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Interactions between carbon nanotubes (CNTs) and fluid flows are central to the operation of several emerging nanotechnologies. In this paper, we explore the fluid-structure interaction of CNT micropillars in wall-bounded shear flows, relevant to recently developed microscale wall shear stress sensors. We monitor the deformation of CNT micropillars in channel flow as the flow rate and wall shear stress are gradually varied. We quantify how the micropillars bend at low wall shear stress, and then will commonly tilt abruptly from their base above a threshold wall shear stress, which is attributed to the lower density of the micropillars in this region. Some micropillars are observed to flutter rapidly between a vertical and horizontal position around this threshold wall shear stress, before settling to a tilted position as wall shear stress increases further. Tilted micropillars are found to kink sharply near their base, similar to the observed buckling near the base of CNT micropillars in compression. Upon reducing the flow rate, micropillars are found to fully recover from a near horizontal position to a near vertical position, even with repeated on–off cycling. At sufficiently high wall shear stress, the micropillars were found to detach at the catalyst particle-substrate interface. The mechanical response of CNT micropillars in airflow revealed by this study provides a basis for future development efforts and the accurate simulation of CNT micropillar wall shear stress sensors. [ABSTRACT FROM AUTHOR]

At the early stages of drug development, the amount of drug materials is rather limited. In this case, viscosity measurement is often postponed to the later stages, where grams of proteins can be produced. Therefore, it is necessary to develop a viscometer capable of measuring the viscosity with high accuracy while requiring low sample volume. This study presents a novel viscosity measurement technique based on measuring the resonance frequency and motional resistance of a micropillar-enhanced acoustic wave (μPAW) device. The μPAW was developed by fabricating micropillars on the quartz crystal microbalance substrate in order to achieve ultra-high sensitivity, thanks to a unique coupling between the micropillar and the resonator. The experimental measurements demonstrated a nonlinear relationship between the density and viscosity of the fluid and the response of μPAW. A calibration correlation was developed using the response of μPAW in aqueous glycerol and sucrose solutions. The measurements were then extended using high-concentration BSA solutions as the model of protein solution. The main advantage of the μPAW device in this work over other viscometers is the ability to simultaneously measure solution viscosity and protein adsorption on the surface. This is a huge step forward in the development of sensing systems for the pharmaceutical industry, where real-time sensing of target biological proteins and measuring the viscosity of a solution is required. [ABSTRACT FROM AUTHOR]

Recent experimental findings have shown that tantalum single crystals display strong anisotropy during Taylor impact testing in stark contrast to isotropic deformation in polycrystalline counterparts. In this study, a coupled dislocation dynamics and finite element model was developed to simulate the complex stress field under dynamic loading of a Taylor impact test and track the intricate evolution of the dislocation microstructure. Our model allowed us to investigate detailed motion of dislocations and their mutual interactions and the effect of varying simulation parameters, such as sample size, initial dislocation density, crystallographic orientation, and temperature. Simulation results show good agreement with experimental observations and shed light on the mechanical response at small-scale under extreme loading conditions. In addition, resolved shear stress analysis incorporating the effect of shear stress from impact was performed to quantitatively support and provide a means to understand the model predictions of the impact foot shape.

AbstractA theoretical model of a quartz crystal microbalance carrying a layer of substrate and an array of micropillars based on the classical and modified Timoshenko beam theory was established. By choosing specific substrate thickness and micropillar height, this composite sensor approaches the coupled resonance state, and thus significantly improving the mass sensitivity. The intentionally designed sensor is extremely sensitive to tiny mass. However, with increasing mass, the mass sensitivity decreases sharply and then tends to be constant. The frequency shifts calculated by two models have some differences, but their mass sensitivity is almost the same. [ABSTRACT FROM AUTHOR]

Oil spill cleanup in water remains a critical challenge due to the harmful secondary pollution from conventional methods such as burning or chemical degradation. Herein, we present a facile method to fabricate a superhydrophobic and superoleophilic polyurethane (PU) foil for efficient and environmentally friendly oil/water separation. More specifically, micropillar arrays were embedded onto the foil surface through a nanoimprinting process. Microporous structures were generated at the foil cross-section by a supercritical carbon dioxide (CO2) saturation method. The dimensions of pillar and pore structures were optimized with the aim of boosting selective wetting (i.e., water repellency and oil attraction) properties. As a result, the developed PU foil shows an oil absorption efficiency nearly 4 times higher than a pristine reference. Moreover, the structured PU foil stably retains the absorbed oil for over a week, demonstrating an absorption capacity of nearly 400%, which is also much superior than the unstructured sample. Our concept of combining both topographical micropillars and cross-sectional micropores onto PU foil provides a novel approach for achieving efficient and environmental friendly oil/water separation. [ABSTRACT FROM AUTHOR]

Single-cell analysis provides a groundbreaking avenue for exploring cell-to-cell variation, the heterogeneity of cell responses to stimuli, and the impact of DNA sequence variations on cell phenotypes. A crucial facet of this analytical approach involves the refinement of techniques for effective single-cell trapping and sustained culture. This study introduces a microfluidic platform based on micropillars for hydrodynamic trapping and prolonged cultivation of individual cells. The proposed biochip design, termed three-micropillars based microfluidic (3µPF) structure, incorporates interleaved trap units, each featuring three-micropillars based microfluidic structure strategically designated to trap single cells, enhance the surface area of cells exposed to the culture medium, and enable dynamic culture, continuous waste removal. This configuration aims to mitigate adverse effects associated with bioparticle collisions compared to conventional trap units. The study employs finite element method to conduct a comprehensive numerical investigation into the operational mechanism of the microfluidic device. The simulation results show that the filled trap unit demonstrates a low-velocity magnitude, reducing shear stress on cells and facilitating extended culture. The hydrodynamic single-cell trap mechanism of the proposed device was also verified. The insights derived from this work are pivotal for optimizing the device and guiding future experimental examinations, thus contributing significantly to the progression of single-cell analysis techniques. [ABSTRACT FROM AUTHOR]

Disk of a Cu38Zr54Al8 bulk metallic glass was subjected to severe plastic deformation by high pressure torsion up to 25 revolutions. X-ray diffraction was utilized to investigate the microstructure of the deformed sample, while the thermal behavior of the glass was analyzed by differential scanning calorimetry. To examine the effect of plastic straining on structural changes, micropillars were fabricated on the cross-section of the disk along the radius at specific locations, i.e. center, half radius and perimeter. Compression tests of these micropillars were conducted in a scanning electron microscope with simultaneous recording of continuous acoustic emissions. Present paper captures the effect of competition between thermal relaxation and deformation induced structural changes. Specifically, probability distributions were constructed for a series of acoustic emission events, revealing that the occurrence of acoustic emission bursts at larger deformations is in correlation with the shift of the X-ray diffraction halos and change in thermal characteristics. Accordingly, a transition was identified from random to correlated acoustic emission behavior parallel with a progressive increase in the accumulation of excess free volume from negative to positive values.

