Preparation of a self-matting, anti-fingerprint and skin-tactile wood coating via biomimetic self-wrinkling patterns

Inspired by natural wrinkled surfaces, artificial surfaces with biomimetic wrinkled structures have been widely used to improve optical properties, wettability, and antibacterial properties. However, the preparation of wrinkled structures has the disadvantages of long-time consumption and complex processes. Herein, we prepared a self-wrinkling polyurethane-acrylate (PUA) wood coating via biomimetic self-wrinkling patterns by using a light-emitting diode (LED)/excimer/mercury lamp curing system, which was capable of self-matting, anti-fingerprint and skin-tactile performance. By adjusting the irradiation intensity in the curing system, the wavelength (λ) and amplitude (A) of wrinkles on the coating surface were controlled to enhance the coating performance. After curing by the LED, excimer, and mercury lamps at energy intensities of 500, 30, and 300 mW/cm2 respectively, the self-wrinkling coating showed excellent surface performance. The self-wrinkling coating represented low gloss of 4.1 GU at 85°, high hardness of 4H. Interestingly, the coating surface had a high hydrophobicity (104.5°) and low surface energy (29-30 mN/m) and low coefficient (COF) of friction (0.1-0.2), which were consistent with those of the human skin surface. Besides, the wrinkled structure also improved the thermal stability of the coating samples. This study provided a promising technique for the mass production of self-wrinkling coatings that could be used in wood-based panels, furniture, and leather.

A study on the fabrication of metal microneedle array electrodes for ECG detection based on low melting point Bi-In-Sn alloys

This study describes the fabrication and characteristics of microneedle array electrodes (MAEs) using Bismuth-Indium-Tin (Bi-In-Sn) alloys. The MAEs consist of 57 pyramid-shaped needles measuring 340 μm wide and 800 μm high. The fabrication process involved micromolding the alloys in a vacuum environment. Physical tests demonstrated that Bi-In-Sn MAEs have good mechanical strength, indicating their suitability for successful skin penetration. The electrode-skin interface impedance test confirmed that Bi-In-Sn MAEs successfully penetrated the skin. Impedance measurements revealed the importance of insulating the microneedle electrodes for optimal electrical performance, and a UV-curable Polyurethane Acrylate coating was applied to enhance insulation. Electrocardiogram measurements using the Bi-In-Sn MAEs demonstrated performance comparable to that of traditional Ag/AgCl electrodes, which shows promise for accurate data collection. Overall, the study demonstrates successful, minimally-invasive skin insertion, improved electrical insulation, and potential applications of Bi-In-Sn microneedle array. These findings contribute to advancements in microneedle technology for biomedical applications.

Robust and Transparent Lossless Directional Omniphobic Ultra-Thin Sticker-Type Film with Re-entrant Micro-Stripe Arrays

Directional droplet-sliding control without wetting the surface is immensely required in advanced surface engineering, including biological and chemical analyses or green technology. However, the development of robust and transparent thin sticker-type directional omniphobic films for portable usage in smart microfluidic platforms is rare. In this study, we report a novel perfluoropolyether (PFPE) directional omniphobic film (PDOF). The PDOF is a robust and transparent ultra-thin sticker-type film that can control the anisotropic sliding of various liquid droplets on the surface. The PFPE is a chemically stable and turgid material compared to polydimethylsiloxane (PDMS), which is often used to fabricate liquid-repellent thin films. A well-designed fabrication criterion through adhesion engineering in the soft-molding process was developed using the PFPE to obtain a PDOF with a thickness of 56 μm, with re-entrant micro-stripe structures on the surface. The fabricated PDOF showed intriguing liquid sliding properties based on the direction and spacing of the microstructures. This aspect is defined as an anisotropic factor.

Recyclable, Antibacterial, Isoporous Through-Hole Membrane Air Filters with Hydrothermally Grown ZnO Nanorods

Reusable, antibacterial, and photocatalytic isoporous through-hole air filtration membranes have been demonstrated based on hydrothermally grown ZnO nanorods (NRs). High-temperature (300~375 °C) stability of thermoset-based isoporous through-hole membranes has enabled concurrent control of porosity and seed formation via high-temperature annealing of the membranes. The following hydrothermal growth has led to densely populated ZnO NRs on both the membrane surface and pore sidewall. Thanks to the nanofibrous shape of the grown ZnO NRs on the pore sidewall, the membrane filters have shown a high (>97%) filtration efficiency for PM2.5 with a rather low-pressure (~80 Pa) drop. The membrane filters could easily be cleaned and reused many times by simple spray cleaning with a water/ethanol mixture solution. Further, the grown ZnO NRs have also endowed excellent bactericidal performance for both Gram-positive S. aureus and Gram-negative S. enteritidis bacteria. Owing to the wide bandgap semiconductor nature of ZnO NRs, organic decomposition by photocatalytic activity under UV illumination has been successfully demonstrated. The reusable, multifunctional membrane filters can find wide applications in air filtration and purification.

