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An overview of the recent progress in the development of gecko-inspired synthetic dry adhesives is presented, with particular emphasis on two major structural elements of nanohairs and nanotubes. With the advance of nanofabrication techniques, recently developed dry adhesives made of nanohairs and nanotubes show excellent adhesion strength, smart directional adhesion as well. as rough surface adaptability by better mimicking gecko foot hairs. After a brief description of the requirements for high-performance artificial dry adhesives, a variety of synthetic adhesives are described based on materials and structural features of the gecko-inspired nanostructures. In addition, current challenges and future directions towards an optimized synthetic dry adhesive are presented. ; This work was supported by the Korea Science & Engineering Foundation through the Nano R&D Program (Grant 2007-02605 and 0428-2008-018), the King Abdullah University of Science and Technology (KAUST) program (No. KUK-F1-037-02), the Korea Research Foundation Grant funded by theKorean Government (MOEHRD) (Grant KRF-J03003), and the Micro Thermal System Research Center at Seoul National University.

We report on detachment nanolithography of an organic thin film at room temperature mediated by ultraviolet (UV) exposure. A nanopatterned, UV curable polyurethane acrylate (PUA) mold was placed on a spin-coated organic film made of 4,4'-bis[N-1-napthyl-N-phenyl-amino]biphenyl (NPB) under a low pressure (1-2 bar). A higher work of adhesion at the organic/mold interface induced detachment of the contacting layer on silicon or gold substrate, resulting in well-defined nanopatterns without a residual layer. The detachment was highly improved by a short-term UV exposure, rendering the film surface free from contaminant hydrocarbons with a lower cohesive force, as confirmed by Fourier transform infrared (FTIR) spectroscopy and measurements of contact angle of water. ; The work was supported by the Korea Science and Engineering Foundation (KOSEF)grant funded by the Korea government (MOST) (No. 2007-02605) and in part supported by the Micro Thermal System Research Center of Seoul National University.

We present the effects of oxygen on the irreversible bonding of a microchannel using an ultraviolet (UV) curable material of polyurethane acrylate (PUA). Microchannels were fabricated by bonding a top layer with impressions of a microfluidic channel and a bottom layer consisting of a PUA coating on a glass or a polyethylene terephthalate (PET) film substrate. The resulting channel is a homogeneous conduit of the PUA material. To find optimal bonding conditions, the bottom layer was cured under different oxygen concentration and UV exposure time at a constant UV intensity (10 mW cm(-2)). Our experimental and theoretical studies revealed that the channel bonding is severely affected by the concentration of oxygen either in the form of trapped air or permeated air out of the channel. In addition, an optimal UV exposure time is needed to prevent clogging or non-bonding of the channel. ; This work was supported by the Korea Science & Engineering Foundation through the Nano R & D Program (Grant 2007–02605) and by the Center for Nanoscale Mechatronics & Manufacturing (Grant 08K1401-00210) under the auspices of the Ministry of Education, Science and Technology, KOREA. This work was also supported in part by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant KRF-J03000).

This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (R01-2007-000-20675-0), the Korean Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2005-041-D00111), and the Minuta Technology (http://www.minuta. co.kr/).

Bridging the gap: Vacuum-assisted capillary force lithography (CFL) allows the fabrication of monolithic, suspended bridge structures (see picture) by exploiting partial curing kinetics and vacuum-assisted hydraulic filling. A small portion of the base microstructure (<4 µm) is molded to create a bridge structure by simply applying a nanoscale mold with the impression of channels, meshes, or circles. ; This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean government (MOST) (R01-2007-000-20675-0), the King Abdullah University of Science and Technology (KAUST) program (No. KUK-F1-037-02), and the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant KRF-J03000). This work was supported in part by the Center for Nanoscale Mechatronics & Manufacturing (Grant 08K1401-00210) and the Grant-in-Aid for Strategy Technology Development Programs from the Korean Ministry of Knowledge Economy (No.10030046).

