Solvent-Free Fabrication of Anisotropic Microparticles with Precise 3D Shape Control Using Dipping-Based Micromolding.

We present an innovative solvent-free micromolding technique for rapidly fabricating complex polymer microparticles with three-dimensional (3D) shapes utilizing a surface tension-induced dipping process. Our fabrication process involves loading a photocurable solution into micromolds through mold dipping. The loaded solution, induced by surface tension, undergoes spatial deformation upon mold removal caused by surface forces, ultimately acquiring an anisotropic shape before photopolymerization. Results show that the amount of photocurable solution loaded depends on the degree of capillary penetration, which can be adjusted by varying the dipping time and mold height. It enables the production of polymer particles with precisely controlled 3D shapes without diluting them with volatile organic solvents. Sequential micromolding enables the spatial stacking of the polymer domain through a bottom-up approach, facilitating the creation of complex multicompartmental microparticles with independently controlled compartments. Finally, we demonstrated the successful simultaneous conjugation of multiple model-fluorescent proteins through the biofunctionalization of microparticles, indicating functional stability and effective conjugation of hydrophilic molecules such as proteins. We also extend our capacity to create bicompartmental microparticles with distinct functionalities in each compartment, revealing spatially controlled functional structures. In summary, these findings demonstrate a straightforward, rapid, and reliable method for producing highly uniform complex particles with precise control over the 3D shape and compartmentalization, all accomplished without the use of organic solvents.

Harnessing protein sensing ability of electrochemical biosensors via a controlled peptide receptor-electrode interface.

BACKGROUND: Cathepsin B, a cysteine protease, is considered a potential biomarker for early diagnosis of cancer and inflammatory bowel diseases. Therefore, more feasible and effective diagnostic method may be beneficial for monitoring of cancer or related diseases. RESULTS: A phage-display library was biopanned against biotinylated cathepsin B to identify a high-affinity peptide with the sequence WDMWPSMDWKAE. The identified peptide-displaying phage clones and phage-free synthetic peptides were characterized using enzyme-linked immunosorbent assays (ELISAs) and electrochemical analyses (impedance spectroscopy, cyclic voltammetry, and square wave voltammetry). Feasibilities of phage-on-a-sensor, peptide-on-a-sensor, and peptide-on-a-AuNPs/MXene sensor were evaluated. The limit of detection and binding affinity values of the peptide-on-a-AuNPs/MXene sensor interface were two to four times lower than those of the two other sensors, indicating that the peptide-on-a-AuNPs/MXene sensor is more specific for cathepsin B (good recovery (86-102%) and %RSD (< 11%) with clinical samples, and can distinguish different stages of Crohn's disease. Furthermore, the concentration of cathepsin B measured by our sensor showed a good correlation with those estimated by the commercially available ELISA kit. CONCLUSION: In summary, screening and rational design of high-affinity peptides specific to cathepsin B for developing peptide-based electrochemical biosensors is reported for the first time. This study could promote the development of alternative antibody-free detection methods for clinical assays to test inflammatory bowel disease and other diseases.

Capsule-based colorimetric temperature monitoring system for customizable cold chain management.

The COVID-19 pandemic and the resulting supply chain disruption have rekindled crucial needs for safe storage and transportation of essential items. Despite recent advances, existing temperature monitoring technologies for cold chain management fall short in reliability, cost, and flexibility toward customized cold chain management for various products with different required temperature. In this work, we report a novel capsule-based colorimetric temperature monitoring system with precise and readily tunable temperature ranges. Triple emulsion drop-based microfluidic technique enables rapid production of monodisperse microcapsules with an interstitial phase-change oil (PCO) layer with precise control over its dimension and composition. Liquid-solid phase transition of the PCO layer below its freezing point triggers the release of the encapsulated payload yielding drastic change in color, allowing user-friendly visual monitoring in a highly sensitive manner. Simple tuning of the PCO layer's compositions can further broaden the temperature range in a precisely controlled manner. The proposed simple scheme can readily be formulated to detect both temperature rise in the frozen environment and freeze detection as well as multiple temperature monitoring. Combined, these results support a significant step forward for the development of customizable colorimetric monitoring of a broad range of temperatures with precision.

Microfluidic fabrication of microparticles for biomedical applications.