Fluid-structure interactions (FSI) are used in a variety of sensors based on micro- and nanotechnology to detect and measure changes in pressure, flow, and viscosity of fluids. These sensors typically consist of a flexible structure that deforms in response to the fluid flow and generates an electrical, optical, or mechanical signal that can be measured. FSI-based sensors have recently been utilized in applications such as biomedical devices, environmental monitoring, and aerospace engineering, where the accurate measurement of fluid properties is critical to ensure performance and safety. In this work, multiphysics models are employed to identify and study parameters that affect the performance of an FSI-based microfluidic viscometer that measures the viscosity of Newtonian and non-Newtonian fluids using the deflection of flexible micropillars. Specifically, we studied the impact of geometric parameters such as pillar diameter and height, aspect ratio of the pillars, pillar spacing, and the distance between the pillars and the channel walls. Our study provides design guidelines to adjust the sensitivity of the viscometer toward specific applications. Overall, this highly sensitive microfluidic sensor can be integrated into complex systems and provide real-time monitoring of fluid viscosity. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel welds (ASSWs) of nuclear components undergo aging-related degradations caused by high temperature and neutron radiation. Since irradiation leads to the change of material characteristics, relevant quantification is important for long-term operation, but limitations exist. Although ion irradiation is utilized to emulate neutron irradiation, its penetration depth is too shallow to measure bulk properties. In this study, a systematic approach was suggested to estimate mechanical properties of ion irradiated 308 ASSW. First of all, weld specimens were irradiated by 2 MeV proton to 1 and 10 dpa. Microstructure evolutions due to irradiation in δ-ferrite and austenite phases were characterized and micropillar compression tests were performed. In succession, dislocation density based stress-strain (S–S) relationships and quantification models of irradiation defects were adopted to define phases in finite element analyses. Resultant microscopic S–S curves were compared to verify material parameters. Finally, macroscopic behaviors were calculated by multiscale simulations using real microstructure based representative volume element (RVE). Validity of the approach was verified for the unirradiated specimens such that the estimated S–S curves and 0.2% offset yield strengths (YSs) which was 363.14 MPa were in 10% agreement with test. For irradiated specimens, the estimated YS were 917.41 MPa in 9% agreement.

Oil spill cleanup in water remains a critical challenge due to the harmful secondary pollution from conventional methods such as burning or chemical degradation. Herein, we present a facile method to fabricate a superhydrophobic and superoleophilic polyurethane (PU) foil for efficient and environmentally friendly oil/water separation. More specifically, micropillar arrays were embedded onto the foil surface through a nanoimprinting process. Microporous structures were generated at the foil cross-section by a supercritical carbon dioxide (CO2) saturation method. The dimensions of pillar and pore structures were optimized with the aim of boosting selective wetting (i.e., water repellency and oil attraction) properties. As a result, the developed PU foil shows an oil absorption efficiency nearly 4 times higher than a pristine reference. Moreover, the structured PU foil stably retains the absorbed oil for over a week, demonstrating an absorption capacity of nearly 400%, which is also much superior than the unstructured sample. Our concept of combining both topographical micropillars and cross-sectional micropores onto PU foil provides a novel approach for achieving efficient and environmental friendly oil/water separation.

Combining bioaffinity-based techniques with microfluidics is an effective strategy for the selective isolation of rare circulating tumor cells (CTCs) among peripheral blood cells. In this scope, designing a microfluidic channel with high cell-surface interaction is crucial, which can be realized by increasing surface area via micropillars. In such microfluidic channels, the interpillar distance represents a critical design parameter, and the value is decided considering the trade-off between the possibility of clogging and CTC capture efficiency. In this study, a curvilinear microfluidic channel with a wide (150 µm) interpillar distance was developed to prevent clogging while maintaining high CTC capture efficiency. Computational fluid dynamics was used to compare the residence time of particles in the designed channels. For the proof-of-concept study, microfabricated channels were biofunctionalized for immunoaffinity-based isolation of CTCs, using anti-EpCAM antibodies. Enhanced CTC capture was enabled through the micropillars inside the channels helping the increased encounters between the cells and the antibody-functionalized surface. The curvilinear channel effectively isolated cells from MCF-7 breast cancer cell line among white blood cells, with more than 85% capture efficiency. The rate of non-specific binding of white blood cells remained below 20%. This study demonstrated the ability to increase the interactions between particles and surfaces without requiring a dense layout of the micropillars inside the microchannel, therefore minimizing the clogging possibility of the channel without sacrificing performance.

[Display omitted] Hypothesis : Horseshoe vortices are known to emerge around large-scale obstacles, such as bridge pillars, due to an inertia-driven adverse pressure gradient forming on the upstream-side of the obstacle. We contend that a similar flow structure can arise in thin-film Stokes flow around micro-obstacles, such as used in textured surfaces to improve wettability. This could be exploited to enhance mixing in microfluidic devices, typically limited to creeping-flow regimes. Experiments : Numerical simulations based on the Navier–Stokes equations are carried out to elucidate the flow structure associated with the wetting dynamics of a liquid film spreading around a 50 μm diameter micro-pillar. The employed multiphase solver, which is based on the volume of fluid method, accurately reproduces the wetting dynamics observed in current and previous (Mu et al., Langmuir, 2019) experiments. Findings : The flow structure within the liquid meniscus forming at the foot of the micro-pillar evinces a horseshoe vortex wrapping around the obstacle, notwithstanding that the Reynolds number in our system is extremely low. Here, the adverse pressure gradient driving flow reversal near the bounding wall is caused by capillarity instead of inertia. The horseshoe vortex is entangled with other vortical structures, leading to an intricate flow system with high-potential mixing capabilities. [ABSTRACT FROM AUTHOR]

The influence of microstructure and processing route on the small-scale mechanical response as well as on the deformation and failure mechanisms of Ti(C,N)-FeNi cermets were investigated by uniaxial compression of micropillars milled by focused ion beam with different sizes. Stress-strain curves were determined and associated deformation mechanisms were observed in-situ using scanning electron microscopy. The appropriate micropillars dimension was assessed, based on the microstructural characteristics of studied cermets, to overcome scale effect issues. A direct relationship was observed between yield strength and ceramic/metal ratio for colloidal samples. Meanwhile, deformation of metallic binder and glide between Ti(C,N)/Ti(C,N) particles were evidenced as dominant mechanisms during the compression for colloidal cermets with 70 and 80 vol% of ceramic phase, respectively. The obtained results illustrate that samples processed from powder attained by colloidal route provide superior mechanical behavior, as compared to that exhibited by specimens shaped following a conventional powder metallurgy one (wet ball-milling/drying). [Display omitted] [ABSTRACT FROM AUTHOR]

