Micropatterning Technique Research Articles

Micro transfer printing on cellulose electro-active paper

A micro-patterning technique regarded as micro transfer printing is studied for goldelectrode patterning on cellulose electro-active paper (EAPap), aiming at biodegradableand flexible MEMS fabrication. EAPap is known as a smart material due to the interestingactuation phenomenon of cellulose paper. Accordingly, EAPap can be used for sensor andactuator devices. Since EAPap is made with cellulose, a biodegradable and flexible MEMSdevice can be made with this material. However, since cellulose-based EAPap ishydrophilic and flexible, conventional lithography and etching techniques cannot beused for micro-patterning. This paper reports a new micro-patterning techniqueusing the micro transfer printing (MTP) method on flexible EAPap material. TheMTP technique consists of a master fabrication, a polydimethylsiloxane (PDMS)stamp construction, and a micro pattern transfer. Details of the technique and keyissues are addressed. To demonstrate the feasibility of the MTP technique, a goldelectrode pattern for a surface acoustic wave (SAW) MEMS device and a goldmicro-strip pattern for a microwave dipole rectenna are made on cellulose papersubstrates.

Polyelectrolyte Micropatterning Using Agarose Plane Stamp and a Substrate Having Microscale Features on Its Surface

We have introduced polyelectrolyte micro-patterning technique employing agarose plane stamp and a hard substrate having microscale features on its surface. With this method, chemically micropatterned surfaces with both positive and negative functionalities were successfully embedded in well-defined microstructures, and selective impartment of charge functionalities was confirmed by patterning bead bearing surface charge. Furthermore, this technique allows highly sensitive immobilization of protein onto targeted surface simply by endowing functionalities, which extends the potential of its use as a tool for high-throughput protein microarray and proteomics. Because plane agarose stamp is free of structures on its surface, there is no concern for pattern collapse, and the combination of agarose plane stamp with patterned substrate is more suited for selective protein patterning compared with adopting surface-patterned agarose stamp with flat substrate. Our technique using agarose plane stamp and a substrate having microscale features on its surface suggests a range of possible applications, including the micropatterning of biofunctionalized copolymer having polyelectrolyte block, immobilization of micro- and nanoparticle with biofunctionalities such as biotin and streptavidine, and establishing optoelectronic microstructures with micro-beads on various surfaces.

Effects of shear stress on endothelial cell haptotaxis on micropatterned surfaces

Endothelial cell (EC) migration plays a critical role in vascular remodeling. Here we investigated the interactions between haptotaxis (induced by extracellular matrix gradient) and mechanotaxis (induced by mechanical forces) during EC migration. A micropatterning technique was used to generate step changes of collagen surface density. Due to haptotaxis, ECs developed focal adhesions and migrated into the area with higher surface density of collagen. Different levels of fluid shear stress were applied on ECs in the direction perpendicular to collagen strips. Shear stress at 2 dyn/cm 2 did not affect haptotaxis, while shear stress at 3 dyn/cm 2 or higher was sufficient to drive the migration of most ECs in the flow direction and against haptotaxis. Immunostaining revealed the increase of focal adhesions and lamellipodial protrusion in the direction of flow. These results suggest that shear stress beyond a certain threshold can be a predominant factor to determine the direction of EC migration.

Micropattern Printing of Adhesion, Spreading, and Migration Peptides on Poly(tetrafluoroethylene) Films To Promote Endothelialization

We report here the development of an original multistep micropatterning technique for printing peptides on surfaces, based on the ink-jet printer technology. Contrary to most micropatterning methods used nowadays, this technique is advantageous because it allows displaying 2D-arrays of multiple biomolecules. Moreover, this low cost procedure allies the advantages of computer-aided design with high flexibility and reproducibility. A Hewlett-Packard printer was modified to print peptide solutions, and Adobe Illustrator was used as the graphic-editing software to design high-resolution checkerboard-like micropatterns. In a first step, PTFE films were treated with ammonia plasma to introduce amino groups on the surface. These chemical functionalities were reacted with heterobifunctional cross-linker sulfo-succinimidyl 4-(N-maleimidomethyl)cycloexane-1-carboxylate (S-SMCC) to allow the subsequent surface covalent conjugation of various cysteine-modified peptides to the polymer substrate. These peptidic molecules containing RGD and WQPPRARI sequences were selected for their adhesive, spreading, and migrational properties toward endothelial cells. On one hand, our data demonstrated that the initial cell adhesion does not depend on the chemical structure and combination of the peptides covalently bonded either through conventional conjugation or micropatterning. On the other hand, spreading and migration of endothelial cells is clearly enhanced while coconjugating the GRGDS peptide in conjunction with WQPPRARI. This behavior is further improved by micropatterning these peptides on specific areas of the polymer surface.

