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Background: Compression experiments are widely used to study the mechanical properties of materials at micro- and nanoscale. However, the conventional engineering stress measurement method used in these experiments neglects to account for the alterations in the material's shape during loading. This can lead to inaccurate stress values and potentially misleading conclusions about the material's mechanical behavior, especially in the case of localized deformation. Objective: Our goal is to calculate true stress in cases of localized plastic deformation from standard experimental data (displacement-force curve, aspect ratio, shear band angle and elastic strain limit). Methods: We use a simple mechanical-geometrical approach based on reasonable physical assumptions to get analytic formulas of true stress and eliminating the need for finite element computations. Furthermore, in numerical simulations of pillar compression, the formula-based true stress demonstrates strong alignment with the theoretical true stress. Results: We propose analytic formulas for calculating true stress in cases of localized plastic deformation commonly encountered in experimental settings for a single band oriented in arbitrary directions with respect to the vertical axis of the pillar. Conclusions: The true stress computed with the proposed formulas provides a more precise interpretation of experimental results and can serve as a valuable and simple tool in material design and characterization. [ABSTRACT FROM AUTHOR]

In the contemporary era, the enhancement of wearable capacitive sensors is achieved through the utilization of polymeric micropillars as filler materials between electrode plates. To gain a deeper understanding of the dynamic response of the system, nonlinear coupled governing equations of a circular microplate motion resting on an array of polymeric micropillars have been derived. These equations are used to model the system's behavior. In addition, the squeezing motion of the micro-pillars is characterized using the incompressible Neo-Hookean model. Both static and dynamic responses, including transient and steady-state solutions, are investigated in detail by discretizing over spatial coordinates using a weak formulation approach. A frequency response analysis is conducted using a continuation-based method. This entails expanding the steady-state solution using a Fourier transform and employing the energy balance principle. The unknown coefficients of the expansion series are calculated using a gradient descent-based learning approach that is physically motivated. Furthermore, a dynamic step size strategy for frequency increments is employed to effectively follow the solution path. This strategy is implemented via the ARC length method. In this study, we examine the impact of varying PDMS (polydimethylsiloxane) hydrogel mechanical and geometrical configurations. It can be reasonably concluded that the mechanical properties of the pillars and the geometrical configuration of the circular plate and micropillars have a significant impact on the maximum tolerable pressure, fast transient response, and frequency response analysis. [ABSTRACT FROM AUTHOR]

Abstract In the contemporary era, the enhancement of wearable capacitive sensors is achieved through the utilization of polymeric micropillars as filler materials between electrode plates. To gain a deeper understanding of the dynamic response of the system, nonlinear coupled governing equations of a circular microplate motion resting on an array of polymeric micropillars have been derived. These equations are used to model the system’s behavior. In addition, the squeezing motion of the micro-pillars is characterized using the incompressible Neo-Hookean model. Both static and dynamic responses, including transient and steady-state solutions, are investigated in detail by discretizing over spatial coordinates using a weak formulation approach. A frequency response analysis is conducted using a continuation-based method. This entails expanding the steady-state solution using a Fourier transform and employing the energy balance principle. The unknown coefficients of the expansion series are calculated using a gradient descent-based learning approach that is physically motivated. Furthermore, a dynamic step size strategy for frequency increments is employed to effectively follow the solution path. This strategy is implemented via the ARC length method. In this study, we examine the impact of varying PDMS (polydimethylsiloxane) hydrogel mechanical and geometrical configurations. It can be reasonably concluded that the mechanical properties of the pillars and the geometrical configuration of the circular plate and micropillars have a significant impact on the maximum tolerable pressure, fast transient response, and frequency response analysis.