A 3D network capture substrate based on poly(lactic-co-glycolic acid) (PLGA) nanofibers was studied and successfully used for high-efficiency cancer cell capture. The arc-shaped glass micropillars were prepared by chemical wet etching and soft lithography. PLGA nanofibers were coupled with micropillars by electrospinning. Given the size effect of the microcolumn and PLGA nanofibers, a three-dimensional of micro-nanometer spatial network was prepared to form a network cell trapping substrate. After the modification of a specific anti-EpCAM antibody, MCF-7 cancer cells were captured successfully with a capture efficiency of 91%. Compared with the substrate composed of 2D nanofibers or nanoparticles, the developed 3D structure based on microcolumns and nanofibers had a greater contact probability between cells and the capture substrate, leading to a high capture efficiency. Cell capture based on this method can provide technical support for rare cells in peripheral blood detection, such as circulating tumor cells and circulating fetal nucleated red cells. [ABSTRACT FROM AUTHOR]

We report the microfabrication and characterization of concentric gold nanoring electrodes (Au NREs), which were fabricated by patterning two gold nanoelectrodes on the same silicon (Si) micropillar tip. Au NREs of 165 ± 10 nm in width were micropatterned on a 6.5 ± 0.2 µm diameter 80 ± 0.5 µm height Si micropillar with an intervening ~ 100 nm thick hafnium oxide insulating layer between the two nanoelectrodes. Excellent cylindricality of the micropillar with vertical sidewalls as well as a completely intact layer of a concentric Au NRE including the entire micropillar perimeter has been achieved as observed via scanning electron microscopy and energy dispersive spectroscopy data. The electrochemical behavior of the Au NREs was characterized by steady-state cyclic voltammetry and electrochemical impedance spectroscopy. The applicability of Au NREs to electrochemical sensing was demonstrated by redox cycling with the ferro/ferricyanide redox couple. The redox cycling amplified the currents by 1.63-fold with a collection efficiency of > 90% on a single collection cycle. The proposed micro-nanofabrication approach with further optimization studies shows great promise for the creation and expansion of concentric 3D NRE arrays with controllable width and nanometer spacing for electroanalytical research and applications such as single-cell analysis and advanced biological and neurochemical sensing. [ABSTRACT FROM AUTHOR]

Quantum dots have the potential to be one of the brightest deterministic single photon sources with high end applications in quantum computing and cluster state generation. In this work, we re-examine the design of plain micropillars by meticulously examining the structural effects of the decay into leaky channels beyond an atom-like cavity estimation. We show that precise control of the side losses with the diameter and avoidance of propagating Bloch modes in the distributed Bragg reflectors can result in easy-to-manufacture broadband ( $\mathit{Q}\approx750$ –2500) micropillars, allowing for broad optical coherent control pulses necessary for high single photon purity ( $ {\gt}$ 99.2%–99.99% achievable) while simultaneously demonstrating extremely high efficiency out the top (90.5%–96.4%). We also demonstrate that such cavities naturally decouple from the phonon sideband, with the phonon sideband reducing by a factor of 5–33 allowing us to predict that the photons should show 98.5%–99.8% indistinguishability without the need for filtering.

Fluid-structure interactions (FSI) are used in a variety of sensors based on micro- and nanotechnology to detect and measure changes in pressure, flow, and viscosity of fluids. These sensors typically consist of a flexible structure that deforms in response to the fluid flow and generates an electrical, optical, or mechanical signal that can be measured. FSI-based sensors have recently been utilized in applications such as biomedical devices, environmental monitoring, and aerospace engineering, where the accurate measurement of fluid properties is critical to ensure performance and safety. In this work, multiphysics models are employed to identify and study parameters that affect the performance of an FSI-based microfluidic viscometer that measures the viscosity of Newtonian and non-Newtonian fluids using the deflection of flexible micropillars. Specifically, we studied the impact of geometric parameters such as pillar diameter and height, aspect ratio of the pillars, pillar spacing, and the distance between the pillars and the channel walls. Our study provides design guidelines to adjust the sensitivity of the viscometer toward specific applications. Overall, this highly sensitive microfluidic sensor can be integrated into complex systems and provide real-time monitoring of fluid viscosity.

To address the burgeoning demand for anti-icing applications in various environments, an effective means of retarding inter-droplet frosting with a high degree of environmental adaptability is urgently required. In this study, frosting experiments were performed on Si micropillar arrays with varying pitches under controlled environmental conditions, especially at low temperatures and high supersaturation, which indicate more severe icing possibilities. The results showed that droplet behavior was highly dependent on the environment and surface geometry. The droplet numbers at the bottom sites increased with humidity, whereas those at the top sites decreased and the transition in droplet diameter proved to be opposite. Dimensionless quantity ƞ b was proposed to describe droplet distribution under each working condition, and six frost propagation regimes were categorized into two groups: 0 < ƞ b < 0.5 and 0. 5 < ƞ b < 1. For each condition, six pillar pitches resulted in two or three different regimes, and the lowest frost propagation velocity was observed at the turning point of the last regime (optimal ratio of the normalized pillar pitch to the pillar diameter [ L / D ]). With the reduction of supersaturation, the optimal L/D was 2 at 10 ℃/90 %RH and 50 %RH, optimal L/D was 3 at 10 ℃/20 %RH, and optimal L/D was 4 at − 5 ℃/90 %RH and 50 %RH. This significantly differed from the room-temperature conditions, as the optimal L/D was found to be larger than 4 in previous studies. These findings provide further understanding of the application of patterned surfaces in anti-icing in harsh and variable environments. [Display omitted] • The optimum pitch length-diameter ratio transforms from 2 to 4 under various SSD s. • Frosting propagation velocity up to 88.9 % under harsh conditions (below 10 °C). • Variation tendency droplet size and droplet number is the opposite. • The lowest propagation velocity appears with droplet density ratio of 0.5 < ƞ b < 1. • Six inter-droplet frosting propagation regimes in harsh environments are proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • High stability Cu 38 Zr 54 Al 8 metallic glass was subjected to high pressure torsion. • Micropillars were fabricated on the cross-section of the disk at specific locations. • Compression tests and acoustic emission detection were carried out on the pillars. • Deformation shows elastic–plastic behavior and stress drops in the plastic regime. • Statistical analysis of the probability distribution of events was carried out. Disk of a Cu 38 Zr 54 Al 8 bulk metallic glass was subjected to severe plastic deformation by high pressure torsion up to 25 revolutions. X-ray diffraction was utilized to investigate the microstructure of the deformed sample, while the thermal behavior of the glass was analyzed by differential scanning calorimetry. To examine the effect of plastic straining on structural changes, micropillars were fabricated on the cross-section of the disk along the radius at specific locations, i.e. center, half radius and perimeter. Compression tests of these micropillars were conducted in a scanning electron microscope with simultaneous recording of continuous acoustic emissions. Present paper captures the effect of competition between thermal relaxation and deformation induced structural changes. Specifically, probability distributions were constructed for a series of acoustic emission events, revealing that the occurrence of acoustic emission bursts at larger deformations is in correlation with the shift of the X-ray diffraction halos and change in thermal characteristics. Accordingly, a transition was identified from random to correlated acoustic emission behavior parallel with a progressive increase in the accumulation of excess free volume from negative to positive values. [ABSTRACT FROM AUTHOR]

