Discontinuous Dewetting Research Articles

Omniphobic Photoresist‐Assisted Patterning of Porous Polymethacrylate Films

AbstractPatterning of various surface properties, including roughness, wettability, adhesiveness, and mechanical properties, can markedly enhance the functionality of test systems. Thus, porous polymethacrylates prepared by polymerization‐induced phase separation (PIPS) represent a promising class of functional materials for the construction of miniaturized test systems. Different porosity, surface chemistry, and wettability are achieved in porous polymethacrylates with different precursor compositions. Nevertheless, only wettability microstructuring has been highlighted for these materials thus far. Here, the study presents a novel method for the direct and selective deposition of porous polymethacrylate films with different surface chemistry and porosity. The selective adhesion of omniphobic–omniphilic wettability patterns is used to facilitate the polymer pattern formation. The feasibility of patterning with different monomers and porogenic solvents is demonstrated. The topological study confirms the selective application of polymer structures with different thickness and roughness. The wettability characterization of the omniphobic material shows no significant changes caused by the operations performed. Thus, a new pattern with a greater difference in the wettability of the areas is produced in the process. Discontinuous dewetting of different liquids is performed. The use of poly(2‐hydroxyethyl methacrylate‐co‐ethylene dimethacrylate) (HEMA‐EDMA) modified patterns for precise living cell patterning is also demonstrated.

Superhydrophilic/Superhydrophobic Droplet Microarrays of Low Surface Tension Biofluids for Nucleic Acid Detection

AbstractSuperhydrophilic/superhydrophobic patterned surfaces can be used to create droplet microarrays. A specific challenge with the liquids needed for various biomedical applications, as compared to pure water, is their lower surface tension and potential for contaminating the surfaces through adsorption. Here, a method is shown to create biofluid droplet microarrays using discontinuous dewetting of pure water, an oil protective layer, and finally biofluid exchange with the water droplet array. With this method, a droplet array of a viscous nucleic acid amplification solution can be formed with a low surface tension of 34 mN m−1 and a contact angle of only 76° with the used hydrophobic coating. This droplet array is applied for nucleic acid detection of SARS‐CoV‐2 virus using strand invasion‐based amplification (SIBA) technology. It is shown that by using an array of 10 000 droplets of 50 µm diameter the limit of detection is 1 RNA copy µL−1. The results demonstrate that SIBA on droplet microarrays may be a quantitative technology.

Single-Cell Enzymatic Screening for Epithelial Mesenchymal Transition with an Ultrasensitive Superwetting Droplet-Array Microchip.

The phenotypic changes of circulating tumor cells (CTCs) during the epithelial-mesenchymal transition (EMT) have been a hot topic in tumor biology and cancer therapeutic development. Here, an integrated platform of single-cell fluorescent enzymatic assays with superwetting droplet-array microchips (SDAM) for ultrasensitive functional screening of epithelial-mesenchymal sub-phenotypes of CTCs is reported. The SDAM can generate high-density, volume well-defined droplet (0.66 nL per droplet) arrays isolating single tumor cells via a discontinuous dewetting effect. It enables sensitive detection of MMP9 enzyme activities secreted by single tumor cells, correlating to their epithelial-mesenchymal sub-phenotypes. In the pilot clinical double-blind tests, the authors have demonstrated that SDAM assays allow for rapid identification and functional screening of CTCs with different epithelial-mesenchymal properties. The consistency with the clinical outcomes validates the usefulness of single-cell secreted MMP9 as a biomarker for selective CTC screening and tumor metastasis monitoring. Convenient addressing and recovery of individual CTCs from SDAM have been demonstrated for gene mutation sequencing, immunostaining, and transcriptome analysis, revealing new understandings of the signaling pathways between MMP9 secretion and the EMT regulation of CTCs. The SDAM approach combined with sequencing technologies promises to explore the dynamic EMT plasticity of tumors at the single-cell level.

