Papers by Silvia Castañeda
Polymer Korea, 2015
This study reports a simple sequential micromolding method to produce monodisperse anisotropic mi... more This study reports a simple sequential micromolding method to produce monodisperse anisotropic microparticles with precisely controllable patchy size and chemistry of 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. We demonstrate the capability of sequential micromolding technique by generating Mickey mouse-shaped particles with precisely controllable patchy size and chemistry of compartment and the fabrication method needs no sophisticated control or expensive facilities. The micromolding technique applied in this study can control the size of patchy diameter from 15 to 31 µm by simply adjusting the concentration of photocurable monomer in ethanol. Finally, the Mickey mouse-shaped microparticles with negatively charged patches are confirmed by selective binding of positively charged fluorescence dyes. These results prove a simple, robust, and scalable fabrication of highly monodisperse and complex anisotropic microparticles in a controlled manner based on sequential micromolding.
Korean Chemical Engineering Research, 2015
This study investigated the effect of different collection methods on physical properties of pect... more This study investigated the effect of different collection methods on physical properties of pectin hydrogels in microfluidic synthetic approach. The pectin hydrogels were simply produced by the incorporation of calcium ions dissolved in continuous mineral oil. Then, different collection methods, pipetting, tubing, and settling, for harvesting pectin hydrogels were applied. The settling method showed most uniform and monodispersed hydrogels. In the case of settling, a coefficient of variation was 3.46 which was lower than pipetting method (18.60) and tubing method (14.76). Under the settling method, we could control the size of hydrogels, ranging from 30 µm to 180 µm, by simple manipulation of the viscosity of pectin and volumetric flow rate of dispersed and continuous phase. Finally, according to the characteristics of simple encapsulation of biological materials, we envision that the pectin hydrogels can be applied to drug delivery, food, and biocompatible materials.
Abstract ? This study presented simple and efficient fabrication of chemical sensors for the dete... more Abstract ? This study presented simple and efficient fabrication of chemical sensors for the detection of acidic gas using 1,3-bisdicyanovinylindane as an indicator because it can be promising materials having property of the rapid color change according to the variation of pH. The dissociation of proton and dye in acidic condition as changing of ion pairs give rise to dramatically change the absorbance intensity of 1,3-bisdicyanovinylindane, which can be easily applied to the development of chemical sensors. In addition, indicator dyes having negatively charge in aqueous phase can be easily fabricated using layer-by-layer (LBL) methods by way of electrostatic interaction. For the proof of concept, we demonstrated the abrupt presentation of skeleton symbol on the chemical sensor, which could be resulted from the reaction of 1,3-bisdicyanovinylindane as background color with acidic gas. Thus, the rapid appearance of symbol will induce user’s caution under the emergency condition. The...
Microspheres are widely used in applications such MEMS, chemical release systems, optical materia... more Microspheres are widely used in applications such MEMS, chemical release systems, optical materials and various biological applications. Here, we report the new micromolding technique for synthesizing spherical monodisperse particles through surface-tension-induced flow. The spherical droplets were prepared using Laplace pressure difference, which is highly depending on geometries of the mold shape, without any pumping system to make flow. We calculated the minimum pressure difference to make the flow moves and form the droplets. It provides a synthetic tool for generating the microspheres using different reaction schemes; UV-polymerization, sol-gel reaction and colloidal assemblies. The monodisperse spherical particles, which are made of various materials, were successfully generated without any surfactant because each droplet can be separately positioned in mold patterns during solidification process.
Micro Total Analysis Systems 2002, 2002
This study introduces a biochemical reaction on a nanofluidic chip by quantitative nanoliter volu... more This study introduces a biochemical reaction on a nanofluidic chip by quantitative nanoliter volume control. The proposed nanoliter metering techniques showed accuracy with 2 % error at the criterion of 20-nL metering. A biochemical reaction on a chip was performed with β-galactosiadase rendering fluorescent product from fluorescein di-β-galactopyranoside (FDG) substrate.
