Elasto-mechanical Properties Research Articles

Commentary on: "Tissue engineering: How to build a heart".

Commentary on: "Tissue engineering: How to build a heart".

P092 Contribution respective des micelles mixtes de sels biliaires et des liposomes dans l’absorption de l’acide oléique et du cholestérol libre par le modèle CACO2-TC7

The liposomes are among the most promising types of drug delivery systems but low stability significantly limits their application. Some approaches proposed to overcome this drawback may affect the liposomes toxicity profile. It is assumed that developed by us and presented here stabilization method involving formation of silicone network within the liposomal bilayer will improve elastomechanical properties of vesicles while not deteriorating their biocompatibility. The silicone-stabilized liposomes were prepared by base-catalyzed polycondensation process of the 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) within the liposomal bilayer. The systematic biological in vitro studies of vesicles obtained were carried out. Moreover, the elastomechanical features investigation employing atomic force microscopy (AFM) measurements was performed. These properties of the liposome membrane are of great importance since they define the nanocarriers' stability as well as play a significant role in their cellular uptake via endocytosis. Applying the Derjaguin–Muller–Toporov (DMT) model, the elastic modulus of the silicone-stabilized liposomes was determined and compared to that characteristic for the pristine liposomes. The in vitro biological evaluation of silicone-stabilized liposomes demonstrated that these vesicles are not toxic for blood cells isolated from healthy donors and they do not induce oxidative stress in HepG2 cells. AFM results confirmed the stabilizing effect of silicone and revealed that the silicone network improves the elastomechanical properties of the resulted liposomes. This is the first report demonstrating that the silicone-stabilized liposomes retain biocompatibility of pristine liposomes’ while acquire significantly better elastomechanical features.

A Basic Theoretical Model for Friction Process at Microasperity Level

This article presents a theoretical model for dry, low-velocity, and wear-less friction based on a single asperity interaction with arbitrary assumed adhesion forces and elastic deformations of the microasperities. Simulations of friction behavior according to the single asperity interaction, as well as the interaction of multiplied single models, are presented. The multiplied model assumes a regular distribution of the single asperities, arbitrarily chosen geometrical properties (based on harmonic function), and elastomechanical properties of the cooperating materials. In the proposed model, the adhesion as a function of asperity deformation is introduced. This enables the simulation of an expedient local coefficient of friction. The model assumes no breaking of the contact between single asperities; however, the proposed model enables detection of such a situation. The results obtained by simulation of the model show both qualitative and quantitative agreement with the known types of friction force dynamic behavior, in particular, nonlinearity of the friction coefficient. At this level of investigation, the model assumes the most important relations connected with its properties, which need further refinement and elaboration, especially according to assumed asperity properties.

Elastomechanical properties of resilin

We report the results of the first investigation on the effect of polarity on the elastic properties of an elastomeric protein resilin found in different insects. We simulate tensile tests on four naturally occurring resilin motifs. We repeat simulations on reduced-polarity counterparts of these motifs by setting the charge on each atom to zero, setting the charge on each atom to one-half of the natural value, as well as by replacing all of the polar amino acids with non-polar substitutes. The results highlight a strong correlation between polarity and extensibility. This is due to the presence of adsorbed water molecules that assist deformation energy transfer from the polar motif, allowing it to stretch further before it undergoes failure. These results unambiguously characterize the influence of charge on the mechanical properties of proteins, thus creating pathways for future formulations of novel bioinspired elastomeric rubbers.

Hydrogen Ion-Induced AlN Thin Layer Transfer: An Elastomechanical Study

The change in the micro-structural properties of epitaxially grown AlN as a function of different H-fluences and thermal evolution was elucidated by nanoindentation and by atomic force microscopy. In this study, we investigated 2 μm-thick AlN layers grown epitaxially on sapphire. The elasto-mechanical properties were measured using a Nanoindenter with continuous stiffness measurement attachment. The AlN samples were implanted with hydrogen ions at 50 keV with various fluences ranging from 0.5 × 1017cm-2 to 3 × 1017 cm-2. The modulus and hardness were carefully determined for each sample. The samples were then annealed in air at temperatures ranging from 300oC to 600oC for 5 min to study the influence of pre-layer splitting treatments on the mechanical properties.

