Surface modification of elastomeric stamps for microcontact printing of polar inks

A simple and efficient transfer method for fabricating stretchable AgNW patterns on PDMS using carboxylated cellulose nanofibers as a sacrificial layer

Silver nanowire (AgNW) networks are one of the most promising materials of transparent electrodes in flexible applications. However, they still face challenges in fabricating AgNW transparent conductive films (TCFs) with excellent comprehensive performance on stretchable substrates. In this work, we developed an efficient and simple water-assisted method to completely transfer AgNW films from glass to polydimethylsiloxane (PDMS). Carboxylated cellulose nanofibers (CNF-C) are introduced between the AgNW network and glass as a sacrificial layer, which is dissolved in water in the transfer process, releasing the AgNW network on the PDMS. The transferred AgNW networks show an increase of sheet resistance less than 30% and a slight decrease of transmittance. The stretchable AgNW TCFs exhibited good opto-electrical performance with a figure of merit of about 200, low surface roughness, good film uniformity, long-term stability, electrical stability and mechanical performance. Two patterning approaches based on the transfer method were proposed and fine stretchable AgNW patterns with a linewidth of 200 μm were fabricated. The fabricated stretchable AgNW patterns were used in flexible wires, a film heater and sensors as a demonstration.

Contact Printing of Multilayered Thin Films with Shape Memory Polymers

This study describes a method for transfer printing microarrays of multilayered organic-inorganic thin films using shape memory printing stamps and microstructured donor substrates. By applying the films on the microstructured donor substrates during physical vapor deposition and modulating the interfacial adhesion using a shape memory elastomer during printing, this method achieves (1) high lateral and feature-edge resolution and (2) high transfer efficiency from the donor to the receiver substrate. For demonstration, polyurethane-acrylate stamps and silicon/silicon oxide donor substrates were used in the large-area transfer printing of organic-inorganic thin-film stacks with micrometer lateral dimensions and sub-200 nm thickness.

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

Solid-Phase Microcontact Printing for Precise Patterning of Rough Surfaces: Using Polymer-Tethered Elastomeric Stamps for the Transfer of Reactive Silanes

We present a microcontact printing (μCP) routine suitable to introduce defined (sub-) microscale patterns on surface substrates exhibiting a high capillary activity and receptive to a silane-based chemistry. This is achieved by transferring functional trivalent alkoxysilanes, such as (3-aminopropyl)-triethoxysilane (APTES) as a low-molecular weight ink via reversible covalent attachment to polymer brushes grafted from elastomeric polydimethylsiloxane (PDMS) stamps. The brushes consist of poly{N-[tris(hydroxymethyl)-methyl]acrylamide} (PTrisAAm) synthesized by reversible addition-fragmentation chain-transfer (RAFT)-polymerization and used for immobilization of the alkoxysilane-based ink by substituting the alkoxy moieties with polymer-bound hydroxyl groups. Upon physical contact of the silane-carrying polymers with surfaces, the conjugated silane transfers to the substrate, thus completely suppressing ink-flow and, in turn, maximizing printing accuracy even for otherwise not addressable substrate topographies. We provide a concisely conducted investigation on polymer brush formation using atomic force microscopy (AFM) and ellipsometry as well as ink immobilization utilizing two-dimensional proton nuclear Overhauser enhancement spectroscopy (¹H-¹H-NOESY-NMR). We analyze the μCP process by printing onto Si-wafers and show how even distinctively rough surfaces can be addressed, which otherwise represent particularly challenging substrates.

