Publications by authors named "Kwang W Oh"

Vascular diseases are widespread, and sometimes such life-threatening medical disorders cause abnormal blood flow, blood particle damage, changes to flow dynamics, restricted blood flow, and other adverse effects. The study of vascular flow is crucial in clinical practice because it can shed light on the causes of stenosis, aneurysm, blood cancer, and many other such diseases, and guide the development of novel treatments and interventions. Microfluidics and computational fluid dynamics (CFDs) are two of the most promising new tools for investigating these phenomena.

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Nanoparticles can be used for drug delivery and consist of many sizes and chemical compositions. They can accommodate a diverse population of drugs and can be made to target specific areas of the body. Fabrication methods generally follow either top-down or bottom-up manufacturing techniques, which have differing production controls, which determine nanoparticle characteristics including but not limited to size and encapsulation efficiency.

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A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called "pysanky" a series of microfluidic devices were created.

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Significance: Photoacoustic tomography has emerged as a prominent medical imaging technique that leverages its hybrid nature to provide deep penetration, high resolution, and exceptional optical contrast with notable applications in early cancer detection, functional brain imaging, drug delivery monitoring, and guiding interventional procedures. Test phantoms are pivotal in accelerating technology development and commercialization, specifically in photoacoustic (PA) imaging, and can be optimized to achieve significant advancements in PA imaging capabilities.

Aim: The analysis of material properties, structural characteristics, and manufacturing methodologies of test phantoms from existing imaging technologies provides valuable insights into their applicability to PA imaging.

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We propose an integrated serial dilution generator utilizing centrifugal force with a degassed polydimethylsiloxane (PDMS) microfluidic device. Using gas-soluble PDMS as a centrifugal microfluidic device material, the sample can be dragged in any arbitrary direction using vacuum-driven force, as opposed to in a single direction, without adding further actuation components. The vacuum-driven force allows the device to avoid the formation of air bubbles and exhibit high tolerance in the surface condition.

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Suitable micropumping methods for flow control represent a major technical hurdle in the development of microfluidic systems for point-of-care testing (POCT). Passive micropumping for point-of-care microfluidic systems provides a promising solution to such challenges, in particular, passive micropumping based on capillary force and air transfer based on the air solubility and air permeability of specific materials. There have been numerous developments and applications of micropumping techniques that are relevant to the use in POCT.

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Microfluidic devices and systems are well-suited for the manipulation of biomolecules, cells, or particles [...

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In this paper, a simple syringe‑assisted pumping method is introduced. The proposed fluidic micropumping system can be used instead of a conventional pumping system which tends to be large, bulky, and expensive. The micropump was designed separately from the microfluidic channels and directly bonded to the outlet of the microfluidic device.

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Objective: We present a new photoacoustic tomography system that provides visualization of angiographic features in a human breast with mammogram-like images.

Methods: The system images a mildly compressed breast, from both top and bottom, using two 128-element, 2.25 MHz linear transducer arrays and line optical fiber bundles.

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In this paper, we presented a straightforward strategy to generate 15 combinations of three samples based on an experimental simplex lattice design using a single-layer microfluidic network. First, we investigated the performances of the plain structural and the groove structural combinatorial devices by computational simulation (CFD-ACE+). The simulated output concentrations were extremely close to the desirable values within an absolute error of less than 1%.

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Life scientists are closely working with engineers to solve biological and biomedical problems through the application of engineering tools.[..

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Although linear transducer arrays have been intensely used in photoacoustic imaging, their geometrical shape constrains light illumination. Today, most linear array based photoacoustic systems utilize side-illumination geometry, which consists of two line fiber bundles attached to the side of the probe. The angled light illumination increases the light travel distance in deep tissue, consequently limiting the imaging depth.

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This paper presents a novel manipulation method for micro-objects using acoustically oscillating bubbles with a controllable position based on the gas permeability of polydimethylsiloxane. The oscillating bubble trapped within the side channel attracts the neighboring micro-objects, and the position of the air-liquid interface is controlled by generating temporary pressure difference between the side channel and the air channel. To demonstrate the feasibility of the method in technological applications, polystyrene microparticles of 10 m in diameter were successfully captured, transported, and released.