Nanoimprint Replication of Biomimetic, Multilevel Undercut Nanostructures

The nanoimprint replication of biomimetic nanostructures can be interesting for a wide range of applications. We demonstrate the process chain for Morpho-blue-inspired nanostructures, which are especially challenging for the nanoimprint process, since they consist of multilayer undercut structures, which typically cannot be replicated using nanoimprint lithography. To achieve this, we used a specially made, proprietary imprint material to firstly allow successful stamp fabrication from an undercut master structure, and secondly to enable UV-based nanoimprinting using the same material. Nanoimprinting was performed on polymer substrates with stamps on polymer backplanes to be compatible with roller-based imprinting processes. We started with single layer undercut structures to finally show that it is possible to successfully replicate a multilayer undercut stamp from a multilayer undercut master and use this stamp to obtain multilayer undercut nanoimprinted samples.

Core-Shell Magnetic Micropillars for Reprogrammable Actuation

Stimuli-responsive micro/nanostructures that exhibit not only programmable but also reprogrammable actuation behaviors are highly desirable for various advanced engineering applications (e.g., anticounterfeiting, information encoding, dynamic imaging and display, microrobotics, etc.) but yet to be realized with state-of-the-art technologies. Here we report a concept and a corresponding experimental technique for core-shell magnetic micropillars enabling simultaneously programmable and reprogrammable actuations using a simple magnetic field. The micropillars are composed of elastomeric hollow shells for shaping encapsulated with liquid magnetic nanocomposite resin cores for actuating. The spatial distribution of the magnetic nanoparticles inside the resin channels can be dynamically modulated within individual micropillars, which consequently regulates the magnetomechanical responses of the pillars upon actuation (bending deformation varied near 1 order of magnitude under the same actuation field). We demonstrate that the micropillars with contrasting bending responses can be configured in an arbitrary spatial pattern by direct magnetic writing, and the written pattern can then be easily magnetically erased to facilitate next-round rewriting and reconfiguration. This reprogrammable actuation capability of the micropillars is further demonstrated by their potential applications for rewritable paper and recyclable displays, where various microscale characteristics can be controlled to dynamically appear and disappear at the same or different locations of one single micropillar array. The core-shell magnetic micropillars reported here provide a universal prototype for reprogrammable responsive micro/nanostructures through rational design and facile fabrication from conventional materials.

Highly Flexible and Photo-Activating Acryl-Polyurethane for 3D Steric Architectures

An acryl-functionalized polyurethane (PU) series was successfully synthesized using poly(tetramethylene ether) glycol-methylene diphenyl diisocyanate (PTMG-MDI) oligomer based on urethane methacrylates to control the flexibility of photo-cured 3D printing architectures. The mass ratio of acryl-urethane prepolymer: 1,4-butanediol (BD) chain-extender: diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiator was 10:0.25:1. To produce suitably hard and precisely curved 3D architectures, the optimal UV absorbance and exposure energy of the acryl-PTMG-MDI resin were controlled precisely. Owing to the optimized viscosity of the acryl-PTMG-MDI resins, they could be printed readily by digital light processing (DLP) to form precisely curved 3D architectures after mixing with 1,6-hexanediol diacrylate (HDDA). The acryl-PTMG-MDI formulations showed much better flexural resolution than the neat resins. The printed 3D structure exhibited high surface hardness, good mechanical strength, and high elasticity for flexible applications in consumer/industrial and biomedical fields.

Electronic effects of nano-confinement in functional organic and inorganic materials for optoelectronics

This review provides a comprehensive overview of the electronic effects of nano-confinement (from 1D to 3D geometries) on optoelectronic materials and their applications.

Self-detachable UV-curable polymers for open-access microfluidic platforms

This study presents an ultraviolet (UV)-curable polymer which is applicable to open-access microfluidic platforms. The UV-curable polymer was prepared by mixing trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), polyethylene glycol-diacrylate (PEG-DA), and Irgacure 184. The polymer resin is optically transparent before and after UV-assisted curing and showed good biocompatibility when culturing multiple types of cells on the nanopatterned polymer substrate. The polymer has good adhesion with poly(dimethylsiloxane) (PDMS) even under large deformation and showed a low swelling ratio when exposed to water, suggesting a possibility to be used as a substrate for an organ on a chip. Furthermore, because the polymers have controllable hydrolysis ability depending on the composition, long-term 3D cell culture and subsequent biological analysis with harvested cells are possible. The self-detachable synthesized UV-curable polymer may help the advancement of biomedical studies using in vitro cell culture.

Preparation and Characterization of Tris(trimethylsiloxy)silyl Modified Polyurethane Acrylates and Their Application in Textile Treatment

Three series of silicone modified polyurethane acrylate (SPUA) prepolymers were prepared from dicyclohexylmethane-4, 4'-diisocyanate (HMDI), PPG1000, triethylene glycol (TEG), 2-hydroxyethyl acrylate (HEA), and multi-hydroxyalkyl silicone (MI-III) with tris(trimethylsiloxy)silyl propyl side groups. Their structures were confirmed by 1H NMR, 13C NMR, and Fourier transformed infrared (FTIR) analysis, and SPUA films were obtained by UV curing. The properties of films were investigated by attenuated total reflection (ATR)-FTIR, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), water contact angle (WCA), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), water and hexane resistance, and tensile testing. The results showed that the structures and dosages of MI-III could influence the polymerization properties, surface properties, water and n-hexane resistance, and thermal and tensile properties of SPUA. For instance, the surface aggregation of tris(trimethylsiloxy)silyl propyl groups (even ~2.5 wt%) could endow SPUA films with less microphase separation, good hydrophobicity, lipophilicity, thermal stability, and mechanical properties. Interestingly, obvious regular winkles appeared on the surfaces of SPUAIII films, which are characterized by relatively high WCA values. However, relatively smooth were observed on the surfaces of SPUAIII films, which also exhibit lower water absorption ratio values. Furthermore, the ordinary cotton textiles would be transformed into hydrophobic and oleophilic textiles after treating with SPUA simply, and they were used in the oil/water separation study. Among them, consistent with water and hexane resistance analysis of SPUA films, SPUAII treated cotton textiles are characterized by relatively small liquid absorption capacity (LAC) values. Thus, phenyl groups and side-chain tris(trimethylsiloxy)silyl propyl groups are helpful to improve the hydrophobicity and lipophilicity of SPUA films. SPUAII-5 (even with 5 wt% MII) treated cotton textiles could efficiently separate the oil/water mixture, such as n-hexane, cyclohexane, or methylbenzene with water. Thus, this material has great potential in the application of hydrophobic treatment, oil/water separation, and industrial sewage emissions, among others.

