Pillar Shape Research Articles

Sharp-edged geometric obstacles in microfluidics promote deformability-based sorting of cells

Sorting cells based on their intrinsic properties is a highly desirable objective, since changes in cell deformability are often associated with various stress conditions and diseases. Deterministic lateral displacement (DLD) devices offer high precision for rigid spherical particles, while their success in sorting deformable particles remains limited due to the complexity of cell traversal in DLDs. We employ mesoscopic hydrodynamics simulations and demonstrate prominent advantages of sharp-edged DLD obstacles for probing deformability properties of red blood cells (RBCs). By consecutive sharpening of the pillar shape from circular to diamond to triangular geometry, a pronounced cell bending around an edge is achieved, serving as a deformability sensor. Bending around the edge is the primary mechanism, which governs the traversal of RBCs through such DLD device. This strategy requires an appropriate degree of cell bending by fluid stresses, which can be controlled by the flow rate, and exhibits good sensitivity to moderate changes in cell deformability. We expect that similar mechanisms should be applicable for the development of novel DLD devices that target intrinsic properties of many other cells.

Room temperature surface emission on large-area photonic crystal quantum cascade lasers

We design and fabricate large-area (1.1 mm × 1.1 mm) photonic crystal quantum cascade lasers, enabling single-mode (wavelength ∼ 8.5 µm) surface emission at room temperature, with a maximum peak power up to 176 mW. The beam divergence is <1∘ and with no side-lobes. Moreover, by introducing asymmetry into the photonic crystal pillar shape, a single-lobed far-field pattern is realized. The photonic band structure is measured with high spectral (0.72 cm−1) and angular (0.1°) resolution by using the photonic crystal quantum cascade laser itself as a detector.

Quantifying the Resistance to Dislocation Glide in Single Phase FeCrAl Alloy

The resistance to dislocation glide associated with slip systems {110} and {112} in single phase FeCrAl alloy is measured via micromechanical testing in a scanning electronic microscopy at room temperature. Two important factors, the shape and orientation of a pillar, are discussed with respect to the glide resistance and stress-strain response. Maximizing Schmid factor of one specific slip system while minimizing others is recommended in order to diminish obvious dislocations-induced hardening during in situ testing. Apparent Schmid factor analysis is conducted to select grains with preferred orientations. Two types of pillars with conventional cylindrical shape or dog-bone shape are tested under compression to estimate the resistance to dislocation glide and evaluate the effect of pillar shape on the compression stress-strain response. One dog-bone pillar is tested under tension to check the tension-compression isotropy. We find that the shape of a pillar to a smaller extent affects the measured resistance but strongly influences the stress strain response. Cylindrical pillars exhibit apparent hardening associated with early yielding due to stress or strain concentration at contact region, while dog-bone pillars show an obvious yielding and continuous shearing without hardening. The resistance is 220 MPa for slip system {110} and 230 MPa for slip system {112} . Finite element analysis is performed to account for the influence of pillar shape and contact condition on mechanical response. Furthermore, slip transmission across two high-angle grain boundaries is experimentally investigated and discussed with respect to the misorientation and the continuity of slips across GBs.

Tunable Adhesion of a Bio-Inspired Micropillar Arrayed Surface Actuated by a Magnetic Field

Bio-inspired functional surfaces attract many research interests due to the promising applications. In this paper, tunable adhesion of a bio-inspired micropillar arrayed surface actuated by a magnetic field is investigated theoretically in order to disclose the mechanical mechanism of changeable adhesion and the influencing factors. Each polydimethylsiloxane (PDMS) micropillar reinforced by uniformly distributed magnetic particles is assumed to be a cantilever beam. The beam's large elastic deformation is obtained under an externally magnetic field. Specially, the rotation angle of the pillar's end is predicted, which shows an essential effect on the changeable adhesion of the micropillar arrayed surface. The larger the strength of the applied magnetic field, the larger the rotation angle of the pillar's end will be, yielding a decreasing adhesion force of the micropillar arrayed surface. The difference of adhesion force tuned by the applied magnetic field can be a few orders of magnitude, which leads to controllable adhesion of such a micropillar arrayed surface. Influences of each pillar's cross section shape, size, intervals between neighboring pillars, and the distribution pattern on the adhesion force are further analyzed. The theoretical predictions are qualitatively well consistent with the experimental measurements. The present theoretical results should be helpful not only for the understanding of mechanical mechanism of tunable adhesion of micropillar arrayed surface under a magnetic field but also for further precise and optimal design of such an adhesion-controllable bio-inspired surface in future practical applications.

