Metal complexation-based gelation imparts load-bearing hydrogels with striking properties like reversibility, self-healing, and mechanical tunability. Using a bio-inspired metal−catechol complex, these properties have been introduced to a variety of polymer hydrogels, except hyaluronic acid, which is widely used in biological applications. In this research, we developed two different hyaluronic acid (HA) hydrogels by regulating the gelation kinetics of Fe 3+ and a catechol cross-linker, including Fe 3+ -induced covalent bonding and coordination bonding. Dual roles of Fe 3+ in catechol-modified HA (HA-CA), Fe 3+ −catechol coordination, and catechol oxidation followed by a coupling reaction were selectively applied for different gelations. Phase-changeable HA-CA gel was attributed to dominant Fe 3+ −catechol coordination with immediate pH control. Alternatively, allowing a curing time to form catechol coupling bonds resulted in color-changeable HA-CA gels with pH control. The gel structure is then preserved by dual cross-linking through covalent catechol-coupling-based coordinate bonds and electrostatic interactions between Fe 3+ and HA-CA. The hydrogels showed enhanced cohesiveness and shock-absorbing properties with increasing pH due to coordinate bonds inspired by marine mussel cuticles. The present gelation strategy is expected to expand the utility of HA hydrogels in biological applications, offering easy control over the phase, gel network, and viscoelastic properties.

This article describes a simple method for the generation of multicomponent gradient surfaces on self-assembled monolayers (SAMs) on gold in a precise and predictable manner, by harnessing a chemical reaction on the monolayer, and their applications. A quinone derivative on a monolayer was converted to an amine through spontaneous intramolecular cyclization following first-order reaction kinetics. An amine gradient on the surface on a scale of centimeters was realized by modulating the exposure time of the quinone-presenting monolayer to the chemical reagent. The resulting amine was used as a chemical handle to attach various molecules to the monolayer with formation of multicomponent gradient surfaces. The effectiveness of this strategy was verified by cyclic voltammetry (CV), matrix assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS), MS imaging, and contact-angle measurements. As a practical application, cell adhesion was investigated on RGD/PHSRN peptide/peptide gradient surfaces. Peptide PHSRN was found to synergistically enhance cell adhesion at the position where these two ligands are presented in equal amounts, while these peptide ligands were competitively involved in cell adhesion at other positions. This strategy of generating a gradient may be further expandable to the development of functional gradient surfaces of various molecules and materials, such as DNA, proteins, growth factors, and nanoparticles, and could therefore be useful in many fields of research and practical applications.

To improve the external quantum efficiency, high quality GaN film was grown on hemispherical patterned sapphire by controlling the V/III ratio during the initial growth stage. The luminous intensity of white flash light emitting diode (LED) grown on hemispherical patterned sapphire (HPS) was estinated to be 5.8 cd at a forward current of 150 mA, which is improved by 20 % more than that of LED grown on conventional sapphire substrate. The improvement of luminous intensity was explained by considering not only an increase of the extraction efficiency via the suppressed total internal reflection at the corrugated interface but also a decrease of dislocation density. 1 Introduction A great deal of research has been devoted to develop prominent solid-state light emitting diodes (LEDs) which are a prerequisite for practical applications in the area of liquid crystal display (LCD) back light, full color display, traffic display, and general illumination [1]. The white light LEDs are the most promising solid-state lighting method to replace the conventional incandescent and fluorescent lamps. It is well known that high density threading dislocations are inherent in the epitaxial GaN films on sapphire substrates due to the large difference in the lattice constant between the epitaxial layer and sapphire substrate. Therefore, how to further reduce the dislocation density is an important issue for fabricating high performance LEDs. Moreover the reflective index of nitride films is higher than that of air and the sapphire substrate. Most of the generated lights in the active layer is absorbed by the electrode at each reflection and gradually disappear due to total internal reflection (TIL). It has been reported that one can reduce the TIL by forming ordered micro-scale hexagonal or rectangular shaped pattern on sapphire substrate which effectively scatters the emission light from the active layer [2,3]. However, growth of high quality GaN film on patterned sapphire substrate is more difficult than that of conventional sapphire substrate (CSS). In order to improve the quality of GaN epitaxial layer, various growth techniques have been devised by adjusting growth parameters, such as III/V ratio, growth pressure, growth temperature, and annealing time [4,5].In this work, we proposed and investigated the metal organic chemical vapour deposition (MOCVD) growth of undoped GaN flims on a hemispherical patterned sapphire (HPS) substrate by controlling the V/III ratio during the initial growth stage. The fabricated white flash LEDs grown on HPS showed an improved luminous intensity and injection current due to both the reduction of the dislocation density and increase of the external efficiency compare to the samples grown on CSS.

Patterned substrates have been widely used in various applications, including arrays of biomolecules and cells, highthroughput assays, and direct target sensing.[1] In practice, those demands have been achieved by either of or a combination of two strategies: 1) direct incorporation of biomolecules or functional-group-containing molecules into desired patterns and 2) generation of functional-group-presenting patterns by way of chemical conversions on the surface. The former encompasses microcontact printing (mCP), [2] dip-pen nanolithography (DPN), [3] polymer-pen lithography (PPL), [4] microfluidic networks (mFNs), [5] and microarrays.[6] The latter utilizes the "turning-on" strategy, in which inactive substrates are switched to an active state to reveal organic functional groups, in most cases by electrochemical or photochemical conversions. [7] Patterned functional groups in both strategies are further used as chemical handles for immobilization of biomolecules, such as cell-adhesion ligands, enzyme substrates, proteins, oligosaccharides, and oligonucleotides, to afford patterned substrates. As a typical recent example, Rozkiewicz et al. reported on modified mCP for the preparation of oligonucleotide micropatterns.[8] In their report, oxidized PDMS stamps were first coated with positively charged dendrimers followed by negatively charged oligonucleotides in a layer-by-layer arrangement, and were transferred to a solid support for the generation of microarrays. Smith and co-workers introduced a photo-labile protecting group to a thiol functionality.[9] Various patterns of small molecules and proteins were prepared by using a photolithographic method in combination with thiol-specific conjugation chemistry. Yousaf et al. showed that ligand density and composition influence the rate of stem-cell differentiation by using hydroquinone-based electroactive substrates, which were patterned with a variety of ligands by using microarray technology.[10] Although these two strategies are reliable, well established, and, therefore, widely used, each of the strategies offers limitations on practical use as a general platform for ligand-patterned substrates. For instance, direct contact printing methods, such as mCP, cannot control ligand density on the surface, which can provide important quantitative information for use in experimental design. A concern with regard to the turning-on strategy is that in some cases activated functional groups require specified conjugation chemistry and, therefore, necessitate preparatory steps (tagging steps) to make the ligands compatible with the conjugation reaction.Herein, we describe a simple, efficient, and straightforward method for ligand patterning on a surface, induced by a non-invasive organic chemical reaction-which we have termed a chemical-reaction-induced patterning (CRIP)-and equipped with the capability for control of ligand density. In addition, our method is compatible with common patterning tools and conjugation chemistry. Herein, we demonstrate our strategy by using...

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