Showing papers in "Polymer Journal in 2020"

Graphene oxide-incorporated hydrogels for biomedical applications

Abstract: Graphene and graphene derivatives (e.g., graphene oxide (GO)) have been incorporated into hydrogels to improve the properties (e.g., mechanical strength) of conventional hydrogels and/or develop new functions (e.g., electrical conductivity and drug loading/delivery). Unique molecular interactions between graphene derivatives and various small or macromolecules enable the fabrication of various functional hydrogels appropriate for different biomedical applications. In this mini-review, we highlight the recent progress in GO-incorporated hydrogels for biomedical applications while focusing on their specific uses as mechanically strong materials, electrically conductive scaffolds/electrodes, and high-performance drug delivery vehicles. Graphene derivatives (e.g., graphene oxide (GO)) have been incorporated in hydrogels to improve the properties (e.g., mechanical strength) of conventional hydrogels and/or develop new functions (e.g., electrical conductivity and drug loading/delivery) for various biomedical applications.

Recent advances in multi-temperature-responsive polymeric materials

Abstract: Temperature-responsive (or thermoresponsive) polymers belong to the most studied class of smart polymers and are mainly classified into two types based on their temperature-responsive behavior: lower critical solution temperature (LCST) and upper critical solution temperature (UCST). Based on polymeric design, when two temperature-responsive segments are connected through a covalent bond at each chain end, the block copolymers are expected to show a dual-temperature-responsive property upon conformational changes. Moreover, in recent years, multi-temperature-responsive properties that can represent complex states/structures have been reported. These multi-temperature-responsive block copolymers can set the stage for development in various research fields, such as drug-delivery carriers, sensors in solvents, model proteins, and memory storage. This review focuses on current multi-temperature-responsive polymeric materials and their applications and is divided into three parts: (1) dual-temperature-responsive block copolymers, (2) dual-temperature-responsive hydrogels, and (3) multi-temperature-responsive block copolymers. Temperature-responsive (or thermoresponsive) polymers belong to the most studied class of smart polymers and are mainly classified into two types based on their temperature-responsive behavior: lower critical solution temperature (LCST) and upper critical solution temperature (UCST). Based on polymeric design, when more than two temperature-responsive segments are connected through a covalent bond, the block copolymers are expected to show a multi-temperature-responsive property upon conformational changes. This review focuses on current multi-temperature-responsive polymeric materials and their future applications such as drug-delivery carriers, sensors in solvents, model proteins, and memory storage.

Stimuli-responsive hydrogels as a model of the dynamic cellular microenvironment

Abstract: Ample evidence has demonstrated that biological cells not only react to biochemical cues from the surrounding microenvironments but also sensitively detect the mechanical properties of the extracellular matrix and neighboring cells to adapt their shape, function, and fate. Mechanical aspects in biology, called mechanobiology, have been attracting biologists, chemists, physicists, and mechanical engineers. However, most in vitro studies to date have heavily relied on covalently cross-linked hydrogels with prefixed and hence unchangeable mechanical properties, although the mechanical properties of the cellular microenvironment are never uniform or static. From this context, stimuli-responsive hydrogels are highly attractive as surrogate materials that can simulate dynamic physical microenvironments in vivo. This review tries to provide a comprehensive overview of previous achievements, present pitfalls and challenges, and future perspectives on the recent development of stimuli-responsive hydrogel materials for the dynamic control of cell behavior. Stimulus-responsive hydrogels are highly attractive as the surrogate materials that can simulate dynamic mechanical microenvironments surrounding biological cells in vivo. This review tries to provide with comprehensive overviews on the previous achievements, present pitfalls and challenges, and future perspectives on the recent development on stimulus-responsive hydrogel materials for the dynamic control of cell behaviors.