Pillar[n]arenes for Construction of Artificial Transmembrane Channels

AbstractPillar[n]arenes have been intensively used during the last decade in supramolecular chemistry as host systems for guest recognition and self‐assembly, toward functional materials and devices. They present electron‐rich and tuneable size cavities, as well as reactive rims for further functionalization. Their unique pillar shape promotes pillar[n]arenes as molecular analogues of carbon nanotubes. For this reasons pillar[n]arenes have been embedded into membranes and used to construct artificial water, proton, ions and molecular channels. This review discusses the incipient developments of the first artificial channels based on pillar[n]arenes. We include also systems that integrate pillar[n]arenes as synthetic elements for the construction of selective pores of nanodevices for ion rectification.

MobilityAnalyser: A novel approach for automatic quantification of cell mobility on periodic patterned substrates using brightfield microscopy images

Background and objectiveSurface topography of biomaterials has been shown to have an effect on cells behaviour. Cell-material interactions can be visually characterized by assessing both cell shape and spreading at initial time-points and, its migration patterns, as a response to the underlying topography. Whilst many have reported the study of cell migration and shape with fluorescence labelling, the focus on evaluating cells response to surface topography is to observe, under real-time conditions, interactions between cells and surfaces. In this manuscript we present a novel approach to automatically detect and remove periodic background patterns in brightfield microscopy images in order to perform automatic cell mobility analysis. MethodsThe developed software, MobilityAnalyser, performs automatic tracking of unmarked cells and allows the user to manually correct any incorrectly detected or tracked cell. Human Mesenchymal Stem Cells (hMSCs) trajectory, migration distance, velocity and persistence were evaluated over line and pillar micropatterned SiO2 films and on a flat SiO2 control substrate. ResultsThe developed software proved to be effective in automatically removing background patterns of both line and pillar shapes and in performing cell detection and tracking. MobilityAnalyser accurately measured cell mobility in a fraction of the time required for manual analysis and eliminated user subjectivity.The results obtained with the software confirmed how different topographies affect cell trajectory, migration pathways and velocities, with a statistically significant increase for micropatterned surfaces, when compared with the flat control. The persistence parameter also proved the influence of both patterns on the directionality of cell movement. ConclusionsMobilityAnalyser is an automatic tool that removes periodic background patterns, detects and tracks cells, and provides cell mobility parameters that characterize the response of cells to different surface topographies. The software is freely available at: https://drive.google.com/open?id=1Fbb321ogLD19SlRjceMETNUqDHgpeBPl.

Effects of geometry and dimension of micro/nano-structures on the heat transfer in dropwise condensation: A theoretical study

Condensation is a phase change phenomenon which has many applications in the field of refrigeration, power plants and air-conditioning. It is well-known that dropwise condensation (DWC) has a considerably higher heat transfer than filmwise condensation. DWC occurs on hydrophobic and superhydrophobic surfaces (SHS). Research has shown that micro/nano structures are necessary for producing SHS. The geometry and dimensions of the structures could affect DWC heat transfer. In this research, a numerical study has been done to explore how much the configuration of these structures could change heat transfer in DWC. To attain this goal, two different structures, including semi-conical and semi-pyramidal and their limit states including prismatic and cylindrical structures have been considered. Effects of different parameters including the shape of the structures, roughness factor, and solid fraction on the single droplet and total heat transfer have been studied. Results show that the configuration of structures could significantly affect DWC heat transfer. For instance, at a constant roughness factor and solid fraction, semi-conical or pyramidal pillars have about 2.5–4.5 times higher total heat transfer than prismatic or cylindrical pillars. The shape of pillars could change the small droplet population by about 10%.

Characterization of Hair Cell-Like Cells Converted From Supporting Cells After Notch Inhibition in Cultures of the Organ of Corti From Neonatal Gerbils.