Additive manufacturing makes fabricating titanium alloy components directly into their near-net shapes possible, reducing the need for machining. However, post-additive manufacturing machining becomes necessary for immediate design adjustments, dimension alterations, and surface quality enhancement. The inherent thermal effects during additive manufacturing make machining challenging due to altered mechanical properties from their wrought counterpart, including increased strength and hardness with reduced ductility. Textured cutting tools are being widely used to enhance the machinability of superalloys. In this work, micro-pillar type textures, created using Reverse Micro Electrical Discharge Machining (RμEDM) on tungsten carbide inserts, aimed to explore machinability in turning operations on selective laser melted (SLM) titanium alloy. The study investigates micro-pillar interaction with SLM Ti6Al4V in chip behavior, tool morphology, cutting forces, and surface roughness under various cutting fluid strategies. Under Minimum Quantity Lubrication (MQL), textured tools show significant improvements, producing untangled chips with reduced curl radius. A considerable decrease of 38 % in the tool/chip contact area indicates a substantial reduction in the seizure zone, hence a decline in the temperature rise of the cutting tool. Dry conditions show a 20.4 % reduction in flank wear width, suggesting prolonged cutting-edge sharpness due to tool texturing. In MQL conditions, a maximum 28.9 % reduction in feed force is observed, indicating improved frictional conditions at the interface. Additionally, a 10.4 % improvement in surface finish is achieved. The work is summarized by claiming micro-pillar textured tools enhance the machinability of additively manufactured Ti6Al4V demonstrated through improvements in titanium adhesion, cutting-edge sharpness, feed force, and surface finish, particularly MQL conditions. [Display omitted] • Fabrication of novel micro-pillar textures on tungsten carbide inserts using RμEDM. • Machining under dry, compressed air, minimum quantity lubrication, and wet conditions. • Investigation of forces, surface roughness, tool wear, and chip morphology is performed. • Enhanced machinability of SLM Ti6Al4V due to micro-texturing of the rake face. • Reduced tool-chip contact and enhanced CF penetration are witnessed in textured tools. [ABSTRACT FROM AUTHOR]

The present study investigates how varying negative micro-pillar densities on H13 alloy, used in hot-forming dies, affect wettability with different fluids and tribological performance, alongside detailed morphological analysis. Recast materials, pockmarks, micro-voids, micro-cracks, and globules of debris are observed on EDM textured surfaces, and challenges are form accuracy and debris entrapment with higher textured density. The functional stressed surfaces, evident from XRD analysis, display hydrophobic properties with water and hydrophilic characteristics with mineral-oil-based emulsion. Increased texture density enhances these properties. Wettability properties transition of fabricated functional surfaces occurs within fluid surface energies of 48 to 72.8 mN/m. The coefficient of friction (COF) of the lower-density patterned surface is 20.42 % lower than the untextured surface, and the higher-density pattern shows a 13.48 % COF reduction compared to the lower-density surface. Key wear mechanisms include abrasion, adhesion, sharp edges and adhered debris deformation, and localized plastic deformation for untextured and textured surfaces. [Display omitted] ● Investigating varying densities of negative micro-pillar textured H13 surfaces on wettability and tribological performance. ● The form accuracy of large-area micro-textured surfaces from form tools is explored. ● Fabricated functional surfaces demonstrate fluid-dependent wetting properties. ● Textured patterns significantly reduced COF and wear rate with increased texture density. [ABSTRACT FROM AUTHOR]

Graphical Abstract

Laser surface texturing and through-mask electrochemical micromachining (TMECMM) are some of the commonly used methods which include multiple steps to achieve micro-textures. However, for large-area applications, it is desirable to have an economical single-step process. In this regard, ECMM is expected to be a promising and economically viable micro-texturing process for micro-manufacturing industries. This paper proposes a novel maskless EC micro-texturing process using tool sinking technique with low voltage and short pulses. Methodology of using edges (∼30 μm each) of printed circuit boards (PCBs) for ECMM of micro-channels and micro-pillars is a unique one. Micro-pillars, micro-dimples and micro-channels are produced through a direct electrochemical cathode sinking process. Analysis of current density and prediction of width and depth of micro-dimples on a flat stainless steel surface are studied through 2D numerical simulation carried out on COMSOL 4.3a. The proposed method implies the use of less toxic electrolyte, low voltage (1-6 V), short pulses (5 to 50 μs) and selective polymer coating on the tool (cathode). A series of experiments of EC sinking for creating various micro-patterns and micro-structures has been carried out on the flat as well as curved metallic surfaces. This paper reports machining of micro-dimples of 200-300 μm diameter, micro-channels of 150-250 μm and square micro-pillars of 300-350 μm. Comparison of the predicted geometrical dimensions of the micro-dimples through the simulation shows reasonable agreement with the experimental results for the given process parameters of ECMM. The paper also reports a brief comparison of laser surface texturing (LSTex) and electrochemical surface texturing (ECSTex). [ABSTRACT FROM AUTHOR]