We present a simple and widely applicable method to fabricate micro- and nanochannels comprised entirely of crosslinked polyethylene glycol ( PEG) by using UV- assisted irreversible sealing to bond partially crosslinked PEG surfaces. The method developed here can be used to form channels as small as similar to 50 nm in diameter without using a sophisticated experimental setup. The manufactured channel is a homogeneous conduit made completely from non-biofouling PEG, exhibits robust sealing with minimal swelling and can be used without additional surface modification chemistries, thus significantly enhancing reliability and durability of microfluidic devices. Furthermore, we demonstrate simple analytical assays using PEG microchannels combined with patterned arrays of supported lipid bilayers ( SLBs) to detect ligand ( biotin) receptor ( streptavidin) interactions. ; This research was supported by the Korean Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2005-041-D00111) and the Micro Thermal System Research Center of Seoul National University, and the Seoul R&BD Program (Seoul Research and Business Development Program).

A simple yet robust method to fabricate an array of stooped nanohairs; is presented, with a proper choice of material and post e-beam exposure even for an aspect ratio of 10. The stooped nanohairs have the unidirectional feature of frictional adhesion with a remarkably high adhesion force (similar to 11 N cm(-2)). ; This work was supported by the Korea Science & Engineering Foundation through the NANO R&D Program (Grant 2007–02605) and the King Abdullah University of Science and Technology (KAUST) program (KUK-F1- 037-02). This work was also supported in part by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant KRF-J03000), the Micro Thermal System Research Center, and the Engineering Research Institute. Supporting Information is available online at Wiley InterScience or from the author.

We present a nanowell (NW)-based biosensing platform for electrochemically detecting biological reactions on the level of single lipid vesicle. The NW geometry of a gently-sloped vertical wall is found to be optimal for selective deposition of single liposomes without capillary resistances. Also, the use of a hydrophilic, non-biofouling PEG copolymer is essential to provide distinctively separated FLV arrays without nonspecific adsorption. ; This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (KRF-2006-003-D00040) and the Micro Thermal System Research Center of Seoul National University. This work was also supported by Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Corporation.

A dual-scale metal transfer technique is presented to generate metal patterns with two different length scales from a single master. An adhesive polymer layer is brought in contact with the metal-coated surface in two sequential steps to transfer metal layers from both ridges and valleys of the mold aided by the difference in adhesive force (see image). ; This work was supported by the Seoul Research & Business Development program (grant no. 10583), the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (grant KRF-J03000), and the LG Display Company under the auspices of the Ministry of Economy Knowledge (MKE). This work was also supported in part by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant KRF-J03000).

We present a simple yet robust method for fabricating angled, hierarchically patterned high-aspect-ratio polymer nanohairs to generate directionally sensitive dry adhesives. The slanted polymeric nanostructures were molded from an etched polySi substrate containing slanted nanoholes. An angled etching technique was developed to fabricate slanted nanoholes with flat tips by inserting an etch-stop layer of silicon dioxide. This unique etching method was equipped with a Faraday cage system to control the ion-incident angles in the conventional plasma etching system. The polymeric nanohairs were fabricated with tailored leaning angles, sizes, tip shapes, and hierarchical structures. As a result of controlled leaning angle and bulged flat top of the nanohairs, the replicated, slanted nanohairs showed excellent directional adhesion, exhibiting strong shear attachment (approximate to 26 N/cm(2) in maximum) in the angled direction and easy detachment (approximate to 2.2 N/cm(2)) in the opposite direction, with a hysteresis value of approximate to 10. In addition to single scale nanohairs, monolithic, micro-nanoscale combined hierarchical hairs were also fabricated by using a 2-step UV-assisted molding technique. These hierarchical nanoscale patterns maintained their adhesive force even on a rough surface (roughness < 20 mu m) because of an increase in the contact area by the enhanced height of hierarchy, whereas simple nanohairs lost their adhesion strength. To demonstrate the potential applications of the adhesive patch, the dry adhesive was used to transport a large-area glass (47.5 x 37.5 cm(2), second-generation TFT-LCD glass), which could replace the current electrostatic transport/holding system with further optimization. ; This work was supported by the Korea Science and Engineering Foundation through Nano R&D Program Grant 2007-02605, the Micro Thermal System Research Center of Seoul National University, National Research Laboratory Program Grant M10104000095-01J0000-04210, and the Center for Ultramicrochemical Process Systems. This work was also supported in part by King Abdullah University of Science and Technology Program KUK-F1-037-02 and a Korea Research Foundation Grant funded by the Korean Government Ministry of Education and Human Resource Development Grant KRFJ03000.

