Microdot Arrays Research Articles

Preparation and Characterization of the Chitosan Micropatterns

Micro-transfer molding was used to prepare four different chitosan(CS) micropatterns on silicon substrates: cylinder,square,groove and sine wave.The as-prepared CS micropatterns were well-formed.Osteoblasts were cultured on various micropatterns to evaluate the effects of micro-geometry on cell behavior.On micro-cylinders and micro-squares,osteoblasts attached on CS micro-dot arrays and displayed irregular morphologies with numerous filopodia-like extensions.These micro-dot arrays had no impact on cell proliferation and differentiation.On micro-grooves and sine wave micropatterns,cells located within the channels and aligned to the direction of channels.Micro-grooves and sine wave micropatterns were unfavorable to cell differentiation,whereas promoted cell proliferation.

G0102 疎水処理を施した陽極酸化基板におけるマイクロドット型感圧センサの形成(GS1 液滴・蒸発)

G0102 疎水処理を施した陽極酸化基板におけるマイクロドット型感圧センサの形成(GS1 液滴・蒸発)

Self-organised microdots formed by dewetting in a highly volatile liquid

Dewetting induced self-organisation was used to prepare an ordered microstructure from a highly volatile liquid. Dewetting of an evaporating iron oxide precursor solute on silicon substrate resulted in arrays of microdots with nearly hexagonal and tetragonal symmetries. Ordered structures form either by stick–slip motion or fingering instability at the receding contact line of evaporating droplets. Subsequent thermal treatment at 550°C yields crystalline Fe2O3 microdots with a diameter range of 1–4μm. The size, density and shape of the microdots can be changed by using patterned substrates with different surface energies.

Gas-Assisted Mold Temperature Control for Double-Sided Heating and Micro-Structures Molding

In this study, a gas-assisted heating system for mold surface temperature control was established. Two gap size control modes (A and B) of the gas channel and the heating results of both cavity and core sides were investigated, moreover, the effective heating area for gas heating expansion angle were determined as well by using gas flow rate 300 l/min. The results show that the mold temperature difference on the gas inlet of core and cavity surface can be reduced from 39.8 oC with A mode to 1.4 oC with B mode under the gap size of 5mm. For the hot gas heating expansion angle, it directly affected heating area, and being relative with the entrance of gas channel. A case study of micro-molding for double sides 0.4mm thin wall plat with micro-dot arrays shows that replication accuracies reach higher than 90% when molding at a mold temperature of 150 oC, an improvement of 25.3% over injection molding at the regular mold temperature of 90 oC.

ToF-SIMS analysis of chemical heterogenities in inkjet micro-array printed drug/polymer formulations

Three different formulations comprising two drugs, felodipine and hydrochlorothiazide (HCT) and two polymers, poly(vinyl pyrolidone) (PVP) and poly(lactic-co-glycolic acid) (PLGA) were inkjet printed as micro-dot arrays and analysed on an individual micro-spot basis by time-of-flight secondary ion mass spectrometry (ToF-SIMS). For the HCT/PLGA formulation, the spots showed heterogeneity of the drug and other chemical constituents. To further investigate these heterogeneities, multivariate curve resolution was applied to the ToF-SIMS hyperspectral image datasets. This approach successfully identified distinct chemical components elucidating the HCT, PLGA, substrate material, and contaminants based on sulphur, phosphorous and sodium chloride. Spots printed using either of the drugs with PVP exhibited full substrate coverage and a uniform distribution of the active ingredient along with all other constituents within the printed spot area. This represents the preferred situation in terms of stability and controlling the release of a drug from a polymer matrix.

Dermal fibroblast behaviour on micropatterned substrates with different pattern geometries

