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Thermoresponsive polymers incorporated with photo-absorbing agents have been widely utilized for controlled drug delivery using light as an external stimulus. However, previously developed thermoresponsive drug carriers have disadvantages such as low biocompatibility and implantation failure. In the present study, gold nanorods (GNRs)-encapsulated poly(N-vinyl caprolactam) (PVCL) (GNR-PVCL) microparticles were synthesized by the stop-flow lithography (SFL) method. The SFL method enabled the fabrication of near-infrared (NIR) light-responsive GNR-PVCL microparticles of uniform size, which can allow localized injection. Doxorubicin (DOX) was encapsulated into GNR-PVCL microparticles to achieve NIR light-responsive anticancer therapy. DOX-loaded GNR-PVCL (DOX-GNR-PVCL) microparticles exhibited NIR light-triggered drug release due to the photothermal effect of GNRs, which increases the local temperature above the volume phase transition temperature of GNR-PVCL microparticles. In addition, DOX-GNR-PVCL exhibited controlled DOX release in response to the periodic irradiation of NIR light. Moreover, we demonstrated the efficient intracellular release of DOX upon NIR light exposure, and thus, NIR light-responsive anticancer activity. This study demonstrates that DOX-GNR-PVCL microparticles have significant potential as implantable drug carriers enabling NIR light-triggered drug release.

microRNAs (miRNAs) have attracted much attention as potential biomarkers for the diagnosis of various fatal diseases. With increasing interest in miRNA detection at practical sites, colorimetric bead-based assays have garnered much attention, because these allow for simple analysis with cheap and portable devices. Among them, the encoded hydrogel microparticle-based colorimetric miRNA assay is considered as one of the promising techniques, due to its strengths, such as large multiplex capacity, acceptable sensitivity, and simple analysis. However, it still imposes a limitation in terms of the assay time, particularly the colorimetric reaction time, which is too long, making the practical application of the assay difficult and undermining its detection accuracy. In this work, we present a rapid colorimetric assay based on encoded hydrogel microparticles, which exhibits a significant decrease in the colorimetric reaction time due to two factors: (1) an increase in the number of enzymes bound to hydrogel microparticles via a post-synthesis functionalization method, and (2) an elevation in the enzyme reaction temperature during colorimetric labeling. We obtained a comparable sensitivity of the colorimetric assay with three different miRNA targets, even with a shortened colorimetric reaction time. Furthermore, we validated that our colorimetric detection method is suitable for multiplex miRNA detection, owing to its low cross-reactivity.

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.

Controlled and targeted delivery of growth factors to biological environments is important for tissue regeneration. Polylactic acid (PLA) hydrogel microparticles are attractive carriers for the delivery of therapeutic cargoes based on their superior biocompatibility and biodegradability, uniform encapsulation of cargoes, and non-requirement of organic solvents during particle synthesis. In this study, we newly present controlled growth factor delivery utilizing PLA-based hydrogel microcarriers synthesized via degassed micromolding lithography (DML). Based on the direct gelation procedure from the single-phase aqueous precursor in DML, bovine serum albumin, a model protein of growth factor, and fibroblast growth factor were encapsulated into microparticles with uniform distribution. In addition, by tuning the monomer concentration and adding a hydrolytically stable crosslinker, the release of encapsulated cargoes was efficiently controlled and extended to 2 weeks. Finally, we demonstrated the biological activity of encapsulated FGF-2 in PLA-based microparticles using a fibroblast proliferation assay.

Hydrogel microparticle-based nucleic acid assays are an attractive detection platform based on their multiplexing capabilities with high sensitivity and specificity. A particular area of interest is single-nucleotide polymorphism (SNP) sensing, where multiple SNPs should be identified in a highly reliable yet economical manner. However, hydrogel microparticles leveraging probe-target hybridization as a key mechanism are hampered by small duplex stability differences arising from single base-pair mismatch. We have developed encoded hydrogel microparticles with DNA probes tailored for multiplex SNP detection. Within the DNA probes, we adopt a widely used base analog (5-nitroindole) so that it substitutes one of the base sequences among DNA probes. The effects of the modification of the probes' structure on SNP sensing has been tested from multiple perspectives, such as specificity, sensitivity, and available assay temperatures at a given ionic strength. We have validated that our hydrogel microparticles exhibit much higher specificity for a single base-pair mismatch with minimal reduction in sensitivity. Our particles can also detect multiple SNPs located in different target strands, which is a significant challenge for conventional particles.

