Volume 47 Issue 2, February 2015

Titanium dioxide (TiO₂) with highly controlled nano (polymorph) and macro (morphology) structures was synthesized from water by hydrothermal method using a series of unique water-soluble titanium complexes. Thanks to their high stability in water, a variety of organic molecules, which act as a shape-controlling agent, can coexist, resulting in the formation of anistropically grown rutile-type TiO₂. The obtained rutile crystals exhibited greatly improved functions with respect to their dielectric or photocatalytic performance. The results suggest that the chemical design of metal-complex precursors leads to achievement of high functionalization of materials.

The binding conformation of aspartic acid (Asp) at the calcite surface is strongly affected by the structure of the surrounding water. On the {104} plane, Asp binds directly to the acute step edge, but not to the obtuse step edge, reflecting a difference in the structure of water near the step edge. This selective binding to the acute step edge causes a change in the step morphology on the {104} plane when Asp is added to real systems.

An approach to create new artificial materials with hierarchical structures and tailored properties using a layer-by-layer assembly of two-dimensional (2D) oxide nanosheets is demonstrated. 2D nanosheets have remarkable potential as building blocks for tailoring fusion materials combined with a range of foreign materials such as organic molecules, gels, polymers, and inorganic and metal nanoparticles. The ability to create functionalized, 2D hierarchical systems will lead to various applications in optoelectronics, spinelectronics, energy and environment technologies.

In nature, there are many strong and tough biomaterials that result from the fusion of soft and hard elements. These materials include nacre, crustacean exoskeletons and spider webs. Here, we review previous studies on such bio-fusion materials, emphasizing the importance of simple models to gain a physical understanding of the emergence of strength and toughness from these structures. Thus, a simple understanding obtained through biologically inspired models provides useful guiding principles for the development of artificial tough composites by mimicking biomaterials.

This review addresses recent developments in angle-independent structurally colored materials composed of submicrometer-sized fine particles. Here, especially, I focused on the possibility of using colloidal amorphous arrays as angle-independent structurally colored stimuli-responsive materials based on the properties of colloidal amorphous arrays that have been elucidated in recent experimental investigations.

Biocompatible and biodegradable polymers have emerged during the past decades to promise extraordinary breakthroughs in a wide range of diagnostic and therapeutic medical devices. Understanding and controlling the interfacial interactions of the polymeric biomaterials with biological elements are of essential towards their successful implementation in biomedical applications. Here, we highlight recent developments of biocompatible and biodegradable fusion polymeric biomaterials for medical devices and overview of the recent progress of the design of the multi-functional biomedical polymers by controlling biointerfacial water structure through precision polymer synthesis and supramolecular chemistry.

Thin-film inorganic/organic hybrids of CaCO₃ and poly(cyclodextrin) were prepared. The cavities of CDs inside the hybrids facilitated functionalization of these fusion materials by dye molecules.

Amphiphilic block copolymers poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] (EOVE-b-MOVE) induce the ring assembly of silica nanospheres (SNSs, ca. 15 nm) in the liquid phase. Nanorings form with appropriate polymer concentration, pH and temperature. EOVE-b-MOVEs with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that polymer’s molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) one-dimensionally assemble into nanochains with these block copolymers under otherwise identical conditions.

A supramolecular gel of DMSO was formed by pyridyl-substituted tris-urea 1 in the presence of an appropriate amount of Pd(OAc)₂. Scanning electron microscopic image of the xerogel revealed a porous spongiform nanostructure. Gel to sol/solution phase transitions of the supramolecular gel were induced by adding chelating agents to prevent the formation of coordination bonds between 1 and the palladium ion. The Wacker oxidation of styrene was performed in the supramolecular gel, and the reaction kinetics were compared with those in a typical bulk solution.

Zn-based two-dimensional layer coordination framework was synthesized by ionothermal synthesis and its solid-to-solid phase transition was studied by X-ray diffraction, solid state nuclear magnetic resonance and impedance spectroscopy. The phase transition is originated from the order-to-disorder behavior of accommodated ammonium cations in the structure. It occurs rapidly and reversibly, and little volume change and high thermal stability were observed.

The decoration of a peptide-based artificial viral capsid with gold nanoparticles (AuNPs) is reported. β-Annulus GGGCG-bearing peptide as a binding site of AuNPs self-assembled into nanocapsules with a diameter of 50 nm. The addition of AuNPs to the peptide nanocapsules afforded relatively uncontrolled assemblies of AuNPs. In contrast, the self-assembly of AuNP–peptide conjugates afforded, after dialysis, controlled assemblies of AuNPs with sizes of 30–60 nm. ζ-Potential measurements revealed that the surface of the artificial viral capsid self-assembled from β-annulus peptide was coated with AuNPs.

An initiating system composed of GaCl₃ and an alkylbenzene was demonstrated to be highly effective for the controlled cationic polymerization of a plant-derived monomer, β-pinene. When two equivalents of hexamethylbenzene were added to GaCl₃ in conjunction with 2-chloro-2,4,4-trimethylpentane as an initiator, cationic polymerization of β-pinene successfully proceeded in a living manner at –78 °C. Successful control over the reaction was attributed to the formation of a complex between GaCl₃ and the alkylbenzene, as confirmed by UV–vis and ⁷¹Ga NMR analyses.

The effect of the content of carboxy groups in oxidized cellulose nanofiber (CeNF) on hydroxyapatite (HAp) formation capability in biomimetic processing using a solution mimicking human body fluid (simulated body fluid; SBF) was systematically investigated. Oxidized CeNF with different carboxy group contents (0–27% per glucose units of cellulose) were soaked in 1.5SBF, in which concentration was 1.5 times higher than that of SBF. It was found that there was optimum amount of carboxy groups for the effective induction of HAp nucleation on CeNF.