The senses of hearing and balance depend upon hair cells, the sensory receptors of the inner ear. Hair cells transduce mechanical stimuli into electrical activity. Loss of hair cells as a result of aging or exposure to noise and ototoxic drugs is the major cause of noncongenital hearing and balance deficits. In the ear of non-mammals, lost hair cells can spontaneously be replaced by production of new hair cells from conversion of supporting cells. Although supporting cells in adult mammals have lost that capability, neonatal supporting cells are able to convert to hair cells after inhibition of Notch signaling. We questioned whether Notch inhibition is sufficient to convert supporting cells to functional hair cells using electrophysiology and electron microscopy. We showed that pharmacological inhibition of the canonical Notch pathway in the cultured organ of Corti prepared from neonatal gerbils induced stereocilia formation in supporting cells (defined as hair cell-like cells or HCLCs) and supernumerary stereocilia in hair cells. The newly emerged stereocilia bundles of HCLCs were functional, i.e., able to respond to mechanical stimulation with mechanotransduction (MET) current. Transmission electron microscopy (TEM) showed that HCLCs converted from pillar cells maintained the pillar cell shape and that subsurface cisternae, normally observed underneath the cytoskeleton in outer hair cells (OHCs), was not present in Deiters’ cells-derived HCLCs. Voltage-clamp recordings showed that whole-cell currents from Deiters’ cells-derived HCLCs retained the same kinetics and magnitude seen in normal Deiters’ cells and that nonlinear capacitance (NLC), an electrical hallmark of OHC electromotility, was not detected from any HCLCs measured. Taken together, these results suggest that while Notch inhibition is sufficient for promoting stereocilia bundle formation, it is insufficient to convert neonatal supporting cells to mature hair cells. The fact that Notch inhibition led to stereocilia formation in supporting cells and supernumerary stereocilia in existing hair cells appears to suggest that Notch signaling may regulate stereocilia formation and stability during development.

Breeding and Characteristics of New Ornamental Peach Cultivars, ‘Hakurakuten’ and ‘Maihiten’, with Pillar Type Tree Shape and Chrysanthemum-like Flowers

Breeding and Characteristics of New Ornamental Peach Cultivars, ‘Hakurakuten’ and ‘Maihiten’, with Pillar Type Tree Shape and Chrysanthemum-like Flowers

Micro-engineered "pillar forests" to study cell migration in complex but controlled 3D environments.

Cells migrating in multicellular organisms steadily traverse complex three-dimensional (3D) environments. To decipher the underlying cell biology, current experimental setups either use simplified 2D, tissue-mimetic 3D (e.g., collagen matrices) or in vivo environments. While only in vivo experiments are truly physiological, they do not allow for precise manipulation of environmental parameters. 2D in vitro experiments do allow mechanical and chemical manipulations, but increasing evidence demonstrates substantial differences of migratory mechanisms in 2D and 3D. Here, we describe simple, robust, and versatile "pillar forests" to investigate cell migration in complex but fully controllable 3D environments. Pillar forests are polydimethylsiloxane-based setups, in which two closely adjacent surfaces are interconnected by arrays of micrometer-sized pillars. Changing the pillar shape, size, height and the inter-pillar distance precisely manipulates microenvironmental parameters (e.g., pore sizes, micro-geometry, micro-topology), while being easily combined with chemotactic cues, surface coatings, diverse cell types and advanced imaging techniques. Thus, pillar forests combine the advantages of 2D cell migration assays with the precise definition of 3D environmental parameters.

The possibility of increasing the efficiency of accessible coal deposits by optimizing dimensions of protective pillars or the scope of exploitation

One of the ways to protect objects exposed to the influences of mining exploitation is establishing protective pillars for them. Properly determined pillar provides effective protection of the object for which it was established. Determining correct dimensions of a pillar requires taking into account contradictory requirements. Protection measures against the excessive influences of mining exploitation require designing the largest possible pillars, whereas economic requirements suggest a maximum reduction of the size of resources left in the pillar. This paper presents algorithms and programs developed for determining optimal dimensions of protective pillars for surface objects and shafts. The issue of designing a protective pillar was treated as a nonlinear programming task. The objective function are the resources left in a pillar while nonlinear limitations are the deformation values evoked by the mining exploitation. Resources in the pillar may be weighted e.g. by calorific value or by the inverse of output costs. The possibility of designing pillars of any polygon shape was taken into account. Because of the applied exploitation technologies the rectangular pillar shape should be considered more advantageous than the oval one, though it does not ensure the minimization of resources left in a pillar. In this article there is also presented a different approach to the design of protective pillars, which instead of fixing the pillar boundaries in subsequent seams, the length of longwall panels of the designed mining exploitation is limited in a way that ensures the effective protection of an object while maximizing the extraction ratio of the deposit.

Open-tubular capillary electrochromatography using carboxylatopillar[5]arene as stationary phase.