Due to the growing interest in multiplex protein detection, encoded hydrogel microparticles have received attention as a possible path to high performance multiplex immunoassays through a combination of high multiplexing capability and enhanced binding kinetics. However, their practical operation in real complex samples is still limited because polyethylene glycol, which is the main component of hydrogel particles, suffers from oxidative damage and relatively high fouling properties in biochemical solutions. Here, we introduce poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC)-based encoded hydrogel microparticles to perform fouling-resistant multiplex immunoassays, where the anti-fouling characteristics are attributed to the zwitterionic PMPC. By applying a newly developed molding lithography technique, viscous PMPCs with low reactivity were successfully incorporated into the hydrogel network while maintaining uniformity and rigidity for use in multiplex immunoassays. Non-specific protein adsorption on the PMPC particles was reduced by about 37.5% compared to that of conventional PEG particles, which leads to better assay sensitivity. We also validate the multiplex capability of the PMPC particles by performing multiplex detection of two target proteins. Furthermore, we verify that the PMPC particles have a 70% enhancement in anti-fouling characteristics compared to PEG particles in human platelet-rich plasma, potentiating a practical immunoassay platform for clinical diagnosis.

The development of photo-triggered drug delivery system is promising for the temporal and spatial control of drug release. However, most of the progress in photothermal drug delivery has been focused on nanosized particles which can be removed from the injected sites by exocytosis. In this study, injectable and implantable near-infrared (NIR) light-responsive microparticles are fabricated using droplet-based microfluidics. The particles are composed of 1-tetradecanol, as a class of non-toxic phase change material, and IR780, as a NIR-absorbing photothermal agent. Doxorubicin, an anticancer drug, is encapsulated in the particles to obtain NIR light-responsive anticancer drug carriers. The photothermal response of IR780 to NIR irradiation facilitates the release of the encapsulated drug through the melting of 1-tetradecanol and demonstrates the NIR light-responsive drug release. This study shows that IR780-encapsulated 1-tetradecanol microparticles fabricated by droplet-based microfluidics have great potential as injectable and implantable drug carriers featuring NIR light-sensitive drug release.

Capacitive deionization (CDI) is an emerging desalination technique by utilizing the electrosorption of porous electrodes. Thus far, only linear concentration profiles in bulk electrolyte between the electrodes have been observed, during ion charging (ion depletion) or ion discharging (ion enrichment). This so-called linear ion concentration polarization (ICP) can be predicted by the simple convective-diffusion model. In this study, we demonstrate that capacitive charging can induce nonlinear concentration profiles in the electrolyte. To visualize nonlinear ICP dynamics, a miniaturized CDI platform is developed to observe in situ ion concentration profiles. Determined by the ion flux mismatching of electrosorption and bulk ion transport, we discovered four ICP regimes in CDI – steady, linear ICP, delayed-nonlinear ICP, and nonlinear ICP. We directly observed the signatures of nonlinear ICP: i) flat depletion zone with extremely low ion concentration, and ii) corresponding exponential current drop. Based on this observation, two scaling models are formulated to predict i) when the nonlinear ICP occurs, and ii) the propagation speed of the flat depletion zone. To the best of our knowledge, this is the first microscopic characterization of ICP in CDI systems, and it firmly establishes the existence of nonlinear ion transport dynamics in CDI's bulk electrolyte.

Recent interests in comprehensive protein surveys and protein biomarker studies have led to an increased demand for simultaneous measurement of multiple proteins in a single sample. Among various multiplex techniques, bead-based immunoassays, which use encoded particles attached with capture probes, have demonstrated distinct advantages of fluid-phase kinetics, high precision, and flexible target selection. In particular, encoded hydrogel particles composed of porous, hydrophilic, three-dimensional polymers have received positive attention because they enhance the binding kinetics of proteins, reduce protein denaturation, and increase the loading density of capture probes. Microfluidic techniques have been extensively used to fabricate the encoded hydrogel particles for multiplex immunoassays, enabling mass-production of highly monodisperse particles with complex morphologies in mild synthesis conditions. In this paper, we review microfluidic techniques available for the synthesis of encoded hydrogel particles and the important design parameters that determine the particles’ immunoassay performance. We also discuss currently reported multiplex immunoassay platforms that are based on encoded hydrogel particles.

Replica molding is widely used to reproduce the surface microstructures that provide living organisms with distinct and useful functions. However, the existing methods are limited by the low resolution resulting from the air trapped in the structures during precursor solution loading. This study investigated replica molding with an air-through-precursor suction (APS) process, which used a degassed polydimethylsiloxane substrate to remove the trapped air through the precursor solution. The liquid loading times are characterized using a model template, and air suction that is up to 36 times faster can be achieved using the APS process relative to a conventional method. Using APS replica molding, biocompatible replicates from human fingerprints and gecko skin are fabricated using only a 3 min precursor solution loading step. Owing to the enhanced and reproducible resolution from APS replica molding, for the first time, the structural changes in the foot of a living gecko at the microscale can be observed when standing on a horizontal or vertical surface.