Thermal Behavior of the Mechanical Properties of GaN throughout Hydrogen-Induced Thin Layer Transfer

We report on the thermoevolution of the mechanical properties of H-implanted bulk GaN under the ion-cut process conditions. The mechanical properties were measured using a nanoindenter equipped with a continuous stiffness measurement attachment. The data were taken in depth control mode. Based on nanoindentation analysis, we obtained a modulus of 321{plus minus}7.3GPa and a hardness of 29.6{plus minus}1GPa for the as-implanted GaN samples. After implantation, the modulus and hardness values were found to be 321{plus minus}25GPa and 29.6{plus minus}3GPa, respectively. The influence of thermal treatment on the elasto-mechanical properties of H-implanted bulk GaN is investigated and its role in ultrathin layer splitting is discussed.

Physical Characterization of Zinc Oxide Thin Films Grown by ALD

We investigated the structural and mechanical properties of 400 nm and 40 nm thick ALD ZnO thin films. Diethyl zinc was used as the precursor for zinc and water vapor was used as the oxygen source. The samples were deposited at 150oC and at a pressure of 2.1x10-1 Torr. A growth rate of 2 Aå per cycles was calculated in the ALD process window. The Nanoindenter XP from MTS was used in conjunction with the continuous stiffness measurement (CSM) in depth control mode to analyze the elasto-mechanical properties of ALD ZnO thin films samples. For comparison we benchmarked the mechanical properties of single crystal bulk ZnO samples against our ALD ZnO thin films. We measured the modulus and hardness values of 125{plus minus}1.6GPa and 5.6{plus minus}0.09GPa respectively for our single crystal bulk ZnO reference sample.

Elastomechanical properties of bovine veins

Veins have historically been discussed in qualitative, relative terms: “more compliant” than arteries, subject to “lower pressures”. The structural and compositional differences between arteries and veins are directly related to the different functions of these vessels. Veins are often used as grafts to reroute flow from atherosclerotic arteries, and venous elasticity plays a role in the development of conditions such as varicose veins and valvular insufficiency. It is therefore of clinical interest to determine the elastomechanical properties of veins. In the current study, both tensile and vibration testing are used to obtain elastic moduli of bovine veins. Representative stress–strain data are shown, and the mechanical and failure properties reported. Nonlinear and viscoelastic behavior is observed, though most properties show little strain rate dependence. These data suggest parameters for constitutive modeling of veins and may inform the design and testing of prosthetic venous valves as well as vein grafts.

Nanoindentation Investigation of HfO2 and Al2O3 Films Grown by Atomic Layer Deposition

The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node have shifted engineers’ attention from the traditional and proven dielectric to materials of higher dielectric constant also known as high- materials such as hafnium oxide and aluminum oxide . These high- materials are projected to replace silicon oxide . In order to address the complex process integration and reliability issues, it is important to investigate the mechanical properties of these dielectric materials in addition to their electrical properties. In this study, and have been fabricated using atomic layer deposition (ALD) on (100) p-type Si wafers. Using nanoindentation and the continuous stiffness method, we report the elastomechanical properties of and on Si. ALD thin films were measured to have a hardness of and a modulus of , whereas the ALD thin films have a hardness of and a modulus of . The two materials are also distinguished by very different interface properties. forms a hafnium silicate interlayer, which influences its nanoindentation properties close to the interface with the Si substrate, while does not exhibit any interlayer.

Nanomechanical Properties of High-K Dielectrics Grown by Atomic Layer Deposition

The challenges of reducing gate leakage current and dielectric breakdown beyond the 45 nm technology node has shifted engineers' attention from SiO2 to higher dielectric constant materials also known as high-k materials such as HfO2 and Al2O3. Therefore, it is important to investigate the electrical and mechanical properties of these materials that are projected to replace SiO2. In this study, HfO2 and Al2O3 have been deposited by atomic layer deposition (ALD) on Si wafers. Using continuous stiffness method (CSM) Nanoindenter® XP, we report elasto-mechanical properties of HfO2 and Al2O3 on Si. HfO2 has a hardness and modulus of 9-10 {plus minus} 2 GPA and 200 {plus minus} 40 GPA respectively. In addition, the hardness and modulus of Al2O3 were determined to be respectively 10-11 {plus minus} 2 GPA and 200 {plus minus} 40 GPA.

Chemical, anatomical and technological properties of Snakewood [Brosimum guianense (Aubl.) Huber

