Woo Kyung Cho

One-step modification of superhydrophobic surfaces by a mussel-inspired polymer coating.

A bio-inspired approach for superhydrophobic surface modification was investigated. Hydrophilic conversion of the superhydrophobic surface was easily achieved through this method, and the superhydrophobic-hydrophilic alternating surface was generated by the method combined with soft-lithography. The resulting patterned surface showed high water adhesion property in addition to superhydrophobic property.

A bio-inspired swellable microneedle adhesive for mechanical interlocking with tissue

Achieving significant adhesion to soft tissues while minimizing tissue damage poses a considerable clinical challenge. Chemical-based adhesives require tissue-specific reactive chemistry, typically inducing a significant inflammatory response. Staples are fraught with limitations including high-localized tissue stress and increased risk of infection, and nerve and blood vessel damage. Here, inspired by the endoparasite Pomphorhynchus laevis which swells its proboscis to attach to its host’s intestinal wall, we have developed a biphasic microneedle array that mechanically interlocks with tissue through swellable microneedle tips, achieving ~ 3.5 fold increase in adhesion strength compared to staples in skin graft fixation, and removal force of ~ 4.5 N/cm2 from intestinal mucosal tissue. Comprising a poly(styrene)-block-poly(acrylic acid) swellable tip and non-swellable polystyrene core, conical microneedles penetrate tissue with minimal insertion force and depth, yet high adhesion strength in their swollen state. Uniquely, this design provides universal soft tissue adhesion with minimal damage, less traumatic removal, reduced risk of infection and delivery of bioactive therapeutics.

In Vitro Developmental Acceleration of Hippocampal Neurons on Nanostructures of Self-Assembled Silica Beads in Filopodium-Size Ranges†

Abstract Topographical cues play an important role in in vitro neuronal development. In their Communication (DOI: 10.1002/anie.201106271), Y. Nam, I. S. Choi, J. S. Lee, and co-workers show that neuritogenetic acceleration occurs on silica-bead monolayers made up of beads with a diameter of more than 200 nm, but not on monolayers of beads with smaller diameters. The biochemical study indicates neurons sense topographical differences in nanostructures and alter their behavior accordingly.

Microstructured barbs on the North American porcupine quill enable easy tissue penetration and difficult removal

North American porcupines are well known for their specialized hairs, or quills that feature microscopic backward-facing deployable barbs that are used in self-defense. Herein we show that the natural quill’s geometry enables easy penetration and high tissue adhesion where the barbs specifically contribute to adhesion and unexpectedly, dramatically reduce the force required to penetrate tissue. Reduced penetration force is achieved by topography that appears to create stress concentrations along regions of the quill where the cross sectional diameter grows rapidly, facilitating cutting of the tissue. Barbs located near the first geometrical transition zone exhibit the most substantial impact on minimizing the force required for penetration. Barbs at the tip of the quill independently exhibit the greatest impact on tissue adhesion force and the cooperation between barbs in the 0–2 mm and 2–4 mm regions appears critical to enhance tissue adhesion force. The dual functions of barbs were reproduced with replica molded synthetic polyurethane quills. These findings should serve as the basis for the development of bio-inspired devices such as tissue adhesives or needles, trocars, and vascular tunnelers where minimizing the penetration force is important to prevent collateral damage.

Pitch‐Dependent Acceleration of Neurite Outgrowth on Nanostructured Anodized Aluminum Oxide Substrates

Nervous systems are composed of microstructured scaffolds with three-dimensional nanofeatured textures. These textures enable the systems to give nanometer-scaled physical cues to the overlying cells, along with biochemical cues. However, the topographical effects on the neurons are still an unexplored territory, although there have been many reports on the biochemical cues for neuronal behavior. It is practically very difficult to investigate the topographical environments in vivo in the biological systems and/or to mimic them precisely in vitro. There is much recent evidence that the cellular response is affected by the physical properties of artificial materials. Studies with such materials could therefore provide us with new insight into the developmental processes of the brain and enable elucidation of the unexplored nanotopographical effects on neuronal behavior. The responses of nerve cells to surface roughness have been studied on various substrates, such as porous silicon, thin titanium nitride films, carbon nanotubes, topographically molded poly(dimethylsiloxane), silicon pillar arrays, gallium phosphide nanowires, aligned nanofiber arrays, and silicon nanowires. Previous studies showed that nerve cells exhibit enhanced attachment and viability as well as the axonal guidance effect on rough surfaces, as opposed to topographically flat surfaces. However, there have been few reports on how nanometer-scaled features regulate neuronal behavior in terms of neurite development. To generate nanotopographical stimuli to neurons in a controllable and systematic manner, it is necessary to make reproducible, rigid structures with variable topographical features. Among the methods for creating topographies on surfaces at the nanometer scale, the fabrication of anodized aluminum oxide (AAO) is highly effective, straightforward,

Counteranion-Directed, Biomimetic Control of Silica Nanostructures on Surfaces Inspired by Biosilicification Found in Diatoms†

Films of several biogenic and nonbiogenic inorganicspecies have already been synthesized under mild conditions(ambient pressure, room temperature or below, and near-neutralpHvalues)thatmimicthephysiologicalconditionsusedinnature.However,structuralcontroloftheinorganicfilmsstillremains challenging in the biomimetic approach.The nanometer-scale, spatial control of silica structures onsurfaces has many potential applications, such as heteroge-neous catalysis,