Droplet microfluidics offers exquisite control over the flows of multiple fluids in microscale, enabling fabrication of advanced microparticles with precisely tunable structures and compositions in a high throughput manner. The combination of these remarkable features with proper materials and fabrication methods has enabled high efficiency, direct encapsulation of actives in microparticles whose features and functionalities can be well controlled. These microparticles have great potential in a wide range of bio-related applications including drug delivery, cell-laden matrices, biosensors and even as artificial cells. In this review, we briefly summarize the materials, fabrication methods, and microparticle structures produced with droplet microfluidics. We also provide a comprehensive overview of their recent uses in biomedical applications. Finally, we discuss the existing challenges and perspectives to promote the future development of these engineered microparticles.

Microfluidic Templated Multicompartment Microgels for 3D Encapsulation and Pairing of Single Cells.

Controlled encapsulation and pairing of single cells within a confined 3D matrix can enable the replication of the highly ordered cellular structure of human tissues. Microgels with independently controlled compartments that can encapsulate cells within separately confined hydrogel matrices would provide precise control over the route of pairing single cells. Here, a one-step microfluidic method is presented to generate monodisperse multicompartment microgels that can be used as a 3D matrix to pair single cells in a highly biocompatible manner. A method is presented to induce microgels formation on chip, followed by direct extraction of the microgels from oil phase, thereby avoiding prolonged exposure of the microgels to the oil. It is further demonstrated that by entrapping stem cells with niche cells within separate but adjacent compartments of the microgels, it can create complex stem cell niche microenvironments in a controlled manner, which can serve as a useful tool for the study of cell-cell interactions. This microfluidic technique represents a significant step toward high-throughput single cells encapsulation and pairing for the study of intercellular communications at single cell level, which is of significant importance for cell biology, stem cell therapy, and tissue engineering.

Directed Assembly of Janus Cylinders by Controlling the Solvent Polarity.

This study demonstrates the possibility of controlling the directed self-assembly of microsized Janus cylinders by changing the solvent polarity of the assembly media. Experimental results are analyzed and theoretical calculations of the free energy of adhesion (ΔGad) are performed to elucidate the underlying basic principles and investigate the effects of the solvent on the self-assembled structures. This approach will pave a predictive route for controlling the structures of assembly depending on the solvent polarity. In particular, we find that a binary solvent system with precisely controlled polarity induces directional assembly of the microsized Janus cylinders. Thus, the formation of two-dimensional (2D) and three-dimensional (3D) assembled clusters can be reliably tuned by controlling the numbers of constituent Janus cylinders in a binary solvent system. Finally, this approach is expanded to stepwise assembly, which forms unique microstructures via secondary growth of primary seed clusters formed by the Janus cylinders. We envision that this investigation is highly promising for the construction of desired superstructures using a wide variety of polymeric Janus microparticles with chemical and physical multicompartments.

Capillarity-induced directed self-assembly of patchy hexagram particles at the air-water interface.

Directed self-assembly can produce ordered or organized superstructures from pre-existing building blocks through pre-programmed interactions. Encoding desired information into building blocks with specific directionality and strength, however, poses a significant challenge for the development of self-assembled superstructures. Here, we demonstrate that controlling the shape and patchiness of particles trapped at the air-water interface can represent a powerful approach for forming ordered macroscopic complex structures through capillary interactions. We designed hexagram particles using a micromolding method that allowed for precise control over the shape and, more importantly, the chemical patchiness of the particles. The assembly behaviors of these hexagram particles at the air-water interface were strongly affected by chemical patchiness. In particular, two-dimensional millimeter-scale ordered structures could be formed by varying the patchiness of the hexagram particles, and we attribute this effect to the delicate balance between the attractive and repulsive interactions among the patchy hexagram particles. Our results provide important clues for encoding information into patchy particles to achieve macroscopic assemblies via a simple molding technique and potentially pave a new pathway for the programmable assembly of particles at the air-water interface.

Controlled fabrication of multicompartmental polymeric microparticles by sequential micromolding via surface-tension-induced droplet formation.

Polymeric multicompartmental microparticles have significant potential in many applications due to the capability to hold various functions in discrete domains within a single particle. Despite recent progress in microfluidic techniques, simple and scalable fabrication methods for multicompartmental particles remain challenging. This study reports a simple sequential micromolding method to produce monodisperse multicompartmental particles with precisely controllable size, shape, and compartmentalization. Specifically, our fabrication procedure involves sequential formation of primary and secondary compartments in micromolds via surface-tension-induced droplet formation coupled with simple photopolymerization. Results show that monodisperse bicompartmental particles with precisely controllable size, shape, and chemistry can be readily fabricated without sophisticated control or equipment. This technique is then extended to produce multicompartmental particles with controllable number of compartments and their size ratios through simple design of mold geometry. Also, core-shell particles with controlled number of cores for primary compartments can be readily produced by simple tuning of wettability. Finally, we demonstrate that the as-prepared multicompartmental particles can exhibit controlled release of multiple payloads based on design of particle compositions. Combined, these results illustrate a simple, robust, and scalable fabrication of highly monodisperse and complex multicompartmental particles in a controlled manner based on sequential micromolding.

