Micropatterning Technique Research Articles

Crosslinkable Ligands for High-Density Photo-Patterning of Perovskite Nanocrystals.

Perovskite nanocrystals (PNCs) are promising luminescent materials for electronic color displays due to their high luminescence efficiency, widely-tunable emission wavelengths, and narrow emission linewidth. Their application in emerging display technologiesnecessitates precise micron-scale patterningwhile maintaining good optical performance. Although photolithography is a well-established micro-patterning technique in the industry, conventional processes are incompatible with PNCs as the use of polar solvents can damage the ionic PNCs, causingsevere luminescence quenching. Here,we report the rational design and synthesis of a new bidentate photo-crosslinkable ligand for the direct photo-patterning of PNCs. Each ligand contains two photosensitive acrylate groups and two carboxylate groups, and is introduced to the PNCs via an entropy-driven ligand exchange process. In a close-packed thin film, the acrylate ligands photo-polymerize and crosslink under ultraviolet light, rendering the PNCs insoluble in developing solvents. A high-density crosslinked PNC film with an optical density of 1.1 is attained at 1.4µm thickness, surpassing industry requirements on the absorption coefficient. Micron-scale patterning is further demonstrated using direct laser writing, producing well-defined 20µm features. This study thus offers an effective and versatile approach for micro-patterning PNCs, and may also be broadly applicable to other nanomaterial systems.

Engineering the Cellular Microenvironment: Integrating Three-Dimensional Nontopographical and Two-Dimensional Biochemical Cues for Precise Control of Cellular Behavior.

The development of biomaterials capable of regulating cellular processes and guiding cell fate decisions has broad implications in tissue engineering, regenerative medicine, and cell-based assays for drug development and disease modeling. Recent studies have shown that three-dimensional (3D) nanoscale physical cues such as nanotopography can modulate various cellular processes like adhesion and endocytosis by inducing nanoscale curvature on the plasma and nuclear membranes. Two-dimensional (2D) biochemical cues such as protein micropatterns can also regulate cell function and fate by controlling cellular geometries. Development of biomaterials with precise control over nanoscale physical and biochemical cues can significantly influence programming cell function and fate. In this study, we utilized a laser-assisted micropatterning technique to manipulate the 2D architectures of cells on 3D nanopillar platforms. We performed a comprehensive analysis of cellular and nuclear morphology and deformation on both nanopillar and flat substrates. Our findings demonstrate the precise engineering of single cell architectures through 2D micropatterning on nanopillar platforms. We show that the coupling between the nuclear and cell shape is disrupted on nanopillar surfaces compared to flat surfaces. Furthermore, our results suggest that cell elongation on nanopillars enhances nanopillar-induced endocytosis. We believe our platform serves as a versatile tool for further explorations into programming cell function and fate through combined physical cues that create nanoscale curvature on cell membranes and biochemical cues that control the geometry of the cell.

Asymmetrical positioning of cell organelles reflects the cell chirality of mouse myoblast cells.

Cell chirality is crucial for the chiral morphogenesis of biological tissues, yet its underlying mechanism remains unclear. Cell organelle polarization along multiple axes in a cell body, namely, apical-basal, front-rear, and left-right, is known to direct cell behavior such as orientation, rotation, and migration. Among these axes, the left-right bias holds significant sway in determining the chiral directionality of these behaviors. Normally, mouse myoblast (C2C12) cells exhibit a strong counterclockwise chirality on a ring-shaped micropattern, whereas they display a clockwise dominant chirality under Latrunculin A treatment. To investigate the relationship between multicellular chirality and organelle positioning in single cells, we studied the left-right positioning of cell organelles under distinct cell chirality in single cells via micropatterning technique, fluorescent microscopy, and imaging analysis. We found that on a "T"-shaped micropattern, a C2C12 cell adopts a triangular shape, with its nucleus-centrosome axis pointing toward the top-right direction of the "T." Several other organelles, including the Golgi apparatus, lysosomes, actin filaments, and microtubules, showed a preference to polarize on one side of the axis, indicating the universality of the left-right asymmetrical organelle positioning. Interestingly, upon reversing cell chirality with Latrunculin A, the organelles correspondingly reversed their left-right positioning bias, as suggested by the consistently biased metabolism and contractile properties at the leading edge. This left-right asymmetry in organelle positioning may help predict cell migration direction and serve as a potential marker for identifying cell chirality in biological models.

