The Role of Substrate Topography and Stiffness on MSC Cells Functions: Key Material Properties for Biomimetic Bone Tissue Engineering

The hypothesis of the present research is that by altering the substrate topography and/or stiffness to make it biomimetic, we can modulate cells behavior. Substrates with similar surface chemistry and varying stiffnesses and topographies were prepared. Bulk PCL and CNTs-reinforced PCL composites were manufactured by solvent casting method and electrospinning and further processed to obtain tunable moduli of elasticity in the range of few MPa. To ensure the same chemical profile for the substrates, a protein coating was added. Substrate topography and properties were investigated. Further on, the feedback of Wharton’s Jelly Umbilical Cord Mesenchymal Stem Cells to substrates characteristics was investigated. Solvent casting scaffolds displayed superior mechanical properties compared to the corresponding electrospun films. However, the biomimetic fibrous texture of the electrospun substrates induced improved feedback of the cells with respect to their viability and proliferation. Cells’ adhesion and differentiation was remarkably pronounced on solvent casting substrates compared to the electrospun substrates. Soft substates improved cells multiplication and migration, while stiff substrates induced differentiation into bone cells. Aspects related to the key factors and the ideal properties of substrates and microenvironments were clarified, aiming towards the deep understanding of the required optimum biomimetic features of biomaterials.

Force performance of trawl system – III: mathematical modeling (part I)

The force performance of trawl systems directly depends on the work performed by these forces.The mechanical work of a trawl system is a physical quantity that depends on the vectors of force (hydrodynamic, tension, compression, etc.) and displacement. Thermodynamic work is the amount of energy transmitted or received by the trawl system by changing its external parameters. There is also the work of the forces of the electrostatic field when the charge moves from one point of the field to another. Equations are obtained for ideal flexible steel ropes and rope-rope products, characterizing the direct proportionality of the ratio of the productivity of forces that are directed perpendicular to each other and depend on the Poisson's ratio and the constructive elongation of ideal flexible steel ropes and cordage products. The ratio of the capacities of the forces or the ratio of the moduli of elasticity in the transverse and longitudinal directions, which arise when steel ropes and rope-rope products are stretched, are inversely proportional to the square of the coefficient k connecting the elongation λ, Poisson's ratio μ and the relative elongation ε at a constant volume of the product and its mass. There has been described an example of stretching perfectly flexible steel ropes and cordage. Such constructive parameters as lay, the number of strands, wire and fiber thickness, type of weaving were not taken into account.

Parametric study on the influence of material properties and geometry on the thermally induced bistability of composite laminates

This paper presents a parametric study on the key parameters that control the thermally induced bistability of cross-ply laminates. The influence of the material properties including the moduli of elasticity and the thermal expansion coefficients and the laminate’s geometry including the aspect ratio (AR) and the width-to-thickness ratio are investigated. The unsymmetric [Formula: see text] and the antisymmetric [Formula: see text] cross-ply laminates are investigated. Five key parameters are varied: the number of plies, the width-to-thickness ratio, the laminate’s aspect ratio, the ratio of the moduli of elasticity, and the ratio of the thermal expansion coefficients of the lamina. The laminate is assumed flat at the cured temperature and a uniform temperature gradient is applied until it is reduced to the room temperature. For each set of parameters, the stable equilibrium shapes of the laminate are obtained using a Ritz model. The ABAQUS finite element package is used to validate the model and an excellent agreement is obtained. Results that show the variation of the curvatures with the width-to-thickness ratio and the onset of the bistability for a variety of parameters are presented. The ratio of the moduli of elasticity and the thermal expansion coefficients significantly affect the critical width-to-thickness ratio at which the laminates become bistable. The unsymmetric laminates show bistability at a lower width-to-thickness ratio compared with the antisymmetric laminates. The results also show that the higher the aspect ratio, the lower the critical width-to-thickness ratio for stability for both laminates.

Concrete Compressive Strength by Means of Ultrasonic Pulse Velocity and Moduli of Elasticity

Developing non-destructive methods (NDT) that can deliver faster and more accurate results is an objective pursued by many researchers. The purpose of this paper is to present a new approach in predicting the concrete compressive strength through means of ultrasonic testing for non-destructive determination of the dynamic and static modulus of elasticity. For this study, the dynamic Poisson’s coefficient was assigned values provided by technical literature. Using ultra-sonic pulse velocity (UPV) the apparent density and the dynamic modulus of elasticity were determined. The viability of the theoretical approach proposed by Salman, used for the air-dry density determination (predicted density), was experimentally confirmed (measured density). The calculated accuracy of the Salman method ranged between 98 and 99% for all the four groups of specimens used in the study. Furthermore, the static modulus of elasticity was deducted through a linear relationship between the two moduli of elasticity. Finally, the concrete compressive strength was mathematically determined by using the previously mentioned parameters. The accuracy of the proposed method for concrete compressive strength assessment ranged between 92 and 94%. The precision was established with respect to the destructive testing of concrete cores. For this research, the experimental part was performed on concrete cores extracted from different elements of different structures and divided into four distinct groups. The high rate of accuracy in predicting the concrete compressive strength, provided by this study, exceeds 90% with respect to the reference, and makes this method suitable for further investigations related to both the optimization of the procedure and = the domain of applicability (in terms of structural aspects and concrete mix design, environmental conditions, etc.).

