Surface modification of elastomeric stamps for microcontact printing of polar inks

Chemical modification of the surface of a stamp used for microcontact printing (microCP) is interesting for controling the surface properties, such as the hydrophilicity. To print polar inks, plasma polymerization of allylamine (PPAA) was employed to render the surface of poly(dimethylsiloxane) (PDMS), polyolefin plastomers (POP), and Kraton elatomeric stamps hydrophilic for long periods of time. A thin PPAA film of about 5 nm was deposited on the stamps, which increased the hydrophilicity, and which remained stable for at least several months. These surface-modified stamps were used to transfer polar inks by microCP. The employed microCP schemes are as follows: (a) a second generation of dendritic ink having eight dialkyl sulfide end groups to fabricate patterns on gold substrates by positive microCP, (b) fluorescent guest molecules on beta-cyclodextrin (beta-CD) printboards on glass employing host-guest recognition, and (c) Lucifer Yellow ethylenediamine resulting in covalent patterning on an aldehyde-terminated glass surface. All experiments resulted in an excellent performance of all three PPAA-coated stamp materials to transfer the polar inks from the stamp surface to gold and glass substrates by microCP, even from aqueous solutions.     

Positive microcontact printing with mercaptoalkyloligo(ethylene glycol)s

The soft lithographic replication of patterns with a low filling ratio by microcontact printing (microCP) is problematic due to the poor mechanical stability of common elastomeric stamps. A recently described strategy to avoid this problem employs a modified patterning method, positive microcontact printing ((+)microCP), in which a stamp with a mechanically more stable inverted relief pattern is used. In contrast to conventional negative microCP ((-)microCP), in the contact areas a self-assembled monolayer (SAM) is printed of a "positive ink", which provides only minor etch protection, whereas the noncontacted areas are subsequently covered with a different, etch-resistant SAM, prior to development by chemical etching. With the aim to identify novel, highly versatile positive inks, the patterning of gold by (+)microCP with mercaptoalkyloligo(ethylene glycol)s (MAOEGs), the subsequent adsorption of octadecanethiol (ODT), and the final development by wet chemical etching have now been studied. A polydisperse mixture of mercaptoundecylocta(ethylene glycol) derivatives was found to provide the best patterning results. The surface spreading of the positive ink during stamping, the exchange of printed MAOEGs with ODT, and the choice of the right etching bath were identified as key parameters that influence the achievable pattern resolution and contrast. Due to the modular composition of functionalized alkyloligo(ethylene glycol) derivatives, (+)microCP with these positive inks has the potential for easy adaptation to a variety of materials and development conditions.     

Bacterial printing press that regenerates its ink: contact-printing bacteria using hydrogel stamps

This paper describes the use of micropatterned agarose stamps prepared by molding against PDMS masters to print patterns of bacteria on agar plates. Topographically patterned agarose stamps were inked with suspensions of bacteria; these stamps generated patterns of bacteria with features as small as 200 microm over areas as large as 50 cm2. Stamps with many small features (>200 microm) were used to study patterns of bacteria growing on media containing gradients of small molecules; stamps with larger features (>750 microm) were used to print different strains of bacteria simultaneously. The stamp transfers only a small percentage of cells that are on its surface to the agar at a time; it is thus possible to replica-pattern hundreds of times with a single inking. The use of soft stamps provides other useful functions. Stamps are easily customized to provide a range of patterns. When culture media is included in the agarose stamp, cells divide and thrive on the surface. The resulting "living stamp" regenerates its "ink" and can be used to pattern surfaces repetitively for a month. This method is rapid, reproducible, convenient, and can be used to control the pattern, spacing, and orientation between colonies of different bacteria.     

Microcontact printing of monodiamond nanoparticles: an effective route to patterned diamond structure fabrication