Highlights • A droplet actuation and manipulation mechanism using freely available surface energy is demonstrated without using external force. • The presented technique can avoid unwanted secondary effects due to external actuation. • Droplet transportation using experimental selective painting surface is validated with lattice Boltzmann model. • A new approach to design lab-on-chip using micro-pillar surface is discussed in LBM framework. Abstract In the digital microfluidic systems, the droplet actuation and control in a chip is an important requirement. Usually, to actuate any droplet operation, an external energy needs to be supplied. We have demonstrated the utilization of the freely available surface energy by the suitable design of partial wetting surfaces to actuate and perform various droplet operations like splitting, transportation and merging. This approach would help us to realize on-chip droplet operations without applying external force like pressure, electric field or magnetic field with required control. The partial wetting surface and interface are synthesized using a selective painting technique and basic operations such as impingement, spreading and transportation are demonstrated. These dynamic properties of the droplet are modelled and analyzed with a multiphase lattice Boltzmann method (LBM). The partial wetting study of droplet dynamics is demonstrated using chemical gradient and structural gradient. The modelling results show good agreement with the experimental study, thus LBM can be used as tool for analyzing such chip designs. Further a microfluidic chip is designed with partial wetting surfaces chemically and by the placement of micro-pillars and basic on-chip operations such as splitting, merging and transportation are illustrated using LBM. [ABSTRACT FROM AUTHOR]

The physico-chemical surface design of implants influences the surrounding cells. Osteoblasts on sharp-edged micro-topographies revealed an impaired cell phenotype, function and Ca2+ mobilization. The influence of edges and ridges on the Wnt/β-catenin pathway in combination with the cells’ stress response has not been clear. Therefore, MG-63 osteoblasts were studied on defined titanium-coated micro-pillars (5 × 5 × 5 µm) in vitro and in silico. MG-63s on micro-pillars indicated an activated state of the Wnt/β-catenin pathway. The β-catenin protein accumulated in the cytosol and translocated into the nucleus. Gene profiling indicated an antagonism mechanism of the transcriptional activity of β-catenin due to an increased expression of inhibitors like ICAT (inhibitor of β-catenin and transcription factor-4). Cells on pillars produced a significant reactive oxygen species (ROS) amount after 1 and 24 h. In silico analyses provided a detailed view on how transcriptional activity of Wnt signaling is coordinated in response to the oxidative stress induced by the micro-topography. Based on a coordinated expression of regulatory elements of the Wnt/β-catenin pathway, MG-63s are able to cope with an increased accumulation of β-catenin on micro-pillars and suppress an unintended target gene expression. Further, β-catenin may be diverted into other signaling pathways to support defense mechanisms against ROS.

Laser surface texturing (LST) processes have great potential to alter surface wetting properties of widely known bioactive Ti–6Al–4V alloy. Micro-pillars arrays of different topography are produced by Nd:YAG laser of 1064 nm wavelength to investigate the influence of its physical and geometrical parameter on wettability. Micro-textures named as: T HS (high density, square pillars of 30 × 30 μm), T MS (medium density, square pillars of 60 × 60 μm), T LS (low density, square pillars of 170 × 170 μm), T LL (low density, landscape pillars of 300 × 100 μm) and T LP (low density, portrait pillars of 100 × 300 μm) are produced to analyze the effect of texture areal density, aspect ratio and shape over surface wetting phenomenon. It is observed that on the flat textured surface shows hydrophilic and spontaneous wetting behavior up to 24 h after machining. Percentage increment in water contact angle (CA) value varies with time, maximum increase in CA was found to be in T HS (215%) followed by T MS (197%), T LS (166%), T LP (144%) and T LL (122%) after 20 days of machining (as compared with the untextured surface). The response of the textured surface to spontaneous wetting behavior with respect to varying viscosity is also studied and validated through Washburn's model. It is found that early viscous regime of capillary rise in the textured surface can be altered by regulating the geometrical parameters of the micro-textures array. Time taken to rise up to 40 mm by low, medium and high viscosity fluids are 200 s, 600 s and 9334 s respectively. The texture ( T HS ) with highest areal density micro-pillars of 60 μm width exhibits maximum capillary action. [ABSTRACT FROM AUTHOR]

