We demonstrate the fabrication of good quality surface alignment layers on glass by Direct Laser Writing method using a 2-photon polymerisation technique. We use commercially available photosensitive resins to print alignment layers by scanning the focal point of a femtosecond laser near the resin-glass interface. This results in down to ~ 100 nm thin alignment layers that provide good planar anchoring of 5CB and MLC13300, with the easy axis of alignment along the scanning direction. The azimuthal anchoring strength is ~ 5 × 10-6 J/m2 and is an order of magnitude weaker compared to commercial rubbed polyimide alignment layer. The threshold voltage for Fréedericksz transition in a 90° twisted nematic cell is slightly increased compared to conventional rubbed polyimide for printed alignment layers. The turn-on switching time is longer for printed layers compared to polyimide alignment layers, whereas the turn-off time is shorter for printed alignment layers. The advantage of this new method is in its flexibility, as we demonstrate printing of complex surface alignment patterns with alignment layer thickness below 100 nm.

The undesirable dendrite growth induced by non-planar zinc (Zn) deposition and low Coulombic efficiency resulting from severe side reactions have been long-standing challenges for metallic Zn anodes and substantially impede the practical application of rechargeable aqueous Zn metal batteries (ZMBs). Herein, we present a strategy for achieving a high-rate and long-cycle-life Zn metal anode by patterning Zn foil surfaces and endowing a Zn-Indium (Zn-In) interface in the microchannels. The accumulation of electrons in the microchannel and the zincophilicity of the Zn-In interface promote preferential heteroepitaxial Zn deposition in the microchannel region and enhance the tolerance of the electrode at high current densities. Meanwhile, electron aggregation accelerates the dissolution of non-(002) plane Zn atoms on the array surface, thereby directing the subsequent homoepitaxial Zn deposition on the array surface. Consequently, the planar dendrite-free Zn deposition and long-term cycling stability are achieved (5,050 h at 10.0 mA cm-2 and 27,000 cycles at 20.0 mA cm-2). Furthermore, a Zn/I2 full cell assembled by pairing with such an anode can maintain good stability for 3,500 cycles at 5.0 C, demonstrating the application potential of the as-prepared ZnIn anode for high-performance aqueous ZMBs.

We report a straightforward method for creating large-area, microscale resolution patterns of functional amines on self-assembled monolayers by the photoinduced local acidification of a flat elastomeric stamp enriched with photoacid. The limited diffusivity of the photoactivated merocyanine acid in poly(dimethylsiloxane) (PDMS) enabled to confine efficient deprotection of N-tert-butyloxycarbonyl amino group (N-Boc) to line widths below 10 μm. The experimental setup is very simple and is built around the conventional HD-DVD optical pickup. The method allows cost-efficient, maskless, large-area chemical patterning while avoiding potentially cytotoxic photochemical reaction products. The activation of the embedded photoacid occurs within the stamp upon illumination with the laser beam and the process is fully reversible. Preliminary positive results highlight the possibility of repeatable use of the same stamp for the creation of different patterns.

We introduce a unique soft lithographic operation that exploits stamp roof collapse-induced gaps to selectively remove an alkanethiol self-assembled monolayer (SAM) on Au to generate surface patterns that are orders of magnitude smaller than structures on the original elastomer stamp. The smallest achieved feature dimension is 5 nm using a micrometer-scale structured stamp in a chemical lift-off lithography (CLL) process. Molecular patterns retained in the gaps between stamp features and their circumscribed or inscribed circles follow mathematical predictions, and their sizes can be tuned by altering the stamp structure dimensions, including height, pitch, and shape. These generated surface molecular patterns can function as biorecognition arrays or be transferred to the underneath Au layer for metallic structure creation. By combining CLL process with this gap phenomenon, soft material properties that are previously thought as demerits can be used to achieve sub-10 nm features in a straightforward sketch.

Due to its wide applicability in industry, devising microstructures on the surface of materials can be easily implemented and automated in technological processes. Laser Surface Texturing (LST) is applied to modify the chemical composition, morphology, and roughness of surfaces (wettability), cleaning (remove contaminants), reducing internal stresses of metals (hardening, tempering), surface energy (polymers, metals), increasing the adhesion (hybrid joining, bioengineering) and decreasing the growth of pathogenic bacteria (bioengineering). This paper is a continuation and extension of our previous studies in laser-assisted texturing of surfaces. Three different patterns (crater array-type C, two ellipses at 90° overlapping with its mirror-type B and 3 concentric octagons-type A) were applied with a nanosecond pulsed laser (active medium Nd: Fiber Diode-pumped) on the surface of a ferritic stainless steel (AISI 430). Micro texturing the surface of a material can modify its wettability behavior. A hydrophobic surface (contact angle greater than 90°) was obtained with different variations depending on the parameters. The analysis performed in this research (surface roughness, wettability) is critical for assessing the surface functionality, characteristics and properties of the stainless steel surface after the LST process. The values of the surface roughness and the contact angle are directly proportional to the number of repetitions and inversely proportional to the speed. Recommendations for the use of different texturing pattern designs are also made.