By combining microcontact printing with a nanodiamond seeding technique, a precise micrometer-sized chemical vapor deposition (CVD) diamond pattern have been obtained. On the basis of the guidance of basic theoretical calculations, monodisperse detonation nanodiamonds (DNDs) were chosen as an "ink" material and oxidized poly(dimethylsiloxane) (PDMS) was selected to serve as a stamp because it features a higher interaction energy with the DNDs compared to that of the original PDMS. The adsorption kinetics shows an approximately exponential law with a maximum surface DND density of 3.4 × 10(10) cm(-2) after 20 min. To achieve a high transfer ratio of DNDs from the PDMS stamp to a silicon surface, a thin layer of poly(methyl methacrylate) (PMMA) was spin coated onto the substrates. A microwave plasma chemical vapor deposition system was used to synthesize the CVD diamond on the seeded substrate areas. Precise diamond patterns with a low expansion ratio (3.6%) were successfully prepared after 1.5 h of deposition. Further increases in the deposition time typically lead to a high expansion rate (～0.8 μm/h). The general pattern shape, however, did not show any significant change. Compared with conventional diamond pattern deposition methods, the technique described here offers the advantages of being simple, inexpensive, damage-free, and highly compatible, rendering it attractive for a broad variety of industrial applications.     

微接触印刷法构造金属银的二维和准三维微图纹结构

以聚二甲基硅氧烷（PDMS）有机硅橡胶为弹性印章，以十八烷基三氯硅烷（OTS）正已烷溶液为“墨水”，用微接触印刷分别在普通盖玻片表面和直径为20 mm的试管外表面直接盖印，以及在直径为10 mm的玻璃棒表面进行滚动式微接触印刷盖印.将这些盖好印的基材放在化学镀银液中进行选择性镀银沉积，得到金属银在平面上的二维微结构和在曲面上的准三维微结构.这些微结构的显微照片显示，采用微接触印刷法制备的微图纹结构，图纹转移效率高，精细度很好，特别是微接触印刷操作方法灵活多变，适用于多种形态的表面，是一类实用的微制造方法.     

Application of microcontact printing to electroless plating for the fabrication of microscale silver patterns on glass

Microcontact printing (microCP) and electroless plating are combined to produce microscale patterns of silver on glass substrates. Silver patterns with feature sizes of 0.6-10 microm stripes are fabricated using two methods. (1) The printing seeding layer (PSL) method is to apply microCP to directly print the catalyst Sn pattern for further electroless plating. (2) The printing masking layer (PML) method is to use microCP to print the octadecyltrichlorosilane (OTS) self-assembled monolayer as a masking layer on glass substrates, which then become Sn-activated in the unstamped regions by immersing the substrates in stannous chloride solution. After the electroless silver plating, the PML method has a better selectivity of silver deposition than the PSL method. In addition, variation of the deposited silver thickness as a function of the plating time and temperature is discussed.     

Chemically patterned flat stamps for microcontact printing

Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the transfer of hydrophobic n-octadecanethiol. In this case a good contrast was obtained, but the pattern was found to be susceptible to defects (cracks) in the barrier layer. Local stamp surface oxidation and subsequent modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane, for use as a barrier in the transfer of n-octadecanethiol, 16-mercaptohexadecanoic acid, and octanethiol, resulted in remarkably good contrast and stable patterns. The improved ink transfer control is ascribed to the reduction of undesired surface spreading and a superior mechanical stability of the stamp pattern. This new approach substantially expands the applicability of microcontact printing and provides a tool for the faithful reproduction of even extremely low filling ratio patterns.     

Reactive microCP on ultrathin block copolymer films: investigation of the microCP mechanism and application to sub-microm (bio)molecular patterning

In this paper, the mechanism of the recently introduced soft lithographic patterning approach of reactive microcontact printing on thin substrate-supported polystyrene-block-poly(tert-butyl acrylate) (PS690-b-PtBA1210) films using trifluoroacetic acid (TFA)-inked elastomeric poly(dimethylsiloxane) (PDMS) stamps is investigated in detail. In this approach, solventless deprotection reactions are carried out with very high spatial definition using TFA as a volatile reagent that partitions into the PtBA skin layer. On the basis of a systematic investigation of the process, ink loading was identified as a crucial parameter for obtaining faithful pattern transfer. Using optimized conditions, submicrometer-sized patterns were successfully fabricated. In combination with subsequent wet chemical covalent coupling of various (bio)molecules, reactive microCP is established as an approach to afford positive, as well as negative, images of the features of the stamps used. In addition, the size of the patterned areas was manipulated by exploiting the controlled spreading of the ink; thus, stamps with identical features yield patterns with different sizes, yet identical periodicity, as shown for bovine serum albumin (BSA)-poly(ethylene glycol) patterns. The reactive microCP methodology affords new pathways for submicrometer-scale patterning of bioreactive surfaces.     