Engineering micropatterned surfaces for the coculture of hepatocytes and Kupffer cells

Bioartificial liver (BAL) devices are used for applications ranging from pharmaceutical testing to temporary liver replacement. The capabilities of these devices can be improved by optimizing the range of hepatocyte functions that the BAL is able to perform. One means of achieving this is to design the BAL such that it establishes communication between hepatocytes and nonparenchymal cells. To understand how these heterotypic interactions can be favorably utilized in BAL design, it is first necessary to establish a culture environment that permits the controlled interactions of multiple cell types. This is the goal of the current study, which focuses on micropatterned cocultures of hepatocytes with Kupffer cells. The micropatterning technique relies on a polydimethylsiloxane (PDMS) membrane to achieve various two-dimensional configurations of the ECM prior to seeding the cell populations. The easy and inexpensive method of making the PDMS membranes differs from that reported in the literature and is detailed in the current study. To demonstrate the success of the method, surface characterization of the resultant micropatterns, as well as morphological and functional results are also presented.

Patterning the Surface Cytophobicity of an Albumin-Physisorbed Substrate by Electrochemical Means

Spatiotemporal control of surface properties under physiological conditions such as those found in culture media is an important technique in fundamental cell biology, tissue engineering, and cell-based bioelectronics. To this end, we have developed a mild, wet cellular micropatterning technique. The principle of the technique is based on the fact that the cell-repellant property of the albumin-coated substrate rapidly switches to cell-adhesive upon exposure to the reactive oxidizing agent, electrochemically generated hypobromous acid. Herein, we report the effect of the hypobromous acid on serum albumin physisorbed on a hydrophobic substrate. It was found that albumin molecules detach from the substrate by application of the oxidizing agent, resulting in exposure of the underlying hydrophobic surface to the liquid phase. The adsorption of extracellular matrix proteins such as fibronectin onto the hydrophobic surface induces cell adhesion and growth.

Protein Micropatterning Using Surfaces Modified by Self-Assembled Polystyrene Microspheres

A technique for micropatterning of proteins on a nonplanar surface to improve the coverage and functionality of biomolecules is demonstrated. A nonplanar microstructure is created by the self-assembly of polystyrene microspheres into an array of microwells on a silicon wafer to allow the integration of a nonplanar spot on a planar chip. After the microspheres were deposited into the microwells, they were conjugated with proteins. The curve surfaces of the microspheres present more surface area for attaching biomolecules which will increase the density of biomolecules and, hence, the sensitivity for detection. Moreover, proteins immobilized on a curved surface can retain their native structures and function better than on a planar surface because of a smaller area of interaction between the protein and the substrate. Patterning of biomolecules was tested with two model fluorescent proteins. The results show that precise patterning of biomolecules on a nonplanar spot can be achieved with this technique.

In Vitro Cell Response to a Polymer Surface Micropatterned by Laser Interference Lithography

This presentation will introduce laser interference lithography to prepare a periodic line and point micropatterns for study of cell-surface interactions. This process provides a straightforward micropatterning technique based on selective laser ablation of polymers utilizing the periodic energy distribution of two or more beam interference patterns. The micropatterns were characterized by atomic force microscopy, while the surface chemical modification was analyzed using X-ray photoelectron spectroscopy. Human pulmonary fibroblasts cultured on the surface of polycarbonate bearing line micropatterns were elongated, spindlelike, and oriented themselves along the line patterns with all different groove widths. In contrast, cells cultured on point patterns were also bipolar but showed no orientation. Further investigations demonstrated that human pulmonary fibroblast cells cultured on line and point micropatterns showed inflammatory response.

Laser interference lithography as a new and efficient technique for micropatterning of biopolymer surface

Laser interference lithography (LIL) is a straightforward technique to prepare linear micropatterns for regulating cellular adhesion behaviors on polymer substratum. This process is based on selective laser ablation directly duplicating the interference patterns of two or more coherent laser beams onto the polymer surface. Micropatterns prepared by LIL on poly(ethylene terephthalate) and Thermanox® were characterized using atomic force microscopy (AFM) and white light interferometer while the chemical surface modification induced by laser was analyzed by X-ray photoelectron spectroscopy (XPS). The AFM photographs show that the micropatterns are well-defined and of great consistency. Polymer properties and laser parameters related to LIL as well as laser ablation mechanisms are discussed in this technical note.