Pillar[n]arenes have achieved much interest in material chemistry and supramolecular chemistry due to unusual pillar shape structure and high selectivity toward guest. However, pillar[n]arenes have not yet been applied in capillary electrochromatography. This work at first time reports that carboxylatopillar[5]arene is used as a stationary phase in open-tubular capillary electrochromatography. Carboxylatopillar[5]arene not only possess the advantages of pillar[n]arenes but also provide free carboxy groups for immobilizing on the inner wall of capillary column via covalent bonding. The characterization of SEM and FT-IR indicated that carboxylatopillar[5]arene was successfully grafted on the inner wall of capillary. The baseline separation of model analytes including neutral, basic, and acidic compounds, nonsteroidal anti-inflammatory drugs and dansyl-amino acids have been achieved thanks to the electron-rich cavity of carboxylatopillar[5]arene and hydrophobic interactions between the analytes and stationary phase. The intraday, interday, and column-to-column precisions (RSDs) of retention time and peak area for the neutral analytes were all less than 3.34 and 9.65%, respectively. This work indicates that pillar[n]arenes have great potential in capillary electrochromatography as novel stationary phase.

Studi karakteristik gerusan lokal pada beberapa tipe pilar jembatan

The local scouringcharacteristicsuroundings several bridge pillars forms have a different characteristics, some forms of pillars of the bridge are considered optimum when equipped with the data: discharge, slope of riverbed, material, and on the same flow direction, that will produce the most shallow scouring. The objective of this study is to find the form of pillars that will generate the most superficial scouring. The study is conducted at the Laboratory of River in Surakarta. The used flume has length of 10.00 m, width 0.40 m and height of 0.40 m. The forms of pillar studied are two cylindrical pillars, sheet pile and full walls pillar. The slope of the riverbed (i) are varied, there are three: 0.006, 0.0125 and 0.020. The flow discharge rate there are five variations: 5,37 m3/s, 8,94 m3/s, 12,52 m3/s, 14,31 m3/s, 17,89 m3/s. Land was used at material for river bed, and, there are three kinds of value D50: 0.60 mm, 0.80 mm and 1.00 mm. The research method includes: a field survey, two dimension physical model test with 1:20 scale.The results showed for each pillar shapes have different characters. The deepest scouring suroundings the pillar beside the point, at the beginning of the first minute to the 20th minute in a sudden deep scour the riverbed and form of river bed suroundings are the pillars up and down irregularly. In the 20th minute until the end of the stream scouring decreased almost linearly lines are horizontzl. In general the pile type pillars was found to cause the minimum scouring than other pillar shapes.

3D-printed cellular structures for bone biomimetic implants

The use of porous cellular structures in bone tissue engineering can provide mechanical and biological environments closer to the host bone. However, poor internal architectural designs may lead to catastrophic failure. In this work, 192 open-porous cellular structures were fabricated using 3D printing (3DP) techniques. The mechanical and biological behavior of four 3D internal structures (octahedral, pillar octahedral, cubic and truncated octahedral) was investigated. It was found that the pillar octahedral shape has not only greater stiffness and strength under compression, shear and torsion but increased rate of pre-osteoblastic cell proliferation. We believe bone implants can be fabricated using 3DP techniques and their mechanical and biological performance can be tailored by modifying the internal architectures.

Mask-assisted electrospray for superoleophobic surfaces: An experimental and numerical study

This paper presents both experimental work and numerical simulations of formation of superoleophobic surfaces created by mask-assisted electrospraying, followed by a second layer overlay and fluoropolymer treatment. The primary electric field focusing in the mask-assisted electrospray effectively guides the electrosprayed particulates into the mesh openings, forming characteristic pyramid-shaped pillars. The secondary focusing occurs during the overlay deposition when the electrosprayed particulates favorably deposit onto the pre-patterned pillars. Systematic studies were conducted on the effects of mask-substrate-gap and duration of the overlay deposition on the pattern morphology and wetting performance. A shorter mask-substrate-gap results in a stronger focusing effect and pillars with a larger aspect ratio. The overlay deposition firstly increases the pillar height and then changes the pillar shape from pyramids to domes with overhangs due to electrostatic interactions. All the surfaces are superhydrophobic, however, superoleophobicity varies. Surfaces that have tall pillars and overhang structures demonstrate robust superoleophobicity when compared to their counterparts with shorter pillars and absence of overhang structures. The primary and secondary electric field focusing effects exerted by the mask and the pre-patterned pillars, and their roles in pattern formation have been numerically investigated by COMSOL Multiphysics simulation. A reasonable agreement has been obtained between the numerical predictions and experimental results.