Biofunctional hydrogels based on host–guest interactions

Abstract: Biological systems involve the most complex materials in the world. Mimicking biological systems is not an easy task. Materials researchers are continuing to push themselves to prepare synthetic materials that can replicate biological systems. Hydrogels have attracted great interest from materials researchers for mimicking biological systems due to their biocompatibility. One approach to preparing hydrogels is using host–guest interactions. Host–guest interactions can be achieved by using cyclodextrins (CDs) as host units and suitable guest units. Hydrogels prepared based on host–guest interactions show several functionalities, such as self-healing ability, stimuli responsiveness, the ability to function as soft actuators for use in artificial muscles, and conductive responsiveness. These functions can be attributed to reversible bond formation between the CDs and guest units. Self-healing materials, which mimic the recovery of injured skin, can be achieved if the association constant between the CDs and guests is sufficiently high. Several specific guest units can also show external stimuli responsivity (redox, pH, temperature, and light) when paired with CDs, allowing them to mimic the responsiveness of the human body to external stimuli. Light-responsive hydrogels can be used to prepare soft actuators that can be employed as artificial muscles to mimic the sliding motion of human sarcomeres. Conductive hydrogels will be required to support the function of artificial muscles in the near future. This review summarizes the advancements made in biofunctional hydrogels based on host–guest interactions. Hydrogels as biocompatible polymer have been attracted materials researchers for mimicking biological systems. One efficient approach to preparing hydrogels is using host–guest interactions between cyclodextrins (CDs) as host units and suitable guest units. The hydrogels formed by CD and guest unit reversible bonds show several biofunctionalities, such as self-healing ability, stimuli responsiveness, the ability to function as soft actuators for use in artificial muscles, and conductive responsiveness.

Crystal polymorphism of polylactide and its composites by X-ray diffraction study

Abstract: Polylactide (PLA) exhibits various types of crystal modifications depending on the preparation conditions, including the components. To solve the open question, a reliable calculation method for crystallinity, crystal forms, and composition in neat PLA and PLA composites was developed on the basis of temperature-dependent synchrotron wide-angle X-ray diffraction results. The relative composition of amorphous, α-form, and α’-form phases of PLA and its composites filled with halloysite nanotubes during heating was successfully obtained. It was found that only 47–56% of α’-form crystals transform into α-form crystals during a 2 °C/min heating process for PLA with a molecular weight of 54,300 g/mol. The loading of halloysite nanotubes decreases the cold crystallization and starting transition (α’ crystals transform into α-form crystals) temperatures of PLA. The crystallinity and the main diffraction peak intensity as a function of temperature were also analyzed. These results suggest that the α’-to-α form transition is a solid-solid phase transition. Polylactide (PLA) exhibits various types of crystal modifications depending on the preparation conditions, including the components. To solve the open question, a reliable calculation method for crystallinity, crystal forms and composition in neat PLA and PLA composites was developed on the basis of temperature-dependent synchrotron wide-angle X-ray diffraction results. The relative composition of amorphous, α-form, and α’-form phases of PLA and its composites filled with halloysite nanotubes during heating was successfully obtained.

Evaluation-oriented exploration of photo energy conversion systems: from fundamental optoelectronics and material screening to the combination with data science.

Abstract: Light is a form of energy that can be converted to electric and chemical energies. Thus, organic photovoltaics (OPVs), perovskite solar cells (PSCs), photocatalysts, and photodetectors have evolved as scientific and commercial enterprises. However, the complex photochemical reactions and multicomponent materials involved in these systems have hampered rapid progress in their fundamental understanding and material design. This review showcases the evaluation-oriented exploration of photo energy conversion materials by using electrodeless time-resolved microwave conductivity (TRMC) and materials informatics (MI). TRMC with its unique options (excitation sources, environmental control, frequency modulation, etc.) provides not only accelerated experimental screening of OPV and PSC materials but also a versatile route toward shedding light on their charge carrier dynamics. Furthermore, MI powered by machine learning is shown to allow extremely high-throughput exploration in the large molecular space, which is compatible with experimental screening and combinatorial synthesis.

How to define and study structural proteins as biopolymer materials

Abstract: Structural proteins, including silk fibroins, play an important role in shaping the skeletons and structures of cells, tissues, and organisms. The amino acid sequences of structural proteins often show characteristic features, such as a repeating tandem motif, that are notably different from those of functional proteins such as enzymes and antibodies. In recent years, materials composed of or containing structural proteins have been studied and developed as biomedical, apparel, and structural materials. This review outlines the definition of structural proteins, methods for characterizing structural proteins as polymeric materials, and potential applications. Structural proteins play an important role in shaping the skeletons and structures of cells, tissues, and organisms. This review outlines the definition of structural proteins, methods for characterizing structural proteins as polymeric materials, and potential applications.