Magnetic hydrogels have been commonly used in biomedical applications. As magnetite nanoparticles (MNPs) exhibit peroxidase enzyme-like activity, magnetic hydrogels have been actively used as signal transducers for biomedical assays. Droplet microfluidics, which uses photoinitiated polymerization, is a preferred method for the synthesis of magnetic hydrogels. However, light absorption by MNPs makes it difficult to obtain fully polymerized and homogeneous magnetic hydrogels through photoinitiated polymerization. Several methods have been reported to address this issue, but few studies have focused on investigating the light absorption properties of photoinitiators. In this study, we developed a simple method for the synthesis of poly(ethylene glycol) (PEG)-based uniform magnetic hydrogels that exploits the high ultraviolet absorption of a photoinitiator. Additionally, we investigated this effect on shape deformation and structural uniformity of the synthesized magnetic hydrogels. Two different photoinitiators, Darocur 1173 and lithium phenyl (2,4,6&ndash, trimethylbenzoyl) phosphinate (LAP), with significantly different UV absorption properties were evaluated based on the synthesis of magnetic hydrogels. The magnetic characteristics of the PEG-stabilized MNPs in hydrogels were investigated with a vibrating sample magnetometer. Finally, the colorimetric detection of hydrogen peroxide and glucose was conducted based on the enzyme-like property of MNPs and repeated several times to observe the catalytic activity of the magnetic hydrogels.

Despite a growing demand for more accessible diagnostic technologies, current methods struggle to simultaneously detect multiple analytes with acceptable sensitivity and portability. Colorimetric assays have been widely used due to their simplicity of signal readout, but the lack of multiplexibility has been a perpetual constraint. Meanwhile, particle-based assays offer multiplex detection by assigning an identity code to each analyte, but they often require lab-based equipment unsuitable for portable diagnostics. Here, by merging the two approaches, this paper reports a colorimetric multiplex immunoassay based on hydrogel microparticles that achieves the best of both worlds. The low-cost portable multiplex assay demonstrates sensitivities as high as and dynamic ranges greater than the lab-based enzyme-linked immunosorbent assay (ELISA). These critical advances are made possible by local precipitation and amplification of insoluble colour dyes inside the hydrogel networks. For the first time, enzymatic accumulation of colour dyes in hydrogel particles is reported and the kinetics of colour development is characterized in this work. By taking advantage of the colour signals in the visible spectrum, the hydrogel microparticles were imaged and analysed using low-cost portable devices. The colorimetric multiplex immunoassay was used to successfully detect three target biomarkers of preeclampsia and validated clinically using healthy and patient-derived plasma samples.

In response to a growing demand for simultaneous detection of multiple proteins in a single sample, multiplex immunoassay platforms have emerged at the forefront of proteomic analysis. In particular, detections using graphically encoded hydrogel microparticles synthesized via flow lithography have received attention for integrating a hydrogel, a substrate that can provide enhanced kinetics and high loading capacity, into the bead-based multiplex platform. Currently, the method of microparticle functionalization involves copolymerization of antibodies with the gel during particle synthesis. However, its practical operation is too precarious to be adopted because antibodies are susceptible to aggregation due to incompatibility with hydrophobic photoinitiators used in the photo-induced gel polymerization. In this work, we present a multiplex immunoassay platform that uses encoded hydrogel microparticles that are functionalized after particle synthesis by conjugating antibodies with remnant active groups readily available in the hydrogels. The method not only precludes antibody aggregation but also augments the loading density of the antibodies, which translates into enhanced detection performance. In addition to multiplexing, our platform demonstrates high sensitivity, a broad assay range, and a fast detection rate that outperform the enzyme linked immunosorbent assay (ELISA).

Encoded hydrogel microparticles synthesized via flow lithography have drawn attention for multiplex biomarker detection due to their high multiplex capability and solution-like hybridization kinetics. However, the current methods for preparing particles cannot achieve a flexible, rapid probe-set modification, which is necessary for the production of various combinations of target panels in clinical diagnosis. In order to accomplish the unmet needs, streptavidin was incorporated into the encoded hydrogel microparticles to take advantage of the rapid streptavidin&ndash, biotin interactions that can be used in probe-set modification. However, the existing methods suffer from low efficiency of streptavidin conjugation, cause undesirable deformation of particles, and impair the assay capability. Here, we present a simple and powerful method to conjugate streptavidin to the encoded hydrogel microparticles for better assay performance and rapid probe-set modification. Streptavidin was directly conjugated to the encoded hydrogel microparticles using the aza-Michael addition click reaction, which can proceed in mild, aqueous condition without catalysts. A highly flexible and sensitive assay was developed to quantify DNA and proteins using streptavidin-conjugated encoded hydrogel microparticles. We also validated the potential applications of our particles conducting multiplex detection of cancer-related miRNAs.

