Kihoon Jang

Surface modification by 2-methacryloyloxyethyl phosphorylcholine coupled to a photolabile linker for cell micropatterning

This report describes a new surface-treatment technique for cell micropatterning. Cell attachment was selectively controlled on the glass surface using a photochemical reaction. This strategy is based on combining 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which is known to reduce non-specific adsorption, and a photolabile linker (PL) for selective cell patterning. The MPC polymer was coated directly on the glass surface using a straightforward surface modification method, and was removed by ultraviolet (UV) light illumination. All the surface modification steps were evaluated using static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), measurements of non-specific protein adsorption, and the cell attachment test. After selective cleavage of the MPC polymer through the photomask, cells attached only to the UV-illuminated region where the MPC polymer was removed, which made the hydrophilic surface relatively hydrophobic. Furthermore, the size of the MC-3T3 E1 cell patterns could be controlled by single cell level. Stability of the cell micropatterns was demonstrated by culturing MC-3T3 E1 cell patterns for 5 weeks on glass slide. The micropatterns were stable during culturing; cell viability also was verified. This method can be a powerful tool for cell patterning research.

Bonding of glass nanofluidic chips at room temperature by a one-step surface activation using an O2/CF4 plasma treatment

A technical bottleneck to the broadening of applications of glass nanofluidic chips is bonding, due to the strict conditions, especially the extremely high temperatures (~1000 °C) and the high vacuum required in the current glass-to-glass fusion bonding method. Herein, we report a strong, nanostructure-friendly, and high pressure-resistant bonding method, performed at room temperature (RT, ~25 °C) for glass nanofluidic chips, using a one-step surface activation process with an O(2)/CF(4) gas mixture plasma treatment. The developed RT bonding method is believed to be able to conquer the technical bottleneck in bonding in nanofluidic fields.

A Microfluidic Hydrogel Capable of Cell Preservation without Perfusion Culture under Cell‐Based Assay Conditions

DOI: 10.1002/adma.201000006 The interest, applications, and need for living cells have been dramatically expanding in the fi elds of medicine, pharmacy, environment, and defense. [ 1–3 ] Cell-based applications, such as drug discoveries, toxin screenings, and cell diagnostics are conventionally performed on cell culture dishes or microplates. Microfl uidic chip systems with micro/nanostructured geometries and microfl uidic channel networks that precisely manage the fl uids and soluble factors can be used to organize cells in dimensions that are comparable to those in vivo. [ 2 , 4 ] In addition, microfl uidic chip systems possess unique advantages over conventional analytical tools including minute reagent consumption, high throughput analysis, and rapid detection. [ 5 , 6 ]

An efficient surface modification using 2-methacryloyloxyethyl phosphorylcholine to control cell attachment via photochemical reaction in a microchannel.

This report describes a direct approach for cell micropatterning in a closed glass microchannel. To control the cell adhesiveness inside the microchannel, the application of an external stimulus such as ultraviolet (UV) was indispensible. This technique focused on the use of a modified 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which is known to be a non-biofouling compound that is a photocleavable linker (PL), to localize cells via connection to an amino-terminated silanized surface. Using UV light illumination, the MPC polymer was selectively eliminated by photochemical reaction that controlled the cell attachment inside the microchannel. For suitable cell micropatterning in a microchannel, the optimal UV illumination time and concentration for cell suspension were investigated. After selective removal of the MPC polymer through the photomask, MC-3T3 E1 cells and vascular endothelial cells (ECs) were localized only to the UV-exposed area. In addition, the stability of patterned ECs was also confirmed by culturing for 2 weeks in a microchannel under flow conditions. Furthermore, we employed two different types of cells inside the same microchannel through multiple removal of the MPC polymer. ECs and Piccells were localized in both the upper and down streams of the microchannel, respectively. When the ECs were stimulated by adenosine triphosphate (ATP), NO was secreted from the ECs and could be detected by fluorescence resonance energy transfer (FRET) in Piccells, which is a cell-based NO indicator. This technique can be a powerful tool for analyzing cell interaction research.

