface pressure versus area curves at oil-water interfaces.     

Measurement of the elasticity modulus of soft tissues

A measurement setup combined with a Finite Element (FE) simulation is presented to determine the elasticity modulus of soft materials as a function of frequency. The longterm goal of this work is to measure in vitro the elasticity modulus of human vocal folds over a frequency range that coincides with the range of human phonation. The results will assist numerical simulations modeling the phonation process by providing correct material parameters. Furthermore, the measurements are locally applied, enabling to determine spatial differences along the surface of the material. In this work the method will be presented and validated by applying it to silicones with similar characteristics as human vocal folds.Three silicone samples with different consistency were tested over a frequency range of 20–250 Hz. The results of the pipette aspiration method revealed a strong frequency dependency of the elasticity modulus, especially below 100 Hz. In this frequency range the elasticity moduli of the samples varied between 5 and 27 kPa.     

A new technique for hard tissues

Fossil tissues generally require specialized processing. Most thin sectioning techniques yield unstained sections or require unwieldy methods to produce stained sections. I outline here two simple techniques for producing stained, ground, thin sections using readily available Romanowsky-type cytology stains and a urine sediment stain. Results are comparable to hematoxylin and eosin stained specimens.     

Preservation of glycogen in decalcified hard tissues

Summary Various fixatives and fixation procedures were tested to evaluate their effects on the preservation of glycogen in sections of decalcified hard tissues. Lower jaws from 1-day-old rats were chosen for the observations. An aqueous solution of glutaraldehyde showed poor preservation of glycogen in the tissues even when employed in the perfusion procedure. Freeze-drying and formaldehyde vapour fixation preserved it much better, but glycogen was still lost to some extent. Freeze-substitution with acetone and various alcoholic fixatives gave a poor result, unless the tissues were fixed with cyanuric chloride. Cyanuric chloride in methanol containing N-methyl morphorine was the best fixative for the preservation of glycogen in the sections. A combination of freeze-substitution with the cyanuric chloride solution, decalcification with the Jenkins's fluid, and subsequent double-embedding in celloidin and paraffin was recommendable for an excellent glycogen preservation.     

Er-YAG激光在牙体硬组织中的应用

随着科学技术的进步,激光技术正以惊人的速度向前发展。激光具有许多优异的性能,已被应用到人类生活的各个领域。伴随激光医学的进展,近来在口腔医学方面的研究已逐步开展起来,除了应用于口腔软组织处理外,激光用于牙体硬组织也得到了越来越多的关注。其中Er-YAG激光在口腔领域的实用性和安全性已得到多方面的认证。该文就激光在口腔医学特别是牙体硬组织中的应用作一综述。     

The mechanical behaviour of some molluscan hard tissues

Pieces of shell from 19 species of molluscs exhibiting various microstructures were tested for tensile strength, modulus of elasticity in bending and modulus of rupture. In tensile strength most shells with cross-foliated, foliated, homogeneous and crossed-lamellar structures did not exceed 60 MNm ² but prismatic and nacreous structures often exceeded this value. Nacreous structure was generally superior to all others in modulus of rupture tests; that of Turbo being about equal to bone. Values of modulus of elasticity were more uniform between structures. There is a general relation between mechanical properties, microstructure and the life style of each animal. Nacreous structure, which is very strong but not widely used, apparently evolved earlier than the less strong but widely used crossed-lamellar structure.     

Er-YAG 激光在牙体硬组织中的应用

随着科学技术的进步,激光技术正以惊人的速度向前发展。激光具有许多优异的性能,已被应用到人类生活的各个领域。伴随激光医学的进展,近来在口腔医学方面的研究已逐步开展起来,除了应用于口腔软组织处理外,激光用于牙体硬组织也得到了越来越多的关注。其中Er-YAG激光在口腔领域的实用性和安全性已得到多方面的认证。该文就激光在口腔医学特别是牙体硬组织中的应用作一综述。     

Electron microscopy of resorbing surfaces of dental hard tissues

Summary The resorbing surfaces of exfoliated or extracted human deciduous molar teeth were studied directly in the scanning electron microscope and indirectly by a single stage carbon replica technique for the transmission electron microscope. Some specimens of resorbing bone were also examined. Some of the material was examined after a simple washing process and some after removal of the organic matrix with hot 12 diamino ethane.The typical crossbanding of collagen could be seen on resorbing cement and dentine surfaces. This is taken as an indication that demineralisation is the first step in resorption. The very highly mineralised peritubular dentine remained proud of the resorbing surfaces thus indicating that its mineral component is in some way selectively protected.Enamel prism sheaths were also found to be selectively resistant to resorption and this is assumed to be related to the protection of the mineral component in these regions by their higher and/or different organic content. No prism sheaths were found next to the enamel-dentine junction and there was only a slight step down from the enamel to the dentine.Large remineralization crystals were found located at the borders between adjacent Howship's lacunae.The natural resorbing surfaces were compared with surfaces subjected to purely physical erosion by 5 keV argon ion beam bombardment (Boyde and Stewart, 1962).Our thanks are due to Mr. A.D.G. Stewart for permission to publish Fig. 5, which was prepared by him. The Cambridge Instrument Company Stereoscan scanning electron microscope was provided by the (U. K.) Science Research Council.     

Elastic modulus variation in mandibular bone: a microindentation study of Macaca fascicularis

We characterized the heterogeneous anisotropic elastic properties of mandibular bone in an adult female specimen of Macaca fascicularis using the technique of microindentation. This approach used an indenter of known mass and geometry to sample bone hardness at a spatial resolution in the order of 100 mum. Hardness values were converted to elastic modulus using empirically derived regression. We determined properties in alveolar, midcorpus, and basal regions of coronal and transverse sections taken from multiple locations along the corpus and ramus. Within sections, we determined properties from endosteal, midcortical, and periosteal regions. We found regional variations in bone structure, including bands of orthotropic circumferential lamellar bone at the endosteal and periosteal corpus base, angular region, and ramus. Transversely isotropic osteonal bone characterizes the midcortices of alveolar and basal regions, with many resorption spaces in alveolar regions restricting sampling opportunities. Regional variations in elasticity include relatively compliant bone in the anterior corpus and ramus. Basal cortical bone is stiffer longitudinally than transversely or superoinferiorly, while the evidence for directional dependence in alveolar bone is equivocal. Alveolar bone appears to be relatively compliant with respect to bone found in midcorpus or basal regions. Considerable variation exists in structure and material properties on a highly localized scale, more so than is discernible through conventional approaches for determining material property variation.     

Elastic properties of bacterial flagellar filaments. II. Determination of the modulus of rigidity

Elongation of a helical bacterial flagellar filament subjected to fluid flow was calculated on the assumption that one end of the filament is firmly attached to a substratum. It was found that the quantity [E(d/2 pi r)2 + 2 mu] could be determined by measuring the elongation at various flow rates, where E is Young's modulus, mu the modulus of rigidity, r the radius of the helix, and d the helical pitch. Experiments were carried out to determine the above quantity for Salmonella flagellar filaments assuming a close-coil form. Because the above quantity is almost equal to 2 mu for a helical form with a large radius/pitch ratio, we were able to determine the modulus of rigidity for this kind of flagellar filament from plots of elongation vs. flow rates. The modulus of rigidity was determined to be about 1 X 10(11) dyn/cm2, i.e., 2 orders of magnitude larger than the previously estimated value.