Al-Zn alloys were processed by high-pressure torsion (HPT) to produce ultrafine-grained (UFG) materials. For low Zn contents, HPT gave strengthening due to grain refinement while for the highest Zn concentration the decomposition of the microstructure yielded an abnormal softening at room temperature. The microstructure decomposition led also to the formation of a Zn-rich phase which wet the Al/Al grain boundaries and enhanced the role of grain boundary sliding with unusually high strain rate sensitivity. The occurrence of intensive sliding in these UFG alloys is demonstrated by deforming micro-pillars. [ABSTRACT FROM AUTHOR]

Deep proton writing (DPW) is a fabrication technology developed for the rapid prototyping of polymer micro-structures. We use SU-8, a negative resist, spincoated in a layer up to 720 μm-thick in a single step on borosilicate glass, for irradiation with a collimated 12 MeV energy proton beam. Micro-pillars with a slightly conical profile are irradiated in the SU-8 layer. We determine the optimal proton fluence to be 1.02 × 10 4 μm −2 , with which we are able to repeatably achieve micro-pillars with a top-diameter of 138 ± 1 μm and a bottom-diameter of 151 ± 3 μm. The smallest fabricated pillars have a top-diameter of 57 ± 5 μm. We achieved a root-mean-square sidewall surface roughness between 19 nm and 35 nm for the fabricated micro-pillars, measured over an area of 5 × 63.7 μm. We briefly discuss initial testing of two potential applications of the fabricated micro-pillars. Using ∼100 μm-diameter pillars as waveguides for gigascale integration optical interconnect applications, has shown a 4.7 dB improvement in optical multimode fiber-to-fiber coupling as compared to the case where an air–gap is present between the fibers at the telecom wavelength of 1550 nm. The ∼140 μm-diameter pillars were used for mold fabrication with silicone casting. The resulting mold can be used for hydrogel casting, to obtain hydrogel replicas mimicking human tissue for in vitro bio-chemical applications. [ABSTRACT FROM AUTHOR]

We report on the design, fabrication, and characterization of a reflective transmitter targeting implementation in passive optical networks (PON) with frequency division multiplexed access (FDMA). It is made up of a Silicon photonic integrated circuit (Si-PIC) comprising a reflective Mach Zehnder modulator and its flip-chipped CMOS electronic integrated circuit driver, the two ICs being interconnected by means of high density and low parasitic copper micro pillars. Several transmissions, in an FDMA PON context, are successfully demonstrated using 500 MBaud QPSK and 16-QAM modulated subcarriers, achieving bit error rate below 2.10−3. For QPSK-modulated subcarriers (respectively, 16-QAM), the available access frequency bandwidth is measured to be 1–7 GHz (respectively, 2–4 GHz) with an available loss budget of 9 dB (respectively, 5 dB). Improvements of the Si-PIC are further identified to achieve compliancy with 31 dB ODN loss. [ABSTRACT FROM PUBLISHER]

The achievement of an adequate accuracy of the microinjection molding process applied to the replication of micro-features is a complex task. The selection of process parameters and the geometry of the molded part influences the filling flow of the melt inside the mold cavity as well as the final quality of the replicated micro-features. In this work, the replication of a micro-structured surface is studied in relation to the thickness of the molded part. In particular, the effects of a rapid heat cycle molding process, cavity air evacuation, part thickness are experimentally evaluated. The analysis of the experimental data showed that the thickness of the main flow region and the molding temperature are significant factor affecting the replication quality. In particular, a combination of small cavity thickness and a high mold temperature (above T g ) can be effective in increasing the replicated height of micro-features. Experimental results also point out the correlation between the holding pressure and the distance from the injection location. An effective approach to the design of both the part and the process, should consider that the selection of process parameters must be related to design of the mold cavity. [ABSTRACT FROM AUTHOR]