Long-term stability of cell micropatterns on poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammonium hydroxide)-patterned silicon oxide surfaces

In this work, we compared the long-term stability and integrity of cell patterns on newly reported, zwitterionic poly((3-(methacryloylamino)propyl)dimethyl(3-sulfopropyl)ammonium hydroxide) (poly(MPDSAH)) films with those on widely used, poly(poly(ethylene glycol) methyl ether methacrylate) (poly(PEGMEMA)) ones. The micropatterns of both polymers were formed on a silicon oxide surface by a combination of micropattern generation of a photoresist, vapor deposition of a silane-based polymerization initiator, and surface-initiated, atom transfer radical polymerization (SI-ATRP) of each monomer, MPDSAH or PEGMEMA. The successful formation of the silane initiator SAMs, and poly(MPDSAH) and poly(PEGMEMA) micropatterns was confirmed by X-ray photoelectron spectroscopy (XPS) and imaging ellipsometry. Onto each substrate patterned with poly(MPDSAH) or poly(PEGMEMA), NIH 3T3 fibroblast cells were seeded, and the cell micropatterns were generated by the selective adhesion of cells on the cell-adhesive region of the patterned surfaces. The cell pattern formed on the poly(MPDSAH)-patterned surface was observed to have a superior ability of finely maintaining its original, line-shaped structure up to for 20 days, when compared with the cell pattern formed on the poly(PEGMEMA)-patterned surface. In order to verify the relationship between the integrity of the cell micropatterns and the stability of the underlying non-biofouling polymer layers, we also investigated the long-term stability of the polymer films themselves, immersed in the cell culture media, for one month, in the aid of ellipsometry, contact goniometry, and XPS.

Water-Collecting Capability of Radial-Wettability Gradient Surfaces Generated by Controlled Surface Reactions

In this work, we developed a controlled oxidation reaction of vinyl-terminated self-assembled monolayers (SAMs) to carboxylic acid-terminated ones to generate radially inward wettability gradient surfaces. The hydrophobicity was introduced on a silicon wafer by SAMs of 10-undecenyltrichlorosilane, and after the initial drop in oxidation, followed by the dilution-by-dropping method, radial-wettability gradient surfaces having hydrophilic centers and hydrophobic exteriors were generated. This direct drop reaction on the SAMs did not require an elastomeric stamp to be fabricated, which allowed for facile tuning of the gradients in terms of sizes and shapes. The fabricated wettability gradient surfaces possessed a water-collecting capability toward the hydrophilic center, which was inactive on previous linear wettability gradient surfaces.

Combined surface micropatterning and reactive chemistry maximizes tissue adhesion with minimal inflammation.

The use of tissue adhesives for internal clinical applications is limited due to a lack of materials that balance strong adhesion with biocompatibility. The use of substrate topography is explored to reduce the volume of a highly reactive and toxic glue without compromising adhesive strength. Micro-textured patches coated with a thin layer of cyanoacrylate glue achieve similar adhesion levels to patches employing large amounts of adhesive, and is superior to the level of adhesion achieved when a thin coating is applied to a non-textured patch. In vivo studies demonstrate reduced tissue inflammation and necrosis for patterned patches with a thinly coated layer of reactive glue, thus overcoming a significant challenge with existing tissue adhesives such as cyanoacrylate. Closure of surgical stomach and colon defects in a rat model is achieved without abdominal adhesions. Harnessing the synergy between surface topography and reactive chemistry enables controlled tissue adhesion with an improved biocompatibility profile without requiring changes in the chemical composition of reactive tissue glues.

Spin–orbit density functional theory calculations for IX (X=F, Cl, Br and I) molecules

Two-component spin–orbit density functional theory (SODFT) calculations for spectroscopic constants of IX (X=F, Cl, Br and I) molecules have been performed with several functionals using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin–orbit operator. The SODFT results obtained with the B3LYP functional are in very good accord with the results of previous two-component CCSD(T) calculations with the same RECP and basis sets. Results of two-component SODFT calculations with RECPs are also in good agreement with reported all-electron relativistic DFT calculations with the same functionals. The spectroscopic constants obtained with ACM and PBE0 functionals display the best agreement with the experimental values among the functionals tested. Spin–orbit effects from the SODFT calculations result in increases of bond lengths and decreases of dissociation energies and harmonic vibrational frequencies and the magnitudes are in reasonable agreement with those from two...Two-component spin–orbit density functional theory (SODFT) calculations for spectroscopic constants of IX (X=F, Cl, Br and I) molecules have been performed with several functionals using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin–orbit operator. The SODFT results obtained with the B3LYP functional are in very good accord with the results of previous two-component CCSD(T) calculations with the same RECP and basis sets. Results of two-component SODFT calculations with RECPs are also in good agreement with reported all-electron relativistic DFT calculations with the same functionals. The spectroscopic constants obtained with ACM and PBE0 functionals display the best agreement with the experimental values among the functionals tested. Spin–orbit effects from the SODFT calculations result in increases of bond lengths and decreases of dissociation energies and harmonic vibrational frequencies and the magnitudes are in reasonable agreement with those from two-component CCSD(T) calculations. Spin–orbit effects appear to be quite insensitive to the choice of functionals for the bond lengths and harmonic vibrational frequencies, but those of the dissociation energies somewhat deviate with the differing class of functionals.