Flow lithography (FL), a versatile technique used to synthesize anisotropic multifunctional microparticles, has attracted substantial interest, given that the resulting particles with complex geometries and multilayered biochemical functionalities can be used in a wide variety of applications. However, after this process, there are double bonds remaining from the cross-linkable groups of monomers. The unreacted cross-linkable groups can affect the particles' biochemical properties. Here, we verify that the microparticles produced by FL contain a significant number of unreacted acrylate double bonds (UADBs), which could cause irreversible biochemical changes in the particle and pernicious effects to biological systems. We also confirm that the particles contain a considerable number of UADBs, regardless of the various synthetic (lithographic) conditions that can be used in a typical FL process. We present an effective way to eliminate a substantial amount of UADBs after synthesis by linking biochemically inert poly(ethylene glycol) based on click chemistry. We verify that eliminating UADBs by using this click chemistry approach can efficiently resolve problems, such as the occurrence of random reactions and the cytotoxicity of UADBs.

Gold nanorods (GNRs) are of great interest in cancer therapy given their ability to ablate tumor cells using deep tissue-penetrating near-infrared light. GNRs coated with tumor-specific moieties have the potential to target tumor tissue to minimize damage to normal tissue. However, perfect targeting is difficult to achieve given that nanoparticles could be broadly dispersed inside the body. Moreover, interaction between targeting groups and biological molecules could lower targeting abilities, resulting in off-target accumulation which might produce nanotoxicity. Here we introduce GNR-encapsulated microcubes (GNR@MCs) that can be utilized as implantable photothermal agents. GNR@MCs are created by encapsulating GNRs in polymeric networks via stop flow lithography (SFL), a one-phase synthesis technique which allows for creation of surfactant-free, uniform particles, and injection of GNR@MCs into the body after a simple rinse step. GNRs are highly packed and firmly encapsulated inside MCs, and entrapped GNRs exhibit optical properties comparable to that of unbound GNRs and photothermal efficiency (58%) in line with that of nano-sized agents (51–95%). Photothermal ablation in murine models is achieved using GNR@MCs stably implanted into the tumor tissue, which suggests that GNR@MCs can be a safe and effective platform for cancer therapy.

Although urinary exosomal microRNAs (miRNAs) have recently emerged as potential biomarkers, clinical applications are still limited due to their low concentration in small volumes of clinical samples. Therefore, the development of a non-invasive, specific diagnostic tool, along with profiling exosomal miRNA markers from urine, remains a significant challenge. Here, we present hydrogel-based hybridization chain reaction (HCR) for multiplex signal amplification to detect urinary exosomal miRNAs from human clinical samples. We succeeded in identifying small amounts (~amol) of exosomal miRNAs from 600 μL of urine with up to ~35-fold amplification and enhanced detection limits by over an order of magnitude for two miRNA biomarker candidates, hsa-miR-6090 and hsa-miR-3665. Furthermore, we proposed ratiometric analysis without requiring normalization to a reference miRNA and validated the clinical diagnostic potential toward differentiating prostate cancer patients from healthy controls. Our hydrogel-based HCR could serve as a new diagnostic platform for a non-invasive liquid biopsy before burdensome tissue biopsy of various diseases, including prostate cancer screening, complementing the PSA test.

There has been increasing attention to the development of multi-stimuli-responsive drug carriers for precisely controlled drug release at target disease areas. In this study, pH- and redox-responsive hybrid drug carriers were fabricated by using both ketal-based acid-cleavable precursors and disulfide-based reducible precursors via stop-flow lithography. pH- and redox-sensitive drug release of the dual stimuli-responsive hybrid particles was confirmed, demonstrating their feasibility for selective and efficient drug release into tumor tissues in acidic and highly reductive environments. It was also found that the drug release rate of the particles was fine-tuned by modulating monomer compositions in the precursor. Importantly, the dual stimuli-responsive hybrid particles exhibited synergistic, controlled drug release in complex stimuli (both pH and redox stimuli) environments. To achieve tumor-selective combination chemotherapy, multicompartmental drug carriers consist of an acid-degradable compartment and a reducible compartment, which can separately encapsulate individual model drugs in each of the compartments. The multicompartmental particles exhibited independent drug release upon exposure to the corresponding stimulus. The dual stimuli-responsive, multicompartmental particles are effective drug carriers for tumor-selective release of a drug cocktail, leading to synergistic combination chemotherapy.