A micro-structured nickel insert was investigated for polyether ether ketone (PEEK) injection moulding. The micro-features were circular holes 4 μm in diameter and 2 μm deep, with a 2-μm edge-to-edge distance. Six thousand moulding cycles were operated. Half of the insert was coated by approximately 200 nm CrN. PEEK parts produced by the coated side and uncoated side were compared. Coating thickness was measured at intervals of production and employed to characterize the coating wear. Pillar geometry at fixed locations on PEEK parts was studied by scanning electron microscope (SEM). Energy-dispersive X-ray spectroscopy (EDS) was conducted on the PEEK parts in order to study the possible nickel and silver contamination. The results show that the studied coating had a very low wear, and no nickel or silver contamination on PEEK was detected for both parts produced by coated and uncoated sides. Coating improved demoulding by reducing small indentations on pillars. [ABSTRACT FROM AUTHOR]

Three dimensional dislocation dynamics ( DD ) simulations are performed to investigate the governing mechanism of size dependent plastic deformation in submicron face-centered cubic ( fcc ) micropillars under uniaxial loading. Based on previous atomistic simulations, we introduce an algorithm for dislocation nucleation at the free surface as a function of stress and temperature in the DD simulation. The simulation results show stochastic behaviors in agreement with experimental observations, and reveal that dislocation nucleation at the free surface is the dominant mechanism of plastic flow in small pillars with diameters less than 200 nm, while the operation of truncated dislocation sources is the governing mechanism in large pillars with diameters exceeding 1 μm. In between, both mechanisms come into play in a stochastic way. [ABSTRACT FROM AUTHOR]

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Experimental and numerical studies of the behavior of a slurry in a shear flow over a rough surface with a defined micro-structure are presented. A new ring shear device was built which contains an optically transparent test chamber. Its bottom wall contains arrays of micro-cantilever force sensors simulating a defined surface roughness created by deep-etching of micro-pillars in a silicon wafer. The results of visual observation of the interaction of the suspension with the structured surface during severe deformation are shown. Observations comprise the liquid phase motion, i.e., the interaction between the liquid phase and solid particles, the movement of separate particles and their interactions with the micro-pillars. Abrupt changes in rotational motion and translational velocity of particles are observed that induce mutual collisions and successive formation and break-up of cluster structures of various types. In addition to the experiments the process was simulated with discrete element (DEM) simulations. Many characteristics found in the experiments are reproduced by the simulations. Furthermore the physical quantities of the process like contact forces or velocities can be quantified which helps us to develop more detailed models of the abrasive behavior of slurries. [ABSTRACT FROM AUTHOR]

Projected light patterns are used to induce electrohydrodynamic instabilities in a polymer thin film sandwiched between two electrodes. Using this optically induced electrohydrodynamic instability (OEHI) phenomenon, we have successfully demonstrated rapid, microscale patterning of polydimethylsiloxane (PDMS) pillar arrays on a thin-film hydrogenated amorphous silicon layer on top of an indium titanium oxide glass substrate. This glass substrate is the bottom electrode in a two-electrode, parallel-plate capacitor configuration with a micron-scale gap. Within this gap are a thin film of spin-coated PDMS and a thin layer of air. Primary pillar growth is first observed within 5-90 s in the dark regions of the projected patterns and pillar growth eventually spreads to the illuminated regions when the initial PDMS thickness is <2 μm. Experimental data characterizing the change in pillar diameters (between 15 and 30 μm in diameter) show that they can be decoupled from the inter-pillar spacing (maintaining a constant ~84 μm pitch between pillar centers) by controlling the applied DC voltage (between 110 and 210 V). Experimental results also show the importance of the optically induced lateral electric field on controlling pillar formation. This OEHI method of rapid pillar generation, with voltage control of the pillar diameter and control of pillar position via projected light patterns, presents new opportunities for low cost, efficient, and simple fabrication of micro, and perhaps nanoscale, polymer structures that could be used in many bioMEMS applications. [ABSTRACT FROM AUTHOR]