Material‐Independent 3D Patterning Via Two‐Photon Lithography and Discontinuous Wetting

AbstractThe fabrication of complex 3D structures composed of micrometer‐sized features made of different functional materials is an immensely important and yet highly challenging task. Here, a method is developed to fabricate multimaterial 3D structures with micrometer precision by combining macroscopic 3D printing (digital light processing), with two‐photon lithography (2PL) and material‐independent discontinuous dewetting. Specifically, 3D inherently superhydrophobic objects are first printed by DLP, followed by creating hydrophilic micropatterns on their surface using 2PL. By exploiting the effect of discontinuous wetting, the selective deposition of solutions of functional materials into microscopic hydrophilic regions on the surface of 3D structures, with high resolution and great design flexibility is demonstrated. Importantly, the method is material‐independent and enables the micropatterning of a variety of functional materials dispersed in aqueous solutions including polydopamine, silica, or Ag nanoparticles. As an exemplary application, it is shown that conductive Ag electrodes can be created on the curved surface of 3D‐printed objects to construct structural electronics. The flexibility, high resolution, and material diversity in designing multimaterial 3D structures open exciting new functionalities and possibilities in a variety of applications including advanced electronics, soft robotics, and chemical or bioengineering.

Discontinuous dewetting dynamics of highly viscous droplets on chemically heterogeneous substrates

HypothesisDroplet spreading on heterogeneous (chemical/structural) surfaces has revealed local disturbances that affect the advancing contact line. With droplet dewetting being less studied, we hypothesize that a receding droplet can be perturbed by localized heterogeneity which leads to irregular and discontinuous dewetting of the substrate. ExperimentsThe sessile drop method was used to study droplet dewetting at a wettability boundary. One-half of a hydrophilic surface was hydrophobically modified with either i) methyloctyldichlorosilane or ii) clustered macromolecules. A Lattice Boltzmann method (LBM) simulation was also developed to determine the effect of contact angle hysteresis and boundary conditions on the droplet dynamics. FindingsThe two surface treatments were optimized to produce comparable water wetting characteristics. With a negative Gibbs free energy on the hydrophilic-half, the oil droplet receded to the hydrophobic-half. On the silanized surface, the droplet was pinned and the resultant droplet shape was a distorted spherical cap, having receded uniformly on the unmodified surface. Modifying the surface with clustered macromolecules, the droplet receded slightly to form a spherical cap. However, droplet recession was non-uniform and daughter droplets formed near the wettability boundary. The LBM simulation revealed that daughter droplets formed when θR > 164°, with the final droplet shape accurately described by imposing a diffuse wettability boundary condition.

Rapid Mass Spectrometric Calibration and Standard Addition Using Hydrophobic/Hydrophilic Patterned Surfaces and Discontinuous Dewetting.

The rapid calibration chip (RCC) is a device that uses the fast and reproducible wetting behavior of hydrophilic/hydrophobic patterned surfaces to confine a series of differently sized droplets on a substrate to obtain a calibration curve. Multiple series of droplets can be formed within seconds by dipping an RCC into a calibration solution. No pipetting, sequential droplet deposition, or advanced equipment is required. The performance and reproducibility of RCCs were evaluated with an electrospray ionization triple-quadrupole mass spectrometer equipped with a liquid microjunction-surface sampling probe (LMJ-SSP) that allows for fast sampling of surfaces. Using circular hydrophilic areas with diameters ranging from 0.25 to 2.00 mm, liquid volumes of 4.6-70.6 nL could be deposited. Furthermore, the use of a second hydrophobic/hydrophilic patterned transfer chip can be used to add internal standard solutions to each calibration spot of the RCC, allowing to transfer a liquid volume of 22.5 nL.

Fish Capsules: A System for High-Throughput Screening of Combinatorial Drugs.