A major objective of scaffold fabrication for tissue-engineering applications in wound healing is to understand the relationship between scaffold topography and cell behaviour. Recently, researchers have focused on arrays of cell adhesion protein styled in linear-grid micropatterns; however, these linear-grid patterns hardly reflect the topographical features of a natural extracellular matrix (ECM). In order to clarify the relationship between substrate adhesion points and cell behaviour, changes of dermal fibroblasts cultured on triangular microdot arrays were investigated. Micropatterns were micro-printed by silicone substrate stamps with collagen, while regions outside of the microdots were functionalized to block cellular adhesion. Cell morphology, expression of α-SMA, cell viability and hydroxyproline levels were examined for dermal fibroblasts cultured on the microdot substrates and on non-patterned control substrates. On patterned substrates, the expression of α-SMA significantly decreased, cell vitality increased and hydroxyproline content decreased with increasing vertex angles of the triangular array. Significantly more hydroxyproline was observed in all experimental groups in comparison to the control group. The results indicate that small vertex angles of the triangular array were detrimental to cell survival, likely due to constraint of the cell to a small adhesion area. We hypothesize that cells actively adapt to this situation by attempting to remodel their microenvironments with secretion of hydroxyproline. This illustrates the existence of feedback between cells and their microenvironments, such that when surroundings are unfavourably altered, the cells attempt to reconstruct the environment with secretion of ECM.

Standing-wave excited soft x-ray photoemission microscopy: Application to Co microdot magnetic arrays

We demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM), with application to a square array of circular magnetic Co microdots. The method is based on excitation with soft x-ray standing-waves generated by Bragg reflection from a multilayer mirror substrate. Standing wave is moved vertically through sample simply by varying the photon energy around the Bragg condition. Depth-resolved PEEM images were obtained for all of the observed elements. Photoemission intensities as functions of photon energy were compared to x-ray optical calculations in order to quantitatively derive the depth-resolved film structure of the sample.

Reading microdots of a molecularly imprinted polymer by surface-enhanced Raman spectroscopy

Writing a molecularly imprinted polymer (MIP) by nano-fountain pen on surface-enhanced Raman scattering (SERS)-active surfaces resulted in site-controlled arrays of microdots of approximately 6–12 μm in diameter. The monitoring of SERS spectra with a micro-Raman system enabled examining the uptake and release of the S-propranolol imprinting template and allowed imaging individual dots as well as multiple dots in an array, revealing the distribution of the imprinted polymer. This distribution was confirmed by atomic force microscopy, showing that even in dots of <300 nm thickness, corresponding to MIP volumes of 0.5 fl, significantly less than previously reported, the target analyte could be detected and identified. This study shows that nanolithography techniques combined with SERS might open the possibility of miniaturized arrayed MIP sensors with label-free, specific and quantitative detection.

Inkjet-Printing-Engineered Functional Microdot Arrays Made of Mesoporous Hybrid Organosilicas

The fabrication of three-dimensional fine-scale microdot arrays of organized mesoporous hybrid organosilicas by the coupling of inkjet printing (IJP) and Pluronic F127 driven evaporation-induced self-assembly (EISA) in the presence of cocondensed silica and organosilica precursors is demonstrated. The mesoorganization can be optimized by tuning both processing and chemical parameters (the drying time between successive layers, droplet volume, chemical composition, temperature, and aging time of the colloidal sol). The feasibility of one-pot multifunctionalization with both TFTS CF3(CF2)5CH2CH2Si(OC2H5)3 and thiol functionalities HSCH2CH2CH2Si(OC2H5)3 is also demonstrated, emphasizing the wide range of accessible nanostructured porous hybrid materials that result from the coupling of IJP and EISA. From this demonstrative concept, many hybrid materials with applications in the field of multiarray sensors and smart membranes can be expected. Moreover, the peculiar role of the hydrophobic organosilane TFTS CF...

Behavior of dermal fibroblasts on microdot arrays yields insight into wound healing mechanisms

The behavior of fibroblasts on patterned substrates was examined in order to elucidate the role of dermal structure in wound healing. Dermal fibroblasts were cultured on micro-patterned silicone elastomer substrates designed to enforce cell adhesion only to fibronectin microdots. The morphology, expression of α-smooth muscle actin (α-SMA), proliferation, apoptotic cells, and soluble collagen production of cells were measured. Cells grown on patterned substrates showed some signs of a scar-fibroblast phenotype such as: elongated pseudopodia, enhanced expression of alpha smooth muscle actin (α-SMA), and increased collagen/pre-collagen, in comparison to unpatterned controls. Cells also showed low proliferation rates and high apoptotic index. The results showed that the microdot arrays, acting as a grid of limited focal adhesion sites, could force cells to adopt constrained morphologies and limited adhesion areas, which affect the cytoskeleton, ultimately leading to expression of a scar-tissue fibroblast phenotype. This study provides insight into the regulatory mechanisms of micro-topology on cell behavior in wound healing.