Quantitative Correlation of Nanotopography with Cell Spreading via Focal Adhesions Using Adipose-Derived Stem Cells

Nanotopography mimicking extracellular environments reportedly impact cell morphological changes; however, elucidating this relationship has been challenging. To control cellular responses using nanostructures, in this study, the quantitative relationship between nanotopography and cell spreading mediated by focal adhesions (FAs) is demonstrated using adipose-derived stem cells (ASCs). The spreading of ASCs and area of FAs are analyzed for the distribution of filamentous actin and vinculin, respectively, using fluorescent images. FAs require a specific area for adhesion (herein defined as effective contact area [ECA]) to maintain cell attachment on nanopillar arrays. An ECA is the area of FAs supported by nanopillars, multiplying the area fraction (AF) of their top surface. Regarding the spreading of cells, the mean area of ASCs linearly decreases as the mean area of FAs increases. Because the area of FAs is inversely correlated to the AF of the nanopillar arrays, the spreading of cells can be quantitatively correlated with nanotopography. The results provide a conceptual framework for controlling cell behaviors to design artificial substrates for tissue-engineering applications.

Electrochemically Exfoliated Functionalized Black Phosphorene and Its Polyurethane Acrylate Nanocomposites: Synthesis and Applications

Owing to its mechanical performance, thermal stability, and size effects, single or few-layer black phosphorus (BP) has the potential to prepare the polymer nanocomposites as a candidate of nanoadditives, similar to graphene. The step to realize the scalable exfoliation of single or few-layer BP nanosheets is crucial to BP applications. Herein, we utilized a facile, green, and scalable electrochemical strategy for generating cobaltous phytate-functionalized BP nanosheets (BP-EC-Exf) wherein the BP crystal served as the cathode and phytic acid served as a modifier and an electrolyte simultaneously. Moreover, high-performance polyurethane acrylate/BP-EC-Exf (PUA/BP-EC) nanocomposites are easily prepared by a convenient UV-curable strategy for the first time. Significantly, the conclusion of introducing BP-EC-Exf into the PUA matrix resulted in enhancement in mechanical properties of PUA in terms of the tensile strength (increased by 59.8%) and tensile fracture strain (increased by 88.1%), in the distinct improvement in flame retardancy of PUA in terms of the decreased peak heat release rate (reduced by 44.5%) and total heat release (decreased by 34.5%), and in lower intensities of pyrolysis products including toxic CO. Moreover, it was confirmed by X-ray diffraction and Raman spectra that the air stability of PUA/BP-EC nanocomposites was maintained after exposure to environmental conditions for 4 months. The air-stable BP nanosheets, which were wrapped and embedded in the PUA matrix, can achieve the isolation and protection effect. This modified electrochemical method toward the simultaneous exfoliation and functionalization of BP nanosheets provides an efficient approach for fabricating BP-polymer-based nanocomposites.

Facile and Microcontrolled Blade Coating of Organic Semiconductor Blends for Uniaxial Crystal Alignment and Reliable Flexible Organic Field-Effect Transistors

The ability to fabricate uniform and high-quality patterns of organic semiconductors using a simple method is necessary to realize high-performance and reliable organic field-effect transistors (OFETs) for practical applications. Here, we report the facile fabrication of chemically patterned substrates in order to provide solvent wetting/dewetting regions and grow patterned crystals during blade coating of a small-molecule semiconductor/insulating polymer blend solution. Polyurethane acrylate is selected as the solvent dewetting material, not only because of its hydrophobicity but also because its patterns are easily produced by selective UV irradiation onto precursor films. 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) crystal patterns are grown on the line-shaped wetting regions of the patterned film, and the crystallinity of TIPS-PEN and alignment of molecules are found using various crystal analysis tools depending on the pattern widths. The smallest width of 5 μm yielded an OFET showing the highest field-effect mobility value of 1.63 cm²/(V·s), which is much higher than the value of the OFET based on the unpatterned TIPS-PEN crystal. Notably, we demonstrate flexible and low-voltage-operating OFETs for practical use of the patterned crystals, and the OFETs show highly stable operation under sustained gate bias stress thanks to the patterned crystals.