Deep-ultraviolet (DUV) light emitting diodes (LEDs) show great potential in a wide range of applications, but suffer from poor external quantum efficiencies (EQEs) when compared to visible LEDs, due to their exceptionally poor light extraction efficiency (ηEXT). One successful method of improving the ηEXT of DUV LEDs is the use of micropillar and nanowire arrays. Our previous works have reported the development of an “inverse taper” profile in AlGaN micropillars during wet etching in heated hydroxyl-based chemistries. Here, we study the effects of inverse tapering on the ηEXT of AlGaN microstructures and nanostructures at 270 nm using finite-difference time-domain simulations, in accordance with our experimental results. Results show that ηEXT can be increased from ∼45% to more than 95% for TM-polarized emission in microstructures with diameters of 1 μm and heights >1 μm, and from ∼35% to more than 85% for TE-polarized emission by an inverse taper angle of 5 °. Results for nanostructures also indicate significant ηEXT improvements through tuning of the inverse taper angle. These findings, along with our demonstration of inverse tapered high Al-content AlGaN micro and nanostructures, could enable the development of record-high EQE DUV LEDs based on arrays of high aspect ratio structures with high ηEXT.

Utilizing superhydrophobic micro/nanostructures to enhance condensation heat transfer (CHT) of copper surfaces has attracted intensive interest in recent years due to its significance in multiple industrial fields including nuclear power generation, thermal management, water harvesting, and desalination. However, superhydrophobic surfaces have instability risk caused by microcavity defect-induced vapor penetration and/or hydrophobic chemistry destruction. Here, we report a superwetting copper hierarchical microgroove/nanocone (MGNC) structure strategy that can realize high-efficiency CHT over a whole range of surface subcooling. By regulating groove width, fin width, groove depth, and nanostructure growth time, we obtain the optimal MGNC structure, where the CHT coefficient is 121% and 107% higher than that of hydrophilic flat surfaces at surface subcooling of 2 and 15 K, respectively. Such remarkable enhancement can be ascribed to the synergy of three interface effects: more nucleation sites for phase-change energy exchanging, thinner condensate films for reducing thermal resistance, and parallel microchannels for timely drainage. Compared with superhydrophobic strategies, our strategy not only can be mass-producible but also has other inherent advantages: no microcavity-induced performance failure risk as well as being free of chemistry modification, which makes the fabrication process simpler and more economic. Hierarchical micropillar/nanocone structure is also fabricated as the contrast sample for highlighting the superiority of the superwetting MGNC structure in enhancing CHT. This work not only enriches research systems of superwettability surfaces but also helps develop high-performance chips' cooling devices and explore more potential applications.

This research investigated heat transfer performance and flow characteristics of three polydimethylsiloxane microchannels full of deionised water as a working fluid. A single micropillar, horizontal micropillars, and vertical micropillars along the flow direction were prepared on the microchannels experimentally. Results show that the Nusselt number of microchannels with two horizontal micropillars is 19% higher than that with a single micropillar. The microchannel with two vertical micropillars has the Nusselt number is 29% higher than that with a single micropillar, which shows the best performance on the heat transfer enhancement. Visualization experiments of the flow field were carried out to explore the enhanced mechanism of the heat transfer for microchannels with various micropillar arrangements. When the flow rate is 7 mLpm, the maximum velocities near the single cylinder and the horizontal micro-column are 0.5 m/s and 0.52 m/s. Fluid velocity in a region between two vertical micropillars reaches 0.72 m/s when the flow rate is 7 mLpm. The fluid in the high-speed region is fully mixed around the micropillar, which reduces the stagnation region area downstream of the vertical micropillar and enhances heat transfer. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printed re-entrant micropillars have demonstrated high static contact angles for an unprecedented variety of liquids, but have yet to achieve this with low contact angle hysteresis and excellent abrasion resistance. We report on the demonstration of 3D printed microcell/nanoparticle structures that exhibit high static contact angle, low contact angle hysteresis, and high mechanical durability. Micropillars and microcells both exhibit high static contact angles with water and ethylene glycol (EG), but suffer from high contact angle hysteresis, indicative of rose petal wetting. Our modeling results indicate that micropillars are able to achieve higher static contact angle and breakthrough pressure simultaneously compared with microcells. However, simulations also indicate that micropillars have higher maximum equivalent stress at their bases, so that they are more prone to mechanical failure. We address contact angle hysteresis and mechanical durability issues by the creation of 3D printed microcell/nanoparticle arrays that demonstrate super-repellency and retain their super-repellency after 100 cycles of mechanical abrasion with a Scotch-Brite abrasive pad under a pressure of 1.2 kPa. The use of interconnected microcell structures as opposed to micropillars addresses mechanical durability issues. Low contact angle hysteresis is realized by coating 3D printed structures with low surface energy nanoparticles, which lowers the solid—liquid contact area fraction. Our results demonstrate new 3D printed structures with mechanical durability and super-repellency through the use of microcell structures integrated with fluorinated nanoparticles. [ABSTRACT FROM AUTHOR]

