Gumhye Jeon

Single-File Diffusion of Protein Drugs through Cylindrical Nanochannels

A new drug delivery device using cylindrical block copolymer nanochannels was successfully developed for controlled protein drug delivery applications. Depending on the hydrodynamic diameter of the protein drugs, the pore size in cylindrical nanochannels could be controlled precisely down to 6 nm by Au deposition. Zero-order release of bovine serum albumin (BSA) and human growth hormone (hGH) by single-file diffusion, which has been observed for gas diffusion through zeolite pores, was realized up to 2 months without protein denaturation. Furthermore, a nearly constant in vivo release of hGH from the drug delivery nanodevice implanted to Sprague-Dawley (SD) rats was continued up to 3 weeks, demonstrating the feasibility for long-term controlled delivery of therapeutic protein drugs.

Electrically Actuatable Smart Nanoporous Membrane for Pulsatile Drug Release

We report on the fabrication of electrically responsive nanoporous membrane based on polypyrrole doped with dodecylbenzenesulfonate anion (PPy/DBS) that was electropolymerized on the upper part of anodized aluminum oxide membrane. The membrane has regular pore size and very high pore density. Utilizing a large volume change of PPy/DBS depending on electrochemical state, the pore size was acutated electrically. The actuation of the pores was experimentally confirmed by in situ atomic force microscopy and in situ flux measurement. We also demonstrated successfully pulsatile (or on-demand) drug release by using fluorescently labeled protein as a model drug. Because of a fast switching time (less than 10 s) and high flux of the drugs, this membrane could be used for emergency therapy of angina pectoris and migraine, which requires acute and on-demand drug delivery, and hormone-related disease and metabolic syndrome.

Functional nanoporous membranes for drug delivery

This feature article reviews controlled drug release based on nanoporous membranes for potential medical applications. First, we describe the preparations of nanoporous membranes by top-down and bottom-up methods, and the combination of the two. Then, sustained long-term drug delivery and stimuli-responsive drug delivery by utilizing the nanoporous membranes are explained. The drug delivery system using nanoporous membranes can be used for a new therapy of various diseases through patient-customized medical treatment.

Highly Ordered Nanoporous Alumina on Conducting Substrates with Adhesion Enhanced by Surface Modification: Universal Templates for Ultrahigh‐Density Arrays of Nanorods