Strong and Reversible Adhesion of Interlocked 3D-Microarchitectures

Diverse physical interlocking devices have recently been developed based on one-dimensional (1D), high-aspect-ratio inorganic and organic nanomaterials. Although these 1D nanomaterial-based interlocking devices can provide reliable and repeatable shear adhesion, their adhesion in the normal direction is typically very weak. In addition, the high-aspect-ratio, slender structures are mechanically less durable. In this study, we demonstrate a highly flexible and robust interlocking system that exhibits strong and reversible adhesion based on physical interlocking between three-dimensional (3D) microscale architectures. The 3D microstructures have protruding tips on their cylindrical stems, which enable tight mechanical binding between the microstructures. Based on the unique 3D architectures, the interlocking adhesives exhibit remarkable adhesion strengths in both the normal and shear directions. In addition, their adhesion is highly reversible due to the robust mechanical and structural stability of the microstructures. An analytical model is proposed to explain the measured adhesion behavior, which is in good agreement with the experimental results.

Roll-to-Roll Manufacturing of Micropatterned Adhesives by Template Compression

For the next generation of handling systems, reversible adhesion enabled by micropatterned dry adhesives exhibits high potential. The versatility of polymeric micropatterns in handling objects made from various materials has been demonstrated by several groups. However, specimens reported in most studies have been restricted to the laboratory scale. Upscaling the size and quantity of micropatterned adhesives is the next step to enable successful technology transfer. Towards this aim, we introduce a continuous roll-to-roll replication process for fabrication of high-performance, mushroom-shaped micropatterned dry adhesives. The micropatterns were made from UV-curable polyurethane acrylates. To ensure the integrity of the complex structure during the fabrication process, flexible templates were used. The compression between the template and the wet prepolymer coating was investigated to optimize replication results without structural failures, and hence, to improve adhesion. As a result, we obtained micropatterned adhesive tapes, 10 cm in width and several meters in length, with adhesion strength about 250 kPa to glass, suitable for a wide range of applications.

Microscale Patterning of Electrochromic Polymer Films via Soft Lithography

We present a direct fabrication technique of patterned polymeric electrochromic (EC) devices via soft lithography, enabling both negative patterning and positive patterning of the polymer. For this work, elastomeric polydimethylsiloxane (PDMS) molds were employed as not only stamps for direct contact printing of polymer inks but also templates for dewetting of polymer solutions under mild experimental conditions. We performed both negative patterning and positive patterning of a prototypical EC polymer and investigated the EC device characteristics according to solvents, solution concentrations, and pattern types. Eventually, the complex patterns, which cannot be realized by conventional shadow masking processes, and large-area structures were successfully demonstrated. We anticipate that these results will be applied to the development of various patterned devices and circuits, which may lead to further applications.

Fabrication and design of mechanically stable and free-standing polymeric membrane with two-level apertures

Herein, we report the fabrication process and the investigation of mechanically stable, flexible and free-standing polymeric membranes with two-level apertures. By using overlapped oxygen inhibition layers (OILs) with variation in diameters of the micro-sized supporting layer, we successfully fabricated the mechanically stable and free-standing polymeric membrane with micro/nano two-level apertures. The nano aperture membrane was stably sustained on the micro aperture membrane with a diameter of 50 μm and 100 μm, but was torn off in the case of 300 μm and 500 μm sized supporting layers. To analyze the results, we propose a simple model to set the criteria of the geometrical features which are mechanically stable during the demolding process. It is worth noting that an appropriate material modulus, length, and thickness of the membrane are required for designing and achieving the robust free-standing hierarchical polymeric membrane.

Long-Term Stable Transferred Organic Photoactive Layer-Based Photodiode with Controlled Wetting through Interface Stabilization

The stamping transfer process, which provides a precise patterning of the target material without the limitation of an underlying layer, has attracted significant attention for large-scale roll-to-roll fabrication. Despite the need to minimize the peeling energy, expressed as the sum of adhesion energies, for a simple transfer process, many studies have not considered this effect. In this study, we introduced a wetting coefficient related with adhesions between polymers for the transfer design of organic photosensitive materials. We observed a difference in adhesion between polymer blends depending on the surface energy of the mold. We designed high-surface-energy polyurethane acrylate to enable a residue-free transfer process. The transfer process significantly contributed to the device stability through changes in dark currents, photocurrents, responsivity, and detectivity over time, compared to spin coating. In particular, the detectivity was maintained over 95% after 360 h, and no burn-in loss of internal resistance was observed in the device with a transferred active layer. X-ray photoelectron spectroscopy showed that a large interfacial change between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5- b']dithiophene-2,6-diyl- alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophene-4,6-diyl):[6,6] phenyl C₇₁ butyric acid methyl ester obtained through spin coating occurred owing to solution penetration, whereas the transfer process provided a constant interface owing to morphology stabilization. Therefore, the transfer process with optimized adhesion properties can improve the device operation durability without burn-in loss, enabling a cost-effective fabrication of organic optoelectronic devices.

Transfer Tiling of Nanostructures for Large-Area Fabrication

The fabrication of nanoscale patterns over a large area has been considered important but difficult, because there are few ways to satisfy both conditions. Previously, visually tolerable tiling (VTT) for fabricating nanopatterns for optical applications has been reported as a candidate for large area fabrication. The essence of VTT is the inevitable stitching of the nanoscale optical component, which is not seen by the naked eye if the boundary is very narrow while the tiles are overlapped. However, it had been difficult to control the shape of the spread of liquid prepolymers in the previous work, and there was room for the development of tiling. Here, we propose a method for transferring various shapes of tiles, which can be defined with a shadow mask. The method of using a transparent shadow mask can provide a wide process window, because it allows the spreading of a liquid prepolymer to be more easily controlled. We optimize the coating condition of a liquid prepolymer and the ultraviolet (UV) exposure time. Using this method, we can attach tiles of various shapes without a significant visible trace in the overlapped region.