The development of variotherm systems has helped to improve the quality of micro-injection molded products. Thin electric heaters have significant advantages in size, efficiency and installation convenience. However, the use of thin electric heaters has brought the problem of non-uniform temperature distribution of the insert. The good replication of the functional surfaces containing microstructures quickly and uniformly is still a challenge. In this work, the heating performance of the thin electric heater in a variotherm system is investigated by combining numerical simulations with experiments. Micro-injection molding of PP micropillars was also performed. The obtained results show that the addition of a transition layer with high thermal conductivity in the heating structure can optimize the uniformity of the temperature distribution of the insert. Furthermore, the replication heights of the micropillars can be significantly increased by the developed variotherm mold, which provides a new idea for the optimal design of a local variotherm system. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of grain boundaries on the mechanical response in the micrometer and submicrometer levels, complementary experiments and molecular dynamics simulations were conducted on a model bcc metal, tantalum. Microscale pillar experiments (diameters of 1 and 2 μm) with a grain size of ~100–200 nm revealed a mechanical response characterized by a yield stress of ~1500 MPa. The hardening of the structure is reflected in the increase in the flow stress to 1700 MPa at a strain of ~0.35. Molecular dynamics simulations were conducted for nanocrystalline tantalum with grain sizes in the range of 20–50 nm and pillar diameters in the same range. The yield stress was approximately 6000 MPa for all specimens and the maximum of the stress–strain curves occurred at a strain of 0.07. Beyond that strain, the material softened because of its inability to store dislocations. The experimental results did not show a significant size dependence of yield stress on pillar diameter (equal to 1 and 2 um), which is attributed to the high ratio between pillar diameter and grain size (~10–20). This behavior is quite different from that in monocrystalline specimens where dislocation ‘starvation’ leads to a significant size dependence of strength. The ultrafine grains exhibit clear ‘pancaking’ upon being plastically deformed, with an increase in dislocation density. The plastic deformation is much more localized for the single crystals than for the nanocrystalline specimens, an observation made in both modeling and experiments. In the molecular dynamics simulations, the ratio of pillar diameter (20–50 nm) to grain size was in the range 0.2–2, and a much greater dependence of yield stress to pillar diameter was observed. A critical result from this work is the demonstration that the important parameter in establishing the overall deformation is the ratio between the grain size and pillar diameter; it governs the deformation mode, as well as surface sources and sinks, which are only important when the grain size is of the same order as the pillar diameter.

Surface design is a promising approach to avoid problems with ice accretion. Here we investigated the water freezing characteristics on a polydimethylsiloxane (PDMS) film with micropillar-array structure. We fabricated a micropillar square array with the pillar diameter of 10 μm, the heigh of 20 μm, and the pitch of 50 μm, using the PDMS–PDMS pattern transfer. Water contact angle and sliding-off angle measurements revealed that the micropillar PDMS film had a superhydrophobic surface. Freezing behaviors were compared for water droplet on different surfaces including a copper plate with a micropillar PDMS film. The case of micropillar PDMS film showed prolonged freezing, and the potential of anti-icing surface design was demonstrated.

• In-situ growth of Sb 2 S 3 micropillar arrays on the template using laser direct writing. • Micropillar arrays enhance light absorption of Sb 2 S 3 -based solar cell. • The textured Sb 2 S 3 film increasing the contact area with the hole transport layer. Sb 2 S 3 has garnered significant attention in photovoltaic applications due to its suitable bandgap, single stable orthogonal phase and excellent stability. However, due to the coexistence of indirect transition parts in the bandgap, a thicker Sb 2 S 3 absorption layer is usually required to achieve decent light absorption in solar cells, which inevitably leads to an increase in trapped states in the bulk. Therefore, it is of great importance to realize more photogenerated carriers without increasing charge recombination. Here, we realized the in-situ growth of high-quality Sb 2 S 3 micropillar arrays on the template prepared by laser direct writing. Compared with the traditional thick layer, this array structure with less material usage can not only achieve more light absorption by enhancing photon scattering, but also optimize carrier transport at the interface by expanding their contact area with the hole transporting layer. This work provides a strategy for controllably achieving enhanced light absorption of Sb 2 S 3 structures, which is a perspective for the improvement of highly efficient solar cells. [ABSTRACT FROM AUTHOR]

The compressive deformation behaviors were investigated in metastable β Ti–7Mo–3Al–3Cr–3Nb alloy single crystal micropillars oriented to [011] β and [001] β. The study demonstrates that the metastable β titanium single crystal oriented to [001] β exhibits nonlinear elastic behavior with hysteresis, which is attributed to reverse β to α″ transformation. Furthermore, the yield strength of the single crystal oriented to [011] β is almost twice as of the single crystal oriented to [001] β , which is influenced by the different roles of ω ath in both pillars due to differences in shear modulus G, in addition to being determined by the deformation mechanism at yielding. The continuous impedance to dislocation motion of ω and α″ phase in the pillar oriented to [011] β leads to a stable plastic flow behavior, but reverse β to ω phase transformation facilitating the formation of massive SIMα″ results in a sudden strain burst in the pillar oriented to [001] β. Finally, we find that the pillar oriented to [011] β is dominated by dislocation slip but SIMα″ occupies a dominant position in the pillar oriented to [001] β in the early deformation stage, which is same as predicted based on the martensitic transformation theory in metastable β titanium alloys. [ABSTRACT FROM AUTHOR]

Compressive strength and stiffness of concrete materials involve the complex interaction of aggregates and hardened cement, which can involve even more complex phases formed through hydration processes. Typically, the strength and stiffness of concrete materials are determined through material-scale testing, focusing on the bulk behavior while ignoring individual constitutive material interactions. This study aims to identify individual cement phase contributions to bulk concrete properties through the characterization of individual hardened cement-paste phases using micro-scale compressive testing. In this study, in-situ micro-compression measurements are used to generate statistical distributions of compressive strength and stiffness for five hardened cement phases and one phase composite. Results from the in-situ micro-compression testing indicate that AFt/AFm and CH/C–S–H micropillars exhibit higher stiffness and strength when compared to hardened C–S–H and C-A-S-H phases. Comparing measured micropillar strength and stiffness values with traditional nano-indentation methods indicates that nano-indentation approaches may provide a higher estimation of individual phase stiffness due to material confinement boundary effects. [ABSTRACT FROM AUTHOR]

A 3D network capture substrate based on poly(lactic-co-glycolic acid) (PLGA) nanofibers was studied and successfully used for high-efficiency cancer cell capture. The arc-shaped glass micropillars were prepared by chemical wet etching and soft lithography. PLGA nanofibers were coupled with micropillars by electrospinning. Given the size effect of the microcolumn and PLGA nanofibers, a three-dimensional of micro-nanometer spatial network was prepared to form a network cell trapping substrate. After the modification of a specific anti-EpCAM antibody, MCF-7 cancer cells were captured successfully with a capture efficiency of 91%. Compared with the substrate composed of 2D nanofibers or nanoparticles, the developed 3D structure based on microcolumns and nanofibers had a greater contact probability between cells and the capture substrate, leading to a high capture efficiency. Cell capture based on this method can provide technical support for rare cells in peripheral blood detection, such as circulating tumor cells and circulating fetal nucleated red cells.