Epoxidized soybean oil grafted with CTBN as a novel toughener for improving the fracture toughness and mechanical properties of epoxy resin

Abstract: We prepared epoxidized soybean oil (ESO) grafted with carboxyl-terminated poly(acrylonitrile-co-butadiene) (CTBN) (ESO-g-CTBN) by a ring-opening reaction between the epoxide group and the carboxyl group. The structural features of the resulting product were determined using modern analytical techniques, such as Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR) spectroscopy, and gel permeation chromatography (GPC). The ESO-g-CTBN was applied as a toughener for an epoxy resin-based composite that was fabricated by blending the epoxy resin with diethylenetriamine (DETA) as the curing agent. The main aim of this procedure is to simultaneously improve the mechanical properties and fracture toughness of a bisphenol A-based epoxy resin. When 15 phr of ESO-g-CTBN was added to the EP/DETA mixture, the resin fracture toughness (KIC) and tensile strength increased from 0.65 to 1.09 MPa m1/2 and from 34.42 to 42.55 MPa, respectively. The ESO-g-CTBN existed in the EP matrix as a separate phase and induced an increase in the KIC via stopping crack growth or changing the crack direction. The epoxydized soybean oil grafted with CTBN (ESO-g-CTBN) was synthesized from ring opening reaction between epoxide group and carboxyl group. The ESO-g-CTBN help to improve the fracture toughness of epoxy resin by the mechanism as shown in the figure.

Modulation of the solid-state luminescent properties of conjugated polymers by changing the connecting points of flexible boron element blocks

Abstract: Flexible molecules are unfavorable for designing luminescent dyes because their excitation states rapidly decay through molecular motions. We recently found that some flexible boron complexes, which potentially show a larger degree of structural relaxation in the excited state, and their polymers exhibit unique optical properties with high environmental sensitivity, such as aggregation-induced emission and luminochromism triggered by external stimuli, upon the addition of structural restrictions. Moreover, these optical properties were drastically changed by modulating the connecting points in the polymers. In this review, recent progress in the development of luminescent polymer films with stimuli responsiveness is illustrated. In particular, the influence of the alteration of connecting points on luminescent behaviors is explained. Polymerization is a versatile strategy not only for transforming a class of nonemissive molecules into luminescent dyes but also for precisely regulating the optical properties of film materials; the resulting materials are promising for application as scaffolds for advanced chemical sensors. Recent progresses in the developments of luminescent polymer films with stimuli responsiveness are illustrated. In particular, the influence of the alteration of connecting points in polymers on luminescent behaviors is explained. It is demonstrated that polymerization is a versatile strategy not only for transforming a class of nonemissive flexible boron complexes to luminescent dyes but also for precisely regulating optical properties of film materials that are promised to be applied as a scaffold for advanced chemical sensors.

Self-assembly and hydrogel formation ability of Fmoc-dipeptides comprising α-methyl-L-phenylalanine

Abstract: Various biofunctional hydrogel materials can be fabricated in aqueous media through the self-assembly of peptide derivatives, forming supramolecular nanostructures and their three-dimensional networks. In this study, we describe the self-assembly of new Fmoc-dipeptides comprising α-methyl-L-phenylalanine. We found that the position and number of methyl groups introduced onto the α carbons of the Fmoc-dipeptides by α-methyl-L-phenylalanine have a marked influence on the morphology of the supramolecular nanostructure as well as the hydrogel (network) formation ability. This article describes the self-assembly of Fmoc-dipeptides comprising α-methyl-L-phenylalanine. The position and number of methyl groups introduced onto the α carbons of the Fmoc-dipeptides as α-methyl-L-phenylalanine have a marked influence on the morphology of supramolecular nanostructures and the hydrogel formation ability.