Nanopatterned Scaffolds for Neural Tissue Engineering and Regenerative Medicine

Biologically inspired approaches employing nanoengineering techniques have been influential in the progress of neural tissue repair and regeneration. Neural tissues are exposed to complex nanoscale environments such as nanofibrils. In this chapter, we summarize representative nanotechniques, such as electrospinning, lithography, and 3D bioprinting, and their use in the design and fabrication of nanopatterned scaffolds for neural tissue engineering and regenerative medicine. Nanotopographical cues in combination with other cues (e.g., chemical cues) are crucial to neural tissue repair and regeneration using cells, including various types of stem cells. Production of biologically inspired nanopatterned scaffolds may encourage the next revolution for studies aiming to advance neural tissue engineering and regenerative medicine.

Surface energy-tunable iso decyl acrylate based molds for low pressure-nanoimprint lithography

We presented surface energy-tunable nanoscale molds for unconventional lithography. The mold is highly robust, transparent, has a minimized haze, does not contain additives, and is a non-fluorinated isodecyl acrylate and trimethylolpropane triacrylate based polymer. By changing the mixing ratio of the polymer components, the cross-linking density, mechanical modulus, and surface energy (crucial factors in low pressure ((1-2) × 10⁵ N m^-2) low pressure-nanoimprint lithography (LP-NIL)), can be controlled. To verify these properties of the molds, we also characterized the surface energy by measuring the contact angles and calculating the work of adhesion among the wafer, polymer film, and mold for successful demolding in nanoscale structures. Moreover, the molds showed high optical clarity and precisely tunable mechanical and surface properties, capable of replicating sub-100 nm patterns by thermal LP-NIL and UV-NIL.

Modulus- and Surface-Energy-Tunable Thiol-ene for UV Micromolding of Coatings

Micromolding of UV-curable materials is a patterning method to fabricate microstructured surfaces that is an additive manufacturing process fully compatible with roll-to-roll systems. The development of micromolding for mass production remains a challenge because of the multifaceted demands of UV curable materials and the risk of demolding-related defects, particularly when patterning high-aspect-ratio features. In this research, a robust micromolding approach is demonstrated that integrates thiol-ene polymerization and UV LED curing. The moduli of cured thiol-ene coatings were tuned over 2 orders of magnitude by simply adjusting the acrylate concentration of a coating formulation, the curing completed in all cases within 10 s of LED exposure. Densely packed 50-μm-wide gratings were faithfully replicated in coatings ranging from soft materials to stiff highly cross-linked networks. Further, surface energy was modified with a fluorinated polymer, achieving a surface energy reduction of more than a half at a loading of 1 wt %, and enabling tall (100 μm) defect-free patterns to be attained. The demolding strengths of microstructured coatings were compared using quantitative peel testing, showing its decrease with decreasing surface energy, coating modulus, and grating height. This micromolding process, combining tunability in thermomechanical and surface properties, makes thiol-ene microstructured coatings attractive candidates for roll-to-roll manufacture. As a demonstration of the utility of the process, superhydrophobic surfaces are prepared using the system modified by the fluorinated polymer.

Repurposing compact discs as master molds to fabricate high-performance organic nanowire field-effect transistors

Organic field-effect transistors (OFETs) have been developed over the past few decades due to their potential applications in future electronics such as wearable and foldable electronics. As the electrical performance of OFETs has improved, patterning organic semiconducting crystals has become a key issue for their commercialization. However, conventional soft lithographic techniques have required the use of expensive processes to fabricate high-resolution master molds. In this study, we demonstrated a cost-effective method to prepare nanopatterned master molds for the fabrication of high-performance nanowire OFETs. We repurposed commercially available compact discs (CDs) as master molds because they already have linear nanopatterns on their surface. Flexible nanopatterned templates were replicated from the CDs using UV-imprint lithography. Subsequently, 6,13-bis-(triisopropylsilylethynyl) pentacene nanowires (NWs) were grown from the templates using a capillary force-assisted lithographic technique. The NW-based OFETs showed a high average field-effect mobility of 2.04 cm² V^-1 s^-1. This result was attributed to the high crystallinity of the NWs and to their crystal orientation favorable for charge transport.