Polydimethylsiloxane (PDMS) microfluidic devices, though they are commonly utilized in microfluidic applications, have several limitations, such as short-term modified surface condition, swelling in the presence of organic solvents, and deformation under high pressure or when built with low aspect ratios. To resolve the restrictions, Norland Optical Adhesive (NOA) has been introduced as an excellent alternative for PDMS. Here, we present a practical protocol for the fabrication of NOA microfluidic devices via a step-wise molding process. Through the indirect molding of NOA on wafers, the damage to the wafers can be significantly reduced. Furthermore, because we use positivepatterned wafers, which are commonly used to fabricate PDMS devices, no additional fabrication of the wafer is required. This simple strategy thus avoids damage to the wafers and simultaneously allows for the mass production of NOA devices without deformation. We also test the performance of NOA devices in oil-in-water droplet production and in a microfluidic process using organic solvents.

The effects of solvents such as water and ethanol on the rheological properties and crosslinking characteristics of poly(ethylene glycol) (PEG) hydrogels were examined. Real-time storage modulus data for pre-polymerized mixtures containing different solvents during the photo-polymerization process successfully explained the differences in the formation of crosslinked networks of the corresponding hydrogels. Various experimental methods for Fourier transform infrared spectroscopy (FT-IR), swelling ratio, Rhodamine-B (Rh-B) loading/release properties, and scratch/indentation depths on hydrogel surfaces, were employed to systematically compare macroscopic structural and mechanical properties of the crosslinked PEG hydrogels with different solvents (water and ethanol). The effects of the solvents on the hydrogel properties were satisfactorily consistent, and the results clearly indicated that water hindered the formation of the crosslinked network more severely than ethanol at the same weight ratio because of the presence of larger number of water molecules in pre-polymerized mixtures, which was a more favorable feature for water than ethanol in the initial crosslinking growth.

Technologies for the detection and isolation of circulating tumor cells (CTCs) are essential in liquid biopsy, a minimally invasive technique for early diagnosis and medical intervention in cancer patients. A promising method for CTC capture, using an affinity-based approach, is the use of functionalized hydrogel microparticles (MP), which have the advantages of water-like reactivity, biologically compatible materials, and synergy with various analysis platforms. In this paper, we demonstrate the feasibility of CTC capture by hydrogel particles synthesized using a novel method called degassed mold lithography (DML). This technique increases the porosity and functionality of the MPs for effective conjugation with antibodies. Qualitative fluorescence analysis demonstrates that DML produces superior uniformity, integrity, and functionality of the MPs, as compared to conventional stop flow lithography (SFL). Analysis of the fluorescence intensity from porosity-controlled MPs by each reaction step of antibody conjugation elucidates that more antibodies are loaded when the particles are more porous. The feasibility of selective cell capture is demonstrated using breast cancer cell lines. In conclusion, using DML for the synthesis of porous MPs offers a powerful method for improving the cell affinity of the antibody-conjugated MPs.

Replica molding techniques, which are used to synthesize microparticles inside anisotropic micromolds, have been developed to enable the mass production of hydrogel particles. However, these techniques are limited in their ability to synthesize only a narrow range of particle compositions and shapes because of the difficulty in loading precursors into the micromolds as well as the low particle homogeneity due to the uneven evaporation of the precursors. Herein, we describe a simple yet powerful technique, called degassed micromolding lithography, which can load precursors within 1 min regardless of the wettability. This technique is based on the gas-solubility of a degassed micromold that acts as a suction pump to completely fill the mold by drawing precursor liquids in. The semi-closed system within the micromold prevents the uneven evaporation of the precursor, which is essential for the production of homogeneous particles. Furthermore, controlled uniformity of the hydrogel microparticles (C.V. < 2%) can be achieved by engineering the design of the micromold array.

An understanding of the contact line dynamics of viscoelastic liquids is essential for the successful application of liquid processing methods in many industries. In this article, the contact line motion of a λ-DNA solution is considered both experimentally and theoretically to understand the contact line motion of polymeric solutions. Experimentally, by using fluorescently tagged λ-DNAs in glycerin, the depletion of λ-DNA near the contact line is observed. The depletion length increases with time in a range near 10 µm. DNA fragments in glycerin did not show such a depletion region. The geometric exclusion of λ-DNA from the region cannot be the proper reason for the depletion because λ-DNA is in the stretched state. It is suggested that the depletion region might be developed by the migration of polymers from the solid wall to the bulk due to the elasticity of polymers. In the theoretical study, the Stokes flow near the contact line region is solved analytically for a drop-spreading problem to obtain the inhomogeneous flow field. Then, the motions of DNAs are considered in the flow using the FENE-P dumbbell model at the dilute limit. Two independent mechanisms of migration of the dumbbells were considered: migration due to wall-bead hydrodynamic interactions and the migration of stretched dumbbells in the inhomogeneous flow. It was found that the migration of stretched dumbbells in the inhomogeneous flow appears to be the dominant reason for the presence of the depletion region. The effects of the severe extension of dumbbells on migration are also discussed for both mechanisms.