Quad Pillars and Delta Pillars: Algorithms for Converting Dexel Models to Polyhedral Models

In the geometric simulation of multi-axis milling, a dexel representation solid model is frequently used. In this modeling method, the object shape is defined as a collection of vertical segments (dexels) based on a two-dimensional regular square grid in the XY plane. In this paper, the authors propose the quad pillars algorithm and its enhanced version named the delta pillars algorithm for converting a dexel model to an equivalent polyhedral stereolithography (STL) model. These algorithms define a series of vertical pillar shapes for each square cell of the grid to represent the object shape as a bundle of pillars. The final polyhedral model is obtained by performing a simplified Boolean union operation of the pillar shapes. Unlike prior methods, the proposed algorithms are simple and fast and are guaranteed to generate a watertight polyhedral model without holes, gaps, or T-junctions. An experimental system is implemented and conversion tests are performed. The system converted a dexel model based on a high-resolution grid to a polyhedral model in a practical amount of time.

Characterization of Micromegas with elongated pillars

We present a resistive Micromegas detector built with two different pillar shapes. The pillars are elongated and extend in the direction orthogonal to the readout strips. One region features pillars of 2 mm × 0.2 mm with 4.8 mm pitch while in the other region the pillars extend over the full width of the detector. The larger surface of the pillars allows for a better adhesion to the readout structure and a more uniform amplification gap. Results on the detector performance for the two regions are presented. No striking performance differences between the two regions were found.

Effect of Bonding Time and Bonding Temperature on Lead-Free Solder Joints Dispersed Pillar Shaped IMCs

The effects of the bonding time and temperature on microstructures and the joint strength of solder joints dispersed pillar shaped intermetallic compounds (IMCs) with Sn-3.0Ag-0.5Cu (mass%, SAC) and Sn-3.0Ag-0.7Cu-5.0In (mass%, SACI) alloys were investigated. The effects of the electrode type and the joint height on them were also investigated. In the Cu/Cu joint with SAC, the length of the pillar shaped IMC increased with increasing the bonding time although the effect of the bonding temperature on it was negligible. The thick joint height was effective to form pillar shaped IMCs in the joint. In the Cu/Ni joint with SAC, thin pillar shaped IMCs formed in the joint. In the joints with SACI, the high bonding temperature was effective to generate a large quantity of pillar shaped IMCs regardless of the electrode type. The small amount of In addition is effective to increase the nucleation site of the primary IMC and the thick joint height is effective to form finer pillar shaped IMCs in the joint. The die shear force measurement revealed that the pillar shape IMC such as to connect both sides is effective to improve the joint strength.

Geometry-dependent compressive responses in nanoimprinted submicron-structured shape memory polyurethane.

High resolution surface textures, when rationally designed, provide an attractive surface engineering approach to enhance surface functionalities. Designing smart surfaces by coupling surface texture with shape memory polymers has garnered attention in achieving tunable mechanical properties. We investigate the structure-mechanical property relationships for programmable, shape-memorizing submicron-scale pillar arrays subjected to flat-punch compression. The geometrically-dependent deformation of structured surfaces with two different aspect ratios (250 nm-pillars 1 : 1 and 550 nm-pillars 2.4 : 1) were investigated, and their moduli were found to be lower than that of non-patterned surface. From finite element analysis, the pillar deformation is correlated to a mechanistic transition from a discrete, unidirectional compression of 250 nm-pillars to lateral constraints caused by interpillar contact in 550 nm-pillars. This lateral pillar-pillar contact in the 550 nm-pillars resulted in an increased and maximum strain-dependent modulus but lower elastic recovery and energy dissipation as compared with the 250 nm-pillars. Furthermore, the compressive responses of temporarily shaped pillars (programmed by stretching) were compared with the permanently shaped pillars. The extent of lateral constraints controlled by pillar shape and spacing in 550 nm-pillars was responsible for the modulus differences between the original and stretched patterns, whereas the modulus of 250 nm-pillars remained as a constant value with different levels of stretching. This study provides mechanistic insights into how the mechanical behavior can be modulated by designing the aspect ratio of shape memory pillar arrays and by programming the surface geometry, thus revealing the potential of developing ingenious designs of responsive surfaces sensitive to mechanical deformation.

Investigation of the binding modes of a positively charged pillar[5]arene: internal and external guest complexation.

The selective binding behavior of a trimethylammonium-derived pillar[5]arene towards different guests in aqueous media and under neutral conditions is reported. Although it is known that this macrocycle has the capability to form complexes with guests, we anticipate that the intrinsic pillar shape of the macrocycle with two positively charged rims should allow a diversity of binding modes. The three guests were selected based on their charge and size. The inclusion binding modes and the affinity of the macrocycle to form host-guest complexes were determined by ITC and NMR techniques. We reveal the ability of a cationic water soluble pillar[5]arene to effectively complex two guest molecules, one in each rim, evidencing the diversity of binding modes. Two different structures for 1 : 1 and three for 1 : 2 complexes are reported showing the pillararene ability for internal/external binding.