2010 WILEY-VCH Verlag Gmb High-density arrays of one-dimensional (1D) nanostructures such as nanorods, nanowires, and nanotubes have attracted a great deal of interest owing to their potential applications as optoelectronics, data storage materials, artificial actuators, surface modifiers with specific wetting behavior, and sensors. One of the most important aims of the fabrication of high-density 1D arrays is to achieve uniform structural parameters (diameter, height, and center-to-center spacing) over a large area, because this is essential for data storagematerials, photonic devices with tunable photonic bandgaps (PBGs), near-field optical waveguides, and devices utilizing surface-enhanced Raman scattering (SERS). SERS, for example, requires periodic arrays of plasmon-resonant nanomaterials with uniform diameter and spacing to detect very accurately chemical and biomolecular species. Of the various methods for the fabrication of high-density arrays of 1D nanostructured materials, electrodeposition or electropolymerization in nanoporous templates has been widely used because of its versatility, large scale, low-temperature operation, cost-effectiveness, and rapid processing speed. Typical nanoporous templates are block copolymer thin films with cylindrical nanopores, anodized aluminum oxide (AAO), and polycarbonate membranes. Among them, AAO with a high areal density (up to 10 pores per cm) and narrow size distribution over a large area has received much attention because of its simple and inexpensive control of structural parameters and excellent thermal and mechanical stability. Many research groups have reported the fabrication of nanorods (or nanotubes) of various metals, semiconductors, and conducting polymers by electrodeposition (or electropolymerization) inside nanopores of AAO. However, since most AAO is fabricated by two-step anodization from aluminum sheet, a thin metal electrode (thickness of hundreds of nanometers) should be prepared at the bottom of pores by evaporation of excess metal (for instance, Au) for electrodeposition (or electropolymerization). A critical drawback to this method is that once AAO is removed, most fabricated nanorods collapse (or at best become bundles) because the thin electrode cannot act as a rigid support. Some research groups simply placed AAO on rigid substrates, and fabricated metal (or semiconductor) nanodot or nanohole arrays. However, this method cannot be used for the fabrication of an array of freestanding nanorods on a conducting substrate by electrodeposition (electropolymerization) because of poor adhesion between AAO and the substrate. Other research groups introduced the ‘‘direct anodizing’’ method. For this purpose, a high-purity Al layer was deposited on a rigid substrate using thermal or electron-beam evaporation, and nanopores were fabricated by direct anodization of the Al layer. However, the first anodization, which is essential in obtaining nanopores with uniform pore size and lateral long-range ordering, could not be carried out for a long time in this method because of a thickness problem. Namely, a relatively thick and high quality Al layer with a thickness of ca. 50mm would be needed for this step, but it is practically difficult to prepare a thick Al layer by evaporation. Also, a metallic adhesive layer (such as Wor Ti) is required between the substrate and Al to prevent cracks, delamination, and the detachment of Al during the anodizing process. Furthermore, owing to the existence of a barrier layer that inhibits direct contact between the pores and the underlying substrate, one cannot avoid undesired pore widening during the removal of this layer by wet etching. Although several pre-texturing processes using soft imprinting, focused ion beams, and positive ceramic molds were performed before the anodization, high-density arrays of nanopores with uniform pore size and lateral long-range ordering on a rigid substrate have not been achieved, in spite of multistep processes. In this study, we achieved excellent adhesion between AAO fabricated by two-step anodization and various conducting substrates (indium tin oxide (ITO)-coated glass, Au, or Au-coated polymer film). For this purpose, we prepared an ultrathin polymer layer of either dihydroxy-terminated polystyrene (PS-dOH) or thiol-terminated PS (PS-SH) on the substrates by utilizing a graft reaction between the functional groups in the polymer chains and the substrate. The graft layer was further exposed to an ozone environment to make a favorable interaction with AAO. Since we used AAO prepared by two-step anodization,

DNA-functionalized nanochannels for SNP detection.

We have developed ultrahigh density array of functionalized nanochannels by using a block copolymer having end di-COOH group. This approach provides a facile route for direct functionalization of wall surface of the nanochannels and immobilization site for molecular recognition agents (MRAs). By using overhanging single-stranded DNA as MRAs, the DNA-functionalized nanochannels showed high resolution to detect a single-base mismatch as well as to discriminate single-mismatched sequence at various locations by hybridization preference with MRAs.

Air-stable inverted structure of hybrid solar cells using a cesium-doped ZnO electron transport layer prepared by a sol–gel process

We have developed an air-stable inverted structure of poly(3-hexylthiophene) (P3HT) : cadmium selenide (CdSe) hybrid solar cells using a cesium-doped ZnO (ZnO:Cs) electron transport layer. The ZnO:Cs layer was simply prepared at low temperature by the sol–gel process using a ZnO solution containing cesium carbonate (Cs2CO3). With increasing Cs-doping concentration, the conduction band edge of ZnO is decreased, as confirmed by scanning Kelvin probe microscopy. The energy level of ZnO:Cs is effective for electron transport from CdSe. Consequently, the power conversion efficiency (PCE) of the inverted P3HT : CdSe hybrid solar cells using the ZnO:Cs electron transport layer is 1.14%, which is significantly improved over that (0.43%) of another device without Cs. X-ray photoelectron spectroscopy analysis revealed that the amount of CdSe on the substrate (or the bottom surface) is larger compared with the air (or top) surface regardless of the P3HT : CdSe weight ratio. The vertically inhomogeneous distribution of CdSe in the hybrid solar cells gives better charge transport from CdSe to ZnO:Cs in the inverted structure of the device compared with that in the normal structure. As a result, the inverted hybrid solar cell consisting of 1 : 4 (wt/wt) P3HT : CdSe shows the best efficiency, while the best efficiency of a normal hybrid solar cell is achieved at 1 : 9 (wt/wt) P3HT : CdSe.