We report the microfabrication and characterization of concentric gold nanoring electrodes (Au NREs), which were fabricated by patterning two gold nanoelectrodes on the same silicon (Si) micropillar tip. Au NREs of 165 ± 10 nm in width were micropatterned on a 6.5 ± 0.2 µm diameter 80 ± 0.5 µm height Si micropillar with an intervening ~ 100 nm thick hafnium oxide insulating layer between the two nanoelectrodes. Excellent cylindricality of the micropillar with vertical sidewalls as well as a completely intact layer of a concentric Au NRE including the entire micropillar perimeter has been achieved as observed via scanning electron microscopy and energy dispersive spectroscopy data. The electrochemical behavior of the Au NREs was characterized by steady-state cyclic voltammetry and electrochemical impedance spectroscopy. The applicability of Au NREs to electrochemical sensing was demonstrated by redox cycling with the ferro/ferricyanide redox couple. The redox cycling amplified the currents by 1.63-fold with a collection efficiency of > 90% on a single collection cycle. The proposed micro-nanofabrication approach with further optimization studies shows great promise for the creation and expansion of concentric 3D NRE arrays with controllable width and nanometer spacing for electroanalytical research and applications such as single-cell analysis and advanced biological and neurochemical sensing.

Ultrafine-grained and nanocrystalline materials frequently show an enhanced rate sensitivity of their mechanical behavior, which is generally assumed to be the consequence of interface sliding or thermally activated dislocation processes at the boundaries. Although this has been well documented on many different materials, the underlying mechanisms and their effect on the ductility of the material are still not well understood. Therefore, here, the deformation behavior of the ultrafine-grained, heterogeneous superplastic alloy Zn-22% Al was analyzed by small-scale nanoindentation and micropillar testing. The results show a breakdown of the superplastic deformation behavior in terms of a reduced strain rate sensitivity at small scales, which has not been reported before, although grain boundary sliding is still prevalent at the nanoscale. These results suggest that grain boundary sliding does not necessarily result in a high strain rate sensitivity and high ductility. Instead, a pronounced strain rate dependent flow behavior requires grain boundary sliding to be controlled by dislocation creep. IMPACT STATEMENT Superplastic flow is shown to persist down to a small material volume corresponding to a few grains. This has far-reaching consequences for the production of small-scale devices with complex geometries by superplastic forming.

Abstract Background Nanoparticles are being increasingly used in biomedical applications owing to their unique physical and chemical properties and small size. However, their biophysical assessment and evaluation of side-effects remain challenging. We addressed this issue by investigating the effects of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate [MNPs@SiO2(RITC)] on biophysical aspects, such as membrane fluidity and traction force of human embryonic kidney 293 (HEK293) cells. We further extended our understanding on the biophysical effects of nanoparticles on cells using a combination of metabolic profiling and transcriptomic network analysis. Results Overdose (1.0 μg/µL) treatment with MNPs@SiO2(RITC) induced lipid peroxidation and decreased membrane fluidity in HEK293 cells. In addition, HEK293 cells were morphologically shrunk, and their aspect ratio was significantly decreased. We found that each traction force (measured in micropillar) was increased, thereby increasing the total traction force in MNPs@SiO2(RITC)-treated HEK293 cells. Due to the reduction in membrane fluidity and elevation of traction force, the velocity of cell movement was also significantly decreased. Moreover, intracellular level of adenosine triphosphate (ATP) was also decreased in a dose-dependent manner upon treatment with MNPs@SiO2(RITC). To understand these biophysical changes in cells, we analysed the transcriptome and metabolic profiles and generated a metabotranscriptomics network, which revealed relationships among peroxidation of lipids, focal adhesion, cell movement, and related genes and metabolites. Furthermore, in silico prediction of the network showed increment in the peroxidation of lipids and suppression of focal adhesion and cell movement. Conclusion Taken together, our results demonstrated that overdose of MNPs@SiO2(RITC) impairs cellular movement, followed by changes in the biophysical properties of cells, thus highlighting the need for biophysical assessment of nanoparticle-induced side-effects.

Research evidence abounds on the effectiveness of micropillar‐based microelectromechanical systems for the detection of a wide variety of ultrasmall biological objects for clinical and non‐clinical applications. However, the standard micropillar‐based sensing platforms rely on a single‐column micropillar with a spot at the tip for binding of objects. Although this long‐standing form has shown immense potential, performance improvement is hindered by the fundamental limits enforced by physical laws. Moreover, the single‐column micropillar has a lower sensing area and is ill‐suited for a simultaneous differential sensing of chemical/biological objects of different mass. Here, we report a new set of nature‐inspired, branched micropillar‐based sensing resonators to address the highlighted issues. The characteristics of the newly proposed branched micropillars are comprehensively examined with three payloads (Bartonella Bacilliformis, Escherichia coli, and Micro magnetic beads). Anchored on the capability of continuum theoretical framework, the mathematical model of the micropillar is formulated through the synthesis of the modified couple stress, the Rayleigh‐Love, and the Timoshenko theories. The finite element method is employed to shed light on the variability of the structures' resonant response under performance reduction factors (payload's rotary inertia, damaged substrate, and density of a surrounding fluid). The results obtained indicate superior performance indicators for the triply‐branched micropillar: enhanced response sensitivity for multiple payloads and less susceptibility to deterioration in resonant frequencies due to fluid immersion. [ABSTRACT FROM AUTHOR]

Abstract We proposed a precise calibration process of Al 0.9 Ga 0.1As/GaAs DBR micropillar cavity to match the single InAs/GaAs quantum dot (QD) exciton emission and achieve cavity mode resonance and a great enhancement of QD photoluminescence (PL) intensity. Light-matter interaction of single QD in DBR micropillar cavity (Q ∼ 3800) under weak coupling regime was investigated by temperature-tuned PL spectra; a pronounced enhancement (14.6-fold) of QD exciton emission was observed on resonance. The second-order autocorrelation measurement shows g (2)(0)=0.070, and the estimated net count rate before the first objective lens reaches 1.6×107 counts/s under continuous wave excitation, indicating highly pure single-photon emission at high count rates.

The ability of cells to recognize and respond to the mechanical properties of their environment is of increasing importance in T cell physiology. However, initial studies in this direction focused on planar hydrogel and elastomer surfaces, presenting several challenges in interpretation including difficulties in separating mechanical stiffness from changes in chemistry needed to modulate this property. We introduce here the use of magnetic fields to change the structural rigidity of microscale elastomer pillars loaded with superparamagnetic nanoparticles, independent of substrate chemistry. This magnetic modulation of rigidity, embodied as the pillar spring constant, changed the interaction of mouse naïve CD4+ T cells from a contractile morphology to one involving deep embedding into the array. Furthermore, increasing spring constant was associated with higher IL-2 secretion, showing a functional impact on mechanosensing. The system introduced here thus separates local substrate stiffness and long-range structural rigidity, revealing new facets of T cell interaction with their environment.