Development of oxidized sulfur polymer films through a combination of plasma polymerization and oxidative plasma treatment

A novel two-step process consisting of plasma polymerization and oxidative plasma treatment is introduced in this article for the first time for the fabrication of -SO(x)(H)-functionalized surfaces. Plasma-polymerized thiophene (PPT) was initially deposited onto silicon wafers and subsequently SO(x)(H)-functionalized using air or oxygen plasma. The effectiveness of both air and oxygen plasma treatments in introducing sulfur-oxygen groups into the PPT film was investigated as the plasma input specific energy and treatment time were varied. The surface chemistries of untreated and treated PPT coatings were analyzed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS), whereas spectroscopic ellipsometry was used to evaluate the film thickness and ablation rate. Surface chemistry analyses revealed that high concentrations of -SO(x)(H) functionalities were generated on the surface upon either air or oxygen plasma treatment. It was found that, at low plasma input energies, the oxidation process was dominant whereas, at higher energies, ablation of the film became more pronounced. The combination of thiophene plasma polymerization and air/oxygen plasma treatment was found to be a successful approach to the fabrication of -SO(x)(H)-functionalized surfaces.

Cyclodextrin-based molecular machines

This chapter overviews molecular machines based on cyclodextrins (CDs). The categories of CD-based molecular machines, external stimuli for CD-based molecular machines, and typical examples of CD-based molecular machines are briefly described.

Grafting of poly-L-lysine dendrigrafts onto polypropylene surface using plasma activation for ATP immobilization - Nanomaterial for potential applications in biotechnology

The present work describes a new environmental friendly strategy for the development of surfaces with high amine density via the grafting of native or modified poly-L-lysine dendrigraft (DGL G3) onto plasma activated polypropylene (PP), polystyrene (PS), polyimide, and polytetrafluoroethylene (PTFE) surface. Modified DGL G3 was prepared by replacement of few peripheral amines by various functionalities. Grafting efficiency was determined by wettability measurements, IRTF, XPS, AFM, and by colorimetry using optimized Coomassie Brilliant Blue method tailored for surface analysis. It was shown that a 4-7nm DGL G3 monolayer with 4×10(14)aminecm(-)(2) was covalently grafted onto various surfaces. Immobilization of adenosine triphosphate on the DGL-g-PP material from dilute solution was studied by bioluminescence and proved the ability of the material to interact with polyanionic biological compounds: 1 ATP complex with 5 amine groups. So, this material has a potential use in diagnostic and more widely for biotechnology due to its high capacity for biomolecule immobilization.

New approaches for bottom-up assembly of tobacco mosaic virus-derived nucleoprotein tubes on defined patterns on silica- and polymer-based substrates

The capability of some natural molecular building blocks to self-organize into defined supramolecular architectures is a versatile tool for nanotechnological applications. Their site-selective integration into a technical context, however, still poses a major challenge. RNA-directed self-assembly of tobacco mosaic virus-derived coat protein on immobilized RNA scaffolds presents a possibility to grow nucleoprotein nanotubes in place. Two new methods for their site-selective, bottom-up assembly are introduced. For this purpose, isothiocyanate alkoxysilane was used to activate oxidic surfaces for the covalent immobilization of DNA oligomers, which served as linkers for assembly-directing RNA. Patterned silanization of surfaces was achieved (1) on oxidic surfaces via dip-pen nanolithography and (2) on polymer surfaces (poly(dimethylsiloxane)) via selective oxidization by UV-light irradiation in air. Atomic force microscopy and X-ray photoelectron spectroscopy were used to characterize the surfaces. It is shown for the first time that the combination of the mentioned structuring methods and the isothiocyanate-based chemistry is appropriate (1) for the site-selective immobilization of nucleic acids and, thus, (2) for the formation of viral nanoparticles by bottom-up self-assembly after adding the corresponding coat proteins.