Three-dimensional clustering of Janus cylinders by convex curvature and hydrophobic interactions.

The three-dimensional (3D) clustering of Janus cylinders is controlled by simply tuning the cylinder geometry and hydrophobic interactions. Janus cylinders were prepared by combining two approaches: micromolding and initiated chemical vapor deposition (iCVD). Hydrophilic cylinders with a flat- or convex-top curvature were prepared by micromolding based on surface tension-induced flow. The iCVD process then provides a hydrophobic domain through the simple and precise deposition of a polymer film on the top surface, forming monodisperse Janus microcylinders. We use these Janus cylinders as building blocks to form 2D or 3D clusters via hydrophobic interactions in methanol. We investigate how cylinder geometry or degree of hydrophobic interaction affects the resulting cluster geometries. The convex-top Janus cylinders lead to 3D clustering through tip-to-tip interactions, and the flat-top Janus cylinders lead to 2D clustering through face-to-face attraction. The number of Janus cylinders in 3D clusters is tuned by controlling the degree of hydrophobic (or hydrophilic) interaction.

Microfluidic design of complex emulsions.

Controllable generation of complex emulsions comprising exceptional features such as several compartments and shape anisotropy is becoming increasingly important. Complex emulsions are attracting great interest due to their significant potential in many applications, including foods, pharmaceuticals, cosmetics, materials, and chemical separations. Microfluidics is emerging as a promising route to the generation of complex emulsions, providing precise control over emulsion shape, size, and compartments. The aim of this Minireview is to mainly describe the progress of microfluidic approaches to design complex emulsions using hydrodynamic control and phase separation. The emulsions formed are classified according to their morphology, anisotropy, and internal structure. Emerging applications of complex emulsions formed using these microfluidic techniques are discussed.

Triblock cylinders at fluid-fluid interfaces.

We present the interactions and assembly of triblock cylinders at oil-water and air-water interfaces. ABA-type triblock cylinders with different block ratios and surface wettabilities are prepared using a micromolding method. These triblock cylinders at fluid-fluid interfaces induce complex interface deformation depending upon their relative block ratio and the surface wettability. It is observed that triblock cylinders generate octapolar interface deformation at the air-water interface, whereas the same cylinders cause quadrupolar deformation at the oil-water interface. Consequently, the interactions and assembly behavior of these triblock cylinders at each fluid interface strongly depend upon the nature of the interface deformation.

A rapid one-step fabrication of patternable superhydrophobic surfaces driven by Marangoni instability.

We present a facile and inexpensive approach without any fluorinated chemistry to create superhydrophobic surface with exceptional liquid repellency, transportation of oil, selective capture of oil, optical bar code, and self-cleaning. Here we show experimentally that the control of evaporation is important and can be used to form superhydrophobic surface driven by Marangoni instability: the method involves in-situ photopolymerization in the presence of a volatile solvent and porous PDMS cover to afford superhydrophobic surfaces with the desired combination of micro- and nanoscale roughness. The porous PDMS cover significantly affects Marangoni convection of coating fluid, inducing composition gradients at the same time. In addition, the change of concentration of ethanol is able to produce versatile surfaces from hydrophilic to superhydrophobic and as a consequence to determine contact angles as well as roughness factors. In conclusion, the control of evaporation under the polymerization provides a convenient parameter to fabricate the superhydrophobic surface, without application of fluorinated chemistry and the elegant nanofabrication technique.

Electrochemical peptide-based biosensor for the detection of the inflammatory disease biomarker, interleukin-1beta.