Knowledge about the adhesion of protective hard coatings on tool materials is of great importance to understand their failure mechanisms in metalworking. Until now, common techniques such as scratch and indentation tests are used to establish a qualitative ranking of a coating’s adhesion on various substrate materials. Nevertheless, there is a lack of quantitative measures to describe the strength of the interfaces between individual microstructural constituents of substrate-coating composites. The current work investigates the interfacial strength and thus the adhesion of TiN deposited as a hard coating on an MC-type carbide, an M6C-type carbide and on martensite being constituents of high speed steels. Tensile stresses were introduced at the interface between TiN and the individual microstructural constituents of a high speed steel via micromechanical testing of a novel MSC specimen within a scanning electron microscope. The tested MSC specimens were subsequently investigated in detail by scanning electron microscopy. Evaluation of the interface stress at fracture via finite element analysis yielded a ranking in interface strength and therefore coating adhesion in a sequence from high to low strength values from MC/TiN over M6C/TiN to martensite/TiN.

Micro-deformation testing has recently gained far-reaching scientific importance as it provides intrinsic information on the dynamics of plastic deformation which is concealed when bulk materials are tested. In this work, single-crystal Mg micropillars favorably oriented for mechanical twinning were tested in compression with concurrent scanning electron microscopy imaging. The experimental data were complemented by the finite element modeling in order to reveal the underlying physical background of the observed twinning dynamics. It was shown that the thickness of a twin should reach a critical value before triggering the nucleation of another twin to accommodate further strain. Nucleation and growth are repeated until the twins form throughout the whole micropillar, from top to bottom. Afterwards, the thickening and coalescence of all these twins take place until the entire micropillar volume is twinned. In addition, a line-by-line analysis of the scanning electron microscopy images was employed to reveal the twin lateral growth rates, which were shown to be on the order of 10−5–10−4 m/s.

Background: Dislocation dynamic simulations are intended as a tool to understand and predict the mechanical behavior of metallic materials, but its prediction has never been directly verified by experiments due to differences in specimen strain rate and size. Objective: In this work, a comprehensive experimental framework is proposed to attempt direct comparison between experiments and discrete dislocation dynamics (DDD) modelling. Methods: By integrating high-throughput sample fabrication and a customized testing apparatus, the sample size and strain rate typically employed in DDD simulations are explored experimentally. Constitutive properties such as stress-strain response are measured, and microstructural information is obtained from transmission electron microscopy (TEM) imaging, electron backscatter diffraction (EBSD), and TEM-based orientation mapping. Results: Magnesium and copper were selected, as case studies, to demonstrate the newly developed experimental procedure. Measured stress-strain responses for Mg are consistent with those obtained with a miniaturized Hopkison bar experiments. By exploiting the validated workflow, the effect of strain rate on micropillar heterogeneous deformation and associated dislocation plasticity were revealed. Conclusion: The work establishes a methodology for the systematic study of not only metals but also other materials and structures at the microscale and high strain rates. [ABSTRACT FROM AUTHOR]

The mechanical properties and deformation mechanisms of single crystal magnesium under c-axis quasi-static and high-strain rate compressions are investigated through in situ scanning electron microscope (SEM) experiments and post-mortem transmission electron microscope (TEM) characterization. The findings revealed that ductility and high rates of hardening are preserved for pillars as large as 15 μm. Furthermore, rate effects result in a mild increase in flow stress with plastic deformations controlled primarily by the slip of type dislocations. Importantly and in contrast to other literature reports, plastic deformation occurs in the absence of twining. As the strain increases and plastic deformation exceeds about 4%, crystal rotation activates basal slip, type dislocations, resulting in a more rate independent flow stress. TEM observation on micropillars compressed at a strain rate of 250/s, revealed the activation of { 11 2 ‾ 2 ‾ } < 1 ‾ 1 ‾ 23 > slip systems and high mobility of screw dislocations as major contributors to plastic strains in excess of 10% without fracture. These findings are relevant to the design of lightweight materials used in transportation systems, e.g., selection of material grain size. Moreover, the experimental data here reported provides the materials science community with a unique opportunity to validate discrete dislocation dynamics (DDD) formulations employed in multiscale design of materials. • First in situ SEM high strain rate investigation of hcp micropillars. • Identification of primary plasticity mechanisms from TEM dislocation measurements. • Condition for plasticity in Mg in the absence of twinning and fracture identified. • The findings have implications on the design and use of lightweight alloys in transportation and space exploration. [ABSTRACT FROM AUTHOR]

This paper focused on the correlation between the (002) texture, columnar grain size and mechanical properties of Ti films prepared by magnetron sputtering. The (002) texture and columnar grain evolution were controlled under a combination of substrate bias voltage and argon flow rate. It was found that the substrate bias voltage was the key factor to dominate the (002) texture and columnar grain size. At constant substrate bias voltage of −100 V, all of Ti films showed a strong (002) texture. The micropillar compression test indicated that the Ti film with a strong (002) texture and nanocolumnar grain obtained an ultra-strength of 3838.2 MPa and an ultra-high work hardening exponent of 0.64 at substrate bias voltage of −100 V and argon flow rate of 20 sccm. The ultra-strength of Ti film stemmed from the fact that the nano-sized grain inhibited the generation of deformation twin and the (002) texture inhibited the activation of slips, and finally the slips with high Peierls-Nabarro stress were forced to be activated. Moreover, based on the TEM observation, the source of the ultra-strength of Ti film was explained by the proposed strength formula. Texture optimization and nanocolumnar strengthening are effective methods to improving the strength of pure Ti films. These results provided a new perspective of designing ultra-strength of Ti film materials. [ABSTRACT FROM AUTHOR]

This study presents an experimental method for investigating the compressive creep behavior of C-S-H micropillars at micro-scale. The micropillars with two different diameters (5 μm and 0.5 μm) in hardened cement paste (HCP) are fabricated using focused ion beam (FIB) milling and subjected to compression using an indenter with flat-end tip. Multi-stage loading protocols are used to sequentially obtain the elastic modulus, creep behavior, and compressive strength of the individual C-S-H micropillar sample. The sinking effect of C-S-H micropillars during the compression introduces a part of irrelevant deformation to the displacement measured by the indenter. To address this, a numerical procedure is used to quantify the sinking deformation and to determine the true stress-strain relationship of the C-S-H micropillar from the measured indentation force-displacement relationship. The results show that the measured specific creep compliance of all C-S-H micropillars can be well described by power-law functions with an average R2 > 0.99. In contrast, if the specific creep curves are fitted by logarithmic functions, the average R2 is only 0.59. It is indicated that the micropillar creep tests capture the short-term creep of C-S-H. Moreover, micropillar creep tests measure the creep compliance of C-S-H that is one order of magnitude faster than the most macroscopic creep tests. This experimental study emphasizes the impact of imposed stress status on the creep behavior of C-S-H at microscale. [ABSTRACT FROM AUTHOR]

