Publications by authors named "Domin Koh"

7 Publications

  • Page 1 of 1

Robust Formation of an Epithelial Layer of Human Intestinal Organoids in a Polydimethylsiloxane-Based Gut-on-a-Chip Microdevice.

Front Med Technol 2020 Aug 7;2. Epub 2020 Aug 7.

Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX, United States.

Polydimethylsiloxane (PDMS) is a silicone polymer that has been predominantly used in a human organ-on-a-chip microphysiological system. The hydrophobic surface of a microfluidic channel made of PDMS often results in poor adhesion of the extracellular matrix (ECM) as well as cell attachment. The surface modification by plasma or UV/ozone treatment in a PDMS-based device produces a hydrophilic surface that allows robust ECM coating and the reproducible attachment of human intestinal immortalized cell lines. However, these surface-activating methods have not been successful in forming a monolayer of the biopsy-derived primary organoid epithelium. Several existing protocols to grow human intestinal organoid cells in a PDMS microchannel are not always reproducibly operative due to the limited information. Here, we report an optimized methodology that enables robust and reproducible attachment of the intestinal organoid epithelium in a PDMS-based gut-on-a-chip. Among several reported protocols, we optimized a method by performing polyethyleneimine-based surface functionalization followed by the glutaraldehyde cross linking to activate the PDMS surface. Moreover, we discovered that the post-functionalization step contributes to provide uniform ECM deposition that allows to produce a robust attachment of the dissociated intestinal organoid epithelium in a PDMS-based microdevice. We envision that our optimized protocol may disseminate an enabling methodology to advance the integration of human organotypic cultures in a human organ-on-a-chip for patient-specific disease modeling.
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http://dx.doi.org/10.3389/fmedt.2020.00002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7849371PMC
August 2020

Three-Dimensional Regeneration of Patient-Derived Intestinal Organoid Epithelium in a Physiodynamic Mucosal Interface-on-a-Chip.

Micromachines (Basel) 2020 Jul 7;11(7). Epub 2020 Jul 7.

Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.

The regeneration of the mucosal interface of the human intestine is critical in the host-gut microbiome crosstalk associated with gastrointestinal diseases. The biopsy-derived intestinal organoids provide genetic information of patients with physiological cytodifferentiation. However, the enclosed lumen and static culture condition substantially limit the utility of patient-derived organoids for microbiome-associated disease modeling. Here, we report a patient-specific three-dimensional (3D) physiodynamic mucosal interface-on-a-chip (PMI Chip) that provides a microphysiological intestinal milieu under defined biomechanics. The real-time imaging and computational simulation of the PMI Chip verified the recapitulation of non-linear luminal and microvascular flow that simulates the hydrodynamics in a living human gut. The multiaxial deformations in a convoluted microchannel not only induced dynamic cell strains but also enhanced particle mixing in the lumen microchannel. Under this physiodynamic condition, an organoid-derived epithelium obtained from the patients diagnosed with Crohn's disease, ulcerative colitis, or colorectal cancer independently formed 3D epithelial layers with disease-specific differentiations. Moreover, co-culture with the human fecal microbiome in an anoxic-oxic interface resulted in the formation of stochastic microcolonies without a loss of epithelial barrier function. We envision that the patient-specific PMI Chip that conveys genetic, epigenetic, and environmental factors of individual patients will potentially demonstrate the pathophysiological dynamics and complex host-microbiome crosstalk to target a patient-specific disease modeling.
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http://dx.doi.org/10.3390/mi11070663DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7408321PMC
July 2020

A Compact, Syringe-Assisted, Vacuum-Driven Micropumping Device.

Micromachines (Basel) 2019 Aug 17;10(8). Epub 2019 Aug 17.

Department of Electrical Engineering, The State University of New York at Buffalo, Buffalo, NY 14260, USA.

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. The pump components were composed of a dead‑end channel which was surrounded by a microchamber. A syringe was then connected to the pump structure by a short tube, and the syringe plunger was manually pulled out to generate low pressure inside the microchamber. Once the sample was loaded in the inlet, air inside the channel diffused into the microchamber through the PDMS (polydimethylsiloxane) wall, acting as a dragging force and pulling the sample toward the outlet. A constant flow with a rate that ranged from 0.8 nl · s - 1 to 7.5 nl · s - 1 was achieved as a function of the geometry of the pump, i.e., the PDMS wall thickness and the diffusion area. As a proof-of-concept, microfluidic mixing was demonstrated without backflow. This method enables pumping for point-of-care testing (POCT) with greater flexibility in hand-held PDMS microfluidic devices.
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http://dx.doi.org/10.3390/mi10080543DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6723763PMC
August 2019

A robust, portable and backflow-free micromixing device based on both capillary- and vacuum-driven flows.