This paper reports the development of a highly sensitive and selective electrochemical peptide-based biosensor for the detection of the inflammatory disease biomarker, interleukin-1beta (IL-1ß). To this end, flower-like Au-Ag@MoS2-rGO nanocomposites were used as the signal amplification platform to achieve a label-free biosensor with a high sensitivity and selectivity. First, a high-affinity peptide for IL-1ß was identified through biopanning with M13 random peptide libraries, and was newly designed by incorporating cysteine at the C-terminus. An IL-1ß specific binding peptide was used as the bio-receptor, and the interaction between the IL-1ß binding peptide and IL-1ß was confirmed via enzyme-linked immunosorbent assay and various physicochemical and electrochemical analyses. Under optimal conditions, the biosensor achieved an ultrasensitive and specific IL-1ß detection in a wide linear concentration range of 0-250 ng/mL with a picomolar-level detection limit (∼2.4 pM), low binding constant (∼0.62 pM), and a low coefficient of variation (<1.65 %). The biosensor was successfully utilized for IL-1ß determination in the serum of Crohn's disease patients with a good correlation coefficient. In addition, the detection performance was comparable to that of commercially available IL-1ß ELISA kit. This indicates that the electrochemical peptide-based biosensor may offer a potentially valuable platform for the clinical diagnosis of various inflammatory disease biomarkers.

Mimicking chronic alcohol effects through a controlled and sustained ethanol release device.

Alcohol consumption, a pervasive societal issue, poses considerable health risks and socioeconomic consequences. Alcohol-induced hepatic disorders, such as fatty liver disease, alcoholic hepatitis, chronic hepatitis, liver fibrosis, and cirrhosis, underscore the need for comprehensive research. Existing challenges in mimicking chronic alcohol exposure in cellular systems, attributed to ethanol evaporation, necessitate innovative approaches. In this study, we developed a simple, reusable, and controllable device for examining the physiological reactions of hepatocytes to long-term alcohol exposure. Our approach involved a novel device designed to continuously release ethanol into the culture medium, maintaining a consistent ethanol concentration over several days. We evaluated device performance by examining gene expression patterns and cytokine secretion alterations during long-term exposure to ethanol. These patterns were correlated with those observed in patients with alcoholic hepatitis. Our results suggest that our ethanol-releasing device can be used as a valuable tool to study the mechanisms of chronic alcohol-mediated hepatic diseases at the cellular level. Our device offers a practical solution for studying chronic alcohol exposure, providing a reliable platform for cellular research. This innovative tool holds promise for advancing our understanding of the molecular processes involved in chronic alcohol-mediated hepatic diseases. Future research avenues should explore broader applications and potential implications for predicting and treating alcohol-related illnesses.

Color-encoded multicompartmental hydrogel microspheres for multiplexed bioassays.

We develop color-encoded multicompartmental hydrogel (MH) microspheres tailored for multiplexed bioassays using a drop-based microfluidic approach. Our method involves the creation of triple emulsion drops that feature thin sacrificial oil layers separating two prepolymer phases. This configuration leads to the formation of poly(ethylene glycol) (PEG) multi-compartmental core-shell microspheres through photopolymerization, followed by the removal of the thin oil layers. The core compartments stably incorporate pigments, ensuring their retention within the hydrogel network without leakage, which facilitates reliable color encoding across varying spatial positions. Additionally, we introduce small molecule fluorescent labeling into the chemically functionalized shell compartments, achieving consistent distribution of functional components without the core's contamination. Importantly, our integrated one-pot conjugation of these color-encoded microspheres with affinity peptides enables the highly sensitive and selective detection of influenza virus antigens using a fluorescence bioassay, resulting in an especially low detection limit of 0.18 nM and 0.66 nM for influenza virus H1N1 and H5N1 antigens, respectively. This approach not only highlights the potential of our microspheres in clinical diagnostics but also paves the way for their application in a wide range of multiplexed assays.

Controllable preparation of monodisperse microspheres using geometrically mediated droplet formation in a single mold.

We present a surfactant-free fabrication method for simultaneous generation of monodisperse microspheres with controllable size manner. Droplets that become microspheres by solidification processes are made in a two-step process: capillary rising-induced fluid division and wetting of immiscible fluid in a micromold. Design of the mold geometry and the monomer concentration primarily determines the microsphere size and the size distribution. Furthermore, the synergistic effect of two parameters is able to efficiently manipulate the microsphere sizes from submicrometers to a few hundred micrometers.

Double hydrophilic Janus cylinders at an air-water interface.

