Focus Review in 2014

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.

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.

This review focuses on using an organic (bio)polymer for the formation of organic/inorganic hybrid materials and on understanding the formation of new hybrid materials via bio-inspired approaches. The structure–function relationships of biomineralization-related proteins and molecular designs to control the properties of the hybrid materials are also described. The combination of experimentation and molecular simulation is also introduced. These studies provide useful ideas for the development of hybrid materials through biomimetic approaches.

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 focuses on the development of donor–acceptor semiconducting polymers using electron-deficient π-building units, such as thiazolo[5,4 -d]thiazole, benzo[1,2-d:4,5-d′]bisthiazole, naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole and thieno[3,2-b]thiophene-2,5-dione. All of the polymers form crystalline structures in thin films and possess deep highest occupied molecular orbital energy levels; consequently, the polymers demonstrate high charge carrier mobilities with high air stability. Several key parameters were identified that must be taken into account when designing high-performance polymers: the symmetry of the building units, backbone shape, and delocalization of the π-electrons along the backbone.

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.

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.

Photocrosslinkable polymers and UV-curable resins are significant materials in relation to the industrial applications for coatings, adhesives, photoresists and printing plates. Recently, much attention has been paid to recovery or recycling of crosslinked polymers due to the environmental regulations. This article reviews our recent research work on the synthesis, properties and applications of photocrosslinkable polymers and UV-curable resins with degradable property.

Low-molecular-weight compounds, which form physical gels, are called ‘gelators’ and have received a great amount of scientific and technological interest. The physical gelation by gelator results from non-covalent bonds, represented by hydrogen bond. Molecules of gelator are first self-assembled in cooling process, producing fibrous assemblies. Then, these fibrous assemblies form a three-dimensional network structure, and gelation occurs by trapping solvent in the networks. Fibrous assemblies can be observed by electron microscope. This is a transmission electron microscopy image of tetrachloromethane gel formed by N-octadecylamide of N-benzyloxycarbonyl-L-isoleucine.

Bio-based amphiphilic polymers having a helical hydrophobic unit have been extensively studied on molecular assemblies and their morphology. Molecular assemblies having complex morphologies could be prepared by using the specific characters of the helical unit, and the unique self-assembling methodology was named as ‘patchwork self-assembling’. Further, application of the obtained molecular assemblies in medicinal fields was examined. Lactosome was accumulated at the targeted tumor region by the EPR effect, and therefore, expected to be an excellent nano-ordered carrier for drug and/or imaging agent delivery.

Inspired by functional systems in nature, chemists have created a number of intriguing and useful molecular systems from porphyrin derivatives. Of the synthetic porphyrin derivatives developed to date, strapped porphyrins are unique because they have three-dimensional architectures based on a built-in two-dimensional porphyrin molecule. Consequently, the structures of strapped porphyrins can be customized through detailed molecular design, thereby allowing the synthesis of sophisticated molecular systems. Herein, we describe strapped porphyrin-based polymeric systems with a particular focus on molecular design concepts that have led to unique photophysical, electronic and mechanical properties.

The recent progress of our research on anion-exchange membranes (AEMs) for alkaline fuel cell applications is reviewed. We have designed and synthesized a novel series of poly(arylene ether)-based AEMs with quaternized ammonium groups. The effect of sequence of polymer main chain (random or block) on the AEM properties, especially anion conductivity, is discussed. Fluorenyl groups serve effectively as scaffolds for the ammonium groups. The results imply that the aromatic AEMs are potentially applicable to alkaline fuel cells using hydrogen or hydrazine as a fuel.

This article reviews the design of polymeric functional spaces with microgel-core star polymers and single-chain folding/crosslinked polymers via living radical polymerization for unique functions. Core-functionalized star polymers were prepared by the intermolecular linking of arm polymers with functional linkers/monomers to provide solubilized microgel spaces for active and recyclable catalysis and selective and stimuli-responsive molecular recognition. Single-chain folding and crosslinked polymers were in turn obtained from the self-folding and/or intramolecular linking of amphiphilic random copolymers carrying hydrophilic poly(ethylene glycol) chains and hydrophobic alkyl pendants in water.

Genetically engineered protein biopolymers belong to a new family of polymers that have recently attracted interest due to their highly modifiable material properties. It is now possible to use a bottom-up engineering process to design advanced, smart materials for biomedical and engineering applications, such as energy storage and bioremediation. This review explores recent developments in these genetically engineered protein biopolymers, with a particular emphasis on elastomeric biopolymers (elastin, silk, resilin and titin). Also discussed are the future directions that this field will likely explore.

Combining gene therapy and tissue engineering, gene-activated matrix (GAM) is able to activate cells in or near the scaffolds to express the desired growth factors at effective levels within the local tissue microenvironment and further to restore the structure and function of damaged or dysfunctional tissues like skin, cartilage, bone, vessel, muscle, tendon and so on.

Fundamental development of nonfouling zwitterionic poly(sulfobetaine methacrylate) (polySBMA) coatings on a wide range of interfaces and membranes for use in the development of hemocompatible medical devices was discussed. The molecular designs of zwitterionic interfaces as well as the evolution of ‘intelligent’ interfaces and correlations between zwitterionic polymeric membrane surface modifications are scrutinized and delineated.

Smart polyplex micelles for systemic gene therapy fabricated by rationally integrating versatile molecular-based technologies. The polyplex micelles, which are formed through an electrostatic interaction-mediated self-assembly process of functional block copolymers and plasmid DNA, assume a task to transport therapeutic gene into nucleus of pathological cells via systemic route for functional protein expression.

Phenylboronic acid (PBA) derivatives are regarded as a synthetic mimic of lectins, often termed ‘boronolectins’, for its ability to interact with various carbohydrates. This unique chemistry has already borne fruit as molecular bases for glucose sensors and some bio-separation applications. This focus review highlights some emerging directions of the PBA-based research toward more versatile diagnostic and therapeutic targets that the authors currently pursue.

Tetra-PEG gel has highly suppressed heterogeneity, which is considered inherent to conventional polymer gels. In this review, we show a series of experimental results on Tetra-PEG gels, and discuss the homogeneity. Tetra-PEG gel is useful as a model system for examining the model predicting physical properties of polymer gels.