Bioinspired Dual Stimuli-Responsive Membranous System with Multiple On-Off Gates.

Stimuli-responsive polymers have been widely used for controlled release of several biomolecules. In general, a single stimulus among various stimuli, for instance, temperature, pH, or light, has been used for these polymers. Although some stimuli are applied together, one cannot control each stimulus independently at a given stimulus-responsive polymer. However, to mimic biological system like cell membrane, multiple on-off gates utilizing independent control of dual (or multiple) stimuli should be used. Here, we introduce a stimuli-responsive membrane controlled by two orthogonal stimuli. For this purpose, the top and the bottom parts of anodized aluminum oxide membrane walls are independently grafted by thermoresponsive poly(N-isopropylacrylamide) and pH-responsive poly(acrylic acid), respectively, by using surface-initiated atom transfer radical polymerization. The membrane clearly showed two independent on-off gates depending on temperature and pH. Furthermore, through light irradiation of two different wavelengths (near-infrared and ultraviolet), temperature and pH were also controlled independently and promptly. Thus, this membrane shows two independent on-off gating of the transport of a model biomolecule of fluorescein isothiocyanate-labeled bovine serum albumin. This strategy suggests the potential of independently modified membrane in layers as stimuli-responsive on-off gates for the application of artificial cell membrane.

Free-Standing Polyimide Nanotips on Substrates for Preparation of Hollow TiO2 Nanotips.

We report a facile method to fabricate free-standing polyimide (PI) nanotips on substrates by using plasma treatment with oxygen gas. The PI nanotips were prepared from the self-organization of unetchable materials deposited on a PI film during the plasma treatment. This approach provides a single-step process for the preparation of polymer nanotips in a large area (>inch scale). Furthermore, a selective patterning of the PI nanotips in a specific area was achieved by using a shadow mask. Due to excellent thermal resistance of PI, the PI nanotips maintained structural integrity at high temperature (~ 300 °C). To demonstrate potential application of PI nanotips as a template for hollow nanostructures, hollow TiO2 nanotips were prepared after atomic layer deposition of TiO2 followed by the burning of PI layer.

A Facile Route for Patterned Growth of Metal-Insulator Carbon Lateral Junction through One-Pot Synthesis.

Precise graphene patterning is of critical importance for tailor-made and sophisticated two-dimensional nanoelectronic and optical devices. However, graphene-based heterostructures have been grown by delicate multistep chemical vapor deposition methods, limiting preparation of versatile heterostructures. Here, we report one-pot synthesis of graphene/amorphous carbon (a-C) heterostructures from a solid source of polystyrene via selective photo-cross-linking process. Graphene is successfully grown from neat polystyrene regions, while patterned cross-linked polystyrene regions turn into a-C because of a large difference in their thermal stability. Since the electrical resistance of a-C is at least 2 orders of magnitude higher than that for graphene, the charge transport in graphene/a-C heterostructure occurs through the graphene region. Measurement of the quantum Hall effect in graphene/a-C lateral heterostructures clearly confirms the reliable quality of graphene and well-defined graphene/a-C interface. The direct synthesis of patterned graphene from polymer pattern could be further exploited to prepare versatile heterostructures.

Interfacing liquid metals with stretchable metal conductors.

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.

Hierarchically self-organized monolithic nanoporous membrane for excellent virus enrichment.

Enrichment of viruses is essential for making high dose viral stocks for vaccines and virus-related research. Since the widely used ultracentrifugation for concentrating viral stock requires ultra-high speed rotation, it easily destroys the activity of some viruses, for instance, hepatitis c virus (HCV), which has a fragile structure and low virus titer. We introduce a novel method to concentrate HCV virus in stock by using a hierarchically self-organized monolithic nanoporous membrane made by stepwise anodization. The pores at the top part of the membrane have very regular sizes that are suitable for the perfect filtration of the virus particles in the stock. On the other hand, the remaining part has large pores that maintain high flux and mechanical strength of the membrane under the high pressure (up to 10 bar). The enrichment efficiency of HCV in crude stocks by using the membrane became over 91%, which is four times higher than that (∼22%) obtained by conventionally used centrifugation. A very high efficiency results from the perfect filtration and no damage to the virion particles during the enrichment process, whereas significant damage to the HCV occurs during centrifugation. The hierarchically self-organized monolithic nanoporous membrane could be effectively employed for concentrating various fragile viruses in stocks, for instance, rabies virus and human immunodeficiency virus in addition to HCV virus.

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.

Free-standing, well-aligned ordered mesoporous carbon nanofibers on current collectors for high-power micro-supercapacitors.

The mesoporous carbon nanofiber arrays that stand on carbon-gold double-layer current collectors are synthesized by self-assembly of a PS-b-PEO copolymer and resol in AAO templates for a high-power micro-supercapacitor at high current densities.

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.

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.

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.