Recent Announcement

New paper in Adv. Funct. Mater.

posted Feb 12, 2018, 4:04 PM by Shin-Hyun Kim

HanGyeol Lee, Tae Yoon Jeon, Su Yeon Lee, Seung Yeol Lee, and Shin-Hyun Kim, "Designing Multicolor Micropatterns of Inverse Opals with Photonic Bandgap and Surface Plasmon Resonance", Advanced Functional MaterialsAccepted for publication (2018). (Corresponding author)

Structural coloration provides unique features over chemical coloration, such as non-fading, color tunability, and high color brightness, rendering it useful in various optical applications. To develop the structural colors, two different mechanisms of coloration—photonic bandgap (PBG) and surface plasmon resonance (SPR)—have been separately utilized. In this work, we suggest a new method to create structurally-colored micropatterns by regioselectively employing SPR in a single film of inverse opal with PBG. The inverse opals are prepared by thermal embedding of opal into a negative photoresist and its subsequent removal. The inverse opals have a hexagonal array of open pores on the surface which serves as a template to make SPR-active nanostructures through a directional deposition of gold; perforated gold film and an array of curved gold disks are formed. With a shadow mask lithographically prepared, the gold is regioselectively deposited on the surface of the inverse opal, which results in two distinct regions of gold-free inverse opal with PBG and gold nanostructure with SPR. As PBG and SPR develop their own structural colors respectively, the resultant micropatterns exhibit pronounced dual colors. More importantly, the micropatterns show the distinguished optical response for evaporation of volatile liquids that occupy the pores.

New Article in Lab Chip

posted Feb 5, 2018, 9:37 PM by Shin-Hyun Kim

Hui-Sung Moon,* Kwanghwi Je, Jae-Woong Min, Donghyun Park, Kyung-Yeon Han, Seungho Shin, Woong-Yang Park, Chang Eun Yoo* and Shin-Hyun Kim,* "Inertial-Ordering-Assisted Droplet Microfluidic for High-Throughput Single-Cell RNA-Sequencing", Lab on a ChipAccepted for publication (2018). (Moon & Je contributed equally, Co-corresponding author) [pdf]

Single-cell RNA-seq reveals the cellular heterogeneity inherent in the population of cells, which is very important in many clinical and research applications. Recent advances in droplet microfluidics have achieved the automatic isolation, lysis, and labeling of single cells in droplet compartments without complex instrumentation. However, barcoding errors occurring in the cell encapsulation process because of the multi-beads-in-droplet and insufficient throughput because of the low concentration of beads for avoiding multi-beads-in-a-droplet remain important challenges for precise and efficient expression profiling of single cell. In this study, we developed a new droplet-based microfluidic platform that significantly improved throughput while reducing barcoding error through deterministic encapsulation of inertially ordered beads. Highly concentrated beads containing oligonucleotide barcodes were spontaneously ordered in a spiral channel by an inertial effect, which was in turn encapsulated in droplets one-by-one, while cells were simultaneously encapsulated in the droplets. The deterministic encapsulation of beads resulted in a high fraction of single-bead-in-a-droplet and rare multi-beads-in-a-droplet although the bead concentration increased to 1000 μL-1, which diminished barcoding error and enabled accurate high-throughput barcoding. We successfully validated our device with single-cell RNA-seq. In addition, we found that multi-beads-in-a-droplet, generated using a normal drop-seq device with a high concentration of beads, underestimated transcript numbers and overestimated cell numbers. This accurate high-throughput platform can expand the capability and practicality of Drop-Seq in single-cell analysis.

New paper in Adv. Mater. Technol.

posted Feb 5, 2018, 5:00 PM by Shin-Hyun Kim   [ updated Feb 5, 2018, 5:38 PM ]

Sangmin Lee, Tae Yong Lee, and Shin-Hyun Kim, "Microfluidic Production of Capsules-in-Capsules for Programmed Release of Multiple Ingredients", Advanced Materials TechnologiesAccepted for publication (2018). (Corresponding author)

Capsules with thin shells have a high loading capacity and are thus well-suited containers for reagents that must be stored in confined volumes. Capsules contained in larger capsules, so-called double capsules, allow the encapsulation of distinct reagents within small, defined, well-separated volumes. Therefore, they offer possibilities to initiate reactions in confined volumes and to release distinct bioactives sequentially while minimizing the risk for cross contaminations. Here, we present a new microfluidic capillary device that enables the assembly of water-oil-water-oil-water (W/O/W/O/W) quadruple-emulsion drops whose oil layers are ultra-thin. These quadruple emulsions can be converted into double capsules with thin membranes through either evaporation-induced consolidation of biodegradable polymers or photopolymerization of monomers. We demonstrate that the membrane composition of the inner and outer capsules can be independently selected to enable programmed release of distinct encapsulants. For example, we employ biodegradable polymers with two different degradation rates as the membrane materials that enable sequential release of two different encapsulants. In addition, the release of the encapsulants can be triggered by external stimuli such as osmotic pressure. This new class of double capsules provides new opportunities for drug delivery and screening assays that require sequential release of multiple water-soluble ingredients.