Colloidal particles spontaneously attach to the interface between two immiscible fluids to minimize the interfacial area between the two phases. The shape and wettability of particles have a strong influence on their configuration and interactions at fluid-fluid interfaces. In this study, we investigate the behavior of asymmetrically hydrophilic Janus cylinders (or double hydrophilic Janus cylinders with two different hydrophilic regions) trapped at an air-water interface. We find that these double hydrophilic Janus cylinders with aspect ratios of 0.9, 1.2, and 2.4 adopt both end-on and tilted configurations with respect to the interface. Our numerical calculations show that the coexistence of these configurations is a result of multiple energy minima present in the attachment energy profile that can be represented as a complex energy landscape. Double hydrophilic Janus cylinders with tilted orientations induce hexapolar interface deformation, which accounts for the pair interactions between the particles as well as the nondeterministic assembly behaviors of these particles at the interface.

reliable Synthesis of Monodisperse Microparticles: Prevention of Oxygen Diffusion and Organic Solvents Using Conformal Polymeric Coating onto Poly(dimethylsiloxane) Micromold.

An effective polymeric thin film deposited by initiated chemical vapor deposition (iCVD) process was presented and its application as a barrier film on the PDMS micromold blocking the penetration of oxygen and organic solvents was investigated. With this barrier film, we were able to synthesize monodisperse polymeric particles of sizes down to 3 µm, which has been reported to be extremely challenging with bare PDMS micromold. The polymeric barrier film on the PDMS micromold enabled this successful synthesis of microparticles by effectively blocking the diffusion of oxygen, which is a well-known radical quencher in radical polymerization, through the PDMS micromold. Furthermore, the iCVD barrier film substantially decreased the penetration of various organic solvents such as acetone, tert-butanol, PDMS oil, and decane as well as organic substances including fluorescent molecules like rhodamine B and fluorescein isothiocyanate (FITC). Therefore, the polymeric barrier film coated on PDMS micromold via iCVD process will broaden the application of PDMS to microfluidic area for the synthesis of smaller microparticles with various organic substances.

Sulfur-doped graphitic carbon nitride: Tailored nanostructures for photocatalytic, sensing, and energy storage applications.

Rapid globalization and industrialization have led to widespread pollution and energy crises, necessitating the development of innovative solutions. Metal-free g-C3N4-based polymeric materials have unique properties but face limitations such as low surface area and inefficient light absorption. Doping, especially sulfur doping, is a prevalent technique to enhance their optical and electronic properties. This comprehensive review focuses on the synthesis techniques employed for sulfur doping of g-C3N4 (S-CN), highlighting the complexities associated with S-doping and the advantages of co-doping. Additionally, the review encompasses the diverse applications of S-CN in catalysis, photocatalysis, sonocatalysis, pollutant remediation, and electrochemical sensing. By incorporating sulfur into the g-C3N4 structure, various desirable properties can be achieved, including improved light absorption efficiency and enhanced charge carrier separation and migration. These advancements have broadened the application potential of S-CN in a range of important fields. S-CN has shown promise as a catalyst, facilitating various chemical reactions, as well as a photocatalyst, harnessing solar energy for environmental remediation and energy conversion processes. Moreover, S-CN exhibits potential in sonocatalysis for ultrasound-mediated reactions, pollutant remediation, and electrochemical sensing applications.

Broad-temperature-range mechanically tunable hydrogel microcapsules for controlled active release.

Here, we report PNIPAm-co-PEGDA hydrogel shelled microcapsules with a thin oil layer to achieve tunable thermo-responsive release of the encapsulated small hydrophilic actives. We use a microfluidic device integrated with a temperature-controlled chamber for consistent and reliable production of the microcapsules by utilizing triple emulsion drops (W/O/W/O) with a thin oil layer as capsule templates. The interstitial oil layer between the aqueous core and the PNIPAm-co-PEGDA shell provides a diffusion barrier for the encapsulated active until the temperature reaches a critical point above which the destabilization of interstitial oil layer occurs. We find that the destabilization of the oil layer with temperature increase is caused by outward expansion of the aqueous core due to volume increase and the radial inward compression from the deswelling of the thermo-responsive hydrogel shell. The copolymerization of NIPAm with PEGDA increases the biocompatibility of the resulting microcapsule while offering the ability to alter the compressive modulus in broad ranges by simply varying crosslinker concentrations thereby to precisely tune the onset release temperature. Based on this concept, we further demonstrate that the release temperature can be enhanced up to 62 °C by adjusting the shell thickness even without varying the chemical composition of the hydrogel shell. Moreover, we incorporate gold nanorods within the hydrogel shell to spatiotemporally regulate the active release from the microcapsules by illuminating with non-invasive near infrared (NIR) light.