Single-cell manipulation by two-dimensional micropatterning

Cells are highly sensitive to their geometrical and mechanical microenvironment that directly regulate cell shape, cytoskeleton and organelle, as well as the nucleus morphology and genetic expression. The emerging two-dimensional micropatterning techniques offer powerful tools to construct controllable and well-organized microenvironment for single-cell level investigations with qualitative analysis, cellular standardization, and in vivo environment mimicking. Here, we provide an overview of the basic principle and characteristics of the two most widely-used micropatterning techniques, including photolithographic micropatterning and soft lithography micropatterning. Moreover, we summarize the application of micropatterning technique in controlling cytoskeleton, cell migration, nucleus and gene expression, as well as intercellular communication.

Development of Cell Micropatterning Technique Using Laser Processing of Alginate Gel

Tissue formation from heterogeneous cell types, similar to those in vivo, is an important technique for development of new drugs and formation of artificial organs. In vivo tissues are complex arrangements of heterogeneous cells that interact with each other. To create such tissues in vitro, it is essential to develop a technique that arranges heterogeneous cells in an arbitrary configuration. Currently, we are developing a new gel patterning technique to create effective cell micropatterns by using photolithography and alginate gel, which inhibits cellular adhesion. In this study, we considered that a more flexible gel patterning technique was required for creating order-made formations of complex tissues. We created gel patterns by removing the alginate gel using laser processing, and cells were cultured on the formed patterns. Complex heterogeneous cell patterns were achieved by adjusting various technical parameters such as the laser power, spot diameter, and alginate gel film thickness. Based on our results, we anticipate that our technique will prove useful for the development of regenerative medicine and tissue engineering.

Exploring Mechanical Responses of Cells to Geometric Information Using Micropatterned DNA-Based Molecular Tension Probes.

The geometric shape of a cell is strongly influenced by the cytoskeleton, which, in turn, is regulated by integrin-mediated cell-extracellular matrix (ECM) interactions. To investigate the mechanical role of integrin in the geometrical interplay between cells and the ECM, we proposed a single-cell micropatterning technique combined with molecular tension fluorescence microscopy (MTFM), which allows us to characterize the mechanical properties of cells with prescribed geometries. Our results show that the curvature is a key geometric cue for cells to differentiate shapes in a membrane-tension- and actomyosin-dependent manner. Specifically, curvatures affect the size of focal adhesions (FAs) and induce a curvature-dependent density and spatial distribution of strong integrins. In addition, we found that the integrin subunit β1 plays a critical role in the detection of geometric information. Overall, the integration of MTFM and single-cell micropatterning offers a robust approach for investigating the nexus between mechanical cues and cellular responses, holding potential for advancing our understanding of mechanobiology.

How Hydrogel Stiffness Affects Adipogenic Differentiation of Mesenchymal Stem Cells under Controlled Morphology.

Matrix stiffness has been disclosed as an essential regulator of cell fate. However, it is barely studied how the matrix stiffness affects stem cell functions when cell morphology changes. Thus, in this study, the effect of hydrogel stiffness on adipogenic differentiation of human bone-marrow-derived mesenchymal stem cells (hMSCs) with controlled morphology was investigated. Micropatterns of different size and elongation were prepared by a photolithographical micropatterning technique. The hMSCs were cultured on the micropatterns and showed a different spreading area and elongation following the geometry of the underlying micropatterns. The cells with controlled morphology were embedded in agarose hydrogels of different stiffnesses. The cells showed a different level of adipogenic differentiation that was dependent on both hydrogel stiffness and cell morphology. Adipogenic differentiation became strong when the cell spreading area decreased and hydrogel stiffness increased. Adipogenic differentiation did not change with cell elongation. Therefore, cell spreading area and hydrogel stiffness could synergistically affect adipogenic differentiation of hMSCs, while cell elongation did not affect adipogenic differentiation. A change of cell morphology and hydrogel stiffness was accompanied by actin filament alignment that was strongly related to adipogenic differentiation. The results indicated that cell morphology could affect cellular sensitivity to hydrogel stiffness. The results will provide useful information for the elucidation of the interaction of stem cells and their microenvironmental biomechanical cues.

