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Herein, this work aims to demonstrate the topological effect on the mechanicalx characteristics of self-assembled block copolymers (BCPs). The lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) can be self-assembled into various nanostructured monoliths with the use of PS-selective solvent for solvent annealing, giving diamond, gyroid, and cylinder structures with increasing the swelling degree of PS domain (the effective volume fraction of the PS segment after solvent annealing followed by evaporation). The stiffness of the self-assembled monoliths is scrutinized by nanoindentation test. For intrinsic PS-b-PDMS monolith with lamellar structure, the reduced elastic modulus as calculated from the measured stiffness is 0.91 GPa. By contrast, the PS-b-PDMS monolith with cylinder structure gives a significant reduction in reduced elastic modulus with the value of 0.52 GPa due to the introduced microporosity to the PS domain from solvent annealing using PS-selective solvent, resulting in the lower confrontation for continuous layer-by-layer deformation of hard PS and soft PDMS domains. In the case of gyroid-structured PS-b-PDMS monolith, it is unexpected to exhibit a significant increase in the reduced elastic modulus with a value of 1.6 GPa: note that the effect of microporosity is still significant. Accordingly, the enhancement of the reduced elastic modulus is attributed to the effect of deliberate structuring with network topology (i.e., three-dimensional co-continuous hard PS and soft PDMS domains) that is able to hold the occurrence of large-scale deformation. In contrast to the gyroid with a three-strut texture, the diamond-structured PS-b-PDMS monolith with a four-strut texture is superior to the gyroid with a reduced elastic modulus of 2.2 GPa, further confirming the suggested topology effect.

The mechanical properties of bed bug (Cimex lectularius L.) tarsi and pretarsi were investigated in order to evaluate their vulnerability to piercing by plant trichomes (sharp microscopic hairs). Nanoindentation was used to measure the force required to insert a sharp probe into the cuticle of these different regions, as well as to determine creep and reduced elastic moduli for the cuticle. Scanning electron microscopy was used to visualize the indents that had been generated by nanoindentation. The force required to insert a cube corner nanoindenter probe into the cuticle was determined for a range of displacements (1 to 9 μm) and strain rates (0.003 to 0.5 s-1). Greater force was required to insert this sharp probe at greater depth or at faster strain rates. A specific region of the pretarsus (membrane with microtrichia) more frequently pierced by trichomes during bed bug locomotion required approximately 20-30% less force, exhibited more creep, and had a lower reduced elastic modulus for the first micron of indentation compared to the other regions; although this pattern was not consistent for greater displacements. These mechanical attributes, which will facilitate the initial stage of puncture in addition to the presence of natural infoldings in the cuticle of this area, may make that area of the pretarsus particularly vulnerable to piercing. This information will help inform development of physical methods for control of insect pests such as bed bugs.

The mechanical properties of bed bug (Cimex lectularius L.) tarsi and pretarsi were investigated in order to evaluate their vulnerability to piercing by plant trichomes (sharp microscopic hairs). Nanoindentation was used to measure the force required to insert a sharp probe into the cuticle of these different regions, as well as to determine creep and reduced elastic moduli for the cuticle. Scanning electron microscopy was used to visualize the indents that had been generated by nanoindentation. The force required to insert a cube corner nanoindenter probe into the cuticle was determined for a range of displacements (1 to 9 μm) and strain rates (0.003 to 0.5 s−1). Greater force was required to insert this sharp probe at greater depth or at faster strain rates. A specific region of the pretarsus (membrane with microtrichia) more frequently pierced by trichomes during bed bug locomotion required approximately 20-30% less force, exhibited more creep, and had a lower reduced elastic modulus for the first micron of indentation compared to the other regions; although this pattern was not consistent for greater displacements. These mechanical attributes, which will facilitate the initial stage of puncture in addition to the presence of natural infoldings in the cuticle of this area, may make that area of the pretarsus particularly vulnerable to piercing. This information will help inform development of physical methods for control of insect pests such as bed bugs.