Biocompatibility and biodegradation of poly(lactic acid) (PLA) and an immiscible PLA/poly(ε-caprolactone) (PCL) blend compatibilized by poly(ε-caprolactone- b -tetrahydrofuran) implanted in horses

Abstract: This paper focuses on the biocompatibility and biodegradation of PLA and a recently developed PLA/PCL blend containing an in vitro nontoxic compatibilizer based on a low-molecular-weight triblock copolymer derived from e-caprolactone and tetrahydrofuran. The polymers were implanted subcutaneously in the lateral surface of the neck of horses. Physical examination, plasma fibrinogen (PF) analysis, infrared thermography (IT), mechanical nociceptive threshold (MNT) analysis, and ultrasonography were performed. After 24 weeks, the biomaterials were removed for histochemical analysis using hematoxylin-eosin (HE) and picrosirius-hematoxylin (PSH) staining. Scanning electron microscopy (SEM) was employed to determine changes in the surface morphology of the PLA and PLA/PCL blend. There were no clinical or PF changes. IT indicated a transient increase in cutaneous temperature (CT), while MNT decreased after the procedure in both the implanted groups. Ultrasonography revealed edema after the procedure and the loss of echogenicity of the polymers after implantation. Both polymers elicited a foreign body response under microscopic analysis. The PSH technique revealed a fibrotic reaction with collagen deposition around the polymers. SEM showed surface roughness, suggesting a biodegradation process. In conclusion, PLA and the PLA/PCL blend were biocompatible and biodegradable, with potential for use in equine medicine. We evaluated the biocompatibility and biodegradability of implants made of pure PLA and a PLA/PCL blend compatibilized with poly(ɛ-caprolactone-b-tetrahydrofuran) in horses by physical examination, plasma fibrinogen, thermographic, mechanical nociceptive threshold, and ultrasound tests. We also conducted histopathological and surface morphology analyses. Pure PLA and PLA/PCL blends subcutaneously implanted stimulated a minimal inflammatory response and supported cellular infiltration, being biocompatible and biodegradable in horses, with potential for use in equine medicine.

Effect of the silica-rubber interface on the mechanical, viscoelastic, and tribological behaviors of filled styrene-butadiene rubber vulcanizates

Abstract: In this research, the effects of the surface modification of silica by low-molecular-weight hydroxyl-terminated polybutadiene (HTPB) are compared with those of bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) on the mechanical, viscoelastic, and tribological properties of styrene-butadiene rubber (SBR) vulcanizates. Both modifiers have the ability to make covalent bonds with the rubber matrix, but with different interfacial characteristics controlling the final properties. The results displayed improvements in the tribological behavior of both modified silica-filled vulcanizates over pristine silica- and carbon black-filled vulcanizates. However, the HTPB modification method, despite providing a finer dispersion of the silica in the rubber, did not result in better tribological properties for the vulcanizates compared with those of the TESPT modification method. It was discussed that the HTPB modifier did not enhance tribological properties, especially abrasion resistance, as much as the TESPT modifier did because of the soft and flexible interface that was created in the presence of the HTPB modifier, in contrast to the rigid interface in the presence of TESPT. Molecular structure of silica surface modifiers greatly controls the performance of silica-filled styrene-butadiene rubber (SBR) through interfacial characteristics of the composites. Soft nature of low molecular-weight hydroxyl terminated polybutadiene (HTPB) and small number of its covalent bounds to the rubber matrix was compared with large number of rigid covalent bounds made between bis(3-triethoxysilylpropyl)tetrasulfide (TESPT) and rubber. Despite the better dispersion of silica modified with the former, the latter ensures higher transfer of stress to particles at large strains, inducing improved strength and abrasion resistance to composites.

Ring-opening (co)polymerization of γ -butyrolactone: a review

Abstract: With increased environmental concerns and the rising demands for sustainable polymers, e.g., degradable polymers and chemically recyclable polymers, studies on ring-opening polymerization (ROP) of cyclic esters have been developed in recent decades. Biorenewable five-membered γ-butyrolactone (γBL) may be a desirable feedstock for the chemical synthesis of poly(γ-butyrolactone) (PγBL) or for the incorporation of γBL units into polyester chains to modify their properties. Although γBL is traditionally considered to be “nonpolymerizable”, some progress was recently made concerning the ROP of γBL. This mini-review is thus specifically focused on the ROP of γBL and its copolymerization with other cyclic esters. Recent progress in ring-opening (co)polymerization of γ-butyrolactone (γBL) in the presence of various initiating/catalyst systems has been reviewed. Low reaction temperatures and high monomer concentrations are critical for the success of such polymerization, regardless of the different initiating/catalyst systems.