TiO2微图纹结构的制作

The representative soft lithographic techniques are used,which are micromolding and microtransfer molding methods to fabricate the micro array patterned titanium dioxide on glass substrates. Firstly titanium dioxide sol was synthesized by sol-gel method using tetrabutyl titanate as the precursor,then the pre-patterned poly（dimethylsiloxane） elastomeric stamp was used to mold the TiO2 sol on glass substrate by micromolding and microtransfer molding methods,micro patterned TiO2 sol was gelled at 70℃ with 0. 5 N pressure applied on the PDMS stamp,further heat treatment of TiO2 gel by annealing at 550℃ for 2 h produced the TiO2 microstructure. The TiO2 microstructure was observed by the optical microscope and the optical micrographs demonstrated the satisfactory yield and fidelity of pattern transfer by micromolding method and microtransfer method. The effect of gel temperature,the pressure applied on the PDMS stamp and the silicone mold on the fidelity and yield of TiO2 microstructure are discussed.     

Microscale plasma-initiated patterning (muPIP)

A novel technique to create biomolecular micropatterns of varying complexity on several types of polymer substrates is presented. This method uses a patterned PDMS stamp to preferentially expose or protect areas of an underlying polymer substrate from oxygen plasma. Following plasma treatment, the substrate is immersed in a biomolecular ink, whereby molecules preferentially adsorb to either the plasma-exposed or plasma-protected substrate regions, depending on the particular substrate/ink combination. Using this method, polyethylene (PE), polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(dimethylsiloxane) (PDMS), and poly(hydroxybutyrate/hydroxyvalerate) (PHBV) were micropatterned with different aqueous-based biomolecular inks (i.e., goat anti-rabbit immunoglobulin G, poly-l-lysine, and bovine serum albumin (BSA)). Water contact angle measurements performed on substrates after oxygen plasma exposure showed that the hydrophilicity of substrate areas exposed to plasma was significantly greater than that of areas protected from plasma by the PDMS stamp. In addition, scanning electron microscopy results demonstrated that substrate areas exposed to plasma were physically modified (e.g., roughened) compared to adjacent, protected areas. Areas in contact with a patterned PDMS stamp during plasma exposure were found to be physically unaffected by plasma treatment, and exhibited spatial features/dimensions consistent with the corresponding features of the patterned stamp. Last, protein patterns of BSA on the polymer substrates were stable and distinct after 4 weeks of incubation at 37 degrees C.     

Interface interaction controlled transport of CdTe nanoparticles in the microcontact printing process

High-quality CdTe nanoparticles stabilized with thioglycolic acid (TGA) are patterned on SiO2/Si surfaces using microcontact printing (microCP). Due to the weak interaction of the nanoparticles with the stamp surface, tailoring of gas flow rate during the inking process as well as the type and scale of the patterns on the stamp are used to control the distribution of the nanoparticles on the structured stamp surface. This distribution is then transferred the printed regions. Either edge printing or homogeneous printing can be achieved under optimized conditions. In addition, new structures such as nanowires form under certain conditions.     

Direct printing of self-assembled lipid tubules on substrates

Lipid tubules formed by rolled-up bilayer sheets have shown promise in drug delivery systems, nanofluidics, and microelectronics. Here we report a method for directly printing lipid tubules on substrates. Preformed lipid tubules of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine are aligned in the recessed channels of a thin poly(dimethylsiloxane) (PDMS) stamp. The aligned lipid tubules then serve as an "ink" for microcontact printing. We demonstrate that two-dimensional (2-D) arrays of aligned lipid tubules can be transferred onto planar, patterned, and curved substrates from the recessed channels of the PDMS stamp by bringing the tubule-inked PDMS stamp into contact with these substrates. We show that the 2-D array of aligned lipid tubules can be transcribed into a 2-D array of aligned silica cylinders through templated sol-gel condensation of tetraethoxysilane.     