Large‐scale screening of molecules heavily relies on phenotyping of small living organisms during preclinical development. However, deep profiling candidate therapeutics on whole animals typically requires laborious manipulations and anesthetic treatment using traditional techniques or automated tools. Here, a novel fish capsule system that combines automated zebrafish encapsulating technology and droplet microarray strategy for in vivo functional screening of mono/polytherapies is described. This platform enables automated, rapid zebrafish orientation and immobilization in agarose to generate large‐scale fish capsules by using a microfluidic device. Based on the effect of discontinuous dewetting, the prompt trapping of fish capsules in the aqueous arrays is successfully demonstrate. This system provides the capability to integrate pharmaceutical treatments with real‐time multispectral microscopic imaging in a simple, pipetting‐free and highly parallel manner. Coupling with machine learning algorithms, a small library of compounds is screened and analyzed, and clues about how to exploit compound combinations as therapeutic candidates are obtained. It is believed that this proposed strategy can be readily applied to multiple fields and is especially useful in the exploration of combinatorial drugs with limited amounts of samples and resources to accelerate the identification of novel therapeutics for precision medicines.

High-Resolution R2R-Compatible Printing of Carbon Nanotube Conductive Patterns Enabled by Cellulose Nanocrystals

Carbon nanotubes (CNTs) with enhanced properties compared to conventional materials are a leading material of choice for fabricating next-generation electronic devices. Nanocellulose-based conductive component-enabled electronics also offer great potential for commercial scalability of environmentally friendly, sustainable, flexible, wearable electronics. Printing these functional materials through R2R printing will enable the economic and high-throughput production of next-generation electronic devices. However, the lateral resolution during R2R printing of these materials is currently limited due to the enhanced aggregation behavior of these high-aspect ratio particles, and the lower lateral resolution limits the performance of the fabricated devices. This article demonstrates high-resolution, R2R-compatible printing of conductive patterns of CNTs using cellulose nanocrystals (CNCs) through the topographical discontinuous dewetting and liquid-bridge transfer patterning technique. The CNC dispersion obtained through acid hydrolysis of spinifex grass biomass was used as a sustainable functional ink and deposited as a structural wetting layer, which necessarily allowed the subsequent deposition of a conductive CNT layer to form high-resolution conductive patterns. Conductive patterns with lateral feature sizes down to ∼4.5 μm were reliably printed and those with feature sizes down to ∼925 nm were also possible. The high-resolution conductive CNC/CNT patterns could be printed on different hydrophilic substrates, including flexible, transparent CNC films, for use in devices. This study represents a proof-of-concept for the realization of the economic and environmentally friendly printing of high-resolution nanocellulose/carbon-based electronics.

Self-Localized Liquid Crystal Micro-Droplet Arrays on Chemically Patterned Surfaces

Liquid crystal (LC) micro-droplet arrays are elegant systems that have a range of applications, such as chemical and biological sensing, due to a sensitivity to changes in surface properties and strong optical activity. In this work, we utilize self-assembled monolayers (SAMs) to chemically micro-pattern surfaces with preferred regions for LC occupation. Exploiting discontinuous dewetting, dragging a drop of fluid over the patterned surfaces demonstrates a novel, high-yield method of confining LC in chemically defined regions. The broad applicability of this method is demonstrated by varying the size and LC phase of the droplets. Although the optical textures of the droplets are dictated by topological constraints, the additional SAM interface is shown to lock in inhomogeneous alignment. The surface effects are highly dependent on size, where larger droplets exhibit asymmetric director configurations in nematic droplets and highly knotted structures in cholesteric droplets.

A low-cost self-dispersing method of droplet array generation enabled by a simple reusable mask for bioanalysis and bioassays.

Discontinuous dewetting is an attractive technique that can produce droplet array of specific volume, geometry and at predefined location on a substrate. Droplet array has great potential in bioanalysis such as high-throughput live cell screening, digital PCR, and drug candidates. Here, we propose a self-dispersing droplet array generation method, which has advantages of low cost, simple operation, and easy large-area production ability. Droplet array of specific volumes was generated on a polymethyl methacrylate (PMMA) substrate using a simple reusable polyimide (PI) adhesive mask. Experiment shows that the generated droplet array can be used to successfully capture single particles which obeys Poisson distribution in a high-throughput manner. Furthermore, a droplet-array sandwiching chip was created based on the self-dispersion method for rapid detection of human serum albumin (HSA) at wide range of 183-11,712μg/mL with low reagent consumption of 2.2 μL, demonstrating its potential applications in convenient high-throughput bioanalysis and bioassays.