Direct (hetero)arylation polymerization: toward defect-free conjugated polymers

Abstract: In a very short time, direct (hetero)arylation polymerization (DHAP) has established itself as a valuable and atom-economical alternative to traditional cross-coupling methods such as the Migita–Stille and Suzuki-Miyaura polymerizations for the synthesis of low cost and efficient conjugated polymers for organic electronics. Because of sustained research efforts combining in-depth theoretical calculations, the development of new ligands and the careful fine-tuning of polymerization conditions, selectivity and reactivity issues should be soon a thing of the past. This focus review highlights the recent advances that lead to defect-free polymeric semiconductors and conductors and the current limitations and challenges of DHAP as it moves toward simultaneously becoming an industrially feasible, environmentally friendly, and synthetically powerful polymerization technique. The implementation of Direct Heteroarylation Polymerization (DHAP) in the synthesis of well-defined and defect-free materials for organic electronics is still in its early stages but giant leaps have been made over the past few years to improve and stir the selectivity of the reaction to avoid unwanted side-reaction such as β-branching or homocoupling. DHAP has proven to be an efficient, cost-effective, green and scalable polymerization method now competing or even surpassing well-established Suzuki-Miyaura or Migita–Stille cross-coupling polymerization methods. This focus review puts emphasis on the synthetic strategies that made DHAP successful.

Responsive laminarin-boronic acid self-healing hydrogels for biomedical applications

Abstract: The precise chemical modification of marine-derived biopolymers provides a unique opportunity for fabricating a toolbox of bioactive (bio)materials with modulated physicochemical and biological properties. Herein, the β-glucan laminarin was functionalized with phenylboronic acid (PBA) moieties that impart chemical reactivity toward diol-containing polymers via boronate esterification. The modification, which involved a two-pot reaction, was successfully confirmed by nuclear magnetic resonance spectroscopy. The resultant biopolymer readily established boronate ester-crosslinked hydrogels with poly(vinyl alcohol) (PVA) within seconds under physiological conditions. These hydrogels exhibited improved rheological properties, which were easily tunable, and revealed a rapid self-healing behavior upon rupture. Moreover, boronate ester bonds enabled the fabrication of reactive oxygen species-responsive and shear-thinning gels that can be administered in situ and respond to the oxidation state of the surrounding microenvironment. Importantly, due to the catalyst-free and mild-crosslinking conditions, the generated laminarin-PBA/PVA hydrogels did not show toxicity upon direct contact with preosteoblasts for up to 48 h, and thus constitute a promising platform for tissue engineering and drug delivery applications. The functionalization of laminarin with boronic acid groups was described. This biopolymer readily established boronate ester-crosslinked gels with poly(vinyl alcohol) within seconds under physiological conditions. The resultant hydrogels exhibited interesting self-healing properties, reactive oxygen species responsiveness and cytocompatibility.

Interconvertible and switchable cationic/PET-RAFT copolymerization triggered by visible light

Abstract: In this work, photoswitchable and interconvertible cationic/radical copolymerization was investigated by combining a Lewis acid-catalyzed cationic polymerization with a photoinduced electron/energy transfer (PET)-reversible addition-fragmentation transfer (RAFT) polymerization, in which the dormant terminal group of the RAFT polymerization was employed as the dual mediator for cationic and photoradical polymerizations. The photoredox catalyst, a zinc porphyrin complex (ZnTPP), was tested with a series of Lewis acids. When coupled with a boron-based Lewis acid, B(C6F5)3, the concurrent and interconvertible cationic/radical copolymerization of vinyl ether and methyl acrylate successfully proceeded in a controlled manner under visible light irradiation, in which the ratio of the generation of cationic and radical species was controlled by irradiation with different wavelengths of visible light. Photoswitchable and interconvertible cationic/radical copolymerization was investigated by combining a Lewis acid-catalyzed cationic polymerization with a photoinduced electron/energy transfer (PET)-reversible addition-fragmentation transfer (RAFT) polymerization, in which the dormant terminal group of the RAFT polymerization was employed as the dual mediator for cationic and photoradical polymerizations. Zinc porphyrin complex (ZnTPP) as the photoredox catalyst and bulky boron-based Lewis acid, B(C6F5)3, was successfully combined to induce the concurrent and interconvertible cationic/radical copolymerization of vinyl ether and methyl acrylate under visible light irradiation.