This work describes a simple aqueous-phase synthesis of single-crystal ZnO nanobolts with sizes of 250 nm by reacting Zn(NO 3 ) 2 with octylamine. The synthesized ZnO nanobolts exhibit a hierarchical structure consisting of two well-defined hexagonal nanorods of different sizes. In a study of the growth behavior of the ZnO nanobolts, we observed that aggregates of around 600 nm in size became single-crystal ZnO nanobolts with sizes of 250 nm. We also investigated the influence of reaction temperature and Zn(NO 3 ) 2 concentration on the synthesis, demonstrating that these experimental factors were critical in terms of the size, morphology, and aggregation of ZnO nanobolts.

Encoded hydrogel microparticles, synthesized by Stop Flow Lithography (SFL), have shown great potential for microRNA assays for their capability to provide high multiplexing capacity and solution-like hybridization kinetics. However, due to the low conversion of copolymerization during particle synthesis, current hydrogel microparticles can only utilize ∼10% of the input probes that functionalize the particles for miRNA assay. Here, we present a novel method of functionalizing hydrogel microparticles after particle synthesis by utilizing unconverted double bonds remaining inside the hydrogel particles to maximize functional probe incorporation and increase the performance of miRNA assay. This allows covalent bonding of functional probes to the hydrogel network after particle synthesis. Because of the abundance of the unconverted double bonds and accessibility of all probes, the probe density increases about 8.2 times compared to that of particles functionalized during the synthesis. This results lead to an enhanced miRNA assay performance that improves the limit of detection from 4.9 amol to 1.5 amol. In addition, higher specificity and shorter assay time are achieved compared to the previous method. We also demonstrate a potential application of our particles by performing multiplexed miRNA detections in human plasma samples.

We report the precise decoding of a shape-modulated hydrogel barcode particle using a micropore fluidic device. Using an electrical simulation, we deduced the optimal pore geometry that yields the maximal sensing signal. We fabricated hydrogel particles with different dimensions and prepared the micropore device along with a fluidic cell and a patch clamp. Accordingly, we experimentally determined the most appropriate shape of the hydrogel barcode particle that allows efficient differentiation between a 0 code and a 1 code. Thus, we successfully decoded 4-bit hydrogel barcode particles with high speed and high accuracy.

Flow lithography (FL) is a microfluidic technique distinguished for its ability to produce hydrogel microparticles of various geometrical and chemical designs. While FL is typically performed in room temperature, this paper reports a new technique called low temperature flow lithography that uses low synthesis temperature to increase the degree of polymerization of microparticles without compromising other aspects of flow lithography. We suggest that decreased oxygen diffusivity in low temperature is responsible for the increase in polymerization. Microparticles that exhibit a higher degree of polymerization display a more developed polymer network, ultimately resulting in a more defined morphology, higher incorporation of materials of interest, and improved functional performance. This work demonstrates the increase in the degree of polymerization by examining the temperature effect on both the physical and chemical structures of particles. We show applications of this technique in synthesizing thin microparticles and enhancing microparticle-based detection of microRNA. Low temperature FL offers a simple and easy method of improving the degree of polymerization, which can be implemented in a wide range of FL applications.

Various thermo-responsive polymers have been developed for controlled drug delivery upon the local application of external heat. The development of thermo-responsive polymers with high biocompatibility and tunable thermo-sensitivity is crucial for safe and efficient therapeutic application. In this study, thermo-responsive drug carriers featuring tunable thermo-sensitivities were synthesized using biocompatible poly(N-vinyl caprolactam) (PVCL) and stop-flow lithography. The PVCL-based particles showed selective drug release depending on temperature, illustrating their feasibility for on-demand controlled drug delivery. The volume phase transition temperature (VPTT) of the PVCL-based particles can be adjusted to vary from room temperature to body temperature by controlling their monomer compositions. In addition, modulated drug release was achieved by constructing multicompartments of different thermo-sensitivities within the PVCL particles. To accomplish thermo-responsive anticancer therapy, doxorubicin (DOX) was encapsulated into the PVCL particles as an anticancer drug. The DOX-loaded PVCL particles exhibited both thermo-responsive drug release and anticancer activity. This study demonstrates that thermo-responsive PVCL particles are highly promising carriers for safe and targeted anticancer therapy.