Highly Magnetized Encoded Hydrogel Microparticles with Enhanced Rinsing Capabilities for Efficient microRNA Detection.

Encoded hydrogel microparticles mounting DNA probes are powerful tools for high-performance microRNA (miRNA) detection in terms of sensitivity, specificity, and multiplex detection capability. However, several particle rinsing steps in the assay procedure present challenges for rapid and efficient detection. To overcome this limitation, we encapsulated dense magnetic nanoparticles to reduce the rinsing steps and duration via magnetic separation. A large number of magnetic nanoparticles were encapsulated into hydrogel microparticles based on a discontinuous dewetting technique combined with degassed micromolding lithography. In addition, we attached DNA probes targeting three types of miRNAs related to preeclampsia to magnetically encoded hydrogel microparticles by post-synthesis conjugation and achieved sensitivity comparable to that of conventional nonmagnetic encoded hydrogel microparticles. To demonstrate the multiplex capability of magnetically encoded hydrogel microparticles while maintaining the advantages of the simplified rinsing process when addressing multiple samples, we conducted a triplex detection of preeclampsia-related miRNAs. In conclusion, the introduction of magnetically encoded hydrogel microparticles not only allowed efficient miRNA detection but also provided comparable sensitivity and multiplexed detectability to conventional nonmagnetic encoded hydrogel microparticles.

Bead-free digital immunoassays on polydopamine patterned perfluorinated surfaces

This paper reports sub-micron resolution patterning of perfluorinated surfaces and the application in bead-free digital immunoassays. We use the negative microcontact printing in conjugation with a composite stamp to fabricate polydopamine patterns with sub-micron resolution on the perfluorinated surfaces. To perform digital assays, polydopamine microspot arrays were fabricated. Using discontinuous dewetting, 106 femtoliter droplets are formed in situ on the microspots. The droplets are kept in air from evaporation for over 90 min. The polydopamine patterns on the perfluorinated surfaces are used not only as the template for microdroplet generation but also as the binding sites for various proteins without further modifications. The detection limit of the bead-free digital immunoassay for human interleukin-6 is 1.2 fM with a dynamic range from 1.2 fM to over 400 fM. The high resolution polydopamine patterned perfluorinated substrate offers a highly-sensitive and low-cost approach for digital immunoassays, showing great potential in high-throughput and digital bioassays.

Thickness/morphology of functional material patterned by topographical discontinuous dewetting

AbstractTopographical discontinuous dewetting (TDD) patterning is a nascent 2D printing technique explored for high‐throughput nanoscale patterning of functional material inks. However, variables affecting the z thickness and morphology of the deposited functional materials inside the patterned microchannels remain unexplored. We developed a theoretical model that can determine the thickness of the deposited functional material layers using the TDD patterning technique. We then confirmed the model with experimental data by depositing colloidal dispersions into microchannels using TDD patterning to systematically study the effects of different processing variables. The contribution of evaporation‐driven flow to the deposited layer thickness was significant, with the relationship of thickness to inking speed different to that previously determined for thin film blade coating of colloidal dispersions in the evaporative regime. Additionally, a viscosity dampening effect was observed, unique to TDD of microchannels, which slowed the evaporation‐driven flow due to local viscosity increase in the microchannels. Channel dimensions and ink dispersion concentration affected thickness as hypothesized. Internal flows in the microchannels normal to the sidewalls and perpendicular to the microchannel length (“coffee ring” effect capillary flow/Marangoni flow) were found to contribute significantly to the final morphology/thickness of the deposited layers for the systems/dispersions experimentally measured.

High-throughput screening of multifunctional nanocoatings based on combinations of polyphenols and catecholamines.