New paper in Adv. Mater. Interfaces

posted Jan 31, 2018, 11:50 PM by Shin-Hyun Kim

Ji-Won Kim, Joon-Seok Lee, and Shin-Hyun Kim, "Biodegradable Inverse Opals with Controlled Discoloration", Advanced Materials InterfacesAccepted for publication (2018). (Corresponding author)

Colloidal crystals and their derivatives possess photonic bandgap property, being useful in various applications, including structural coloration and colorimetric sensing. In this work, we prepare inverse opals with a biodegradable polymer, poly(lactic-co-glycolic acid) (PLGA), to provide a controlled discoloration. To make PLGA inverse opals, a monolayer of silica particles is first deposited on the surface of PLGA film by spin-coating, which is then partially embedded into the film by thermal annealing. Opal is deposited on the monolayer-coated PLGA film by dip-coating, and then embedded into the underlying PLGA film. Selective removal of silica particles leaves behind a face-centered cubic lattice of air cavity in PLGA matrix. The inverse opals whose framework is made of PLGA exhibit a pronounced structural color in dried state. When they are subjected to water, PLGA degrades by hydrolysis of ester groups, which results in the gradual discoloration. The discoloration rate is controllable by varying the pH of surrounding medium and cavity sizes, so that it can act as a colorimetric indicator of valid periods for drugs, foods, and cosmetics. In addition, high biocompatibility and unique optical appearance of PLGA further renders the inverse opals useful as edible anti-counterfeiting materials for valuable drugs.

Our work on SERS-active microgels is selected as 100 R&Ds for 2025

posted Dec 27, 2017, 4:12 PM by Shin-Hyun Kim

Our work on SERS-active microgels is selected as 100 R&Ds for 2025 by the national academy of engineering of Korea (2025년, 대한민국을 이끌 100대 기술과 주역, 한국공학한림원).

New paper in Adv. Mater. Interfaces

posted Dec 18, 2017, 3:06 AM by Shin-Hyun Kim

Bomi Kim, Sangmin Lee, and Shin-Hyun Kim, "Double-Emulsion-Templated Anisotropic Microcapsules for pH-Triggered Release", Advanced Materials InterfacesAccepted for publication (2017). (Corresponding author)

Biocompatible microcapsules with a function of pH-triggered release are promising for the site-specific release of bio-actives in the human body. In this work, we produce smart microcapsules with three distinct configurations of membranes to control the rate of pH-triggered release. The microcapsules are prepared with a template of water-in-oil-in-water double-emulsion drops. The oil shells of drops contain two polymers dissolved in an organic solvent: one is a biodegradable polymer selected from poly(lactic acid), poly(lactic-co-glycolic acid), and polycaprolactone and the other is a pH-responsive cationic polymer. Upon the depletion of organic solvent, two polymers confined in the shell undergo phase separation and double-emulsion drops transform to microcapsules with the solid membrane. Three different configurations of the membranes—spherical, snowman-like, and eyeball-like structures—are exclusively produced according to the selection of biodegradable polymers. Although all the microcapsules release hydrophilic encapsulant loaded in the core when they are subjected to a weakly acidic condition, the release kinetics strongly depends on the configuration of the membrane. Larger surface coverage and thinner membrane of pH-responsive domains result in faster release.

New Article in Chem. Mater.

posted Dec 10, 2017, 4:38 AM by Shin-Hyun Kim

Jaehoon Oh, Bomi Kim, Sangmin Lee, Shin-Hyun Kim, and Myungeun Seo, "Semipermeable Microcapsules with a Block Polymer-Templated Nanoporous Membrane", Chemistry of MaterialsAccepted for publication (2017). (J. Oh & B. Kim contributed equally, Co-corresponding author) [pdf]

Microcapsule with nanoporous membranes can regulate transmembrane transport in a size-dependent fashion while protecting active materials in the core from the surrounding, thereby being useful as artificial cell models, carriers for cells and catalyst, and microsensors. In this work, we report a pragmatic microfluidic approach to producing such semipermeable microcapsules with precise control of the cut-off threshold of permeation. Using a homogeneous polymerization mixture for polymerization-induced microphase separation (PIMS) process as the oil phase of water-in-oil-in-water (W/O/W) double emulsions, a densely crosslinked shell composed of a bicontinuous nanostructure that percolates through the entire thickness is prepared, which serves as a template for a monolithic nanoporous membrane of microcapsules with size-selective permeability. We demonstrate the nanopores with precisely controlled size by the block polymer self-assembly governs molecular diffusion through the membrane and renders manipulation of the cut-off threshold.

