Focus Review

Sacrificial bonds break to dissipate energy and can increase the toughness of materials. Incorporating sacrificial bonds into hydrogels through the double network process enabled the first extremely tough hydrogels. In this Focus Review, we discuss the nature of sacrificial bonds, and how they can be used on the macroscale to enable tough soft composite materials. By matching the essence of the double network concept, we can make tough materials from macroscale composites for biomedical and engineering applications.

This focus review describes a biosensing strategy called “chemical tongue”, which mimics the human taste system by employing fluorogenic materials containing various chemical structures in conjunction with statistical techniques. The focus is on the design of polymer-based chemical tongues and their applications with various complex biological samples. The chemical-tongue strategy is capable of recognizing biological samples in a unique manner that does not, in contrast to conventional approaches, rely on specific interactions, thereby potentially opening avenues for unexplored uses of polymers in a wide range of research areas.

Reverse osmosis (RO) membranes are widely used as energy-saving and environmentally friendly materials for water purification. This Focus Review reports on the nanoscale structure and permeation mechanism of crosslinked fully aromatic polyamide RO membranes. First, the research on the morphology of protuberance structures of the polyamide separation functional layer is described. Next, hydrated structure of the functional layer is focused, which was analyzed using neutron scattering and molecular dynamics simulations. Innovative RO membranes are being developed that can obtain higher quality water with less energy by precisely controlling nanostructures.

Bacterial cellulose (BC) has been utilized as a biopolymer matrix for various applications. The advancement of synthetic biology has brought new approaches for its production and functionalization. In this mini-review, we briefly discuss the conventional methods employed to improve BC production and functionalization as well as their challenges. We summarize the applications of synthetic biology to address the challenges and its use to develop novel hybrid living materials. Finally, we consider the opportunities and future prospects of synthetic biology and engineered biological materials.

Polysaccharides and “imogolite” (a natural aluminum silicate nanoclay) were used as building blocks to prepare environmentally benign (organic/inorganic) hybrid materials of natural origin. Cellulose nanocrystals (CNCs), cellulose fibers (CFs), and sacran were employed as polysaccharides. By utilizing oppositely charged organic and inorganic components, polysaccharide/imogolite hybrids were prepared by spin-assisted layer-by-layer assembly and solution blending. The fine dispersion and attractive interactions of imogolite with polysaccharides afforded hybrids with improved physicochemical properties.

The self-assembly of carbohydrate-based block copolymer systems has allowed recently the conception of novel glyconanoparticles and high-resolution patterning thin films with sub_10nm resolution (high χ) that has never been attained by petroleum-based copolymers and provides these new nanostructured biomaterials with novel properties such as next generation nanolithography, memory devices, OPV and biosensors. The glyconanoparticles can be designed to meet the targeted applications in terms of size, encapsulation and decoration. The control of the lamellar/cylindrical phases orientation can be achieved using thermal, solvent vapor or microwave annealing processes in thin films.

Random pH-responsive copolymers, P(A/AaU) have been prepared from a pH-responsive pendant fatty acid-containing monomer (AaU) and a pendant sulfonate-containing monomer (AMPS). In water, P(A/AaU) formed unimer micelles under acidic conditions. Under basic conditions, the P(A/AaU) polymer chains expand due to the electrostatic repulsions. Although pH-responsive sunscreen shows waterproof properties under neutral conditions, it disperses under weakly basic conditions such as soap water. pH-responsive diblock copolymers with a pendant fatty acid-containing block were prepared. This review also discusses pH-responsive gelling agents based on ABA triblock copolymers.

A supramolecular complex termed “hemoCD1” was constructed as the aqueous synthetic Hb/Mb model using a 1:1 inclusion complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(II) with a per-O-methylated β-cyclodextrin dimer with a pyridine linker. HemoCD1 was used as a selective CO scavenger in vivo due to its extremely high binding affinity to CO. In addition, hemoCD1 was utilized to quantify the accumulation of endogenous and exogenous CO in organs/tissues. Finally, hemoCD1 was employed as an antidote for CO poisoning in animals.

Regenerated fibers of β-1,3-glucan (curdlan) and α-1,3-glucan were fabricated by dry-jet wet spinning, and the fiber properties and structures are summarized in this review. The flexible and water-absorbent curdlan and the stiff and strong α-1,3-glucan would be utilized in different applications from conventional cellulose. As a new type of post-treatment, a two-step stretching method in water was developed for α-1,3-glucan by utilizing its crystal transition. This can be applied to various polysaccharides for future production of high-performance fibers.