Microglia are the resident macrophages of the central nervous system and contribute to maintaining brain's homeostasis. Current 2D "petri-dish" in vitro cell culturing platforms employed for microglia, are unrepresentative of the softness or topography of native brain tissue. This often contributes to changes in microglial morphology, exhibiting an amoeboid phenotype that considerably differs from the homeostatic ramified phenotype in healthy brain tissue. To overcome this problem, multi-scale engineered polymeric microenvironments are developed and tested for the first time with primary microglia derived from adult rhesus macaques. In particular, biomimetic 2.5D micro- and nano-pillar arrays (diameters = 0.29-1.06 µm), featuring low effective shear moduli (0.25-14.63 MPa), and 3D micro-cages (volume = 24 × 24 × 24 to 49 × 49 × 49 μm 3 ) with and without micro- and nano-pillar decorations (pillar diameters = 0.24-1 µm) were fabricated using two-photon polymerization (2PP). Compared to microglia cultured on flat substrates, cells growing on the pillar arrays exhibit an increased expression of the ramified phenotype and a higher number of primary branches per ramified cell. The interaction between the cells and the micro-pillar-decorated cages enables a more homogenous 3D cell colonization compared to the undecorated ones. The results pave the way for the development of improved primary microglia in vitro models to study these cells in both healthy and diseased conditions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sharaf, Roos, Timmerman, Kremers, Bajramovic and Accardo.)

A GaN waveguide structure with micro-pillar arrays is designed and fabricated to measure the extraction of optical modes that would be waveguided in the absence of the pillars. Electroluminescence (EL) measurements of waveguide light-emitting diodes (LEDs) with pillar diameters in the 2-10 µm range revealed increasing light-extraction efficiency (LEE) enhancement with decreasing pillar diameter. Ray tracing simulations of LED far-field patterns confirmed experimental trends. A 54% enhancement is demonstrated for GaN waveguides cladded with a triangular lattice of graded-refractive-index (GRIN) TiO2SiO2 micro-pillars of 2 µm diameters compared to GaN waveguides cladded with an unpatterned GRIN TiO2SiO2 layer. [ABSTRACT FROM AUTHOR]

At ambient temperature and pressure, most of the semiconductor materials are brittle: this is the case of the III–V compound semiconductor indium antimonide, InSb. To study the role of dislocation nucleation at the onset of brittle-to-ductile transition, InSb micro-pillars have been fabricated by focused ion beam and in situ compressed at room temperature in a scanning electron microscope, in order to correlate the observation of slip traces at the pillar surface and features of the stress–strain curve. Transmission electron microscopy (TEM) thin foils have been cut out of the pillars to study the deformation microstructure. The TEM study of dislocations and the observation of slip traces at surfaces show that increasing the surface-to-volume ratio of the pillars modifies the dislocation nucleation conditions and favors plasticity even at room temperature. The role of dislocation nucleation from free surfaces is thus discussed within the larger context of the micro-pillar compression technique and extrinsic size effects. [ABSTRACT FROM AUTHOR]

Abstract: The thermal and hydrodynamic performance of passive two-phase cooling devices such as heat pipes and vapor chambers is limited by the capabilities of the capillary wick structures employed. The desired characteristics of wick microstructures are high permeability, high wicking capability and large extended meniscus area that sustains thin-film evaporation. Choices of scale and porosity of wick structures lead to trade-offs between the desired characteristics. In the present work, models are developed to predict the capillary pressure, permeability and thin-film evaporation rates of various micropillared geometries. Novel wicking geometries such as conical and pyramidal pillars on a surface are proposed which provide high permeability, good thermal contact with the substrate and large thin-film evaporation rates. A comparison between three different micropillared geometries – cylindrical, conical and pyramidal – is presented and compared to the performance of conventional sintered particle wicks. The employment of micropillared wick structure leads to a 10-fold enhancement in the maximum heat transport capability of the device. The present work also demonstrates a basis for reverse-engineering wick microstructures that can provide superior performance in phase-change cooling devices. [Copyright &y& Elsevier]

Micro-hairs are profound elements widely used in nature. A great variety of animals use them as sensors to gather information about their surroundings. To artificially fabricate these kinds of sensors, we present a method to produce micro-hairs made of polydimethylsiloxane (PDMS). We investigated the laser micro-drilling of wax and polycarbonate (PC) substrates with a 193-nm ArF laser to produce molds suitable for casting micro-hairs. Especially PC molds lead to high-quality micro-hairs. Thus, laser ablation of PC was intensively studied. In order to obtain micro-hair arrays, experiments where performed to optimize the casting techniques of PDMS in PC molds. The possibilities and limitations of the investigated method of micro-hair production are presented. [ABSTRACT FROM AUTHOR]