Simple and scalable preparation of master mold for nanoimprint lithography

Nanoimprint lithography (NIL) is one of the most prominent bottom-up techniques for duplicating nanostructures with a high throughput. However, fabrication of starting master mold commonly requires expensive equipment of top-down techniques, or additional steps to transfer the fabricated patterns from bottom-up methods. Here we demonstrate that a SiO₂ nanostructure manufactured from a self-assembled block copolymer, polystyrene-b-polydimethylsiloxane (PS-b-PDMS), directly serves as a master mold for NIL without further modification. A hexagonally aligned pattern over the entire substrate is established using a simple technique; solvent annealing and etching. Etching also plays an important role in endowing fluorine on the surface of SiO₂, thus promoting smooth demolding upon imprinting. The obtained pattern of the SiO₂ nanostructure is transferred to a polymer surface using UV nanoimprint. Identical patterns of the SiO₂ nanostructure are elaborately reproduced on Ni and Cu nanodot arrays via electroplating on the polymer transcript, which was verified by morphological observations. The uniformity of the replicated Ni nanodot array is evaluated using spectroscopic ellipsometry. The measured optical response of the Ni nanodot is validated by electromagnetically simulated results, indicating that the pattern transfer is not limited to a small local area. In addition, the durability of the SiO₂ mold pattern is corroborated after the imprinting process, thus guaranteeing the reusability of the fabricated nanostructure as a master mold. The proposed approach does not require any high-end lithographic techniques; this may result in significant cost and time reductions in future nanofabrication.

Dry-Stamping-Transferred PC71BM Charge Transport Layer via an Interface-Controlled Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells

The study of interlayers is important to enhance the performance of inverted perovskite solar cells (PSCs) because interlayers in PSCs align energy levels and improve charge transport. However, previous research into applying interlayers for PSCs has focused only on wet-coated methods, such as spin coating, to form the interlayer. Here, we fabricated planar-type PSCs deposited with a 6,6-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) layer onto a CH₃NH₃PbI₃ (MAPbI₃) layer by stamping transfer through a relatively dry process condition. We demonstrated the effects of a stamping-transferred PC₇₁BM layer using polyurethane acrylate (PUA), the surface energy of which was modified by 2-hydroxyethyl methacrylate (HEMA) to increase the transfer reproducibility. In PSCs with a stamping-transferred PC₇₁BM layer, we observed an enhanced J_SC and a comparable power conversion efficiency (PCE), which were caused by an enhanced coverage of the electron transport layer onto the MAPbI₃ layer with preserved crystallinity, which occurs owing to improved electron mobility and exciton dissociation. The optimized device PCE through the dry-transferred PC₇₁BM exhibited a J_SC, fill factor, and PCE of 21.65 mA/cm², 76.0%, and 15.46%, respectively. Moreover, morphological analysis and electrical measurements confirmed the improved durability of dry-stamping-transferred PSCs.

Area-Selective Lift-Off Mechanism Based on Dual-Triggered Interfacial Adhesion Switching: Highly Facile Fabrication of Flexible Nanomesh Electrode

With the recent emergence of flexible and wearable optoelectronic devices, the achievement of sufficient bendability and stretchability of transparent and conducting electrodes (TCEs) has become an important requirement. Although metal-mesh-based structures have been investigated for TCEs because of their excellent performances, the fabrication of mesh or grid structures with a submicron line width is still complex due to the requirements of laborious lithography and pattern transfer steps. Here, we introduce an extremely facile fabrication technique for metal patterns embedded in a flexible substrate based on submicron replication and an area-selective delamination (ASD) pattern. The high-yield, area-specific lift-off process is based on the principle of solvent-assisted delamination of deposited metal thin films and a mechanical triggering effect by soft wiping or ultrasonication. Our fabrication process is very simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. Moreover, their outstanding optical and electrical properties (e.g., sheet resistances of 0.43 Ω sq^-1 at 94% transmittance), which are markedly superior to those of other flexible TCEs, are demonstrated. Furthermore, there is no significant change of resistance over 1000 repeated bending cycles, with a bending radius of 5 mm, and immersion in various solvents such as salt water and organic solvents. Finally, we demonstrate high-performance transparent heaters and flexible touch panels fabricated using the nanomesh electrode, confirming the long-range electrical conduction and reliability of the electrode.

Scalable Fabrication of Flexible Microstencils by Using Sequentially Induced Dewetting Phenomenon

We present the physics of sequential dewetting phenomenon and continuous fabrication of a polymeric microstencil using dewetting phenomenon with roll-to-roll imprinting equipment. To realize dewetting-assisted residual-free imprinting, mold material, polymer resin, and substrate were selected via interfacial surface energy analysis. In addition, optimal parameters of the continuous process were also studied by experimentally comparing the resultant shape of the microstencil depending on the process speed, aspect ratio of the mold, and applied pressure. As a result, the polymeric microstencil was produced continuously in very high yields, and its maximum resolution reached 20 μm in diameter. For an easy, continuous demolding during the roll-to-roll process, the material chosen for the substrate film was paraffin-coated film, which has the surface energy low enough for dewetting while having a higher adhesion value than polydimethylsiloxane mold. This versatile, high-throughput microstencil fabrication process can be used in many applications requiring flexibility, scalability, and specific material, and high productivity.

Artificial Slanted Nanocilia Array as a Mechanotransducer for Controlling Cell Polarity

We present a method to induce cell directional behavior using slanted nanocilia arrays. NIH-3T3 fibroblasts demonstrated bidirectional polarization in a rectangular arrangement on vertical nanocilia arrays and exhibited a transition from a bidirectional to a unidirectional polarization pattern when the angle of the nanocilia was decreased from 90° to 30°. The slanted nanocilia guided and facilitated spreading by allowing the cells to contact the sidewalls of the nanocilia, and the directional migration of the cells opposed the direction of the slant due to the anisotropic bending stiffness of the slanted nanocilia. Although the cells recognized the underlying anisotropic geometry when the nanocilia were coated with fibronectin, collagen type I, and Matrigel, the cells lost their directionality when the nanocilia were coated with poly-d-lysine and poly-l-lysine. Furthermore, although the cells recognized geometrical anisotropy on fibronectin coatings, pharmacological perturbation of PI3K-Rac signaling hindered the directional elongation of the cells on both the slanted and vertical nanocilia. Furthermore, myosin light chain II was required for the cells to obtain polarized morphologies. These results indicated that the slanted nanocilia array provided anisotropic contact guidance cues to the interacting cells. The polarization of cells was controlled through two steps: the recognition of underlying geometrical anisotropy and the subsequent directional spreading according to the guidance cues.