Lab Chip 2018 01;18(2):276-284

SMALL (Sensors and MicroActuators Learning Lab), Department of Electrical Engineering, University at Buffalo, The State University of New York (SUNY at Buffalo), Buffalo, New York 14260, USA.

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. Then, using manual syringe-assisted vacuum-driven pumping that operated based on the high gas permeability of polydimethylsiloxane, the two pre-balanced liquid streams could synchronously enter a dead-end micromixing channel without any backflow. To test the performance of this device, we first used it to mix two aqueous solutions of different coloured dyes. We varied the initial volume difference between the solutions to study the effect of gravity-induced pressure difference on mixing. Next, as a proof-of-concept application, ABO/Rh blood groups were successfully determined through detection of blood antigen-antibody agglutination. The filling time of agglutinated samples, driven by the simple syringe-assisted pumping, in the dead-end mixing channel was consistently 10% longer than that of blood samples without the agglutination reaction. Thus, the proposed device shows great potential for use in a wide variety of blood typing assays, agglutination-based assays and point-of-care or lab-on-a-chip testing applications.
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http://dx.doi.org/10.1039/c7lc01077jDOI Listing
January 2018

Introduction of a Chemical-Free Metal PDMS Thermal Bonding for Fabrication of Flexible Electrode by Metal Transfer onto PDMS.

Micromachines (Basel) 2017 Sep 15;8(9). Epub 2017 Sep 15.

SMALL (Sensors and MicroActuators Learning Lab), Department of Electrical Engineering, State University of New York at Buffalo (SUNY-Buffalo), Buffalo, NY 14260, USA.

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. The fabrication process using a chemical treatment or sacrificial layer is complicated and expensive, which is the major limitation of using PDMS in the fabrication of flexible electrodes. This paper discusses the findings of a possible solution to create strong bonding between PDMS and various metals (copper, nickel and silver) using a chemical-free metal to PDMS thermal bonding technique. This method is the same as the PDMS curing process, but with a variation in the curing condition. The condition required to create strong bonding was studied by observing copper transferred by various PDMS curing conditions, including the standard condition. The condition creating the strong bonding was baking PDMS (5:1 = base polymer: curing agent) at 150 °C for 20 min. Experimentation showed that the optimum thickness of the transferred metal shows that the optimum thickness is approximately 500 nm, which allows for a higher resistance to stresses. The successful transfer of copper, nickel and silver layers onto PDMS with a stronger adhesion force opens up many new applications dealing with the fabrication of flexible electrodes, sensors, and flexible soft magnets.
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http://dx.doi.org/10.3390/mi8090280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6190368PMC
September 2017

A Simple Method for Fabrication of Microstructures Using a PDMS Stamp.

Micromachines (Basel) 2016 Oct 1;7(10). Epub 2016 Oct 1.

Sensors and MicroActuators Learning Laboratory (SMALL), Department of Electrical Engineering, University at Buffalo, State University of New York, Buffalo, NY 14260, USA.

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. For the cell-to-cell adhesion, four different types of PDMS arrays (e.g., rectangle, bowtie, wide-rhombus, and rhombus) were designed to vary the cell-to-cell contact length. The transfer success rates of the microwell arrays were measured as a function of both the contact area of the PDMS and the glass substrate and the different ratios between the base polymers and the curing agent. This method of generating the microwell arrays will enable a simple and robust construction of PDMS-based devices for various biological applications.
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http://dx.doi.org/10.3390/mi7100173DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6190059PMC
October 2016

Various on-chip sensors with microfluidics for biological applications.

Sensors (Basel) 2014 Sep 12;14(9):17008-36. Epub 2014 Sep 12.

Department of Electrical Engineering, University at Buffalo, State University of New York (SUNY at Buffalo), Buffalo, NY 14260, USA.

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. We describe an optical image sensor with a simpler platform for better performance over a larger field of view (FOV) and greater depth of field (DOF). As a new trend, we review consumer electronics such as smart phones, tablets, Google glasses, etc. which are being incorporated in point-of-care (POC) testing systems. In addition, we discuss in detail the current optical sensing system integrated with a microfluidic chip.
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http://dx.doi.org/10.3390/s140917008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4208211PMC
September 2014
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