Poly(l-lactic acid-co-glycolic acid)/hydroxyapatite composites were prepared by in situ polymerization of l-lactide and glycolide in porous HAp pellets for their application to the artificial bone materials. Effect of l-lactic acid/glycolic acid ratio on the mechanical properties and biocompatibility were investigated.

Gold nanoparticles capped with a simplified ionic liquid-like ligand were prepared, which were incorporated into the fusion materials with ionic liquids at concentrations of up to 40 wt% of inorganic content. The fusion material of gold nanoparticles with an ionic liquid monomer was readily converted into a polymeric composite, in which gold nanoparticles showed high thermal stability.

A ‘box-shaped’ three-dimensional (3D) DNA origami of ~40-nm dimensions was selectively formed by closing a symmetric open motif with three orthogonal faces. This 3D DNA origami was used as an intelligent nano-container to encapsulate exactly one 10-nm gold nanoparticle (AuNP). AuNPs were functionalized with thiol-modified DNA strands and attached to one of the faces of the open motif, which was designed to be an interior surface of the box and decorated with three complementary strands. The open motif was then closed into the box shape as triggered by the addition of DNA strands joining the remaining edges. An examination of the suitable folding path of an M13 scaffold using fluorescently labeled staple strands revealed that the flexibility at the hinge was essential for the efficient closing of the DNA origami container. Atomic force microscope and transmission electron microscope imaging of agarose-gel-purified complexes clearly showed the successful encapsulation of one AuNP inside the shell.

Dendritic morphologies of a metal oxide, metal and conductive polymer were obtained by using the dendrites of a transition metal salt as a template. Dendrites of the transition metal salt, copper acetate monohydrate (Cu(CH₃COO)₂·H₂O), were prepared under diffusion-controlled conditions in a polymer matrix, such as poly(vinyl alcohol). The resultant dendritic morphologies of Cu(CH₃COO)₂·H₂O were replicated to copper oxide (CuO), metallic copper (Cu) and polypyrrole without morphological changes. These methods can be applied to other metal oxides, metals and polymers.

Anti-reflective coating films were fabricated via the layer-by-layer assembly of mesoporous silica nanoparticles and cationic polyelectrolytes. The thickness and packing density of coating films can be controlled by layer number and concentration of mesoporous silica nanoparticle dispersion to obtain excellent anti-reflective performance.

Polymeric chain-structured complexes were prepared with helical lanthanide complexes (LnL) and benzene-dicarboxylate derivatives (benzene-1,4-dicarboxylate (bdc), 2-aminoterephtalate (atpa) and 2-hydoloxyterephtalate (htpa)), which show some noteworthy physicochemical properties, photo-luminescence and thermal stabilities. The complex EuL-bdc shows bright luminescence originating from Eu^III by UV excitation. The emission color can be tuned by the mixing of TbL. The structures of these chain complexes were clarified by synchrotron X-ray powder diffraction measurements. The derivation of the linker moiety (bdc to atpa or htpa) affects the inter-metal energy transfer from Tb^III to Eu^III.

Protein nanogels were prepared by using the vitamin B₆ (pyridoxal)-bearing pullulan (PLPP) as a bio-crosslinker. The binding of the PLPP to the serum albumin via the formation of Schiff bases was significantly enhanced in the presence of zinc ions because of the coordination of the Schiff base to metal ions. Dynamic light scattering measurements, high-performance liquid chromatography, and transmission electron microscopy confirmed that the zinc ions enhanced the ability of PLPP to form nanogels by crosslinking with the anionic BSA despite the strong electrostatic repulsion between the two molecules.

Novel organic–inorganic hybrid nanoparticles with a bisphenol A (BPA)-responsive hydrogel layer on the surface of SiO₂ nanoparticles were prepared via surface-initiated atom transfer radical polymerization of acrylamide (AAm), acryloyl-modified β-cyclodextrin (CD) and N, N′-methylenebisacrylamide. The resulting CD-PAAm/SiO₂ nanoparticles shrank in response to BPA because of an increase in the crosslinking density of the CD-PAAm hydrogel layer, which resulted from the formation of sandwich-like CD-BPA-CD complexes acting as dynamic crosslinks.

Electropolymerization of pendant groups in a copolymer of TEMPO- and aniline-substituted norbornene gave a layer of TEMPO-populated polynorbornene in which polyaniline chains were incorporated. The polyaniline chain served as a conducting path to reduce charge-transfer resistance for redox mediation, which gave rise to an excellent rate performance for charging/discharging process.

Nanogel particles (NP) that bind with the Fc fragment of immunoglobulin G (IgG) were immobilized on the pore surface of macroporous hard gel beads (GB) containing quaternary ammonium cations on the surface via multipoint electrostatic interactions. The model target protein (IgG) was reversibly captured by the NP-immobilized GBs through NP–IgG interactions. NP-immobilized GBs have potential applications as a novel affinity purification medium for proteins, combining an inexpensive and stable ligand with a high-performance support.

The February 2015 special issue of Polymer Journalon Fusion Materials: Creative Development of Materials and Exploration of their function through Molecular Control is a collection of papers contributed by the members of the research project of same title, focusing on the innovative researches in construction of high-functional structural materials. The accompanying web focus offers access to relevant articles selected from across Nature Publishing Group to provide further insights to readers of the special issue.