Relationship between the primary structures and their properties is recognized as an important research subject for polymer chemists. To make progress in this academic field, innovative synthetic procedures of cyclic polymers are essential. The synthetic strategy has two typical pathways: one is the ring closure of functional linear polymers and the other is ring expansion polymerization using cyclic monomers, an initiator, or a catalyst. This focus review deals with the recent synthetic evolution of cyclic polymers, focusing on our new strategy: ring closing without highly dilute conditions.

The recent advances of the novel signal-amplification method, “supramolecular allosteric signal-amplification sensing” (SASS), are shown and summarized in this review. The SASS using polymers, polythiophenes and glucans introduced herein will be expandable to further smart polymeric systems, i.e., dynamic supramolecular assemblies.

Acidic pH is identified for various types of tumors, whereby it can be employed for crafting tumor-targeted nanomaterials. Cationic net charge of the nanomaterials at tumorous pH achieves selective interaction with anionic tissue constituents at tumor sites, for the effective tumor accumulation. However, tumorous pH is ca. 6.5, whereas pH of normal tissues is 7.4, and therefore responsiveness to the small pH window is the key toward the success for tumor delivery. The present manuscript highlights the polymer designs that recognize tumorous pH to make tumor-targeted nanomaterials.

The structural characterization of DDS carriers, including transdermal DDS, is one of the essential factors in the understanding of the biological properties and useful for the development of new carriers. This review introduces a quantitative evaluation of the surface coating on a carrier with the contrast variation technique of SAXS in the first section and the localization determination of drug molecules in liposomes in the second section. The final section describes the microemulsions containing deep eutectic solvents in the inner phase for use in transdermal DDS.

Silk fibroin (SF) is a natural protein polymer material and has been fabricated and studied as a scaffold for tissue engineering and regenerative medicine. To append new functions to SF scaffolds and understand their in vivo behaviors, researchers have addressed modifications of SF scaffolds by using transgenic silkworm and peptide modification technologies. These modified SF scaffolds had on-target functions and showed their potential as a material for tissue engineering applications. This review summarizes the methodologies and characteristics of functionalized SF scaffolds.

Water-gated polymer thin-film transistors (WG-PTFTs) fabricated by a simple procedure can be operated at an ultralow voltage, whereby the WG-PTFTs with molecular recognition units allow chemical sensing. Upon the addition of analytes, the electric double layer capacitance of the WG-PTFTs can be changed by accumulation and desorption of charged species at the interface of the semiconductor and electrolytes. For example, the WG-PTFTs have successfully detected biogenic amines and a herbicide glyphosate. In short, our proposed WG-PTFTs are among the most promising platforms for sensing applications based on π-conjugated polymer materials.

Boronic acids (BA) are known for their ability to reversibly interact with the diol groups, a common motif of biomolecules including sugars, ribose, and catechols. One can tailor BAs to elicit a divergent profile of binding strength and specificity on the basis of stereochemistry and controlled electronic effects. This focus review provides an overview of a phenylboronic acid (PBA)-based, totally synthetic platform for insulin delivery applications developed in our group, with focuses on the development of new PBA derivatives, glucose-responsive gels, and the gel-combined medical devices.

Electrospinning (ES) is a technique that can produce nanofiber mats from arbitrary polymers. We prepared actuators consisting of nanofiber mat electrodes and ionic liquid gel using three methods, and examined the effect of the preparation method on actuator performance. The results showed that actuators with nanofiber mat electrodes spun from the lowest spinning solution concentration showed a larger strain against an applied voltage. Furthermore, we prepared two types of actuators with different fiber directions and examined the effect of nanofiber alignment on actuator performance.

Strategic design and synthesis of semiconducting polymers with intrinsic ductility and/or stretchability are introduced in this review. The best polymer films show high charge mobilities over 1 cm²V⁻¹s⁻¹ even at 100% tensile strain. On the other hand, their mechanical properties remain inadequate, with high elastic moduli over 0.1 GPa. For semiconducting polymers to be promising candidates in applications such as wearable electronics, electronic skins, and bioelectronics, the trade-off relationship between their electronic and mechanical performance must be prevented by further developing and combining versatile and efficient approaches.

This focused review introduces our rheological studies on static and dynamic polymer networks using Tetra gel, host-guest gel, and telechelic associative polymer networks. Although the characteristics of crosslinks strongly influence the rheological properties of polymer networks, the understanding of the molecular origin of these properties remains incomplete owing to structural complexity. Our multiple experimental characterizations, including multiaxial stretching and the combination of dynamic viscoelastic and spectroscopic measurements, will add to the molecular understanding and further provide important information on the design of novel polymer network materials.