A Combined Photolithographic and Molecular‐Assembly Approach to Produce Functional Micropatterns for Applications in the Biosciences

AbstractChemical patterns have attracted substantial interest for applications in the field of biosensors, fundamental cell–surface interaction studies, tissue engineering, and biomaterials. A novel micropatterning technique is proposed here that combines a top–down approach based on photolithography and a bottom–up strategy through self‐organization of multifunctional molecules. The development of the molecular‐assembly patterning by lift‐off (MAPL) has been driven by the need to economically produce patches incorporating a controlled surface density of bioligands while inhibiting non‐specific adsorption. In the MAPL process, a photoresist pattern is transferred into the desired biochemical pattern by means of spontaneous adsorption of biologically relevant species and photoresist lift‐off. The surface between the interactive patches is subsequently rendered non‐fouling through immobilization of a polycationic poly(ethylene glycol) (PEG)‐graft polymer. We demonstrate that surface density of biotin molecules inside adhesive islands can be tailored quantitatively and that cells grow selectively on cell‐adhesive peptide patterns. MAPL is considered to be a valuable addition to the toolbox of soft‐lithography techniques for life‐science applications combining simplicity (no clean‐room equipment needed), cost‐effectiveness, reproducibility on the scale of whole wafer surfaces, and flexibility in terms of pattern geometry, chemistry, and substrate choice.

Photolithographic Technique for Direct Photochemical Modification and Chemical Micropatterning of Surfaces

We describe a photolithographic method for the direct modification and micropatterning of the surface chemical structure of self-assembled monolayers. End-functional azobenzene alkanethiols are designed and synthesized so that, when self-assembled onto gold substrates, an acid-sensitive tert-butyl ester end group is positioned at the air−monolayer interface. Upon exposure to UV radiation in the presence of a photoacid generator, the tert-butyl ester groups are removed in the form of butylene gas to form surface carboxylic acid groups. The orientation of the monolayers and photochemical surface modification reactions are characterized by X-ray photoelectron spectroscopy measurements. The photochemical change from hydrophobic tert-butyl ester groups to hydrophilic carboxylic acid groups causes a significant change in wettability reflected in a water contact angle change from 89 to 28°, respectively. Surface chemical modifications may be patterned on a microscale by simply irradiating the self-assembled mono...

Plasma printing: patterned surface functionalisation and coating at atmospheric pressure

A new plasma-based micropatterning technique, here referred to as plasma printing, combines the well known advantages given by the nonequilibrium character of a dielectric barrier discharge (DBD) and its operation inside small gas volumes with dimension between tens and hundreds of micrometres. The discharge is run at atmospheric pressure and can be easily implemented for patterned surface treatment with applications in biotechnology and microtechnology. In this work the local modification of dielectric substrates, e.g. polymeric films, is addressed with respect to coating and chemical functionalisation, immobilisation of biomolecules and area-selective electroless plating.

CVD diamond anisotropic film as electrode for electrochemical sensing

The unique electrochemical properties of diamond such as a large working potential window, low background current and prolonged stability make it attractive for applications in electroanalysis. High quality and conductive diamond films are known to exhibit active voltammetric response without the need for surface pretreatment. This paper reports on the design, fabrication and characterization of CVD diamond film for electrochemical sensing. Two types of planar boron-doped diamond electrodes were achieved by plasma enhanced chemical vapor deposition (PECVD) using in situ gas phase doping method. The first utilizes the “as grown” diamond surface with randomly microstructured topology as a planar diamond electrode. The second utilizes a micropatterning technique to produce a well-defined pyramidal diamond tips array with good uniformity control. The fabrication process for the electrodes is described. The diamond microelectrodes were evaluated electrochemically for the detection of ferrocyanide, Fe(CN) 6 4−, using cyclic voltammetry. The results suggest that diamond electrodes can be used in electrochemical sensing application.

Two-Dimensional Protein Micropatterning for Sensor Applications Through Chemical Selectivity Technique

Two-dimensional protein micropatterning with immobil-ization of IgG and poly (ethylene glycol) (PEG) on patterned Au and Si surfaces was performed through a new technique. The technique for micropatterning is based on a chemical selectivity method by creating chemical bonding between protein, self-assembled monolayers (SAMs) and substrates rather than physical means. The substrates used in this study are pre-fabricated with silicon wafer patterned with arrays of gold squares. The silicon regions of the substrate are modified with polyethylene glycol (PEG) to resist protein adsorption and cell adhesion. The gold regions on the substrate are first immobilized with bifunctional SAM layers that can covalently bound adhesion proteins for individual cell attachment against a PEG background. The surface coatings are characterized by contact angle measurement, ellips-ometry, and atomic force microscopy (AFM). The patterns of fluorescence-labeled proteins are examined using fluorescence microscopy. Our study demonstrated that the PEG modified silicon region showed an effective protein reduction while the gold regions were successfully covalently bonded with proteins. This technique also demonstrated a combined feature of ensuring the activity, selectivity, and stability of the immobilized proteins. A simple lift-off microfabrication process was introduced in this study to pattern metal on silicon substrates without using expensive metal etching.