Selective depositions on polyelectrolyte multilayers: self-assembled monolayers of m-dPEG acid as molecular template

This paper describes the fabrication of self-assembled monolayer (SAM) patterns of m-d-poly(ethylene glycol) (m-dPEG) acid molecules onto polyelectrolyte multilayers (PEMs). The patterned SAMs on PEMs were created by ionic interactions using microcontact printing (microCP) technique. The created m-dPEG acid monolayer patterns on PEMs act as resistive templates, and thus further depositions of consecutive poly(anion)/poly(cation) pairs of charged particles result in the formation of three-dimensional (3-D) patterned PEM films or selective particle depositions atop the original multilayer thin films. In this study, we illustrate nonlithographic methods of patterning and controlling 3-D PEM architectures and selective particle depositions. We investigated the effect of variables--the choice of solvent, concentration, pH, substrate pretreatment, and stamp contact times--on microcontact printing of m-dPEG acid molecules onto PEM films to determine the optimal conditions for these parameters to achieve efficient transfer of m-dPEG acid patterns onto PEMs. Among the variables, the pH of the m-dPEG acid ink solution played the most important role in the transfer efficiency of the patterns onto the multilayer films. The patterned films were characterized by optical microscopy and atomic force microscopy (AFM).     

Diffusion of alkanethiols in PDMS and its implications on microcontact printing (muCP)

n-Alkanethiols HS-(CH2)n-CH3 such as hexadecanethiol (HDT, n = 15), octadecanethiol (ODT, n = 17), and eicosanethiol (ECT, n = 19) have been shown to provide highly protective etch resists on microcontact-printed noble metals. As the quality of the printed pattern strongly depends on the mobility of the ink compound, we focused on understanding the diffusion behavior of HDT, ODT, and ECT in poly(dimethylsiloxane) (PDMS) stamps. We used a commercial PDMS material (Sylgard184), which is commonly used for microcontact printing (muCP), and a custom-synthesized one with a higher modulus. On the basis of linear-diffusion experiments, which maintained realistic printing conditions, we showed that the ink transport in the stamp follows Fick's law of diffusion. We then determined the diffusion coefficient by analytical and numerical modeling of the diffusion experiments. Numerical calculations were carried out with the finite-difference method applying more realistic boundary conditions (ink adsorption). Values for the diffusion coefficients of the three ink compounds in the two different PDMS materials all are on the order of (4-7) x 10(-7) cm2 s(-1). The scope and limits of the mathematical models are discussed. To demonstrate the potential of such models for microcontact printing, we simulate multiple printing cycles of an inked stamp and compare the results with experimental data.     

Adhesion enhancement through micropatterning at polydimethylsiloxane-acrylic adhesive interfaces

Adhesion at polydimethylsiloxane (PDMS)-acrylic adhesive interfaces is shown to be enhanced through micropatterning of the PDMS substrate. By varying the geometry of the patterns (groves and hexagonal arrays of pillars of micrometer sizes, obtained through soft lithography techniques) and comparing rigid and deformable substrates, the respective roles of the geometry and the size and flexibility of the pattern features on the level of adhesion have been analyzed. For cylindrical pillars, two regimes are clearly identified: for a relatively low aspect ratio (h/r < 3, with h and r, respectively, the height and the radius of the pillars), soft patterned substrates are more efficient than rigid ones at increasing adhesion, pointing out the role of the elastic energy associated with the deformation of the pattern that is lost when the adhesive detaches from the substrate. Using scaling laws, the predominant contribution to that elastic energy can be further identified: deformation of the substrate underlying the pillars for h/r < 1.6 or bending of the pillars for h/r > 1.6.; for a high aspect ratio (h/r > 3), only rigid patterned substrates enhance adhesion, then the only possible contribution to energy dissipation comes from the enhanced viscoelastic losses associated with the pattern that induce modifications of the strain field within the adhesive layer. Soft, high aspect ratio patterns lose their efficiency even if still bent under the effect of the peel forces. This is because when bent, some of the pillars touch each other and remain stuck together, lying flat on the surface after the passage of the peel front. The bending elastic energy of the pillars (which is still lost) is then balanced by the corresponding gain in surface energy of the substrate in the peeled region. These systematic experiments demonstrate that the ability of the patterned surface to be deformed plays a crucial role in enhancing adhesion and allow us to propose a way to fine tune the level of adhesion at PDMS-acrylic adhesive interfaces, independently of the chemistry of the adhesive.     

Dip-pen patterning and surface assembly of peptide amphiphiles

This paper presents results on controlling the surface morphology of evaporation-driven self-assembly of peptide amphiphile (PA) nanofibers by dip-pen nanolithography. These PA nanofibers, which measure only a few nanometers in diameter, can be oriented perpendicularly to the receding edge of a solution. Dragging a meniscus of PA ink with an atomic force microscope (AFM) tip creates reproducibly aligned arrays of isolated and close-packed PA nanofiber patterns on silicon substrates, utilizing surface coating of poly(ethylene glycol) to suppress the self-assembly of nanofibers on AFM tips. We also demonstrate the ability to construct double-layer patterns of differing nanofiber orientations at the same position. This result could be important in producing a complex, multilayer pattern of these peptide-based supramolecular nanostructures.     