Encoded hydrogel particles have attracted attention in diagnostics as these particles can be used for high-performance multiplexed assays. Here, we present encoded tetragonal hydrogel microparticles for multiplexed detection of miRNAs that are strongly related to Alzheimer's disease (AD). The particles are comprised of vertically distinct code and probe regions, and incorporated with quantum dots (QDs) in the code regions. By virtue of the particle geometry, the particles can be synthesized at a high production rate in vertically stacked micro-flows using hydrodynamic focusing lithography. To detect multiple AD-miRNAs, various code labels to identify the loaded probes are designed by changing wavelengths of QDs, increasing the number of code layers and adjusting the thickness of code layers. The probe regions are incorporated with complementary sequences of target miRNAs, and optimized for accurate and timely detection of AD-miRNAs. For proof of concept, we demonstrate the multiplexed capability of the particles by performing a 3-plexed assay of AD-miRNAs.

Semiconducting WS2 nanohybrids with different sizes of silver nanoparticles are designed via amine-assisted in situ reduction and growth of Ag(+) ions. These nanohybrids exhibit characteristic photocatalytic activity for the reduction of 4-nitrophenol as a function of their structure.

Microalgae, unicellular photoautotrophic microorganisms, have attracted great attention for the production of biofuel and high-value products, but the commercial use of microalgae has been limited by low photosynthetic productivity. To overcome this limitation, it is required to develop an efficient platform for the rapid evaluation of photoautotrophic growth performance and productivity of microalgal strains. Here we describe a droplet-based photobioreactor for high-throughput analysis of the photoautotrophic growth of microalgal cells. By integrating micropillar arrays and adjusting the height of the microchamber, we could accurately monitor the growth kinetics of microalgae in an immobilized microdroplet and improve the transfer rate of CO2 into the microdroplet photobioreactor with an increased contact area between the microdroplet and PDMS surface. The improvement of CO2 transfer into the microdroplet was also confirmed by improved microalgal cell growth and a decrease in pH measured using colorimetric and fluorescence-based assays. The photoautotrophic growth kinetics of Chlorella vulgaris were measured under different CO2 concentrations (ambient, 1%, 2.5%, 5% and 7.5%) and light intensity (35, 55, 100, 150, and 200 μmol photons per m(2) per s) conditions, which are key factors for photoautotrophic growth. Chlorella vulgaris in a microdroplet showed better cell growth performance compared to a flask culture due to the reduced shading effects and improved mass transfer. Finally, we could evaluate the photoautotrophic growth performance of four microalgal strains (Chlorella vulgaris, Chlorella protothecoides, Chlorella sorokiniana and Neochloris oleoabundans) for 120 hours. These results demonstrate that our microdroplet system can be used as an efficient photobioreactor for the rapid evaluation of the photoautotrophic growth of microalgal strains under various conditions.

Transition metals, such as iron (Fe)- or cobalt (Co)-based nanomaterials, are promising electrocatalysts for oxygen reduction reactions (ORR) in fuel cells due to their high theoretical activity and low cost. However, a major challenge to using these metals in place of precious metal catalysts for ORR is their low efficiency and poor stability, thus new concepts and strategies should be needed to address this issue. Here, we report a hybrid aciniform nanostructures of Fe nanofragments embedded in thin nitrogen (N)-doped graphene (Fe@N-G) layers via a heat treatment of graphene oxide-wrapped iron oxide (Fe2O3) microparticles with melamine. The heat treatment leads to transformation of Fe2O3 microparticles to nanosized zero-valent Fe fragments and formation of core-shell structures of Fe nanofragments and N-doped graphene layers. Thin N-doped graphene layers massively promote electron transfer from the encapsulated metals to the graphene surface, which efficiently optimizes the electronic structure of the graphene surface and thereby triggers ORR activity at the graphene surface. With the synergistic effect arising from the N-doped graphene and Fe nanoparticles with porous aciniform nanostructures, the Fe@N-G hybrid catalyst exhibits high catalytic activity, which was evidenced by high E1/2 of 0.82 V, onset potential of 0.93 V, and limiting current density of 4.8 mA cm−2 indicating 4-electron ORR, and even exceeds the catalytic stability of the commercial Pt catalyst.