Biomimetic surface coatings based on plant polyphenols and catecholamines have been used broadly in a variety of applications. However, the lack of a rational cost-effective platform for screening these coatings and their properties limits the true potential of these functional materials to be unleashed. Here, we investigated the oxidation behavior and coating formation ability of a library consisting of 45 phenolic compounds and catecholamines. UV–vis spectroscopy demonstrated significant acceleration of oxidation and polymerization under UV irradiation. We discovered that several binary mixtures resulted in non-additive behavior (synergistic or antagonistic effect) yielding much thicker or thinner coatings than individual compounds measured by ellipsometry. To investigate the properties of coatings derived from new combinations, we used a miniaturized high-throughput strategy to screen 2,532 spots coated with single, binary, and ternary combinations of coating precursors in one run. We evaluated the use of machine learning models to learn the relation between the chemical structure of the precursors and the thickness of the nanocoatings. Formation and stability of nanocoatings were investigated in a high-throughput manner via discontinuous dewetting. 30 stable combinations (hits) were used to tune the surface wettability and to form water droplet microarray and spot size gradients of water droplets on the coated surface. No toxicity was observed against eukaryotic HeLa cells and Pseudomonas aeruginosa (strain PA30) bacteria after 24 h incubation at 37 °C. The strategy introduced here for high-throughput screening of nanocoatings derived from combinations of coating precursors enables the discovery of new functional materials for various applications in science and technology in a cost-effective miniaturized manner.

High-resolution and scalable printing of highly conductive PEDOT:PSS for printable electronics

Topographical discontinuous dewetting (TDD) and liquid bridge transfer (LBT) was used for submicron resolution, R2R-compatible, high thickness, low line edge roughness patterning of PEDOT:PSS. High conductivities up to ∼2590 S cm−1 were achieved.

Discontinuous Dewetting in a Degassed Mold for Fabrication of Homogeneous Polymeric Microparticles.

Discontinuous dewetting (DD) is an attractive technique that enables the production of large liquid arrays in microwells and is applicable to the synthesis of anisotropic microparticles with complex morphologies. However, such loading of liquids into microwells presents a significant challenge, as the liquids used in this technique should exhibit low mold surface wettability. This study introduces DD in a degassed mold (DM), a simple yet powerful technique that achieves uniform loading of microparticle precursors into large microwell arrays within 1 min. Using this technique, hydrogel microparticles are produced by different polymerization mechanisms with various shapes and sizes, ranging from a few micrometers to hundreds of micrometers. Hydrophobic oil microparticles are produced by the simple plasma treatment of the DM, and agarose microparticles encapsulating bovine serum albumin (in a well-dispersed state) are produced by submerging the DM in fluorinated oil. To demonstrate additional functionality of microparticles using this technique, high concentrations of magnetic nanoparticles are loaded into microparticles for particle-based immunoassays performed in a microwell plate, and the immunoassay performance is comparable to that of ELISA.

High‐Throughput and Controllable Fabrication of Soft Screen Protectors with Microlens Arrays for Light Enhancement of OLED Displays

AbstractIn this work, soft polydimethylsiloxane (PDMS) screen protectors with microlens arrays (MLAs) are fabricated through a feasible high‐throughput approach. Based on the lateral size scaling effect during discontinuous dewetting, desired SU‐8 convex MLAs with simultaneously controlled focal length (f) and numerical aperture (NA) are produced on a single substrate. A replication technique is employed to prepare PDMS MLAs with the same structure as that of the SU‐8 MLAs. The contact angle and other optical parameters of the MLAs can be tuned over a wide range based on the number of sliding times and lateral size. When the diameter of the MLAs decreases from 100 to 10 µm, the curvature changes from 0.07 to 0.17 for the single‐layer MLAs and from 0.15 to 0.31 for the three‐layer MLAs. The enhancement effect of MLAs on the light from wide‐angle organic light‐emitting diode (OLED) packaging modules is investigated. It is found that PDMS films containing MLAs can increase the brightness of an OLED by 14.13%. The fabricated PDMS concave MLAs can serve as flexible screen protectors to shield OLEDs from damage while enhancing the brightness to improve the energy efficiency.