Polyelectrolyte multilayers as a platform for luminescent nanocrystal patterned assemblies

The fabrication of uniform and patterned nanocrystal (NC) assemblies has been investigated by exploiting the possibility of carefully tailoring colloidal NC surface chemistry and the ability of polyelectrolyte (PE) to functionalize substrates through an electrostatic layer-by-layer (LbL) strategy. Appropriate deposition conditions, substrate functionalization, and post-preparative treatments were selected to tailor the substrate surface chemistry to effectively direct the homogeneous electrostatic-induced assembly of NCs. Water-dispersible luminescent NCs, namely, (CdSe)ZnS and CdS, were differently functionalized by (1) ligand-exchange reaction, (2) growth of a hydrophilic silica shell, and (3) formation of a hydrophilic inclusion complex, thus providing functional NCs stable in a defined pH range. The electrostatically charged functional NCs represent a comprehensive selection of examples of surface-functionalized NCs, which enables the systematic investigation of experimental parameters in NC assembly processes carried out by combining LbL procedures with microcontact printing and also exploiting NC emission, relevant for potential applications, as a prompt and effective probe for evaluating assembly quality. Thus, an ample showcase of combinations has been investigated, and the spectroscopic and morphological features of the resulting NC-based structures have been discussed.

Surface patterning by microcontact chemistry

In this Feature Article we describe recent progress in covalent surface patterning by microcontact chemistry. Microcontact chemistry is a variation of microcontact printing based on the transfer of reactive "ink" molecules from a microstructured, elastomeric stamp onto surfaces modified with complementary reactive groups, leading to a chemical reaction in the area of contact. In comparison with other lithographic methods, microcontact chemistry has a number of advantageous properties including very short patterning times, low consumption of ink molecules, high resolution and large area patterning. During the past 5 years we and many others have investigated a set of different reactions that allow the modification of flat and also spherical surfaces in an effective way. Especially click-type reactions were found to be versatile for substrate patterning by microcontact chemistry and were applied for chemical modification of reactive self-assembled monolayers and polymer surfaces. Microcontact chemistry has already found broad application for the production of functional surfaces and was also used for the preparation of DNA, RNA, and carbohydrate microarrays, for the immobilization of proteins and cells and for the development of sensors.

Site-selective surface modification using enzymatic soft lithography

Surface modification with functional polymers or molecules offers great promise for the development of smart materials and applications. Here, we describe a versatile and easy-to-use method of site-selective surface modification based on the ease of microcontact printing and the exquisite selectivity of enzymatic degradation. A micropatterned poly-L-lysine (PLL) layer on solid substrates was prepared by enzymatic degradation using trypsin enzyme immobilized on a prestructured poly(dimethlylsiloxane) (PDMS) stamp. After the enzymatic degradation of PLL and the removal of the degradation products, very well defined patterning was revealed over a large scale by fluorescence microscopy and atomic force microscopy (AFM). We investigate the advantage of our method by comparison with traditional microcontact printing and found that lateral diffusion was reduced, yielding a more accurate reproduction of the master. We also demonstrate that the stamp can be reused without reinking. The patterned surface was used for site-selective modification. The strategy was applied to two applications: the first is dedicated to the creation of amino-silane patterned surfaces, and the second illustrates the possibility of patterning polyelectrolyte multilayered thin films.

Controllable photoluminescence properties of an anion-dye-intercalated layered double hydroxide by adjusting the confined environment

This article reports a novel method to tune the photoluminance properties of ammonium 1-anilinonaphthalene-8-sulfonate (ANS) in a 2D matrix of layered double hydroxide (LDH) by changing the interlayer microenvironment. ANS and a series of surfactants with different alkyl chain lengths (pentanesulphonate (PES), hexanesulphonate (HES), heptanesulphonate (HPS), decanesulphonate (DES), and dodecylsulphonate (DDS)) were respectively cointercalated into the galleries of ZnAl-LDH by the anion exchange method. Thin films of ANS/surfactant-LDHs obtained by the solvent evaporation method possess good c orientation as revealed by XRD and SEM. It was found that the ANS/HPS-LDH film showed the maximum fluorescence efficiency and the longest intensity-average lifetime among these ANS/surfactant-LDH composites owing to the "size-matching" rule between the organic dye and surfactant. Moreover, the fluorescence properties can be tuned by changing the relative molar ratio of ANS/HPS, and the film containing 20% ANS (molar percentage, expressed as ANS(20%)/HPS-LDH) exhibits the maximum fluorescence efficiency, the longest average lifetime, and significantly enhanced photo and thermal stability. In addition, the composite films show fluorescence anisotropy, attributed to the preferential orientation of ANS in the LDH gallery. Therefore, this work demonstrates a feasible approach to tuning the photoluminescence properties of a dye confined in an inorganic 2D matrix via changing the interlayer microenvironment, which may be considered to be a good candidate for solid photoluminescence materials, nonlinear optics, and polarized luminescence materials.