Photomechanical materials driven by photoisomerization or photodimerization

Abstract: Light is an adjustable, multiparameter stimulus that can be used for fine, noncontact manipulation or as an energy supply. Recently, deformable light-controlled macroscopic materials have gained attention both from a fundamental research perspective and for various actuator applications. The main challenge in developing these materials is converting the photoinduced effects at the molecular level to macroscopic movements in the working pieces; a variety of mechanisms have been proposed for this. Both crystals and polymers containing photoreactive compounds have been intensively studied and have exhibited different advantages. Crosslinked liquid crystalline polymers have also attracted attention because they combine the advantages of macroscopically deformable polymers and crystals. In most circumstances, photodeformable materials contain photoreactive molecules that absorb light of a specific wavelength and thus undergo structural changes. This is followed by concomitant changes in their physical and chemical properties, resulting in macroscopic mechanical movements. Therefore, various photoreactions have been studied to induce macroscopic deformations using light. The purpose of this review is to highlight key examples in the design of photodeformable materials using various photoreactions and to introduce some new and evolving trends by highlighting recent research. Macroscopic deformable materials controlled by light have been the subject of growing research interest in the last few decades due to both their fundamental properties and their wide applicability. In this review, examples of photomechanical effects in crystals, polymers, and CLCPs based on photoisomerization and photodimerization are reviewed.

Cyclodextrin-based nanoparticles encapsulating α-mangostin and their drug release behavior: potential carriers of α-mangostin for cancer therapy

Abstract: α-Mangostin (MGS), an anti-cancer compound, is a xanthone derivative and is extracted from the pericarps of mangosteen. MGS exhibits a variety of bioactivities, such as antioxidant, cytotoxic, anti-inflammatory, and antibacterial effects, as well as anticancer activity. However, MGS has not been approved for clinical use because of its poor bioavailability. There have been many efforts to solve this problem by use of drug carriers. Cyclodextrins (CDs) are well known as nontoxic and biodegradable drug carriers and can encapsulate MGS. In this study, we prepared CD-based nanoparticles (CDNPs) by a polyaddition reaction using epichlorohydrin and characterized them by dynamic light scattering and static light scattering coupled with fractionation. The encapsulation of MGS into CDNPs was examined, and we found that the loading ratio of MGS for CDNPs is much higher than that for CDs themselves. The cytotoxicity of the CDNP/MGS complex was examined, indicating the potential of CDNP as a carrier of MGS. In this study, we synthesized and characterized cyclodextrin-based nanoparticles (CDNPs) by polyaddition reactions using epichlorohydrin and three different type of CDs (α-, β-, and γ-CD). We found that cyclodextrin tended to cover surface of our nanoparticles; while epichlorohydrin network enlarged when weight ratio of epichlorohydrin/cyclodextrin increased. Our CDNPs demonstrated a very high loading ratio against α-mangostin (MGS), and getting close to 1:1 ratio.

Intracellular self-assembly of supramolecular gelators to selectively kill cells of interest

Abstract: The significant progress in supramolecular chemistry since the end of last century includes the development of supramolecular gels. In particular, the spatiotemporal self-assembly of synthetic small gelator molecules has attracted increasing attention owing to their ability to achieve certain functional properties in a designated space at a designated time. Peptides conjugated with hydrophobic moieties are typical examples of supramolecular gelators (low molecular weight gelators, LMWGs), which can be designed or programmed to self-assemble to form nanofibers/nanosheets in response to a broad range of stimuli or microenvironments. In the last decade, several groups have reported that the self-assembly of small gelator molecules achieved inside living cells or on the surfaces of living cells induced selective cell death, which would lead to a novel therapeutic approach or a novel cell selection tool. This focused review outlines the self-assembly of small gelator molecules inside living cells that control cell fate. Peptides conjugated with hydrophobic moieties are typical examples of supramolecular gelators (low molecular weight gelators, LMWGs), which can be designed or programmed to self-assemble to form nanofibers/nanosheets in response to stimuli or microenvironments. In the last decade, several groups have reported that the self-assembly of small gelator molecules achieved inside living cells or on the surfaces of living cells induced selective cell death. This focused review outlines the self-assembly of small gelator molecules inside or around living cells that control cell fate.