Engineering cell morphology using maskless 2D protein micropatterning on 3D nanostructures

Mechanical cues such as the 2-Dimensional (2D) and 3-Dimensional (3D) shape of cellular microenvironments affect several cellular processes including adhesion and proliferation. Recent studies provide controlled conditions to recapitulate the 2D and 3D microenvironments to understand the mechanisms of cellular response to these mechanical cues. Microengineering surfaces such as micropatterning techniques are widely used to modulate 2D cell shapes. Additionally, nanostructured surfaces are used to modulate 3D substrate nanotophography. By confining cells to micropatterns, cells reorganize their cytoskeleton architecture to the microenvironment by remodeling the actin and microtubule fibers. In this study, we present a micropatterning technique on nanostructured surfaces based on a maskless laser-assisted technique to study the cellular response to 3D nano-topographies in a controlled 2D microenvironment. We used a two-step dry and wet etching technique to fabricate transparent (SiO2) 3D nanostructured surfaces. Next, we micropatterned extracellular matrix proteins directly on the fabricated nanostructures by maskless micropatterning (PRIMO, Alvéole) system mounted on an inverted microscope. Briefly, UVO treatment was performed to clean the surface followed by surface incubation with Poly-L-Lysine. Subsequently, the surface was passivated with m-PEG-SVA, and a photosensitizer reagent (PLPP) applied to the surface to remove the PEG layer upon UV exposure. After UV illumination and washing the surface, nanopillars were incubated with ECM proteins (Fibronectin and Gelatin). Next, we demonstrated the 2D control of cell and nuclear shape on 3D nanostructured surfaces for an epithelial-like cell line (U2OS, ATCC) by seeding them on Fibronectin/Gelatin micropatterns of various geometries. We then used fluorescent microscopy to characterize the organization of intracellular components such as the nucleus and cytoskeletal elements. Moreover, we analyzed the spreading of cells over time, the effect of 2D micropattern geometry on cell morphology, and cytoskeleton reorganization on various 2D and 3D configurations.

Nanotopography and Microconfinement Impact on Primary Hippocampal Astrocyte Morphology, Cytoskeleton and Spontaneous Calcium Wave Signalling.

Astrocytes' organisation affects the functioning and the fine morphology of the brain, both in physiological and pathological contexts. Although many aspects of their role have been characterised, their complex functions remain, to a certain extent, unclear with respect to their contribution to brain cell communication. Here, we studied the effects of nanotopography and microconfinement on primary hippocampal rat astrocytes. For this purpose, we fabricated nanostructured zirconia surfaces as homogenous substrates and as micrometric patterns, the latter produced by a combination of an additive nanofabrication and micropatterning technique. These engineered substrates reproduce both nanotopographical features and microscale geometries that astrocytes encounter in their natural environment, such as basement membrane topography, as well as blood vessels and axonal fibre topology. The impact of restrictive adhesion manifests in the modulation of several cellular properties of single cells (morphological and actin cytoskeletal changes) and the network organisation and functioning. Calcium wave signalling was observed only in astrocytes grown in confined geometries, with an activity enhancement in cells forming elongated agglomerates with dimensions typical of blood vessels or axon fibres. Our results suggest that calcium oscillation and wave propagation are closely related to astrocytic morphology and actin cytoskeleton organisation.