A high density array of free standing alumina nanotubes aligned vertically on solid substrates in a large area

We report an innovative fabrication of a high density array of free standing alumina nanotubes (ANTs) aligned vertically on substrates. A nanoporous polyimide (PI) template was first prepared by dry etching with the aid of an anodized aluminum oxide (AAO) membrane mask followed by atomic layer deposition (ALD) of alumina. ANTs with various diameters, lengths, and wall thicknesses were obtained by controlling the pore size, the thickness of the nanoporous PI template, and the deposition thickness of alumina through ALD, respectively. Optical properties of an ANT array were also tuned by changing the wall thickness of ANTs, and an ANT array on a glass showed excellent antireflectance with less than 0.1% reflectance at a visible wavelength. The nanoporous polymer template fabricated in this study could also be used to obtain a high density array of various inorganic nanotubes with uniform wall thickness and length in a large area. It also enables on-demand patterning of the nanotube array.

Enhanced adhesion of osteoblastic cells on polystyrene films by independent control of surface topography and wettability.

We independently controlled surface topography and wettability of polystyrene (PS) films by CF4 and oxygen plasma treatments, respectively, to evaluate the adhesion and proliferation of human fetal osteoblastic (hFOB) cells on the films. Among the CF4 plasma-treated PS films with the average surface roughness ranging from 0.9 to 70 nm, the highest adhesion of hFOB cells was observed on a PS film with roughness of ~11 nm. When this film was additionally treated by oxygen plasma to provide a hydrophilic surface with a contact angle less than 10°, the proliferation of bone-forming cell was further enhanced. Thus, the plasma-based independent modification of PS film into an optimum nanotexture for human osteoblast cells could be appplied to materials used in bone tissue engineering.

Interfacing Liquid Metals with Stretchable Metal Conductors

UNLABELLED Highly stretchable conductors are essential components in deformable electronics. Owing to their high stretchability and conductivity, liquid metals have attracted significant attention for use as circuits and interconnections. However, their poor wettability to stretchable metal electrodes prevents the formation of stable electrical connections. This study examined two approaches for creating a stable interface between a liquid metal (EGaIn) and stretchable metal electrodes via: (i) the use of honeycomb-structured stretchable metal electrodes and (ii) the addition of a conducting polymer interlayer. The line width of the honeycomb had a significant influence on the formation of a stable interface. The liquid metal formed a stable film layer on honeycomb metal electrodes, which have line widths of less than 50 μm. Coating PEDOT PSS with a nonionic surfactant lowered the interfacial energy of EGaIn with flat stretchable metal surfaces; hence EGaIn was coated uniformly on the stretchable metal surfaces. Strain sensors were fabricated as a demonstrative example of an application that utilizes the stable interface.

High aspect ratio cylindrical microdomains oriented vertically on the substrate using block copolymer micelles and temperature-programmed solvent vapor annealing

We report a novel, yet simple, method for the preparation of high aspect ratio cylindrical microdomains oriented vertically on a substrate by using block copolymer micelles and temperature-programmed solvent vapor annealing. Multilayered spherical micelles were first prepared by spin-coating of polystyrene-block-poly(4-vinylpyridine) copolymer (PS-b-P4VP) in toluene solution on a silicon wafer. When temperature-programmed solvent vapor annealing was performed, the spherical micelle cores consisting of P4VP chains were transformed into vertically oriented cylindrical microdomains spanning the entire film thickness up to 550 nm corresponding to the aspect ratio of 15.2. Since nitrogen in the P4VP block could be easily coordinated with many metal precursors, we also fabricated a high density array of gold nanoparticle/polymer nanocomposite nanorods oriented vertically on the substrate.