Development of a superabsorbent polymer using iodine transfer polymerization

Abstract: We succeeded in developing a novel class of acrylic acid (AA)-based superabsorbent polymers (SAPs) with remarkably improved absorption performance by applying iodine transfer polymerization (ITP). A specific organoiodine chain transfer agent was newly developed and found to provide moderate to good control over the polymerization of AA in aqueous solution. Dynamic light scattering (DLS) measurements revealed that the polymer network prepared using our ITP technology is relatively homogeneous. Our new SAP exhibits a good balance between absorption capacity and gel strength, and it enables a quick response to diversified customer needs in the diaper industry. To the best of our knowledge, this work is the first case in which reversible-deactivation radical polymerization (RDRP) has been practically applied to commodity polymer products. This review focuses on how we connected the old but highly practical ITP and SAP production. This review summarizes the successful development and commercialization of a superabsorbent polymer (SAP) using iodine transfer polymerization (ITP). We found that the overall absorption performance of the SAP was improved by applying ITP and that this improvement was related to the homogenization of the polymer network. This innovation enables the quick response to diversified customer needs in the diaper industry. We believe that this achievement will contribute to improving the quality of life of people around the world.

Characterization of 3D matrix conditions for cancer cell migration with elasticity/porosity-independent tunable microfiber gels

Abstract: The mechanics and architectures of the extracellular matrix (ECM) critically influence 3D cell migration processes, such as cancer cell invasion and metastasis. Understanding the roles of mechanical and structural factors in the ECM could provide an essential basis for cancer treatment. However, it is generally difficult to independently characterize these roles due to the coupled changes in these factors in conventional ECM model systems. In this study, to solve this problem, we developed elasticity/porosity-tunable electrospun fibrous gel matrices composed of photocrosslinked gelatinous microfibers (nanometer-scale-crosslinked chemical gels) with well-regulated bonding (tens-of-micron-scale fiber-bonded gels). This system enables independent modulation of microscopic fiber elasticity and matrix porosity, i.e., the mechanical and structural conditions of the ECM. The elasticity of fibers was tuned with photocrosslinking conditions. The porosity was regulated by changing the degree of interfiber bonding. The influences of these factors of the fibrous gel matrix on the motility of MDA-MB-231 tumorigenic cells and MCF-10A nontumorigenic cells were quantitatively investigated. MDA-MB-231 cells showed the highest degree of MMP-independent invasion into the matrix composed of fibers with a Young’s modulus of 20 kPa and a low degree of interfiber bonding, while MCF-10A cells did not show invasive behavior under the same matrix conditions. To understand the roles of mechanical and structural factors in the extracellular matrix on cancer cell migration, elasticity/porosity-tunable gel matrices of gelatinous microfibers were developed. The elasticity of fibers and the porosity of matrix were tuned with photocrosslinking conditions and degree of interfiber bonding, respectively. Highly malignant MDA-MB-231 cells showed the highest degree of MMP-independent invasion into the matrix composed of fibers with a Young’s modulus of 20 kPa and a low degree of interfiber bonding, while nontumorigenic MCF-10A cells did not show invasive behavior under the same matrix conditions.