Stop Flow Lithography (SFL) is a microfluidic-based particle synthesis method for creating anisotropic multifunctional particles with applications that range from MEMS to biomedical engineering. Polydimethylsiloxane (PDMS) has been typically used to construct SFL devices as the material enables rapid prototyping of channels with complex geometries, optical transparency, and oxygen permeability. However, PDMS is not compatible with most organic solvents which limit the current range of materials that can be synthesized with SFL. Here, we demonstrate that a fluorinated elastomer, called perfluoropolyether (PFPE), can be an alternative oxygen permeable elastomer for SFL microfluidic flow channels. We fabricate PFPE microfluidic devices with soft lithography and synthesize anisotropic multifunctional particles in the devices via the SFL process – this is the first demonstration of SFL with oxygen lubrication layers in a non-PDMS channel. We benchmark the SFL performance of the PFPE devices by comparing them to PDMS devices. We synthesized particles in both PFPE and PDMS devices under the same SFL conditions and found the difference of particle dimensions was less than a micron. PFPE devices can greatly expand the range of precursor materials that can be processed in SFL because the fluorinated devices are chemically resistant to most organic solvents, an inaccessible class of reagents in PDMS-based devices due to swelling., Kwanjeong Educational Foundation (Korea), Singapore-MIT Alliance for Research and Technology (SMART), National Science Foundation (U.S.) (Grants CMMI-1120724 and DMR- 1006147)

Flow Lithography (FL) is the technique used for the synthesis of hydrogel microparticles with various complex shapes and distinct chemical compositions by combining microfluidics with photolithography. Although polydimethylsiloxane (PDMS) has been used most widely as almost the sole material for FL, PDMS microfluidic chips have limitations: (1) undesired shrinkage due to the thermal expansion of masters used for replica molding and (2) interfacial delamination between two thermally cured PDMS layers. Here, we propose the utilization of ultraviolet (UV)-curable PDMS (X-34-4184) for FL as an excellent alternative material of the conventional PDMS. Our proposed utilization of the UV-curable PDMS offers three key advantages, observed in our study: (1) UV-curable PDMS exhibited almost the same oxygen permeability as the conventional PDMS. (2) The almost complete absence of shrinkage facilitated the fabrication of more precise reverse duplication of microstructures. (3) UV-cured PDMS microfluidic chips were capable of much stronger interfacial bonding so that the burst pressure increased to ∼0.9 MPa. Owing to these benefits, we demonstrated a substantial improvement of productivity in synthesizing polyethylene glycol diacrylate microparticles via stop flow lithography, by applying a flow time (40 ms) an order of magnitude shorter. Our results suggest that UV-cured PDMS chips can be used as a general platform for various types of flow lithography and also be employed readily in other applications where very precise replication of structures on micro- or sub-micrometer scales and/or strong interfacial bonding are desirable.

Stimuli-responsive carriers releasing multiple drugs have been researched for synergistic combinatorial cancer treatment with reduced side-effects. However, previously used drug carriers have limitations in encapsulating multiple drug components in a single carrier and releasing each drug independently. In this work, pH-sensitive, multimodulated, anisotropic drug carrier particles are synthesized using an acid-cleavable polymer and stop-flow lithography. The particles exhibit a faster drug release rate at the acidic pH of tumors than at physiological pH, demonstrating their potential for tumor-selective drug release. The drug release rate of the particles can be adjusted by controlling the monomer composition. To accomplish multimodulated drug release, multicompartmental particles are synthesized. The drug release profile of each compartment is programmed by tailoring the monomer composition. These pH-sensitive, multicompartmental particles are promising drug carriers enabling tumor-selective and multimodulated release of multiple drugs for synergistic combination cancer therapy.

We present the synthesis of nonspherical magnetic microparticles with multiple functionalities, shapes, and chemistries. Particle synthesis was performed in two steps: polymeric microparticles functionalized homogenously with carboxyl groups were generated using stop-flow lithography, and then in situ coprecipitation was used to grow magnetic nanoparticles at these carboxyl sites. With successive growth of magnetic nanoparticles, we obtained polymeric particles with saturation magnetizations of up to 42 emu/g microparticle. The growth in the magnetic nanoparticle mean size and polydispersity was determined from the magnetization curves obtained following each growth cycle; nanoparticle sizes were limited by the physical constraint of the effective mesh within the hosting gel microparticle. Particles with spatially segregated domains of varying magnetic properties (e.g., Janus particles, particles with step changes in magnetite concentration, etc.) can be synthesized readily using this approach.

We report on modeling and experimental studies of the synthesis of opaque microparticles made via stop-flow lithography. Opaque magnetic beads and UV-absorbing dyes incorporated into hydrogel microparticles during synthesis changed the height and the degree of cross-linking of the polymer matrices formed. The effect of the concentration of these opaque materials on the particle height was determined experimentally and agreed well with model predictions based on the photopolymerization process over a wide range of UV absorbance. We also created particles with two independent anisotropies, magnetic and geometric, by applying magnetic fields during particle synthesis. Our work provides a platform for rational design of lithographic patterned opaque particles and also a new class of structured magnetic microparticles.