We present wetting transition of a water droplet on microstructured polymer surfaces using materials with different hydrophilicity or hydrophobicity: hydrophobic polydimethyl siloxane (PDMS) (theta(water) similar to 110 degrees) and hydrophilic Norland Optical Adhesive (NOA) (theta(water) similar to 70 degrees). The microstructures were fabricated by replica molding and self-replication with varying pillar geometry [diameter: 5 mu m, spacing-to-diameter ratio (s/d): 1-10 (equal interval), height-to-diameter ratio (h/d): 1-5] over an area of 100 mm(2) (10 mm x 10 mm). Measurements of contact angle (CA) and contact angle hysteresis (CAH) demonstrated that wetting state was either in the homogeneous Cassie regime or in the mixed regime of Cassie and Wenzel states depending on the values of s/d and h/d. These two ratios need to be adjusted to maintain stable superhydrophobic properties in the Cassie regime: s/d should be smaller than similar to 7 (PDMS) and similar to 6 (NOA) with h/d being larger than similar to 2 to avoid wetting transition by collapse of a water droplet into the microstructure. Based on our observations, optimal design parameters were derived to achieve robust hydrophobicity of a microstructured surface with hydrophobic and hydrophilic materials. ; This work was supported by a Grant-in-Aid for Strategy Technology Development Programs from the Korea Ministry of Knowledge Economy (No. 10030046). This work was also supported in part by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (Grant KRF-J03003), the Micro Thermal System Research Center, and the Engineering Research Institute.

Density variation of nanoscale patterns in thermal nanoimprint lithography was studied both by experiments and molecular dynamics simulations. A simple soft imprinting technique was used to fabricate various nanopatterns (70 nm and 600 nm lines and 150 nm dots) over a large area (2x3 cm(2)). Local density was measured by the relative magnitude of van der Waals interactions between a sharp tip and the patterned surface. In order to investigate the mechanism of density variation, molecular dynamic simulations were performed. Experimental and simulation results demonstrated that the density of the pressed region (valleys) was higher than that of the cavity region (hills) when a simple amorphous polymer is thermally imprinted with a patterned mold. ; This research was supported by a grant (07K1401-01020) from the Center for Nanoscale Mechatronics and Manufacturing, one of the 21st century frontier research programs,SRC/ERC program (R11-2005-065), the micro thermal system research center, and the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (2007-03437).

Hyaluronic acid (HA) has a number of potential biomedical applications in drug delivery and tissue engineering. For these applications, a prerequisite is to understand the characteristic of HA films directly immobilized to solid substrates. Here, we demonstrate that high molecular weight HA can be directly immobilized onto hydrophilic substrates without any chemical manipulation, allowing for the formation of an ultrathin chemisorbed layer. Hyaluronic acid is stabilized on these surfaces through hydrogen bonding between the hydrophilic moieties in HA [such as carboxylic acid (-COOH) or hydroxyl (-OH) groups] with silanol (-SiOH), carboxylic acid or hydroxyl groups on the hydrophilic substrates. Despite the water solubility, the chemisorbed HA layer remained stable on glass or silicon oxide substrates for at least 7 days in phosphate-buffered saline. Furthermore, HA immobilized on silicon and other dioxide surfaces in much higher quantities than other polysaccharides including dextran sulfate, heparin, heparin sulfate, chondroitin sulfate, dermatan sulfate, and alginic acid. This behavior is related to the molecular entanglement and intrinsic stiffness of HA as a result of strong internal and external hydrogen bonding as well as high molecular weight. These results demonstrate that HA can be used to coat surfaces through direct immobilization. ; Dr. Suh thanks the support by the Brain Korea 21 Project in 2004 and Dr. Yang thanks the support from the National Science Council of Republic of China and the partial support from Chang Gung Hospital. D. Berry is supported by a Howard Hughes Medical Institute predoctorial fellowship. This work was supported by the U.S. Army Research Office through the Institute for Soldier Nanotechnologies of MIT (grant number: DAAD-19-02-D0002) and the content of the information does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.