We have fabricated micro-/nano-pillars of two metallic glasses (MGs), Cu-based Cu47Ti33Zr11Ni6Sn2Si1 and Zr-based Zr50Ti16.5Cu15Ni18.5, respectively, with pillar tip diameters ranging from ∼650 to ∼90 nm. These pillars were mechanically tested in situ in transmission electron microscopy as a function of pillar diameters. It turns out that the yield strengths of both MGs are close to those of the bulk glasses and are essentially size independent. Statistical physics description of strength for small size metallic glass is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Cubic silicon carbide (3C-SiC) micro-pillars were fabricated on Si (100) substrate by vapor–liquid–solid (VLS) process. The microstructure and residual stress of the micro-pillars were investigated by electron microscopy and micro-Raman spectroscopy, respectively. The selected area diffraction pattern of the SiC micro-pillar indicated that the micro-pillar was 3C-SiC single crystal. The residual stress of about 0.3 GPa in the micro-pillar calculated from Raman spectrum indicated that the VLS grown 3C-SiC micro-pillars had good crystalline quality. [Copyright &y& Elsevier]

To explore the deformation mechanism of α-Ti with high oxygen doping, micro-pillars of single crystal with orientations of near 0°, 45°, and 90° inclined to c -axis were fabricated via focused ion beam (FIB) milling from a high oxygen content commercial purity Ti (CP–Ti). The micro-pillars were loaded under quasi-static compression. Post-mortem analysis reveals that only prismatic slip activated for 45° and 90° oriented samples with their critical resolved shear stress (CRSS) values of about 457 MPa and 596 MPa, and only {10–11}< c + a > the first-order pyramidal slip activated on the 0° sample with a CRSS of around 1019 MPa. The results suggest that the oxygen addition remarkably reduces the CRSS ratio between non-prismatic and prismatic slips of α-Ti. In addition, the results indicate that the Schmid law may not be applicable for α-Ti single crystal at micro-size level. [ABSTRACT FROM AUTHOR]

Abstract: In biotechnology and chemistry, extraction of target molecules from a primary liquid and concentration of these molecules in a secondary liquid are now recognized as essential operations before analysis and recognition processes. Many continuous-flow chemical processing (CFCP) micro-devices have been developed in the last years, using the principle of diffusion across an interface maintained stable between the two liquids. So far, the development of such devices is mostly experimental. In this work, we focus on the physical phenomena governing the stability of the interfaces and the extraction. Our system is constituted of two adjacent microchannels geometrically separated by vertical micro-pillars. The primary and secondary liquids are immiscible, and vertical interfaces attached to the pillars separate the two fluids. Two main constraints apply for such systems: first, the interfaces must be stable and remain attached to the pillars at all times, second the interfacial area must be sufficient to provide an efficient mass transfer. In this work, we develop a model for the stability of interfaces attached to pillars and a model for the determination of the efficiency of the mass transfer. Optimization rules are deduced from these two models. [Copyright &y& Elsevier]

A microfluidic device integrated with a nanoliter volume enzyme pre-reactor and an enzyme-modified electrode was developed for the highly selective continuous measurement of glutamate (Glu). The device consists mainly of two glass plates. One plate incorporates an electrochemical cell that consists of working electrode (WE), reference electrode (RE) and counter electrode (CE). The WE is modified with a bilayer film of Os-polyvinylpyrridine-based mediator containing horseradish peroxidase (Os-gel-HRP). The WE was operated at −50 mV versus Ag. The other plate has a thin layer flow channel integrated with a pre-reactor. The reactor has a number of micropillars (20 μm in diameter, 20 μm high and separated from each other by a 20 μm gap) modified with ascorbate oxidase (AAOx) to eliminate l-ascorbic acid (AA). The enzymatic oxidation of AA is superior to that obtained with our previously reported pre-electrolysis type micro-reactor since electrochemically reversible transmitters such as catecholamines do not provide a cathodic current at the WE. In addition, the high operation potential of the pre-reactor causes unknown electroactive species, which also cause interference at the detection electrode. As a result, we were able to detect 1 μM Glu continuously at a low flow rate even when AA concentration was 100 μM. [Copyright &y& Elsevier]