Patterned Nafion Membranes for Improved Transport in PGM-Free PEMFC Cathodes

Substantial cost reduction is needed to commercialize polymer electrolyte fuel cells. As PGM catalysts are projected to account for ~42% cost of a fuel cell stack (1), replacement of PGMs with PGM-free catalysts is an attractive route to cost reduction. Over the past decade, extensive research efforts have led to significant improvements in kinetic activity (2), but conventional PGM-free catalyst continues to have lower volumetric activity than PGM catalysts. The lower volumetric activity requires use of a thicker cathode catalyst layer (CL), resulting in significant proton and oxygen transport losses (3). Therefore, along with kinetic improvements in oxygen reduction reaction, improved transport of H+ and O2 is needed to achieve performance comparable to PGM catalyst. In this study, we adopt a micro-patterning technique to incorporate non-tortuous ionomer channels in the cathode to increase the ionic conductivity of the thick catalyst layer. As shown in Figure 1, cathode ionomer channels enable rapid transportation of H+ throughout the catalyst layer, compared to thin and tortuous ionomer films in the conventional electrode. Polarization curves obtained in H2/air show significantly higher performance for the CL with ionomer channels compared to the conventional cathode. Electrochemical impedance spectroscopy data in H2/N2 also demonstrate a significant decrease in H+ resistance in the catalyst layer. The ionomer channels lead to a reduction in the H+ transport resistance, reducing ohmic overpotential in the catalyst layer. Further improvement in performance in the mass transport region is achieved through implementing optimized design of the dedicated ionomer channel.AcknowledgmentThis research was supported by the US Department of Energy, the Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office and the LANL LDRD program.References D. Papageorgopoulos, DOE Hydrogen and Fuel Cells Program FY2019 Annual Merit Review Proceedings, https://www.hydrogen.energy.gov/pdfs/review19/plenary_fuel_cell_papageorgopoulos_2019.pdf (2019).H. Zhang, S. Hwang, M. Wang, Z. Feng, S. Karakalos, L. Luo, Z. Qiao, X. Xie, C. Wang, D. Su, Y. Shao and G. Wu, (2017).S. Komini Babu, H. T. Chung, P. Zelenay and S. Litster, ACS Appl Mater Interfaces, 8, 32764-32777 (2016). Figure 1

High-throughput bioengineering of homogenous and functional human-induced pluripotent stem cells-derived liver organoids via micropatterning technique.

Human pluripotent stem cell-derived liver organoids are emerging as more human-relevant in vitro models for studying liver diseases and hepatotoxicity than traditional hepatocyte cultures and animal models. The generation of liver organoids is based on the Matrigel dome method. However, the organoids constructed by this method display significant heterogeneity in their morphology, size, and maturity. Additionally, the formed organoid is randomly encapsulated in the Matrigel dome, which is not convenient for in situ staining and imaging. Here, we demonstrate an approach to generate a novel type of liver organoids via micropatterning technique. This approach enables the reproducible and high-throughput formation of bioengineered fetal liver organoids with uniform morphology and deterministic size and location in a multiwell plate. The liver organoids constructed by this technique closely recapitulate some critical features of human liver development at the fetal stage, including fetal liver-specific gene and protein expression, glycogen storage, lipid accumulation, and protein secretion. Additionally, the organoids allow whole-mount in-situ staining and imaging. Overall, this new type of liver organoids is compatible with the pharmaceutical industry’s widely-used preclinical drug discovery tools and will facilitate liver drug screening and hepatotoxic assessment.

All-Back-Contact Perovskite Solar Cells Using Cracked Film Lithography

All-back-contact perovskite solar cells promise greater power conversion efficiency compared to conventional planar device architectures. However, the best-performing devices to date use photolithography to fabricate electrodes, which is expensive for deployment and a barrier for research facilities. Herein, we utilize cracked film lithography, a solution-processed micropatterning technique, to form an interconnected, defect-tolerant back-contact electrode network. We introduce a crack widening technique to control the optical transparency and sheet resistance while decoupling the relative areas of the electron and hole contacts in the back-contact network. Wider cracks increase the area of the hole-selective contact, which increases photocurrent and power conversion efficiency.

Tailoring an Interface Microstructure for High-Performance Reversible Protonic Ceramic Electrochemical Cells via Soft Lithography.

Micropatterning is considered a promising strategy for improving the performance of electrochemical devices. However, micropatterning on ceramic is limited by its mechanically fragile properties. This paper reports a novel imprinting-assisted transfer technique to fabricate an interlayer structure in a protonic ceramic electrochemical cell with a micropatterned electrolyte. A dense proton-conducting electrolyte, BaCe0.7Zr0.1Y0.1Yb0.1O3-δ, is micropatterned in a chevron shape with the highest aspect ratio of patterns in electrode-supported cells to the best of our knowledge, increasing surface areas of both electrode sides more than 40%. The distribution of relaxation time analysis reveals that the chevron-patterned electrolyte layer significantly increases the electrode contact areas and active electrochemical reaction sites at the vicinity of the interfaces, contributing to enhanced performances of both the fuel cell and electrolysis operations. The patterned cell demonstrates improved fuel cell performance (>45%) and enhances electrolysis cell performance (30%) at 500 °C. This novel micropatterning technique is promising for the facile production of layered electrochemical cells, further opening a new route for the performance enhancement of ceramic-based electrochemical cells.