Direct fabrication of electrochromic devices with complex patterns on three-dimensional substrates using polymeric stencil films

This article describes a direct fabrication technique for electrodes and further electrochromic devices with complex shapes on three-dimensional substrates.

Hierarchically Micro- and Nanopatterned Topographical Cues for Modulation of Cellular Structure and Function

Living cells receive biochemical and physical information from the surrounding microenvironment and respond to this information. Multiscale hierarchical substrates with micro- and nanogrooves have been shown to mimic the native extracellular matrix (ECM) better than conventional nanopatterned substrates; therefore, substrates with hierarchical topographical cues are considered suitable for investigating the role of physical factors in tissue functions. In this study, precisely controllable, multiscale hierarchical substrates that could mimic the micro- and nanotopography of complex ECMs were fabricated and used to culture various cell types, including fibroblasts, endothelial cells, osteoblasts, and human mesenchymal stem cells. These substrates had both microscale wrinkles and nanoscale patterns and enhanced the alignment and elongation of all the cells tested. In particular, the nanotopography on the microscale wrinkles promoted not only the adhesion, but also the functions of the cells. These findings suggest that the hierarchical multiscale substrates effectively regulated cellular structure and functions and that they can be used as a platform for tissue engineering and regenerative medicine.

Multilength Scale Patterning of Functional Layers by Roll-to-Roll Ultraviolet-Light-Assisted Nanoimprint Lithography

Top-down fabrication of nanostructures with high throughput is still a challenge. We demonstrate the fast (>10 m/min) and continuous fabrication of multilength scale structures by roll-to-roll UV-nanoimprint lithography on a 250 mm wide web. The large-area nanopatterning is enabled by a multicomponent UV-curable resist system (JRcure) with viscous, mechanical, and surface properties that are tunable over a wide range to either allow for usage as polymer stamp material or as imprint resist. The adjustable elasticity and surface chemistry of the resist system enable multistep self-replication of structured resist layers. Decisive for defect-free UV-nanoimprinting in roll-to-roll is the minimization of the surface energies of stamp and resist, and the stepwise reduction of the stiffness from one layer to the next is essential for optimizing the reproduction fidelity especially for nanoscale features. Accordingly, we demonstrate the continuous replication of 3D nanostructures and the high-throughput fabrication of multilength scale resist structures resulting in flexible polyethylenetherephtalate film rolls with superhydrophobic properties. Moreover, a water-soluble UV-imprint resist (JRlift) is introduced that enables residue-free nanoimprinting in roll-to-roll. Thereby we could demonstrate high-throughput fabrication of metallic patterns with only 200 nm line width.

Facile Multiscale Patterning by Creep-Assisted Sequential Imprinting and Fuel Cell Application

The capability of fabricating multiscale structures with desired morphology and incorporating them into engineering applications is key to realizing technological breakthroughs by employing the benefits from both microscale and nanoscale morphology simultaneously. Here, we developed a facile patterning method to fabricate multiscale hierarchical structures by a novel approach called creep-assisted sequential imprinting. In this work, nanopatterning was first carried out by thermal imprint lithography above the glass transition temperature (Tg) of a polymer film, and then followed by creep-assisted imprinting with micropatterns based on the mechanical deformation of the polymer film under the relatively long-term exposure to mechanical stress at temperatures below the Tg of the polymer. The fabricated multiscale arrays exhibited excellent pattern uniformity over large areas. To demonstrate the usage of multiscale architectures, we incorporated the multiscale Nafion films into polymer electrolyte membrane fuel cell, and this device showed more than 10% higher performance than the conventional one. The enhancement was attributed to the decrease in mass transport resistance because of unique cone-shape morphology by creep-recovery effects and the increase in interfacial surface area between Nafion film and electrocatalyst layer.

Inkjet-Assisted Nanotransfer Printing for Large-Scale Integrated Nanopatterns of Various Single-Crystal Organic Materials

Inkjet-assisted nanotransfer printing (inkjet-NTP) facilitates spatial control of many arrays of various organic functional materials on a single substrate with a high-throughput integration process, enabling monolithic integration of various organic nanopatterns. Inkjet-NTP enables wafer-scale organic electronic circuits composed of field-effect transistors, complementary inverters, and p-n diodes, demonstrating its capability to produce a high-performance, multifunctional organic chip.

A Lattice-Strained Organic Single-Crystal Nanowire Array Fabricated via Solution-Phase Nanograting-Assisted Pattern Transfer for Use in High-Mobility Organic Field-Effect Transistors

A 50 nm-wide 6,13-bis(triisopropylsilylethynyl) pentacene nanowire (NW) array is fabricated on a centimeter-sized substrate via a facile nanograting-assisted pattern-transfer method. NW growth under a nanoconfined space adopts a lattice-strained packing motif of the NWs for strong intermolecular electronic coupling, and thus a NW-based organic field-effect transistor shows high field-effect mobility up to 9.71 cm(2) V(-1) s(-1) .