Micropillar patterns were fabricated and used to study cell adhesion, morphology, and function. Micropillars were produced in poly(2-hydroxyethyl methacrylate (HEMA)/N,N-(dimethylaminoethyl)methacrylate (DMAEMA)/tetraethylene glycol dimethacrylate (TEGDMA)) hydrogels using soft lithography, had dimensions of 1 μm diameter, and were either 2.05 or 4.91 μm tall. The patterned hydrogel substrates increased adhesion and induced the formation of cellular aggregates. Digital micrographs were used to quantify aggregate size and number. Differentiation of hMSCs toward adipocytes and chondrocytes was performed using the respective complete culture and differentiation medium for 2 weeks. Cells were stained for Oil red O, Alcian blue, and Type II collagen. Hydrogel substrates supported the differentiation of hMSCs to adipocytes and chondrocytes. The taller micropillar patterns supported the attachment and growth of larger aggregates and were more amenable to aid chondrogenic differentiation.

Membranes used for desalination still face challenges during operation. One of these challenges is the buildup of salt ions at the membrane surface. This is known as concentration polarization, and it has a negative effect on membrane water permeance and salt rejection. In an attempt to decrease concentration polarization, a line-and-groove nanopattern was applied to a nanofiltration (NF) membrane. Aqueous sodium sulfate (Na2SO4) solutions were used to test the rejection and permeance of both pristine and patterned membranes. It was found that the nanopatterns did not reduce but increased the concentration polarization at the membrane surface. Based on these studies, different pattern shapes and sizes should be investigated to gain a fundamental understanding of the influence of pattern size and shape on concentration polarization.

In nanofluidics, surface control is a critical technology because nanospaces are surface-governed spaces as a consequence of their extremely high surface-to-volume ratio. Various surface patterning methods have been developed, including patterning on an open substrate and patterning using a liquid modifier in microchannels. However, the surface patterning of a closed nanochannel is difficult. In addition, the surface evaluation of closed nanochannels is difficult because of a lack of appropriate experimental tools. In this study, we verified the surface patterning of a closed nanochannel by vacuum ultraviolet (VUV) light and evaluated the surface using streaming-current measurements. First, the C18 modification of closed nanochannels was confirmed by Laplace pressure measurements. In addition, no streaming-current signal was detected for the C18-modified surface, confirming the successful modification of the nanochannel surface with C18 groups. The C18 groups were subsequently decomposed by VUV light, and the nanochannel surface became hydrophilic because of the presence of silanol groups. In streaming-current measurements, the current signals increased in amplitude with increasing VUV light irradiation time, indicating the decomposition of the C18 groups on the closed nanochannel surfaces. Finally, hydrophilic/hydrophobic patterning by VUV light was performed in a nanochannel. Capillary filling experiments confirmed the presence of a hydrophilic/hydrophobic interface. Therefore, VUV patterning in a closed nanochannel was demonstrated, and the surface of a closed nanochannel was successfully evaluated using streaming-current measurements.

Cell adhesion to extracellular matrices (ECM) is critical to physiological and pathological processes as well as biomedical and biotechnological applications. It has been known that a cell can adhere on an adhesive microisland only over a critical size. But no publication has concerned critical adhesion areas of cells on microislands with nanoarray decoration. Herein, we fabricated a series of micro-nanopatterns with different microisland sizes and arginine-glycine-aspartate (RGD) nanospacings on a nonfouling poly(ethylene glycol) background. Besides reproducing that nanospacing of RGD, a ligand of its receptor integrin (a membrane protein), significantly influences specific cell adhesion on bioactive nanoarrays, we confirmed that the concept of critical adhesion area originally suggested in studies of cells on micropatterns was justified also on the micro-nanopatterns, yet the latter exhibited more characteristic behaviors of cell adhesion. We found increased critical adhesion areas of human mesenchymal stem cells (hMSCs) on nanoarrayed microislands with increased RGD nanospacings. However, the numbers of nanodots with respect to the critical adhesion areas were not a constant. A unified interpretation was then put forward after combining nonspecific background adhesion and specific cell adhesion. We further carried out the asymptotic analysis of a series of micro-nanopatterned surfaces to obtain the effective RGD nanospacing on unpatterned free surfaces with densely grafted RGD, which could be estimated nonzero but has never been revealed previously without the assistance of the micro-nanopatterning techniques and the corresponding analysis.
UNASSIGNED: Supplementary materials and methods (details of fabrication of micro-nanopatterns), and supplementary results (selective adhesion or localization of hMSCs on nanoarrayed microislands with non-fouling background, calculation of critical number of integrin-ligand binding N*, etc.) are available in the online version of this article at 10.1007/s12274-021-3711-6.

A sweat sensor is expected to be the most appropriate wearable device for noninvasive healthcare monitoring. However, the practical use of sweat sensors is impeded by irregular and low sweat secretion rates. Here, a sweat-collecting patch that can collect sweat efficiently for fast and continuous healthcare monitoring is demonstrated. The patch uses cactus-spine-inspired wedge-shaped wettability-patterned channels on a hierarchical microstructured/nanostructured surface. The channel shape, in combination with the superhydrophobic/superhydrophilic surface materials, induces a unidirectional Laplace pressure that transports the sweat to the sensing area spontaneously even when the patch is aligned vertically. The patch demonstrates superior sweat-collecting efficiency and reduces the time required to fill the sensing area by transporting sweat almost without leaving it inside the channel. Therefore, a sensor based on the patch responds quickly to biochemicals in sweat, and the patch enables the continuous monitoring of changes in sweat biochemicals according to their changes in the wearer\'s blood.