New Article in ACS Applied Materials and Interfaces

posted Nov 22, 2017, 4:51 PM by Shin-Hyun Kim

Yongjoon Heo, Su Yeon Lee, Ji-Won Kim, Tae Yoon Jeon, and Shin-Hyun Kim, "Controlled Insertion of Planar Defect in Inverse Opals for Anti-counterfeiting Applications", ACS Applied Materials & InterfacesAccepted for publication (2017). 

Inverse opals have been used for structural coloration and photonic applications owing to their photonic bandgap properties. When the photonic structures contain planar defects, they provide defect modes, which are useful for lasing, sensing, and waveguiding. However, it remains a challenge to insert a planar defect into inverse opals in a reproducible manner. Here, we report a new method for producing planar-defect-inserted inverse opals using sequential capillary wetting of colloidal crystals and creating micropatterns through photolithography. Three cycles of deposition and thermal embedding of colloidal crystals into the underlying film of negative photoresist are performed. In the three cycles, opal, particle monolayer, and opal are sequentially employed, which yields the monolayer-templated planar defect sandwiched by two inverse opals after particle removal. The planar defect provides a passband whose wavelength can be controlled by adjusting the diameter of particles for the defect layer. Moreover, the defect-inserted inverse opals can be micropatterned by photolithography as the negative photoresist is used as a matrix. The resulting micropatterns deliver a unique spectral code featured by a combination of stop band and defect mode and a graphical code dictated by photolithography, being useful for anti-counterfeiting applications.

New Article in ACS Nano

posted Nov 2, 2017, 4:57 PM by Shin-Hyun Kim

Gun Ho Lee, Tae Min Choi, Bomi Kim, Sang Hoon Han, Jung Min Lee, and Shin-Hyun Kim, "Chameleon-Inspired Mechanochromic Photonic Films Composed of Nonclose-Packed Colloidal Arrays", ACS NanoAccepted for publication (2017).

Chameleon uses a nonclose-packed array of guanine nanocrystals in iridophores to develop and tune skin colors in full visible range. Inspired from the biological process uncovered in panther chameleons, we design photonic films containing a nonclose-packed face-centered cubic (fcc) array of silica particles embedded in an elastomer. The nonclose-packed array is formed by interparticle repulsion exerted by solvation layers on the particle surface, which is rapidly captured in the elastomer by photo-curing of the dispersion medium. The artificial skin exhibits the structural color that shifts from red to blue under stretching or compression. The separation between inelastic particles enables the tuning without experiencing significant rearrangement of particles, providing elastic deformation and reversible color change, as chameleons do. The simple fabrication procedure consists of film casting and UV irradiation, potentially enabling the continuous high-throughput production. The mechanochromic property of the photonic films enables the visualization of deformation or stress with colors, which is potentially beneficial for various applications, including mechanical sensors, sound-vision transformers, and color display.

New paper in Adv. Mater. Interfaces

posted Oct 13, 2017, 6:30 AM by Shin-Hyun Kim

Kwanghwi Je, Ju Hyeon Kim, Tae Soup Shim, Minhee Ku, Jaemoon Yang, and Shin-Hyun Kim, "Lithographically-Designed Conical Microcarriers for Programed Release of Multiple Actives", Advanced Materials InterfacesAccepted for publication (2017).  (Corresponding author)

The programmed release of multiple ingredients is important in the therapeutics and pharmaceutical fields. A variety of core–shell microcarriers have been designed to fulfill the release function; however, encapsulating multiple actives in their own compartments and releasing them in a programmed manner remains a challenge due to restrictions on the material sets that may be used to form the compartments. In this work, we report the development of lithographically featured core–shell microcarriers composed of double cones and a cap that encapsulate and release various combinations of multi-actives in a pre-defined fashion. Active-free caps were first prepared on a photomask using conventional photolithography. Onto each cap were formed, sequentially, an active-loaded small cone and large cone in two steps of reaction diffusion-mediated photolithography (RDP). The release kinetics of the actives stored in the inner and outer cones were controlled by tailoring the cross-linking density of the photocured polymers that composed each compartment. The cap prevented direct diffusion from the inner cone to the surrounding. The RDP-based lithographic means for creating core–shell microcarriers provides new opportunities for delivering synergistic combinations of drugs in pharmacotherapy.

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