Spreading of 16-mercaptohexadecanoic acid in microcontact printing

Spreading in microcontact printing refers to the process or processes by which the ink molecules end up in the parts of the substrate that are adjacent to the contacted areas but which are not contacted themselves. This has been investigated for different inking concentrations of 16-mercaptohexadecanoic acid (MHDA). Spreading of MHDA takes place with retention of a well-defined demarcation. Feature sizes can be controlled by varying the contact times. Spreading, however, only takes place beyond a certain threshold concentration. For low ink concentrations the edges of stamp features dominate the ink transfer. For these low concentrations the extent of this edge dominance depends strongly on ink concentration rather than on contact time. These observations indicate a dominant role of the stamp surface in the processes of pattern formation and spreading.     

Patterning polymerized lipid vesicles with soft lithography

The applications of soft lithography in patterning polymerized lipid vesicles of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine on glass substrates are reported. We demonstrate that the polymerized vesicles can be used as a high molecular weight ink to be transferred from a PDMS stamp onto a glass substrate to form two-dimensional stripes with a controlled separation. By combining channel flow with dewetting within microfluidic networks, we assemble the polymerized vesicle into three-dimensional stripes and one-dimension lines on glass substrates. Atomic force microscopy shows that these patterned vesicle structures are stable on glass substrates. The simple, stable, and precise immobilization of lipid vesicles on solid substrates will open up the possibility of integrating them in biosensors and microelectronic devices.     

Direct transfer of preformed patterned bio-nanocomposite films on polyelectrolyte multilayer templates

Microarrays containing multiple, nanostructured layers of biological materials would enable high-throughput screening of drug candidates, investigation of protein-mediated cell adhesion, and fabrication of novel biosensors. In this paper, we have examined in detail an approach that allows high-quality microarrays of layered, bionanocomposite films to be deposited on virtually any substrate. The approach uses LBL self-assembly to pre-establish a multilayered structure on an elastomeric stamp, and then uses microCP to transfer the 3-D structure intact to the target surface. For examples, different 3-D patterns containing dendrimers, polyelectrolyte multilayers and two proteins, sADH and sDH, have been fabricated. For the first time, the approach was also extended to create overlaid bionanocomposite patterns and multiple proteins containing patterns. The approach overcomes a problem encountered when using microCP to establish a pattern on the target surface and then building sequential layers on the pattern via LBL self-assembly. Amphiphilic molecules such as proteins and dendrimers tend to adsorb both to the patterned features as well as the underlying substrate, resulting in low-quality patterns. By circumventing this problem, this research significantly extends the range of surfaces and layering constituents that can be used to fabricate 3-D, patterned, bionanocomposite structures. [image in text]     

Poly(dimethylsiloxane) contamination in microcontact printing and its influence on patterning oligonucleotides

It is well-established that, during microcontact printing (muCP) using poly(dimethylsiloxane) (PDMS)-based stamps, some unexpected siloxane fragments can be transferred from the stamp to the surface of the sample. This so-called contamination effect coexists with the delivery of the molecules constituting the ink and by this way influences the printing process. The real impact of this contamination for the muCP technique is still partially unknown. In this work, we investigate the kinetics of this contamination process through the surface characterization of both the sample and the stamp after imprinting. The way both the curing conditions of the PDMS material and the contact time influence the degree of contamination of the surface is investigated on silicon and glass substrates. We propose a cleaning process of the stamp during several hours which eliminates any trace of contamination during printing. We show that hydrophobicity recovery of PDMS surfaces after hydrophilic treatment using oxygen plasma is considerably slowed down when the PDMS material is cleaned using our procedure. Finally, by comparing cleaned and uncleaned PDMS stamps, we show the influence of contamination on the quality of muCP using fluorescent DNA molecules as an ink. Surprisingly, we observe that the amount of DNA molecules transferred during muCP is higher for the uncleaned stamp, highlighting the positive impact of the presence of low molecular weight siloxane fragments on the muCP process. This result is attributed to the better adsorption of oligonucleotides on the stamp surface in presence of these contaminating molecules.