Mechanism of Photoinduced Phase Segregation in Mixed-Halide Perovskite Microplatelets and Its Application in Micropatterning.

Photoinduced phase segregation (PPS) is considered as a dominant factor that greatly deteriorates the performances of mixed-halide perovskite devices. However, the mechanism of PPS is still under fierce debate. Herein, CsPb(Brx/Cl1-x)3 microplatelets (MPs) with homogeneous and heterogeneous surfaces are obtained by controlling the growth conditions. Under continuous irradiation, a new photoluminescence (PL) band at 516 nm gradually appears in the heterogeneous MPs, accompanied with the decreased emission of the mixed phase at 480 nm, revealing the occurrence of PPS, while the photoirradiation only leads to slight PL dimming without PPS in the homogeneous MPs. The direct correlation between PPS and the structural heterogeneity indicates that the localized electric field-induced drift (LEFD) of halide ions/carriers is responsible for the PPS. In situ microfluorescence images evidence that the migration of halide ions is directed by the structural heterogeneity-induced localized electric field. Our refined model not only consolidates that PPS can be suppressed by eliminating the defects but also reveals that PPS can be directed by the distribution of defects. Therefore, a fluorescence micropatterning technique is developed based on PPS.

Tunable Multicolor Fluorescence of Perovskite-Based Composites for Optical Steganography and Light-Emitting Devices.

Multicolor fluorescence of mixed halide perovskites enormously enables their applications in photonics and optoelectronics. However, it remains an arduous task to obtain multicolor emissions from perovskites containing single halogen to avoid phase segregation. Herein, a fluorescent composite containing Eu-based metal-organic frameworks (MOFs), 0D Cs4PbBr6, and 3D CsPbBr3 is synthesized. Under excitations at 365 nm and 254 nm, the pristine composite emits blue (B) and red (R) fluorescence, which are ascribed to radiative defects within Cs4PbBr6 and 5D0→7FJ transitions of Eu3+, respectively. Interestingly, after light soaking in the ambient environment, the blue fluorescence gradually converts into green (G) emission due to the defect repairing and 0D-3D phase conversion. This permanent and unique photochromic effect enables anticounterfeiting and microsteganography with increased security through a micropatterning technique. Moreover, the RGB luminescence is highly stable after encapsulation by a transparent polymer layer. Thus, trichromatic light-emitting modules are fabricated by using the fluorescent composites as color-converting layers, which almost fully cover the standard color gamut. Therefore, this work innovates a strategy for construction of tunable multicolor luminescence by manipulating the radiative defects and structural dimensionality.

Femtosecond laser induced in-situ crystallization of Tb-based luminescent metal organic framework.

Luminescent metal-organic frameworks (LMOFs) are a class of interesting and well-investigated MOF materials, which have shown remarkable prospects in the past and have been widely applied in different fields. However, due to their organic hybrid aspect, micro-/nano-patterning LMOFs in devices via a conventional semiconductor process is very challenging. In this work, we have introduced an elegant technique via nonlinear photon-chemical effect to induce the synthesis and growth of LMOFs. A facile technique for local synthesis and micro-pattering Tb-based luminescent metal organic frameworks (Tb(BTC)·G) from a solution of precursors is achieved. A single step approach micro-patterning for device integration with simultaneous chemical synthesis was proposed. Micro-devices with excellent fluorescence performance based on Tb(BTC)·G have been demonstrated. This work first suggested a high resolution bottom-up micro-patterning technique for MOF device fabrication using femtosecond laser direct writing, showing great potential on MOF based micro/nano-devices integration, especially promising for patterning high resolution luminescent MOF devices.