Discontinuous Dewetting, Template-Guided Self-Assembly, and Liquid Bridge-Transfer Printing of High-Resolution Single-Walled Carbon Nanotube Lines for Next-Generation Electrodes and Interconnects

A template-guided, self-assembly patterning technique called discontinuous dewetting (DD) and liquid bridge transfer (LBT) was applied to successfully pattern single-walled carbon nanotubes (SWCNTs): the first 1D nanomaterials patterned using the technique. The technique could efficiently and simply pattern SWCNTs with 2.5-10 mu m resolution using little energy, low temperature (<= 90 degrees C), and low cost and is potentially compatible with roll-to-roll manufacturing. Many variables were investigated to determine successful patterning conditions. The SWCNT patterning technique demonstrates the potential to obtain the often mutually exclusive properties for SWCNT patterning of high resolution and fast throughput/manufacturability. Due to the low concentration attainable in SWCNT dispersions, a preliminary wetting layer and evaporation-driven deposition were required to achieve a uniform and high-density deposition of SWCNTs inside the patterned cavities of a polydimethylsiloxane transfer stamp. The wetting layer allowed for uniform SWCNT deposition inside the cavities by preventing depinning of the SWCNT ink solution in the cavities. The wetting layer also doubled as a release layer during LBT, allowing easy transfer of the SWCNT lines onto hydrophilic substrates. SWCNT lines were patterned with widths down to 2.5 mu m, up to centimeter lengths, and a resistivity of 1.9 X 10(-3 )Omega m without any annealing. This work demonstrates the potential of DD and LBT patterning of SWCNTs for high-resolution R2R printing of cheap and/or flexible next-generation electrodes and interconnects.

Lateral Size Scaling Effect during Discontinuous Dewetting

AbstractDiscontinuous dewetting on a prepatterned surface with regions of different dewettability is an attractive way to assemble a material into 2D microstructures with a predefined lateral size and spatial distribution on a surface. However, few studies have examined the aspect ratio or contact angles of the microstructures. In this Communication, it is found that the static contact angle changes with the lateral size of droplets and variation relationship between them shows two phases: an exponential decrease phase when lateral size is &lt;80 µm, and a minimum plateau phase when lateral size is &gt;80 µm, which is defined as lateral size scaling effect. After dynamically studying the droplet generation, it is proposed that liquid retraction after liquid thin film ruptures is responsible for the lateral size scaling effect. The effect of liquid viscosity and sliding speed on the lateral size scaling effect is also assessed and the lateral size scaling effect in droplet evaporation models is investigated. Finally, differently oriented single metal‐organic framework crystal arrays based on the lateral size scaling effect are successfully fabricated. This work demonstrates a novel 2.5D top‐down strategy to guide bottom‐up assembly.

Stable Blue Luminescent CsPbBr3 Perovskite Nanocrystals Confined in Mesoporous Thin Films

AbstractCreating CsPbBr3 perovskite nanocrystals with bright blue emission is challenging because their optical properties depend sensitively on structure. Growing perovskites in mesoporous templates bypasses some of these purification issues because the size of the nanocrystal is governed by the dimensions of the pores. Mesoporous silica consisting of aligned channels with tunable diameter can be easily synthesized and used as a template. When the perovskite solution evaporates and retreats, some of the liquid remains trapped in the interconnecting pores by discontinuous dewetting. The precursor crystallizes, generating stable ca. 3.1 nm blue‐emitting perovskite nanocrystals. The mesoporous template also serves as a protective barrier to preserve the optical properties of the CsPbBr3 from atmospheric conditions. Compared to the bulk crystals and the powder composite, the strong blue‐shift of the emission peak in the film is accompanied by a decrease in the longer lifetime component and an 8‐fold increase in the external quantum efficiency.