Hyeong Jin Jeon

Hollow-core polymeric nanoparticles for the enhancement of OLED outcoupling efficiency

Abstract This work presents the possibility of the hollow core nanoparticles to improve luminance in an organic light emitting diode device. The finite difference time domain simulation estimates the effect of the hollow core nanoparticles on the external quantum efficiency of the organic light emitting diode device. The efficiency depends on the size and the volume fraction of the hollow core nanoparticles in the polymer layer, together with the refractive index and the thickness of the polymer layer. It is shown that the hollow core nanoparticles dispersed in a polymer layer can enhance the external quantum efficiency by a factor of 2.5. This work also introduces a continuous production method of the hollow core nanoparticles by using the microfluidic self-assembly of amphiphilic polymers and the layer formation dispersed with them for the rigorous light scattering.

Microfluidic synthesis of pH-sensitive multiamine hydrogel microparticles and release characterization of anticancer drug of doxorubicin (Dox)

In this paper, pH sensitive hydrogel microparticles (HMs) were synthesized in a microfluidic system with easy and controllable regulation of pH, and flow rate for drug delivery. The HMs originated from PEG derivative demonstrated low toxicity, which is an important characterization in pharmacy. Especially, an injectable multiamine hydrogel was synthesized by using condensation reaction process. The well-defined hydrogel droplets of water-in-oil was continuously generated in a cross microchannel. The size of the hydrogel droplets could be controlled by both the inlet flow rate and the pH of the pre-synthesized hydrogel in water. The hydrogel microparticles have been produced in a size ranging from 5 to 35 μm. By using MTT assay of in vitro cell viability, the hydrogel microparticles do not show cytotoxicity. The doxorubicin loaded in the hydrogel microparticles was released at low pH conditions. From in vitro testing of the pH effect on the release of a drug, HMs is a potential for drug delivery strategy to treat cancer. Also, hydrogel microparticles loaded with a drug can be applied to deliver it to human tissues with a low pH.

Development of a 3D circular microfluidic centrifuge for the separation of mixed particles by using their different centrifuge times

This paper presents a circular microfluidic centrifuge with two inlets and two outlets to separate mixed microparticles with a specially designed sample injection hole. To separate the mixed particles, it uses a rotational flow, generated in a chamber by counter primary flows in the microchannels. The shape and sizes of the circular microfluidic centrifuge have been designed through numerical evaluation to have a large relative centrifugal force. The difference of centrifuge times of the mixed particles of 1 μm and 6 μm was determined to be 8.2 s at an inlet Reynolds number of 500 and a sample Reynolds number of 20. In the experiment, this was measured to be about 10 s. From the separation of the two polymer particles analogous to the representative sizes of platelets and red blood cells, the circular microfluidic centrifuge shows a potential to separate human blood cells size-selectively by using the difference of centrifuge times.

Preparation of Protein Nanoparticles Using NTA End Functionalized Polystyrenes on the Interface of a Multi-Laminated Flow Formed in a Microchannel

This paper challenges the production of the protein nanoparticles using the conjugation of Ni2+ complexed nitrilotriacetic acid end-functionalized polystyrene (Ni-NTA-PS) and histidine tagged GFP (His-GFP) hybrid. The microfluidic synthesis of the protein nanoparticle with the advantages of a uniform size, a fast reaction, and a precise control of preparation conditions is examined. The self-assembly occurs on the interfacial surface of the multi-laminated laminar flow stably formed in the microchannel. The clogging of the produced protein nanoparticles on the channel surface is solved by adding a retarding inlet channel. The size and shape of the produced protein nanoparticles are measured by the analysis of transmission electron microscopy (TEM) and scanning electron microscope (SEM) images, and the attachment of the protein is visualized with a green fluorescent image. Future research includes the encapsulation of vaccines and the coating of antigens on the protein surface.

Virus-mimetic polymer nanoparticles displaying hemagglutinin as an adjuvant-free influenza vaccine

The generation of virus-mimetic nanoparticles has received much attention in developing a new vaccine for overcoming the limitations of current vaccines. Thus, a method, encompassing most viral features for their size, hydrophobic domain and antigen display, would represent a meaningful direction for the vaccine development. In the present study, a polymer-templated protein nanoball with direction oriented hemagglutinin1 on its surface (H1-NB) was prepared as a new influenza vaccine, exhibiting most of the viral features. Moreover, the concentrations of antigen on the particle surface were controlled, and its effect on immunogenicity was estimated by in vivo studies. Finally, H1-NB efficiently promoted H1-specific immune activation and cross-protective activities, which consequently prevented H1N1 infections in mice.