Enhanced Bone Repair by Guided Osteoblast Recruitment Using Topographically Defined Implant

The rapid recruitment of osteoblasts in bone defects is an essential prerequisite for efficient bone repair. Conventionally, osteoblast recruitment to bone defects and subsequent bone repair has been achieved using growth factors. Here, we present a methodology that can guide the recruitment of osteoblasts to bone defects with topographically defined implants (TIs) for efficient in vivo bone repair. We compared circular TIs that had microgrooves in parallel or radial arrangements with nonpatterned implants for osteoblast migration and in vivo bone formation. In vitro, the microgrooves in the TIs enhanced both the migration and proliferation of osteoblasts. Especially, the microgrooves with radial arrangement demonstrated a much higher efficiency of osteoblast recruitment to the implants than did the other types of implants, which may be due to the efficient guidance of cell migration toward the cell-free area of the implants. The expression of the intracellular signaling molecules responsible for the cell migration was also upregulated in osteoblasts on the microgrooved TIs. In vivo, the TI with radially defined topography demonstrated much greater bone repair in mouse calvarial defect models than in the other types of implants. Taken together, these results indicate that implants with physical guidance can enhance tissue repair by rapid cell recruitment.

One step fabrication of polymeric ratchet structures of diverse tilting angles

A novel method to fabricate asymmetric ratchet-like micro structures with various tilting angles is presented by controlling the light transmission pathway with double-layered Lucius prism arrays.

Synthesis and characterization of polyurethanes bearing carbosilane segments

New polyurethanes bearing carbosilane segment (1a–c) were synthesized and found to exhibit lower glass transition temperature and storage moduli than corresponding reference polyurethanes 2a–c, while thermal stability was retained.

Cellular modulation by the elasticity of biomaterials

The elasticity of the extracellular matrix has been increasingly recognized as a dominating factor of cell fate and activities. This review provides an overview of the general principles and recent advances in the field of matrix elasticity-dependent regulation of a variety of cellular activities and functions, the underlying biomechanical and molecular mechanisms, as well as the pathophysiological implications.

Robust microzip fastener: repeatable interlocking using polymeric rectangular parallelepiped arrays

We report a highly repeatable and robust microzip fastener based on the van der Waals force-assisted interlocking between rectangular parallelepiped arrays. To investigate zipperlike interlocking behaviors, various line arrays were fabricated with three different spacing ratios (1, 3, and 5 of 800 nm in width) and width of parallelepipeds (400 nm, 800 nm, and 5 μm with the spacing ratio of 1). In addition, the different rigidity of line arrays was inspected for a repeatable microzip fastener. The normal and shear locking forces were measured with variation of the material rigidity as well as geometry of the array, in good agreement with a proposed theory based on the contact area and force balance. The maximum adhesion forces as high as ∼8.5 N cm(-2) in the normal direction and ∼29.6 N cm(-2) in the shear direction were obtained with high stability up to 1000 cycles. High stability of our fastening system was confirmed for preventing critical failures such as buckling and fracture in practical applications.

Continuous and scalable fabrication of bioinspired dry adhesives via a roll-to-roll process with modulated ultraviolet-curable resin

A simple yet scalable strategy for fabricating dry adhesives with mushroom-shaped micropillars is achieved by a combination of the roll-to-roll process and modulated UV-curable elastic poly(urethane acrylate) (e-PUA) resin. The e-PUA combines the major benefits of commercial PUA and poly(dimethylsiloxane) (PDMS). It not only can be cured within a few seconds like commercial PUA but also possesses good mechanical properties comparable to those of PDMS. A roll-type fabrication system equipped with a rollable mold and a UV exposure unit is also developed for the continuous process. By integrating the roll-to-roll process with the e-PUA, dry adhesives with spatulate tips in the form of a thin flexible film can be generated in a highly continuous and scalable manner. The fabricated dry adhesives with mushroom-shaped microstructures exhibit a strong pull-off strength of up to ∼38.7 N cm(-2) on the glass surface as well as high durability without any noticeable degradation. Furthermore, an automated substrate transportation system equipped with the dry adhesives can transport a 300 mm Si wafer over 10,000 repeating cycles with high accuracy.

Extracellular matrix elasticity and topography: material-based cues that affect cell function via conserved mechanisms

Chemical, mechanical, and topographic extracellular matrix (ECM) cues have been extensively studied for their influence on cell behavior. These ECM cues alter cell adhesion, cell shape, and cell migration and activate signal transduction pathways to influence gene expression, proliferation, and differentiation. ECM elasticity and topography, in particular, have emerged as material properties of intense focus based on strong evidence these physical cues can partially dictate stem cell differentiation. Cells generate forces to pull on their adhesive contacts, and these tractional forces appear to be a common element of cells' responses to both elasticity and topography. This review focuses on recently published work that links ECM topography and mechanics and their influence on differentiation and other cell behaviors. We also highlight signaling pathways typically implicated in mechanotransduction that are (or may be) shared by cells subjected to topographic cues. Finally, we conclude with a brief discussion of the potential implications of these commonalities for cell based therapies and biomaterial design.