Through compressing polycrystalline NiTi micropillars down to a 40% height reduction by nanoindentation equipment and subsequently manufacturing them by focused ion beam, cuboidal NiTi micropillars with a nanocrystal/nanolaminate heterostructure were obtained. Mechanical behavior and fatigue tests show that the heterostructured NiTi micropillars processed by micro severe plastic deformation (MSPD) have a large recoverable strain (4.5%), small hysteresis (4.3 MPa), and ultrahigh fatigue resistance (> 106 cycles) under a maximum applied stress of 2.5 GPa. These properties were attributed to the extreme grain refinement and homogeneous phase transformation occurring in the nanocrystals. The findings suggest that the MSPD holds great potential for fabricating superior materials for applications in small-scale engineering devices. • Through uniaxial compression of polycrystalline NiTi micropillar using a nanoindenter, the NiTi with a nano heterostructure can be in-situ fabricated. • The plastically deformed NiTi micropillar exhibits a large recoverable strain (4.5%), a small hysteresis (4.3 MPa), and ultrahigh fatigue resistance (> 106 cycles) under a maximum compressive stress of 2.5 GPa. • Micro severe plastic deformation could be potent a manufacturing tool to develop superior materials in small-scale engineering applications. [ABSTRACT FROM AUTHOR]

The 1.55-μm quantum-dot (QD) micropillar cavities are strongly required as single photon sources (SPSs) for silica-fiber-based quantum information processing. Theoretical analysis shows that the adiabatic distributed Bragg reflector (DBR) structure may greatly improve the quality of a micropillar cavity. An InGaAsP/InP micropillar cavity is originally difficult, but it becomes more likely usable with inserted tapered (thickness decreased towards the center) distributed DBRs. Simulation turns out that, incorporating adiabatically tapered DBRs, a Si/SiO2-InP hybrid micropillar cavity, which enables weakly coupling InAs/InP quantum dots (QDs), can even well satisfy strong coupling at a smaller diameter. Certainly, not only the tapered structure, other adiabatic designs, e.g., both DBR layers getting thicker and one thicker one thinner, also improve the quality, reduce the diameter, and degrade the fabrication difficulty of Si/SiO2-InP hybrid micropillar cavities. Furthermore, the problem of the thin epitaxial semiconductor layer can also be greatly resolved by inserting adiabatic InGaAsP/InP DBRs. With tapered DBRs, the InGaAsP/InP-air-aperture micro-pillar cavity serves as an efficient, coherent, and monolithically producible 1.55-μm single-photon source (SPS). The adiabatic design is thus an effective way to obtain prospective candidates for 1.55-μm QD SPSs.

The development of variotherm systems has helped to improve the quality of micro-injection molded products. Thin electric heaters have significant advantages in size, efficiency and installation convenience. However, the use of thin electric heaters has brought the problem of non-uniform temperature distribution of the insert. The good replication of the functional surfaces containing microstructures quickly and uniformly is still a challenge. In this work, the heating performance of the thin electric heater in a variotherm system is investigated by combining numerical simulations with experiments. Micro-injection molding of PP micropillars was also performed. The obtained results show that the addition of a transition layer with high thermal conductivity in the heating structure can optimize the uniformity of the temperature distribution of the insert. Furthermore, the replication heights of the micropillars can be significantly increased by the developed variotherm mold, which provides a new idea for the optimal design of a local variotherm system.

Heat pipes and vapor chambers have been widely utilized for the thermal management of electronic devices due to their effective heat transport, passive cooling operation, and high reliability. In these devices, a wick structure transports a working fluid from the heat sink to the heat source via capillary action in the wick structure. This paper provides a broad overview of the latest studies on the development of Micro-/Nanostructured wicks for passive cooling systems. Micro/nanopillar-based wick structures provide a high capillary pressure, a large permeability, and larger areas for evaporation, resulting in a significantly higher heat removal capability and dryout heat flux. A special emphasis is placed on the various types and geometries of wick structures and their performance. Additionally, limitations and recommendations for future investigations are discussed. [ABSTRACT FROM AUTHOR]

A hybrid manufacturing method consisting of micro-electrical discharge machining and focused ion beam milling to fabricate single-crystal Cu micropillars with a diameter of several tens of microns or more was proposed. The method first utilized micro-electrical discharge machining, which adopted a micro-tool made of WC-Co material, to fabricate the coarse micropillars, one by one. It took approximately 70 s to fabricate each coarse micropillar. Seventy-six coarse micropillars were fabricated in the process of exploring optimum input parameters of supply voltage and capacitance value. Energy dispersive spectroscopy and electron backscatter diffraction analyses revealed that pristine Cu material could be obtained by removing only 1.2 μm of surface layer. The micropillar was finished using a focused ion beam to form a 15 μm diameter smooth micropillar with an aspect ratio of 3. The desired micropillar was produced by removing a surface layer of 6 μm or more from the side surface to avoid the micro-electrical discharge machining effect. It took approximately 2.5 h to complete the fabrication of a micropillar by stepwise annular milling. In the case of the hybrid method, it was possible to fabricate a high-quality micropillar 17 times faster than the focused ion beam only method. [ABSTRACT FROM AUTHOR]

Background: Nanoparticles are being increasingly used in biomedical applications owing to their unique physical and chemical properties and small size. However, their biophysical assessment and evaluation of side-effects remain challenging. We addressed this issue by investigating the effects of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate [MNPs@SiO2(RITC)] on biophysical aspects, such as membrane fluidity and traction force of human embryonic kidney 293 (HEK293) cells. We further extended our understanding on the biophysical effects of nanoparticles on cells using a combination of metabolic profiling and transcriptomic network analysis. Results: Overdose (1.0 μg/µL) treatment with MNPs@SiO2(RITC) induced lipid peroxidation and decreased membrane fluidity in HEK293 cells. In addition, HEK293 cells were morphologically shrunk, and their aspect ratio was significantly decreased. We found that each traction force (measured in micropillar) was increased, thereby increasing the total traction force in MNPs@SiO2(RITC)-treated HEK293 cells. Due to the reduction in membrane fluidity and elevation of traction force, the velocity of cell movement was also significantly decreased. Moreover, intracellular level of adenosine triphosphate (ATP) was also decreased in a dose-dependent manner upon treatment with MNPs@SiO2(RITC). To understand these biophysical changes in cells, we analysed the transcriptome and metabolic profiles and generated a metabotranscriptomics network, which revealed relationships among peroxidation of lipids, focal adhesion, cell movement, and related genes and metabolites. Furthermore, in silico prediction of the network showed increment in the peroxidation of lipids and suppression of focal adhesion and cell movement. Conclusion: Taken together, our results demonstrated that overdose of MNPs@SiO2(RITC) impairs cellular movement, followed by changes in the biophysical properties of cells, thus highlighting the need for biophysical assessment of nanoparticle-induced side-effects. [ABSTRACT FROM AUTHOR]