3D microfluidic perfuison cell culture system with linear concentration gradient and air bubble trapping

This paper presents a 3D microfluidic perfusion cell culture system to mimic microenvironments. The perfusion system is integrated with bubble trapping reservoir, linear concentration generator and meandered microchannel mixer. The sudden expansion reservoir to prevent incoming of air bubbles by using buoyancy is examined. Also, for high throughput screening, the linear concentration gradient generator connected with efficient meandered channel mixer is developed. We evaluate the performance of key components numerically and experimentally. Finally, the 3D perfusion system with linear gradient of concentration of H2O2 examines cytotoxicity of muscle cells with Ewings sarcoma.

Continuous Preparation of Hollow Polymeric Nanocapsules Using Self-Assembly and a Photo-Crosslinking Process of an Amphiphilic Block Copolymer

This paper presents a fabrication method of hollow polymeric nanocapsules (HPNCs). The HPNCs were examined to reduce light trapping in an organic light emitting diodes (OLED) device by increasing the refractive index contrast. They were continuously fabricated by the sequential process of self-assembly and photo-crosslinking of an amphiphilic block copolymer of SBR-b-PEGMA, poly(styrene-r-butadiene)-b-poly(poly(ethylene glycol) methyl ether methacrylate) in a flow-focusing microfluidic device. After the photo-crosslinking process, the produced HPNCs have a higher resistance to water and organic solvents, which is applicable to the fabrication process of optical devices. The morphology and hollow structure of the produced nanocapsules were determined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Also, their size control was examined by varying the ratio of inlet flow rates and the morphological difference was studied by changing the polymer concentration. The size was measured by dynamic light scattering (DLS). The refractive index of the layer with and without the HPNCs was measured, and a lower refractive index was obtained in the HPNCs-dispersed layer. In future work, the light extraction efficiency of the HPNCs-dispersed OLED will be examined.

Microfluidic Separation of a Soluble Substance Using Transverse Diffusion in a Layered Flow

This paper presents a practical flow-through method to separate anisole and ethyl phenylacetate, respectively, from a polystyrene mixture. The microfluidic separation uses different diffusive dynamics of the substances transverse to the lamination flow formed in a microchannel. The effect of inlet flow rates and ambient temperature on separation is examined. Additionally, the possibility of the separation of the light substance from the mixture with different molecular weight is shown numerically and experimentally. The separation efficiency is explained by the facts that the relaxation time depends on the inlet flow rate and that the diffusivity depends on the ambient temperature. This method can be applied to separate monomers from aggregates.

Performance Evaluation of Rotational Flow of a 2×2 Microfluidic Centrifuge with varying Inlet Conditions and Chamber Sizes

This paper describes the measurement of performance evaluation of rotational flow varying chamber size and Reynolds number. Through the experimental visualization of the flow rotation, the number and position of flow rotation in the microfluidic centrifuge were examined. At a chamber width of 250, single flow rotation was obtained over at a Reynolds number of 300, while at a chamber width of 500 , single flow rotation did not appear. For performance evaluation, the intensity in microchamber was measured during 20 sec. At a chamber width of 250 , performance of rotational flow increased as Reynolds number increased. However, the variation of intensity in microchamber remained unchanged at a chamber width of 500 . The numerical analysis showed that the threshold centrifugal acceleration to obtain rotational flow for ejected particles was 200g.

Visualization of Rotational Flow for Chamber Size of a 2×2 Microfluidic Centrifuge

Abstract. This paper introduces a new parameter to design the 2×2 microfluidic centrifuge with singleflow rotation positioned at the center of microchamber. The dimensional centrifugal acceleration momen-tum flux which is defined as the interfacial momentum flux divided by distance from the center of thechamber explains the flow rotation and its threshold provides a reference to expect single flow rotation.Through the numerical and experimental visualization of the flow rotation, the number and position offlow rotation in the 2×2 microfluidic centrifuge were examined. At a channel width of 50µm and cham-ber width of 250µm, single flow rotation was obtained over at a Reynolds number of 300, while at achannel width of 100µm and chamber width of 500µm, single flow rotation did not appear. The numer-ical analysis showed that the threshold centrifugal acceleration momentum flux to obtain single flow rota-tion was 3500 kg/m·s 2 . Key Words:Microfluidic centrifuge(마이크로 유체 원심분리기), Flow rotation(회전 유동), Centrifugalacceleration momentum flux(원심가속 운동량 유속), Visualization(가시화)