The very decorative heartwood of Brosimum guianense is internationally well known. Snakewood, as it is colloquially known, is represented in wood databases (e.g. the DELTA or InsideWood) as well as in lists of commercial timbers of many timber trading companies. The very decorative heartwood is hardly available and gains prices of up to 25 €/kg in form of half stems. In the present study, the chemical composition and especially the subcellular cell structure was analysed by means of UV microspectrophotometry to explain the high natural durability and some extraordinary physical properties in addition to the anatomical composition. The heartwood consists of approximately 39% lignin, 54% carbohydrates and 0.4% lipophilic compounds of unspecified origin. The fibres are very thick-walled. Numerous sclerotic tyloses and organic deposits are present in the vessel. The extractives in high content are also components of parenchyma cells as well as in tyloses, respectively. These detected phenolic extractives, partly of flavonoid character, are also part of the cell wall. Calcium oxalate crystals are deposited in the upright and square cells of rays and sporadically in axial parenchyma cells. These facts are reasons for the famous natural durability of Snakewood. The sapwood density ranges from 1.1 to 1.4 g/cm3 for heartwood (12% mc). The compression strength (119 N/mm2), the bending strength (241 N/mm2), the modulus of elasticity (23,200 N/mm2) and the hardness (196 N/mm2) indicate exceedingly high elastomechanical properties.

Determination of Young’s and shear moduli of common yew and Norway spruce by means of ultrasonic waves

Despite the exceptional position of yew among the gymnosperms concerning its elastomechanical properties, no reference values for its elastic constants apart from the longitudinal Young’s modulus have been available from literature so far. Hence, this study’s objective was to determine the Young’s moduli E L, E R and E T and the shear moduli G LR, G LT and G RT of yew wood. For that purpose, we measured the ultrasound velocities of longitudinal and transversal waves applied to small cubic specimens and derived the elastic constants from the results. The tests were carried out at varying wood moisture contents and were applied to spruce specimens as well in order to put the results into perspective. Results indicate that E L is in the same order of magnitude for both species, which means that a high-density wood species like yew does not inevitably have to have a high longitudinal Young’s modulus. For the transverse Young’s moduli of yew, however, we obtained 1.5–2 times, for the shear moduli even 3–6 times higher values compared to spruce. The variation of moisture content primarily revealed differences between both species concerning the shear modulus of the RT plane. We concluded that anatomical features such as the microfibril angle, the high ray percentage and presumably the large amount of extractives must fulfil important functions for the extraordinary elastomechanical behaviour of yew wood which still has to be investigated in subsequent micromechanical studies.

Wood characteristics of Podocarpus oleifolius var. macrostachyus (Parl.) Buchholz and Gray native to Costa Rica: their significance for wood utilization

Due to over-exploitation in the past, native conifer species in many tropical countries are hardly available anymore for wood utilization. In the last decades Costa Rica has undertaken considerable efforts to study the silvicultural characteristics of the native species of the family Podocarpaceae, in particular Podocarpus oleifolius var. macrostachyus (Parl.) Buchholz and Gray, in order to evaluate its suitability for cultivation in mixed plantations with preference for native species. However, sufficient information on the structural, chemical and physical characteristics of the wood of this species are not available. This investigation reports on selected wood characteristics of old-growth trees from the Cordillera de Talamanca (approximately 2,700 m a.s.l.), Costa Rica. Tracheids occupy 93% of total volume; average tracheid length is 4 mm, wall thickness ranges 2.5–4.5 (–6.5) μm throughout the annual increment. Lignin content is between 33.6 and 34.7% excluding any lignin-like compounds. Cellular UV microspectrophotometry reveals that the compound middle lamella (CML) and S2 layer are characterized by a higher absorbance than is commonly observed in e.g. Pinaceae, and with a distinct gradient from S1 to S3. The carbohydrate (cellulose and hemicelluloses) composition reflects the typical proportions as found in other conifers. A low content of organic extractives explains the only moderate (white rot) to low (brown rot) natural durability of the heartwood against wood destroying fungi. The wood density (12% mc) ranges 0.5–0.68 g cm-³; compression strength (44±2.38 MPa) and corresponding modulus of elasticity (8,600±1,720 MPa) indicate good elastomechanical properties. Accordingly, the wood is recommended for multiple indoor enduses. For exterior applications, effective protective measures and/or preservative treatment are required.

Nanomechanics of silicon nanowires

The stability and elasto-mechanical properties of tetragonal and cagelike or clathrate nanowires of $\mathrm{Si}$ are investigated and compared using molecular dynamics simulations. Our results show that cagelike nanowires, while possessing lesser density, are able to maintain their structural integrity over a larger range of strain conditions than the tetrahedral nanowires, making them a better candidate for structural strength, chemical sensor, and electronics applications under strain conditions. This could have important technological implications.