Abstract Alginate microbeads are extensively used in tissue engineering as microcarriers and cell encapsulation vessels. In this study, we used atomic force microscopy (AFM) based indentation using 20 µm colloidal probes to assess the local reduced elastic modulus (E *) using a novel method to detect the contact point based on the principle of virtual work, to measure microbead mechanical stability under cell culture conditions for 2 weeks. The bead diameter and swelling were assessed in parallel. Alginate beads swelled up to 150% of their original diameter following addition of cell culture media. The diameter eventually stabilized from day 2 onwards. This behaviour was mirrored in E * where a significant decrease was observed at the start of the culture period before stabilization was observed at ~ 2.1 kPa. Furthermore, the mechanical properties of freeze dried alginate beads after re-swelling them in culture media were measured. These beads displayed vastly different structural and mechanical properties compared those that did not go through the freeze drying process, with around 125% swelling and a significantly higher E * at values over 3 kPa. Graphical abstract fx1 Highlights • Alginate bead diameter was stable in cell culture media over a 2-week culture. • Mechanical properties of alginate beads were characterised by AFM indentations. • E * of freeze dried alginate beads was stiffer than freshly made beads. • E * of freshly made beads denotes bead stability over the 2-week period. [ABSTRACT FROM AUTHOR]

Among W alloys, Fe-W has seen much attention recently, due to the need of moving toward the design of environmentally friendly materials. Coatings with 4, 16 and 24 at.% of W were electrodeposited from an environmental friendly Fe(III)-based glycolate-citrate bath. The samples were annealed in vacuum at different temperatures up to 800 °C. Different crystalline phases are formed upon annealing: α-Fe, Fe 2 W, Fe 3 W 3 C, Fe 6 W 6 C, and FeWO 4 . Their grain size and distribution within the coating was studied by means of Electron Backscattered Diffraction (EBSD) technique. The effect of annealing on the mechanical properties of the coatings was analyzed performing nanoindentation measurements. The results show a considerable increase of the hardness followed by a rapid decrease at higher temperatures. The highest hardness value, i.e. 16.5 GPa, is measured for the sample with 24 at.% of W after annealing at 600 °C owing to the precipitation of α-Fe crystallites. This study indicates the possibility to substantially increase the hardness of electrodeposited Fe-W coatings by optimization of the annealing treatment. In addition, the critical influence of the carbide and oxide phases on the mechanical properties of alloys is discussed. Hence, Fe-W coatings rich in W can be applied as a possible candidate for protective coating applications at elevated temperatures. [ABSTRACT FROM AUTHOR]

The mechanical properties of zirconium hydrides were studied using nano-indentation technique between 25 and 400 °C. Temperature dependency of reduced elastic modulus and hardness of δ- and ε-zirconium hydrides were obtained by conducting nanoindentation experiments on bulk hydride samples with independently heating capability of indenter and heating stage. The reduced elastic modulus of δ-zirconium hydride (H/Zr ratio = 1.61) decreased from ∼113 GPa at room temperature to ∼109 GPa at 400 °C, while its hardness decreased significantly from 4.1 GPa to 2.41 GPa in the same temperature range. For ε-zirconium hydrides (H/Zr ratio = 1.79), the reduced elastic modulus decreased from 61 GPa at room temperature to 54 GPa at 300 °C, while its hardness from 3.06 GPa to 2.19 GPa. [ABSTRACT FROM AUTHOR]

Although the Hertz theory is not applicable in the analysis of the indentation of elastic-plastic materials, it is common practice to incorporate the concept of indenter/specimen combined modulus to consider indenter deformation. The appropriateness was assessed of the use of reduced modulus to incorporate the effect of indenter deformation in the analysis of the indentation with spherical indenters. The analysis based on finite element simulations considered four values of the ratio of the indented material elastic modulus to that of the diamond indenter, E/Ei (0, 0.04, 0.19, 0.39), four values of the ratio of the elastic reduced modulus to the initial yield strength, Er/Y (0, 10, 20, 100), and two values of the ratio of the indenter radius to maximum total displacement, R/δmax (3, 10). Indenter deformation effects are better accounted for by the reduced modulus if the indented material behaves entirely elastically. In this case, identical load-displacement (P - δ) curves are obtained with rigid and elastic spherical indenters for the same elastic reduced modulus. Changes in the ratio E/Ei, from 0 to 0.39, resulted in variations lower than 5% for the load dimensionless functions, lower than 3% in the contact area, Ac, and lower than 5% in the ratio H/Er. However, deformations of the elastic indenter made the actual radius of contact change, even in the indentation of elastic materials. Even though the load dimensionless functions showed only a little increase with the ratio E/Ei, the hardening coefficient and the yield strength could be slightly overestimated when algorithms based on rigid indenters are used. For the unloading curves, the ratio δe/δmax, where δe is the point corresponding to zero load of a straight line with slope S from the point (Pmax, δmax), varied less than 5% with the ratio E/Ei. Similarly, the relationship between reduced modulus and the unloading indentation curve, expressed by Sneddon's equation, did not reveal the necessity of correction with the ratio E/Ei. The most affected parameter in the indentation curve, as a consequence of the indentation deformation, was the ratio between the residual indentation depth after complete unloading and the maximum indenter displacement, δr/δmax (up to 26%), but this variation did not significantly decrease the capability to estimate hardness and elastic modulus based on the ratio of the residual indentation depth to maximum indentation depth, hr/hmax. In general, the results confirm the convenience of the use of the reduced modulus in the spherical instrumented indentation tests. [ABSTRACT FROM AUTHOR]