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In capillary- or vacuum-driven microfluidics, surge backflow events are common when merging or pumping two similar or dissimilar liquids together if a pressure difference exists between them. In this work, a robust, portable micromixing device that is insensitive to backflow was designed, fabricated and characterised. A capillary-driven pressure balancing bypass connected between two inlet ports diminished the initial pressure difference caused by capillarity and gravity present in each liquid at the two inlet ports.

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Polydimethylsiloxane (PDMS) is a flexible and biocompatible material widely used in the fabrication of microfluidic devices, and is often studied for the fabrication of flexible electrodes. The most popular method of fabricating a flexible electrode using PDMS is done by transferring a metal electrode onto said PDMS. However, the transfer process is difficult and the transferred metal layer is easily damaged due to inherently weak adhesion forces between the metal and PDMS, thus requiring a chemical treatment or sacrificial layer between the two.

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We report a simple method to fabricate PDMS (polydimethylsiloxane) microwell arrays on glass by using a PDMS stamp to study cell-to-cell adhesion. In the cell-to-cell study, a glass substrate is required since glass has better cell attachment. The microwell arrays are replicated from an SU-8 master mold, and then are transferred to a glass substrate by lifting the PDMS stamp, followed by oxygen plasma bonding of the PDMS stamp on the glass substrate.

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Suitable pumping methods for flow control remain a major technical hurdle in the path of biomedical microfluidic systems for point-of-care (POC) diagnostics. A vacuum-driven power-free micropumping method provides a promising solution to such a challenge. In this review, we focus on vacuum-driven power-free microfluidics based on the gas solubility or permeability of polydimethylsiloxane (PDMS); degassed PDMS can restore air inside itself due to its high gas solubility or gas permeable nature.

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We propose a blood separation microfluidic device suitable for point-of-care (POC) applications. By utilizing the high gas permeability of polydimethylsiloxane (PDMS) and phaseguide structures, a simple blood separation device is presented. The device consists of two main parts.

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In this paper, we propose a microfluidic platform toseparate magnetic particles with a constant volumetric flow condition. In order to realize this architecture, three main functions for a droplet manipulation based system are integrated into a single device: synchronization of droplets by matching a location of droplets; lateral electro-coalescence; and magnetic particle manipulation. For an optimized condition of this device, a droplet generation was controlled by varying a droplet size at a fixed flow rate ratio 0.

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Introduction: The advent of precision medicine will increase the demand for molecular testing on patient tumor specimens. Cytology specimens have been shown to be ideal substrates for molecular testing, but their often paucicellular nature can lead to conflicts in prioritizing sample management. A microfluidic platform was investigated to determine whether cytologic and molecular data could be procured from the same cells, obviating the need for partitioning a sample by multiplexing it instead.

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In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The droplet-based washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets.

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In this paper, we review recent advances in on-chip sensors integrated with microfluidics for biological applications. Since the 1990s, much research has concentrated on developing a sensing system using optical phenomena such as surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) to improve the sensitivity of the device. The sensing performance can be significantly enhanced with the use of microfluidic chips to provide effective liquid manipulation and greater flexibility.

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We report the development of a programmable surface-enhanced Raman scattering (SERS)-based micro-network gradient platform to simultaneously detect two different types of DNA oligomer mixtures. The utility of this platform was demonstrated by quantitative analysis of two breast cancer-related (BRCA1) DNA oligomer mixtures. To generate on-demand concentration gradients, the microfluidic circuit was designed using an electric-hydraulic analogy.

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We propose a robust droplet fusion and sorting method for two parallel trains of droplets that is relatively insensitive to frequency and phase mismatch. Conventional methods of droplet fusion require an extremely precise control of aqueous/oil flows for perfect frequency matching between two trains of droplets. In this work, by combining our previous two methods (i.

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Here we report the development of a programmable and fully automatic gold array-embedded gradient microfluidic chip that integrates a gradient microfluidic device with gold-patterned microarray wells. This device provides a convenient and reproducible surface-enhanced Raman scattering (SERS)-based immunoassay platform for cancer biomarkers. We used hollow gold nanospheres (HGNs) as SERS agents because of their highly sensitive and reproducible characteristics.

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