Plywood Made from Plasma-Treated Veneers: Investigation of Performance Differences between Plasma-Pretreated and Untreated Beech Veneers at Comparable Melamine Resin Load

In this study, the dimensional stability and mechanical properties of plywood made from untreated and plasma-pretreated beech veneers were compared. The wood veneers used (native and thermally modified) were impregnated with melamine resin in a simple dipping process prior to plywood production. The duration of the impregnation process was adjusted to give the same melamine resin loading for the different veneer types, with the plasma-pretreated veneers requiring only a fraction of the impregnation time compared with non-plasma-pretreated veneers. With comparable melamine loading, testing of the mechanical properties of the plywood for the different specimen collectives showed significant differences in some cases with respect to compressive strength, bending strength and tensile strength (with the associated moduli of elasticity). For example, it was shown that plywood made from plasma-pretreated native beech veneers shows an increase in bending strength of about 8%, and from plasma-pretreated and thermally modified beech veneers, there is an increase of about 10% compared to the reference.

Energy Dissipation in Viscoelastic Multilayered Inhomogeneous Beam Structures: An Analytical Study

The present work is concerned with analysis of the dissipated energy in viscoelastic multilayered inhomogeneous beam structure. The layers of the beam are continuously inhomogeneous along the thickness. The Maxwell mechanical model is used for treating the viscoelastic behaviour of the beam. The moduli of elasticity and the coefficients of viscosity vary continuously along the thickness of each layer. The dissipated energy is obtained by integrating of the unit dissipated energy in the volume of the beam. A parametric investigation of the dissipated energy is carried-out by applying the solution derived in order to evaluate the influence of various factors.

Vibrational characteristics of four wood species commonly used in wood products

The effects of the moisture content, density, and striking direction of a hammer on the vibrational characteristics, i.e., the fundamental frequency and dynamic modulus of elasticity, of four wood species, i.e., poplar (Populus tomentosa), mahogany (Swietenia mahagoni), beech (Fagus orientalis), and ash (Fraxinus excelsior), commonly used in wood products were investigated, aiming to provide basic evidence for the nondestructive testing of wood materials. The results showed that the effect of the wood species on the fundamental frequency, dynamic modulus of elasticity, and static modulus of elasticity was statistically significant. The dynamic moduli of elasticity of the four wood species were higher than the corresponding static moduli of elasticity. The effect of the striking direction on the dynamic modulus of elasticity was not significant, indicating that no matter where the hammer struck, i.e., radial and tangential surfaces, the fundamental frequency was essentially constant. Negative relationships were found between the fundamental frequency and the density and moisture when the data of the four wood species were viewed as a population sample. The vibrational characteristics of each wood species varied, which can be applied to the nondestructive testing of wood.

Can Fluid-Substitution Models Continue to Ignore the Complex Physico-Chemical Properties of Crude Oil?

The mechanical nature of fluid-substitution models has always been recognized as a major cause of their limited predictive power. Saturants, for instance, are typically treated as simple fluids characterized only by their densities, viscosities, and moduli of elasticity; their chemistry is just ignored, even when that fluid is crude oil. However, crude oil is a complex mixture of several thousands of organic compounds characterized by a variety of molecular weights, polarities, and polarizabilities, and the response of its rheological behavior to acoustic wave propagation is difficult to predict, especially when it resides inthe pore space of rocks. Here, we report ultrasonic-velocity measurements performed on carbonate core plugs saturated with brine and with a light crude oil that are mechanically similar (i.e., having comparable densities, viscosities, and moduli of elasticity) and that show a significant and consistent excess of hardening when the saturant is oil. Dispersion and wettability are excluded as explanations for the data. We hypothesize that asphaltene aggregation and adsorption, as well as paraffin-wax crystallization (and possibly volumetric expansion), combine to cause crude oil to exhibit a dilatant-like behavior within the pore space of carbonates at ultrasonic frequencies. Roughly speaking, the observed effect would be similar to the hardening of oobleck at high deformation rates. This hypothesis could betested in the future by an adequate combination of high-resolution imaging and microfluidic setups. This and similar studies would be beneficial in developing physical fluid-substitution models with a more consistent predictive power.

Polymer Fibers in Foam Concrete Application Efficiency

The urgency of improving the performance properties of concrete, as the most common building materials, is noted. The reasons for the increased demand for products made of high-strength gas-filled concrete are stated. It is shown that the current volume of polymer fibers production makes it possible to predict the possibility of their widespread use in construction. The information on the physical and mechanical properties of synthetic fiber, which is important for its successful use as dispersed reinforcement of foam concrete mixtures, is presented. The technology of manufacturing experimental samples and methods of their testing are described. It has been established that the introduction of any synthetic fiber into the foam mixture formulation improves the structural properties of foam concrete, however, the measure of efficiency depends on the ratio between the concrete moduli of elasticity and fiber. The greater the value of the elastic modulus of the fiber used, the higher the technical effect of its use in fiber-reinforced concrete for structural purposes can be.