Niobium oxide coatings deposited on Ti 6 Al 4 V substrates by electron beam deposition and annealed in air at 600 °C and 800 °C were evaluated for their suitability towards dental, maxillofacial or orthopaedic implant applications. A detailed physico-chemical properties investigation was carried out in order to determine their elemental and phase composition, surface morphology and roughness, mechanical properties, wettability, and corrosion resistance in simulated body fluid solution (pH = 7.4) at room temperature. The biocompatibility of the bare Ti 6 Al 4 V substrate and coated surfaces was evaluated by testing the cellular adhesion and viability/proliferation of human osteosarcoma cells (MG-63) after 72 h of incubation. The coatings annealed at 800 °C exhibit more phase pure nanocrystalline Nb 2 O 5 surfaces with enhanced wettability, reduced porosity and enhanced corrosion resistance properties making them good candidate for dental, maxillofacial or orthopaedic implant applications. [ABSTRACT FROM AUTHOR]

• Nanoindentation of two different clays in extrusion direction and normal to it. • Loading protocol allowing a deep look into the mechanical properties of clay phases. • Determination of plastic and viscoelastic material response. • Determination of elastic moduli of different material phases. A systematic experimental identification approach for fired clay, the base material of bricks and clay block masonry, is essential to optimize the mechanical and thermal properties and, in this way, extending the field of application of this sustainable and high-performant building material. For this reason, a comprehensive nanoindentation campaign was performed on two clays, one of them carbonate bearing, each fired at 880 °C and 1100 °C, in extrusion direction x and normal to it. A carefully defined load function, including a short preloading step, a holding phase of 20 s, and a very fast unloading step, allowed for (i) the decomposition of plastic and viscoelastic material response, (ii) the identification of the time-dependent behaviour as well as (iii) a neat determination of elastic moduli of different material phases. A well-developed sample preparation protocol, resulting in a very low surface roughness and, thus, allowing for very small indentation forces, together with the information of scanning electron microscopy images enabled the assignment of indentation responses to single material phases. An orientation dependency of the stiffness response for the matrix of both clays fired at 880 °C was identified, which, however, disappears at a firing temperature of 1100 °C. Furthermore, the indentation results revealed that every material phase within the investigated fired clay samples, even the quartz phase, has a distinct time-dependent behaviour, which could be sufficiently captured within the second loading phase of 20 s and described very well with three different rheological models. Finally, through the analysis of representative area elements of eight different fired clay samples, comprehensive 2D information about the elastic as well as viscous behaviour is given within this work, representing a basis and input for the development of micromechanical models for fired clay material. [ABSTRACT FROM AUTHOR]

Niobium oxide coatings deposited on Ti 6 Al 4 V substrates by electron beam deposition and annealed in air at 600 °C and 800 °C were evaluated for their suitability towards dental, maxillofacial or orthopaedic implant applications. A detailed physico-chemical properties investigation was carried out in order to determine their elemental and phase composition, surface morphology and roughness, mechanical properties, wettability, and corrosion resistance in simulated body fluid solution (pH = 7.4) at room temperature. The biocompatibility of the bare Ti 6 Al 4 V substrate and coated surfaces was evaluated by testing the cellular adhesion and viability/proliferation of human osteosarcoma cells (MG-63) after 72 h of incubation. The coatings annealed at 800 °C exhibit more phase pure nanocrystalline Nb 2 O 5 surfaces with enhanced wettability, reduced porosity and enhanced corrosion resistance properties making them good candidate for dental, maxillofacial or orthopaedic implant applications., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2019. Published by Elsevier Ltd.)