Saemi Park

Micropatterning of a nanoporous alumina membrane with poly(ethylene glycol) hydrogel to create cellular micropatterns on nanotopographic substrates

In this paper, we describe a simple method for fabricating micropatterned nanoporous substrates that are capable of controlling the spatial positioning of mammalian cells. Micropatterned substrates were prepared by fabricating poly(ethylene glycol) (PEG) hydrogel microstructures on alumina membranes with 200 nm nanopores using photolithography. Because hydrogel precursor solution could infiltrate and become crosslinked within the nanopores, the resultant hydrogel micropatterns were firmly anchored on the substrate without the use of adhesion-promoting monolayers, thereby allow tailoring of the surface properties of unpatterned nanoporous areas. For mammalian cell patterning, arrays of microwells of different dimensions were fabricated. These microwells were composed of hydrophilic PEG hydrogel walls surrounding nanoporous bottoms that were modified with cell-adhesive Arg-Gly-Asp (RGD) peptides. Because the PEG hydrogel was non-adhesive towards proteins and cells, cells adhered selectively and remained viable within the RGD-modified nanoporous regions, thereby creating cellular micropatterns. Although the morphology of cell clusters and the number of cells inside one microwell were dependent on the lateral dimension of the microwells, adhered cells that were in direct contact with nanopores were able to penetrate into the nanopores by small extensions (filopodia) for all the different sizes of microwells evaluated.

Multiplex Immunoassay Platforms Based on Shape-Coded Poly(ethylene glycol) Hydrogel Microparticles Incorporating Acrylic Acid

A suspension protein microarray was developed using shape-coded poly(ethylene glycol) (PEG) hydrogel microparticles for potential applications in multiplex and high-throughput immunoassays. A simple photopatterning process produced various shapes of hydrogel micropatterns that were weakly bound to poly(dimethylsiloxane) (PDMS)-coated substrates. These micropatterns were easily detached from substrates during the washing process and were collected as non-spherical microparticles. Acrylic acids were incorporated into hydrogels, which could covalently immobilize proteins onto their surfaces due to the presence of carboxyl groups. The amount of immobilized protein increased with the amount of acrylic acid due to more available carboxyl groups. Saturation was reached at 25% v/v of acrylic acid. Immunoassays with IgG and IgM immobilized onto hydrogel microparticles were successfully performed with a linear concentration range from 0 to 500 ng/mL of anti-IgG and anti-IgM, respectively. Finally, a mixture of two different shapes of hydrogel microparticles immobilizing IgG (circle) and IgM (square) was prepared and it was demonstrated that simultaneous detection of two different target proteins was possible without cross-talk using same fluorescence indicator because each immunoassay was easily identified by the shapes of hydrogel microparticles.

Cell-based biosensor system using micropatterned polymer nanofiber

In this study, to improve efficiency and functionality of cell-based biosensor microarrays, we introduced nano-topographical features on cell adhesive region. Micropatterned surface was created by poly (ethylene glycol) (PEG) hydrogel microstructures via photolithography. Nano-topographical features were introduced using polymeric nanofibers which were produced by electrospinning technique. Combining PEG hydrogel microstructure and polymeric nanofibers created a clear contrast between adhesion resist hydrogel walls and adhesion promoting nanofiber surfaces. When mammalian cells were seeded onto micropatterned nanostructure, cells only selectively adhered to nanofiber maintaining their viability, while adherent cells were not present on the hydrogel wall.

Immunoassays using hydrogel microparticles for multiplex detection-enabled shape-coded array

Suspension arrays for protein-based assays have been developed using shape-coded poly(ethylene glycol)(PEG) hydrogel microparticles to overcome the problems with current systems which use color-coded rigid microparticles. In this study, we fabricated various shapes of PEG hydrogel microparticles. PEG hydrogel microparticles were photo-crosslinked with the specific amount of acrylic acid to provide functional groups that enables protein immobilization via EDC/NHS method in the PEGDA(poly(ethyleneglycol) diacrylate, Mw575) precursor. After that, immunoglobulin G(IgG) or immunoglobulin M(IgM) species of primary antibody, were chemically bonded on the surface of the hydrogel microparticles with different shapes and sizes. Then, we captured specific binding molecules. The advantages of this technique are facile recognition of different type of antibodies by the shapes and sizes of the hydrogel particles, and the simple process of particle preparation by photopatterning.

Development of phenol detecting biosensor using PEG hydrogel microparticles

In this study, a simple and sensitive detection method for phenols were investigated using poly(ethylene glycol) (PEG) hydrogel microarray entrapping quantum dot (QD) and tyrosinase enzyme. Hydrogel microarrays were fabricated by using photo-patterning methods, and size of resultant hydrogel micropattern was ranged from 10 to 300 µm. The enzymatic reaction used for the detection of phenol is the oxidation of phenolic compounds via tyrosinase. In such reaction, phenol is oxidized to o-quinone which is a classic electron accepting chemical that can quench the fluorescence of QDs. Accuracy of the system was verified by measurement of photoluminescence (PL) quenching in free solution state with different concentrations of phenol. The PL quenching of QDs was investigated by varying the molecular weight of PEG, and concentration of QDs and/or enzymes.