Multilayer analysis: quantitative scanning acoustic microscopy for tissue characterization at a microscopic scale

An in vitro acoustic microscopy method for the quantitative characterization of biological hard tissues at a microscopic scale is described. At a frequency of 900 MHz, the acoustic impedance is measured as a tissue parameter, which is closely related to its elastomechanical properties. Contrast influences caused by defocus, edges, and surface inclinations, respectively, are either compensated or excluded from the measurement by a special data acquisition and analysis concept. A raster grid was used to validate the capabilities and limitations of the method, and results obtained from human cortical bone are shown. The comparison of different evaluation methods demonstrate the significance of a sophisticated analysis under consideration of topographical and system parameters. Cortical bone impedance maps showed a strong dependence on the anatomical structures, and the mean values were found to be in the range from 3.5 to 6.5 Mrayl within one single osteon.

Investigation of elasto-mechanical properties of alginate microcapsules by scanning acoustic microscopy.

High-frequency scanning acoustic microscopy (SAM) was used for investigation of acoustic impedance and 3D-surface topography of full alginate microspheres that act as model of artificial biological cells. Elasto-mechanical properties of the investigated specimens have been characterized by acoustic impedance. Mean surface impedance of microspheres (diameter: 300 microm) was measured with SAM at 900 MHz with a spatial resolution of 1.5 microm. The sensitivity and reproducibility of SAM had to be increased considerable to receive and quantify signals in the very low impedance region. The multilayer analysis method was used to get quantitative data of acoustic impedance with SAM at a microscopic level. 3D images show details of structure and surface topography. As a reference, bulk measurements were performed on full alginate cylinders. The acoustical impedance and the mechanical stiffness c(11) were obtained from mass density and longitudinal ultrasound velocity at 6 MHz. The impedances received with both methods are in close agreement. The results demonstrate the SAM as a powerful tool for characterizing mechano-elastical parameters as well as surface structure and topography of microspheres with high spatial resolution.

Realistic modeling of elasto-mechanical properties of soft tissue and its evaluation

Computer-based techniques for the simulation of craniofacial surgical procedures and for the prediction of the surgical outcome have been shown to be very useful. However, the assessment of the accuracy of the simulated surgical outcome is difficult. In this paper, a technique is described, which allows to compare the simulated surgical outcome and the actual surgical result. The surgery simulation is based on a preoperative CT scan of the patient's head and on a preoperative surface scan of the patient's face. The simulated postoperative patient's appearance is compared to a second surface scan, which is obtained postoperatively. The pre- and postoperative surface scans, which are different due to the surgery, are registered employing a robust registration method, which minimizes the median of Euclidean distances of corresponding points. Parameters of the soft-tissue model, which is used for the surgical simulation process, can be adapted with respect to minimized differences of corresponding points of the simulated postoperative and the actual postoperative surface of a patient's face.

Elastomechanical properties of young beech trees ( Fagus sylvatica L.) grown at elevated and ambient CO 2 content

We investigated the influence of the CO2 content of the atmosphere on the elastomechanical features of beech wood. Tests of the longitudinal compression strength and the longitudinal modulus of elasticity in compression were carried out on stem sections of four-year old beech trees from six European provenances. The trees had been cultivated in a green-house for three years, one half at doubled CO2 content, the other half in ambient air for reference.

Physical and elasto-mechanical wood properties of young Sentang ( Azadirachta excelsa ) planted in Sabah, Malaysia

) is being increasingly promoted and planted in Malaysia as plantation species for timber. A study of wood properties of 10-year-old planted Sentang produced the following average values: initial moisture content 49.2%; green density 0.74 g/cm3; ovendry density 0.48 g/cm3; green to standard climate (airdry) shrinkage 3.1% (tang.), 1.7% (rad.), 0.2% (long.); green to ovendry shrinkage 5.5% (tang.), 3.7% (rad.), 0.4% (long.); modulus of rupture 75.7 N/mm2; modulus of elasticity 7060 N/mm2; compression strength (parallel to grain) 39.5 N/mm2; shear strength 14.0 N/mm2 (tang.), 11.7 N/mm2 (rad.); Janka hardness 3.74 kN (tang.), 3.24 kN (rad.).

Quantitative Ultraschallrastermikroskopie zur Bestimmung der akustischen Impedanz von kortikalem Knochengewebe

An in vitro scanning acoustic microscopy measurement technique is described to assess the elastomechanical properties of human bone tissue at the level of cellular organizational structures. The technique allows to measure the acoustic impedance as a material describing parameter. Contrast influences caused by defocus, surface edges and inclinations, respectively are separated or eliminated and the microscopic acoustic impedances of the remaining data points are determined by a dynamic calibration method. Cortical bone samples of the human femur embedded in polymethylmethacrylate (PMMA) were investigated at a frequency of 900 MHz. The resulting impedance maps showed a strong structural dependence and the mean values were found to be in the range from 2 to 6 Mrayl, which is significantly lower than macroscopic bulk values of the bone compound measured by acoustic low frequency methods.