Clinical Infectious Diseases
Background To compare clinical characteristics, outcomes, and resource consumption of patients wi... more Background To compare clinical characteristics, outcomes, and resource consumption of patients with coronavirus disease 2019 (COVID-19) and seasonal influenza requiring supplemental oxygen. Methods Retrospective cohort study conducted at a tertiary-care hospital. Patients admitted because of seasonal influenza between 2017 and 2019, or with COVID-19 between March and May 2020 requiring supplemental oxygen were compared. Primary outcome: 30-day mortality. Secondary outcomes: 90-day mortality and hospitalization costs. Attempted sample size to detect an 11% difference in mortality was 187 patients per group. Results COVID-19 cases were younger (median years of age, 67; interquartile range [IQR] 54–78 vs 76 [IQR 64–83]; P < .001) and more frequently overweight, whereas influenza cases had more hypertension, immunosuppression, and chronic heart, respiratory, and renal disease. Compared with influenza, COVID-19 cases had more pneumonia (98% vs 60%, <.001), higher Modified Early War...
Lab on a Chip, 2021
Cellular communication-based screening for strains with improved secretion.
Lab on a Chip, 2021
A novel gear-shaped micromixer utilizing inertio-elastic flow instability and its application to ... more A novel gear-shaped micromixer utilizing inertio-elastic flow instability and its application to the continuous synthesis of silica nanoparticle.
Infection, 2021
Background The ISARIC prospective multinational observational study is the largest cohort of hosp... more Background The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs...
Biomolecules, 2018
Polydimethyl-siloxane (PDMS) is often applied to fabricate cell chips. In this study, we fabricat... more Polydimethyl-siloxane (PDMS) is often applied to fabricate cell chips. In this study, we fabricated an adipocyte microcell pattern chips using PDMS to analyze the inhibition activity of lipid droplets in mouse embryo fibroblast cells (3T3-L1) with anti-obesity agents. To form the PDMS based micropattern, we applied the micro-contact printing technique using PDMS micro-stamps that had been fabricated by conventional soft lithography. This PDMS micro-pattern enabled the selective growth of 3T3-L1 cells onto the specific region by preventing cell adhesion on the PDMS region. It then allowed growth of the 3T3-L1 cells in the chip for 10 days and confirmed that lipid droplets were formed in the 3T3-L1 cells. After treatment of orlistat and quercetin were treated in an adipocyte micro-cell pattern chip with 3T3-L1 cells for six days, we found that orlistat and quercetin exhibited fat inhibition capacities of 19.3% and 24.4% from 0.2 µM of lipid droplets in 3T3-L1 cells. In addition, we conducted a direct quantitative analysis of 3T3-L1 cell differentiation using Oil Red O staining. In conclusion, PDMS-based adipocyte micro-cell pattern chips may contribute to the development of novel bioactive compounds.
Frontiers of Chemical Science and Engineering, 2017
Precise control of each individual reaction that constitutes a multistep reaction must be perform... more Precise control of each individual reaction that constitutes a multistep reaction must be performed to obtain the desired reaction product efficiently. In this work, we present a microfluidic dual loops reactor that enables multistep reaction by integrating two identical loop reactors. Specifically, reactants A and B are synthesized in the first loop reactor and transferred to the second loop reactor to synthesize with reactant C to form the final product. These individual reactions have nano-liter volumes and are carried out in a stepwise manner in each reactor without any cross-contamination issue. To precisely control the mixing efficiency in each loop reactor, we investigate the operating pressure and the operating frequency on the mixing valves for rotary mixing. This microfluidic dual loops reactor is integrated with several valves to realize the fully automated unit operation of a multistep reaction, such as metering the reactants, rotary mixing, transportation, and collecting the product. For proof of concept, CdSeZn nanoparticles are successfully synthesized in a microfluidic dual loops reactor through a fully automated multistep reaction. Taking all of these features together, this microfluidic dual loops reactor is a general microfluidic screening platform that can synthesize various materials through a multistep reaction.
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Papers by Silvia Castañeda