Fabric‐Assisted MXene/Silicone Nanocomposite‐Based Triboelectric Nanogenerators for Self‐Powered Sensors and Wearable Electronics

AbstractSurface modification of triboelectric negative layers is an essential factor for boosting the output performance of triboelectric nanogenerators (TENGs). Herein, a novel scalable surface modification method is introduced using a fabric‐assisted micropatterning technique on a highly negative MXene/silicone nanocomposite surface (charge generating) with MXene layer (charge trapping) for self‐powered sensors and wearable electronics. The microstructured surface is fabricated directly from a fabric template requiring no surface‐active agent, high‐pressure equipment, or high vacuum. To boost the proposed double‐side‐contact TENG (DSC‐TENG) output performance, different parameters of the fabric textures are tested and optimized for the roughened microstructures, namely the MXene layer and relative humidity. Under optimal conditions, the fabricated DSC‐TENG improves the voltage and peak current density by factors of 9.8 and 20, respectively, regarding flat silicone. It exhibits a maximum peak power density of 55.47 W m−2 at load resistance of 0.18 MΩ, and a corresponding decrease in resistance by 75% using MXene content of 3 mg cm−2. Also, DSC‐TENG‐based smart home control of electrical appliances, theft protection, self‐powered electronic devices, password authentication, and human motion monitoring via smartphone for the IoT are demonstrated. The proposed method can be implemented for different types of polymers, thereby enabling the large‐scale fabrication of high‐performance TENGs in industrial applications.

Selective Growth and Micropatterning Technique for Oxide Thin Films by Sacrificial a-CaO Layer

Selective growth and micropatterning through a water lift-off (WLO) process utilizing a sacrificial amorphous CaO (a-CaO) layer were demonstrated to fabricate hetero-epitaxial all-oxides film capacitors. Patterned Pb(Zr,Ti)O3 (PZT) and SrRuO3 (SRO) films were grown on (100) SrTiO3 (STO) substrate by pulsed laser deposition, and the subsequent lift-off process for target oxides was carried out using pure water. The results showed that selective growth and micropatterning of an all-oxides capacitor structure could be realized through WLO process using a-CaO as the sacrificial layer. Electron backscattered diffraction results revealed that SRO/PZT/SRO capacitor structures were grown hetero-epitaxially on the STO substrate. Furthermore, the electrical properties of patterned SRO/PZT/SRO film capacitors could be improved by suppressing the height of overgrown parts of the SRO bottom electrodes with a thick a-CaO sacrificial layer.

Control of Cell Geometry through Infrared Laser Assisted Micropatterning.

Micropatterning is an established technique in the cell biology community used to study connections between the morphology and function of cellular compartments while circumventing complications arising from natural cell-to-cell variations. To standardize cell shape, cells are either confined in 3D molds or controlled for adhesive geometry through adhesive islands. However, traditional micropatterning techniques based on photolithography and deep UV etching heavily depend on clean rooms or specialized equipment. Here we present an infrared laser assisted micropatterning technique (microphotopatterning) modified from Doyle et al. that can be conveniently set up with commercially available imaging systems. In this protocol, we use a Nikon A1R MP+ imaging system to generate micropatterns with micron precision through an infrared (IR) laser that ablates preset regions on poly-vinyl alcohol coated coverslips. We employ a custom script to enable automated pattern fabrication with high efficiency and accuracy in systems not equipped with a hardware autofocus. We show that this IR laser assisted micropatterning (microphotopatterning) protocol results in defined patterns to which cells attach exclusively and take on the desired shape. Furthermore, data from a large number of cells can be averaged due to the standardization of cell shape. Patterns generated with this protocol, combined with high resolution imaging and quantitative analysis, can be used for relatively high throughput screens to identify molecular players mediating the link between form and function.

Programmable surface anisotropy from polarization-driven azopolymer reconfiguration

The ability to accurately realize complex textures is of great relevance for tailoring surface-driven functionalities as wettability, adhesion and light diffraction. The fabrication of superficial micro-textures, in a simple and cost-effective way, is high desiderable in this framework. A versatile technique for surface micropatterning is based on reconfiguration of photosensitive azobenzene-containing polymers, in which a macroscopic light-induced motion of polymer chains, fueled by the photo-isomerizing azobenzene molecules, allows the controlled optical reshaping of prestructured superficial micro-textures. Here, azopolymer surfaces, prepatterned with an array of discrete cylindrical micropillars, are reconfigured through a polarization-driven large-scale surface deformation until achieving superficial gratings with programmable amplitude, orientation and periodicity. The high degree of structural surface anisotropy, the possibility to program the directionality of such anisotropy from the reconfiguration of basic pristine surfaces, and the simplicity of the optical setup, make the proposed structuration method attractive for versatile and cost-effective surface patterning.