Single-cell attachment and culture method using a photochemical reaction in a closed microfluidic system

Recently, interest in single cell analysis has increased because of its potential for improving our understanding of cellular processes. Single cell operation and attachment is indispensable to realize this task. In this paper, we employed a simple and direct method for single-cell attachment and culture in a closed microchannel. The microchannel surface was modified by applying a nonbiofouling polymer, 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, and a nitrobenzyl photocleavable linker. Using ultraviolet (UV) light irradiation, the MPC polymer was selectively removed by a photochemical reaction that adjusted the cell adherence inside the microchannel. To obtain the desired single endothelial cell patterning in the microchannel, cell-adhesive regions were controlled by use of round photomasks with diameters of 10, 20, 30, or 50 μm. Single-cell adherence patterns were formed after 12 h of incubation, only when 20 and 30 μm photomasks were used, and the proportions of adherent and nonadherent cells among the entire UV-illuminated areas were 21.3%±0.3% and 7.9%±0.3%, respectively. The frequency of single-cell adherence in the case of the 20 μm photomask was 2.7 times greater than that in the case of the 30 μm photomask. We found that the 20 μm photomask was optimal for the formation of single-cell adherence patterns in the microchannel. This technique can be a powerful tool for analyzing environmental factors like cell-surface and cell-extracellular matrix contact.

The biological performance of cell-containing phospholipid polymer hydrogels in bulk and microscale form.

The biological performances of a cell-containing phospholipid polymer hydrogel in bulk and miniaturized formats without an additional culture medium support were investigated and compared. The cell-containing hydrogel was formed spontaneously when solutions of commercial polyvinyl alcohol (PVA) and the phospholipid polymer poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)-co-p-vinylphenylboronic acid (VPBA)] (PMBV) suspended with cells in a cell culture medium are mixed together. Bulk and miniaturized hydrogels, with approximate thicknesses of 3.1 mm and 400 μm, respectively, were prepared in a 96-well microplate and a glass microchip, respectively. In both cases, the hydrogels were homogeneous, and cells were spatially encapsulated. The long-term observation (4 and 8 days) of cell morphology suggested that cells were passively attached to the interface of the hydrogel but were unable to spread and flatten, which inhibited cell growth in both hydrogels. Viability evaluations revealed that cells in both hydrogel formats maintained the same high viability levels after long-term encapsulation. Cytotoxicity assays indicated that the cells in the miniaturized hydrogel maintained a high degree of correlation in cytotoxic sensitivity with the cells in the bulk hydrogel and a routine medium culture. The PMBV/PVA hydrogel not only provides a beneficial cytocompatible microenvironment for long-term cell survival without an additional culture medium support but also creates a static condition for cell sustainment in a microchip similar to that in bulk. The uniform long-term performances of PMBV/PVA hydrogels in bulk and miniaturized formats make them ideal for the development of long-term, flexible, three-dimensional, living cell-based tools for routine cell-based assays and applications on bulk to microscale levels.

Micropatterning of biomolecules on a glass substrate in fused silica microchannels by using photolabile linker-based surface activation

AbstractWe report on a straightforward method for creating micropatterns of multiple biomolecules. The anti-fouling agent 2-methacryloyloxyethylphosphorylcholine (MPC) polymer and a photolabile linker (PL) were covalently linked to an amino-terminated silane surface. Patterns were generated by selective removal of the MPC polymer via UV irradiation. Multiple micropatterns of fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA) and rhodamine-labeled goat fragment antigen-binding fragments (FAB) were deposited on a same glass substrate. We also employed micropatterning of multiple biomolecules in that Texas red-labeled BSA and FITC-labeled rabbit anti-mouse IgG were placed inside a microchannel. FigureThis technique was based on combining 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, which is known to non-biofouling compound, photocleavable linker (PL) that was modified to localize cells and to connect between MPC polymer and amino-terminated silanized surface. Using ultraviolet (UV) light illumination, MPC polymer can be selectively eliminated by photochemical reaction in order which resulted in micropatterning of multiple biomolecules.

Selective cell capture and analysis using shallow antibody-coated microchannels

Demand for analysis of rare cells such as circulating tumor cells in blood at the single molecule level has recently grown. For this purpose, several cell separation methods based on antibody-coated micropillars have been developed (e.g., Nagrath et al., Nature 450, 1235-1239 (2007)). However, it is difficult to ensure capture of targeted cells by these methods because capture depends on the probability of cell-micropillar collisions. We developed a new structure that actively exploits cellular flexibility for more efficient capture of a small number of cells in a target area. The depth of the sandwiching channel was slightly smaller than the diameter of the cells to ensure contact with the channel wall. For cell selection, we used anti-epithelial cell adhesion molecule antibodies, which specifically bind epithelial cells. First, we demonstrated cell capture with human promyelocytic leukemia (HL-60) cells, which are relatively homogeneous in size; in situ single molecule analysis was verified by our rolling circle amplification (RCA) method. Then, we used breast cancer cells (SK-BR-3) in blood, and demonstrated selective capture and cancer marker (HER2) detection by RCA. Cell capture by antibody-coated microchannels was greater than with negative control cells (RPMI-1788 lymphocytes) and non-coated microchannels. This system can be used to analyze small numbers of target cells in large quantities of mixed samples.