Control of shape and size of vascular smooth muscle cells in vitro by plasma lithography.

The ability to control the shape and size of cells is an important enabling technique for investigating influences of geometrical variables on cell physiology. Herein we present a micropatterning technique ("plasma lithography") that uses photolithography and plasma thin-film polymerization for the fabrication of cell culture substrates with a cell-adhesive pattern on a cell-repellent (non-fouling) background. The micron-level pattern was designed to isolate individual vascular smooth muscle cells (SMC) on areas with a projected area of between 25 and 3600 microm(2) in order to later study their response to cytokine stimulation in dependence of the cell size and shape as an indication for the phenotypic state of the cells. Polyethylene terephthalate substrates were first coated with a non-fouling plasma polymer of tetraglyme (tetraethylene glycol dimethyl ether). In an organic lift-off process, we then fashioned square- and rectangular-shaped islands of a thin fluorocarbon plasma polymer film of approximately 12-nm thickness. Electron spectroscopy for chemical analysis and secondary ion mass spectroscopy were used to optimize the deposition conditions and characterize the resulting polymers. Secondary ion mass spectroscopy imaging was used to visualize the spatial distribution of the polymer components of the micropatterned surfaces. Rat vascular SMC were seeded onto the patterned substrates in serum-free medium to show that the substrates display the desired properties, and that cell shape can indeed be controlled. For long-term maintenance of these cells, the medium was augmented with 10% calf serum after 24 h in culture, and the medium was exchanged every 3 days. After 2 weeks, the cells were still confined to the areas of the adhesive pattern, and when one or more cells spanned more than one island, they did not attach to the intervening tetraethylene glycol dimethyl ether (tetraglyme) background. Spreading-restricted cells formed a well-ordered actin skeleton, which was most dense along the perimeter of the cells. The shape of the nucleus was also influenced by the pattern geometry. These properties make the patterned substrates suitable for investigating if the phenotypic reversion of SMC can be influenced by controlling the shape and size of SMC in vitro.

Controlling cell interactions by micropatterning in co-cultures: hepatocytes and 3T3 fibroblasts.

The repair or replacement of damaged tissues using in vitro strategies has focused on manipulation of the cell environment by modulation of cell-extracellular matrix interactions, cell-cell interactions, or soluble stimuli. Many of these environmental influences are easily controlled using macroscopic techniques; however, in co-culture systems with two or more cell types, cell-cell interactions have been difficult to manipulate precisely using similar methods. Although microfabrication has been widely utilized for the spatial control of cells in culture, these methods have never been adapted to the simultaneous co-cultivation of more than one cell type. We have developed a versatile technique for micropatterning of two different cell types based on existing strategies for surface modification with aminosilanes linked to biomolecules and the manipulation of serum content of cell culture media. This co-culture technique allowed manipulation of the initial cellular microenvironment without variation of cell number. Specifically, we were able to control the level of homotypic interaction in cultures of a single cell type and the degree of heterotypic contact in co-cultures over a wide range. This methodology has potential applications in tissue engineering, implant biology, and developmental biology, both in the arena of basic science and optimization of function for technological applications.

Magnetization measurements in epitaxial films of the YBa2Cu3Oy compound.

Systematic measurements of magnetization in epitaxial ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$ (Y-Ba-Cu-O) films have been performed. Y-Ba-Cu-O films have been prepared by coevaporation in an ultrahigh-vacuum system for molecular-beam epitaxy. These epitaxial films are oriented with their c axis perpendicular to the MgO(100) substrates. The dc magnetization of these films was measured by means of a superconducting-quantum-interference-device magnetometer, and the sample size was precisely controlled by means of a micropatterning technique. At low temperatures and low magnetic fields, the zero-field-cooled magnetization showed almost perfect diamagnetism, and the demagnetization effect was observed as the sample size was changed. In the transition region of zero-field-cooled magnetization, the temperature and magnetic-field dependences of the magnetization also showed the sample-size dependence and were consistent with that of the Bean critical-state model, which indicated that there was no granularity in these epitaxial Y-Ba-Cu-O films. The magnetization data were consistent with the flux-density distribution, which was directly observed by means of the magneto-optical Faraday effect. In addition, the field-cooled magnetization was carefully measured, and the susceptibility of thin films in the field-cooled process was estimated. From these experimental results, a quantitative discussion of the magnetization and the observation of granularity characteristics in the oxide superconductor films have become possible under various temperature and magnetic-field conditions.