Fabrication of Hierarchical Pillar Arrays from Thermoplastic and Photosensitive SU‐8

By exploiting the thermoplastic and photosensitive nature of SU-8 photoresists, different types of hierarchical pillar arrays with variable aspect ratios are fabricated through capillary force lithography (CFL), followed by photopatterning. The thermoplastic nature of SU-8 enables the imprinting of micropillar arrays with variable aspect ratios by CFL using a single poly(dimethylsiloxane) mold, simply by tuning the initial film thickness of SU-8 on a substrate. The pillar array is subsequently photopatterned through a photomask, followed by post-exposure baking above the glass transition temperature (T(g)) of SU-8. The pillars in the exposed region become highly crosslinked and, therefore, neither soluble nor able to reflow above T(g), whereas the pillars in the unexposed regions can reflow and flatten out. Two developing strategies are investigated after UV exposure of the SU-8 pillar arrays including i) solvent development and drying and ii) thermal reflow to create bilevel hierarchical structures with short pillars and single-level, dual-scaled, high-aspect-ratio (up to 7.7) pillars in a microdot array, respectively.

Spontaneous Formation of Microwrinkles on Metal Microdot Arrays by Shrinkage of Thermal Shrinkable Substrate

Honeycomb-patterned polymer films prepared by the simple casting of a polymer solution under humid conditions were used as templates for metal microdot arrays formed on shrinkable polymer substrates by metal sputtering. After thermal shrinkage of the substrate, the periodicity of the metal microdots was reduced. In addition, microwrinkles were formed on the metal microdots. The wavelength and arrangement of the microwrinkles were changed with the metal sputtering time and the diameter of the metal microdots. A clear confinement effect was observed in the formation of the microwrinkles.

Nano- and microdot array formation by laser-induced dot transfer

Fabrication of FeSi 2 nano- and microdot array was performed by utilizing droplet ejection through laser-induced forward transfer, which we named laser-induced dot transfer (LIDT). An amorphous FeSi 2 alloy source film on a transparent support was illuminated from the support by a nanosecond excimer laser pulse patterned into migcrogrid form, resulting in size- and site-controlled dot deposition. Micro-Raman spectroscopy confirmed β-FeSi 2 semiconducting crystalline phase even on unheated substrates. Moreover, the microdots exhibited near-infrared photoluminescence at the peak wavelength of 1.57 μm, which comes from the β-FeSi 2 crystalline phase precipitated during the LIDT process. The dot size was successfully reduced to approximately 500 and 300 nm in diameter and height, respectively. This technique is useful for integrating functional nano- and microdots under atmospheric room-temperature conditions.

Micro‐fabrication and monitoring of three‐dimensional microstructures based on laser‐induced thermoplastic formation

This article reports a novel laser-induced micro-fabrication method and its monitoring system for three-dimensional (3D) microstructures. The mechanism of the method is that a small zone of thermoplastic material melted by laser heating grows in liquid surrounding environment, solidifying into a convex microstructure, such as micro-dot or micro-pillar. A laser diode (808 nm) with maximum power output of 130 mW is used as power source, and a kind of paraffin mixed with stearic acid and paint serves as the thermoplastic material for 3D microstructure formation experiments. A light microscope system consisting of a charge-coupled device (CCD) and a computer is utilized to realize real-time observation of the micro-fabricating process. The distribution of local temperature rise on material surface created by laser irradiation is simulated. The effects of liquid environment on microstructure formation have been theoretically analyzed and experimentally studied. Experiments are further carried out to investigate the relationship between laser spot and fabricated microstructures. The results indicate that the widths of micro-dots or micro-pillars are mostly determined by the size of focal spot, and their heights increase with the enlargement of laser power density. With this method, a micro-dot array of Chinese characters meaning "China" has been successfully fabricated through computer programming. This method has the advantages of implementing direct, mask-less, real-time and inexpensive 3D microstructure fabrication. Therefore, it would be widely applied in the fields of micro/nano-technology for practical fabrication of different kinds of 3D microstructures.