The interface debonding caused by mismatched thermal expansion is a key issue in graphene nanoplatelets/Ti matrix composites (GNPs/TiMCs), which significantly decreases the composites' mechanical properties. In this study, GNPs/Ti composites were fabricated by spark plasma sintering (SPS) followed by heat treatment (HT) routes. A novel strategy that strengthening the GNPs-Ti interface bonding via tailored three-dimensional (3D) interface configuration was proposed for the first time. Characters of interface evolution (before and after HT processes) were discussed detailedly in conjunction with the in-situ formed TiB whiskers (TiBw). The interfacial microstructure displayed that GNPs was used as template for the heteroepitaxial growth of TiBw, then TiBw connected the TiC layer and the adjacent Ti matrix. Tensile tests showed that GNPs-(TiBw)/Ti composites exhibited excellent strength-plasticity compatibility as compared to GNPs/Ti. Ex-situ compression tests of micro-pillars fabricated from the bulk composites revealed that the 3D interface configuration in GNPs-(TiBw)/Ti possessed significantly higher strain accommodation and strain-hardening ability during deformation. This study highlights the importance of interface optimization, which is helpful for developing the interfacial engineering and achieving good properties in GNPs/TiMCs. [ABSTRACT FROM AUTHOR]

Abstract: The friction stress resulting from alloying elements in industrial alloys is an important strengthening mechanism. Since the preparation of single crystal from industrial material is difficult, no direct measurement of this quantity has been reported in literature. In this paper we present a new experimental method for the measurement of the Critical Resolved Shear Stress (CRSS) of single crystals cut from individual grains. It is shown that the size of the single crystal must be large enough to avoid size effects. Using transmission electron microscopy the measurement of the dislocation density allows for the decomposition of the CRSS into forest hardening and friction components. The friction stress is found to be the principal component of the materials strength. [Copyright &y& Elsevier]

Abstract: The size-dependent flow stress in uniformly loaded pillars has been modeled using a discrete dislocation dynamics tool. Starting from Frank-Read sources of given length and random orientation, the simulated flow stress at 0.15% plastic strain shows a clear size effect, similar to experimental findings for larger strains. The scattering of the simulated stress–strain curves decreases with increasing sample size, which reflects that plasticity of small scale samples is very sensitive to the underlying dislocation microstructure. [Copyright &y& Elsevier]

The physico-chemical surface design of implants influences the surrounding cells. Osteoblasts on sharp-edged micro-topographies revealed an impaired cell phenotype, function and Ca2+ mobilization. The influence of edges and ridges on the Wnt/β-catenin pathway in combination with the cells' stress response has not been clear. Therefore, MG-63 osteoblasts were studied on defined titanium-coated micro-pillars (5 × 5 × 5 µm) in vitro and in silico. MG-63s on micro-pillars indicated an activated state of the Wnt/β-catenin pathway. The β-catenin protein accumulated in the cytosol and translocated into the nucleus. Gene profiling indicated an antagonism mechanism of the transcriptional activity of β-catenin due to an increased expression of inhibitors like ICAT (inhibitor of β-catenin and transcription factor-4). Cells on pillars produced a significant reactive oxygen species (ROS) amount after 1 and 24 h. In silico analyses provided a detailed view on how transcriptional activity of Wnt signaling is coordinated in response to the oxidative stress induced by the micro-topography. Based on a coordinated expression of regulatory elements of the Wnt/β-catenin pathway, MG-63s are able to cope with an increased accumulation of β-catenin on micro-pillars and suppress an unintended target gene expression. Further, β-catenin may be diverted into other signaling pathways to support defense mechanisms against ROS. [ABSTRACT FROM AUTHOR]

This research was devoted to studying the influence of the taper angle on the micro-compression of micro-pillars fabricated from near-amorphous and nanocrystalline Mo-B-C coatings. A series of micro-pillars with a taper angle between 4–14° was fabricated by focused ion beam technique. The deformation mechanism was found to be dependent on the taper and, also, on the crystallinity of the coating. In order to obtain correct values of yield strength and Young's modulus, three empirical models of stress correction were experimentally tested, and the results were compared with nanoindentation measurements. It was shown that the average stress correction model provided comparable results with nanoindentation for the yield strength for taper angles up to ~10°. On the other hand, the average radius or area model gave the most precise results for Young's modulus if the taper angle was <10°. [ABSTRACT FROM AUTHOR]