Stamps, inks and substrates: polymers in microcontact printing

It's all about polymers! Polymers play a key role in the patterning and functionalization of surfaces by microcontact printing. Polymers are versatile stamps, inks and substrates and microcontact printing can provide microstructured polymer surfaces in a single printing step.

Porous multilayer-coated PDMS stamps for protein printing

A polyelectrolyte multilayer was assembled on top of a patterned PDMS stamp employing the layer-by-layer (LbL) assembly technique. By post-treatment with a base and further cross-linking, a porous multilayer-coated PDMS composite stamp was obtained. With the pore structures acting as an ink reservoir, the multiple printing of proteins was successfully achieved without the need to re-ink the stamp.

Microfluidic patterning of miniaturized DNA arrays on plastic substrates

This paper describes the patterning of DNA arrays on plastic surfaces using an elastomeric, two-dimensional microcapillary system (muCS). Fluidic structures were realized through hot-embossing lithography using Versaflex CL30. Like elastomers based on poly(dimethylsiloxane), this thermoplastic block copolymer is able to seal a surface in a reversible manner, making it possible to confine DNA probes with a level of control that is unparalleled using standard microspotting techniques. We focus on muCSs that support arrays comprising up to 2 x 48 spots, each being 45 mum in diameter. Substrates were fabricated from two hard thermoplastic materials, poly(methylmethacrylate) and a polycyclic olefin (e.g., Zeonor 1060R), which were both activated with 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride and N-hydroxysuccinimide to mediate covalent attachment of DNA molecules. The approach was exemplified by using 0.25-32 muM solutions of amino-modified oligonucleotides labeled with either Cy3 or Cy5 fluorescent dye in phosphate-buffered saline, allowing for a direct and sensitive characterization of the printed arrays. Solutions were incubated for durations of 1 to >48 h at 22, 30, and 40 degrees C to probe the conditions for obtaining uniform spots of high fluorescence intensity. The length (l) and depth (d) of microfluidic supply channels were both important with respect to depletion as well as evaporation of the solvent. While selective activation of the substrate proved helpful to limit unproductive loss of oligonucleotides along trajectories, incubation of solution in a humid environment was necessary to prevent uncontrolled drying of the liquid, keeping the immobilization process intact over extended periods of time. When combined, these strategies effectively promoted the formation of high-quality DNA arrays, making it possible to arrange multiple probes in parallel with a high degree of uniformity. Moreover, we show that resultant arrays are compatible with standard hybridization protocols, which allowed for reliable discrimination of individual strands when exposed to a specific ssDNA target molecule.

Microcontact printing of dendrimers, proteins, and nanoparticles by porous stamps

Porous stamps fabricated by one-step phase separation micromolding were used for microcontact printing of polar inks, in particular aqueous solutions of dendrimers, proteins, and nanoparticles. Permanent hydrophilicity was achieved without any additional treatment by tailored choice of the polymer components. Pores with several hundred nanometers to micrometers were obtained during the phase separation process. These pores can act as ink reservoirs. The porous stamps were thoroughly characterized by SEM, NMR, and contact angle measurement. The versatility of the porous stamps was shown in three printing schemes. First, positive microcontact printing was achieved by printing a polar thioether-modified dendrimer as the ink, followed by backfilling and wet etching. Second, the porous stamps were used for multiple printing of fluorescent proteins without reinking. Third, nanoparticles of about 60 nm in diameter, which cannot be directly transferred by oxidized PDMS stamps, were successfully printed onto substrates by using these porous stamps.