Dewetting of the Thin Liquid Bilayers on Topographically Patterned Substrates: Formation of Microchannel and Microdot Arrays

A long-wave nonlinear analysis of the defect induced instabilities engendered by van der Waals forces in thin (<100 nm) viscous bilayers is presented. The major focus of this study is on generation of periodic patterns and its miniaturization by exploiting the self-organized instabilities of thin bilayers on topographically patterned substrates. A large variety of self-organized interfacial patterns such as periodic arrays of open and closed micro/nanochannels, isolated and encapsulated micro/nanodroplets, and membranes with ordered pores are obtained on different types of prepatterned substrates. In addition, we show that a bilayer can also be a suitable tool for (i) pattern transfer involving replication of the morphology of the lower layer interface to the free surface of the upper layer and (ii) generation of a mold by the upper layer material filling the periodic interstitial spaces formed by dewetting of the lower layer. Simulations suggest a profound influence of the substrate pattern directed lateral confinement, which governs the length scale of the dewetted structure when the substrate pattern periodicity is well below the spinodal length scale of the unstable bilayer. The influence of the initial configuration of the interfaces on the dewetting pathway and the dewetted structures are also shown.

Probing Arrays of Circular Magnetic Microdots by Ferromagnetic Resonance

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field H(r) was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patterned magnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Preparation of Metal Microdots and Microdiscs by Using Honeycomb Template Prepared by Self‐organization

AbstractHoneycomb‐patterned films were prepared by using orderly arranged water droplets as templates. By using the honeycomb‐patterned films as templates, Pt/Pd metal microdot arrays were formed on solid substrates. Silver layer was formed on the Pt/Pd layer by electroless deposition, and then, the microdiscs of Ag were obtained by removing the substrate.

Fabrication of micro-dot arrays and micro-walls of acrylic acid/melamine resin on aluminum by AFM probe processing and electrophoretic coating

Micro-dot arrays and micro-walls of acrylic acid/melamine resin were fabricated on aluminum by anodizing, atomic force microscope (AFM) probe processing, and electrophoretic deposition. Barrier type anodic oxide films of 15 nm thickness were formed on aluminum and then the specimen was scratched with an AFM probe in a solution containing acrylic acid/melamine resin nano-particles to remove the anodic oxide film locally. After scratching, the specimen was anodically polarized to deposit acrylic acid/melamine resin electrophoretically at the film-removed area. The resin deposited on the specimen was finally cured by heating. It was found that scratching with the AFM probe on open circuit leads to the contamination of the probe with resin, due to positive shifts in the potential during scratching. Scratching of the specimen under potentiostatic conditions at −1.0 V, however, resulted in successful resin deposition at the film-removed area without probe contamination. The rate of resin deposition increased as the specimen potential becomes more positive during electrophoretic deposition. Arrays of resin dots with a few to several tens μm diameter and 100–1000 nm height, and resin walls with 100–1000 nm height and 1 μm width were obtained on specimens by successive anodizing, probe processing, and electrophoretic deposition.

Color Surface Plasmon Resonance Imaging of Protein Microdot Arrays

Abstract A novel method for readout of protein microdot arrays was presented by using a laboratory-built color SPR imaging system which used multiwavelength light as an excitation source and color CCD as an image detector. True color images were directly recorded from IgG microdot arrays. At the incident angles of 44–47°, the colors complementary to the resonance absorption were recorded, depending on the concentration of IgG between 0.05 and 1.00 mg/mL, which indicates that the color signals contain both qualitative and quantitative information.

Direct Patterning of Molecularly Imprinted Microdot Arrays for Sensors and Biochips

We have used fountain pen microlithography to deposit arrays of molecularly imprinted polymer microdots on flat substrates. We visualize analyte binding to the dots by fluorescence microscopy with the aid of fluorescein as a model analyte. Elution and readsorption of the analyte to the MIP dots were possible if the porosity of the dots was improved by a sacrificial polymeric porogen. The imprinting effect was confirmed by using compounds structurally related to fluorescein. In addition, we show with another MIP specific to 2,4-D that, apart from the direct measurement of the binding of fluorescent compounds, a competitive immunoassay-type format can also be used to transduce the binding. We believe that this technique has a strong potential for the fabrication of biomimetic microchips and other types of integrated biosensors.