Delocalization boosts charge separation in organic solar cells

Abstract: Organic solar cells (OSCs) utilizing π-conjugated polymers have attracted widespread interest over the past three decades because of their potential advantages, including low weight, thin film flexibility, and low-cost manufacturing. However, their power conversion efficiency (PCE) has been far below that of inorganic analogs. Geminate recombination of charge transfer excitons is a major loss process in OSCs. This paper reviews our recent progress in using transient absorption spectroscopy to understand geminate recombination in bulk heterojunction OSCs, including the impact of polymer crystallinity on charge generation and dissociation mechanisms in nonfullerene acceptor-based OSCs. The first example of a high PCE with a small photon energy loss is also presented. The importance of delocalization of the charge wave function to suppress geminate recombination is highlighted by this focus review. When light is shined on semiconducting polymers, singlet excitons are promptly generated in organic solar cells. At a donor–acceptor heterojunction, excitons separate into holes on the donor and electrons on the acceptor as a result of the energetic offset of the molecular orbital. If the electron and hole separate further, they become free from Coulombic attraction and hence survive up to nano- or microseconds, long enough to be transported to each electrode. Otherwise, the geminate electron–hole pairs are likely to recombine to the ground state.

Dressing up artificial viral capsids self-assembled from C-terminal-modified β-annulus peptides

Abstract: A variety of chemical approaches for the rational design of artificial proteins and peptides have been developed in recent years for the construction of self-assembled nanocapsules. It was previously found that a synthetic 24-mer β-annulus peptide, which participates in the formation of the dodecahedral internal skeleton of the tomato bushy stunt virus capsid, spontaneously self-assembled into artificial viral capsids with a size of 30–50 nm. These artificial viral capsids were established to encapsulate various guest molecules, such as anionic dyes, DNA, quantum dots, and His-tagged proteins. The artificial viral capsids could also be dressed up with gold nanoparticles, single-stranded DNA, coiled-coil spikes, and proteins by modifying with these molecules at the C-terminus of β-annulus peptides. The artificial viral capsids were notably stabilized by dressing up with human serum albumin and acquired enzymatic activity by dressing up with ribonuclease. It was found that a synthetic 24-mer β-annulus peptide, which participates in the formation of the dodecahedral internal skeleton of the tomato bushy stunt virus capsid, spontaneously self-assembled into artificial viral capsids with a size of 30–50 nm. The artificial viral capsids could be dressed up with gold nanoparticles, single-stranded DNA, coiled-coil spikes, and proteins by modifying with these molecules at the C-terminus of β-annulus peptides. The artificial viral capsids were notably stabilized by dressing up with human serum albumin and acquired enzymatic activity by dressing up with ribonuclease.

Dodecyl sulfate-doped polypyrrole derivative grains as a light-responsive liquid marble stabilizer

Abstract: Polypyrrole, poly(N-methyl pyrrole) and poly(N-ethyl pyrrole) grains were synthesized by aqueous chemical oxidative polymerization in the presence of sodium dodecyl sulfate as both a dopant and a hydrophobizing agent. The resulting grain products were characterized in terms of their size, morphology, surface and bulk chemical compositions, hydrophilic–hydrophobic balance, (photo)thermal property, and conductivity. Scanning electron microscopy studies indicated that the grains were aggregates of atypical particles with submicrometer size. Elemental microanalysis and thermogravimetric analysis confirmed the production of dodecyl sulfate-doped polypyrrole, poly(N-methyl pyrrole) and poly(N-ethyl pyrrole) materials, and they showed near-infrared light-to-heat photothermal properties, which was confirmed by thermography. The data obtained through X-ray photoelectron spectroscopy indicated the presence of dodecyl sulfate dopants on the surface of the grains. The dried polypyrrole and poly(N-ethyl pyrrole) grains showed hydrophobic character, and therefore, they can adsorb to the air–water interface and act as a light-responsive liquid marble stabilizer. Locomotion of the liquid marble can be driven by near-infrared laser irradiation-induced Marangoni flow on a planar air–water surface. The release of internal liquid can be achieved by controlled disruption of liquid marbles via external stimulus application. Polypyrrole and poly(N-alkyl pyrrole) grains were synthesized by aqueous chemical oxidative polymerization in the presence of sodium dodecyl sulfate as both a dopant and a hydrophobizing agent. The dried polypyrrole and poly(N-ethyl pyrrole) grains showed hydrophobic character and can act as a light-responsive liquid marble stabilizer. Locomotion of the liquid marble can be driven by near-infrared laser irradiation-induced Marangoni flow on a planar air–water surface. Furthermore, the release of internal liquid can be achieved by controlled disruption of liquid marbles via external stimulus application.

Effect of UV-curing conditions on the polymer structures: a comparison between coating and adhesive

Abstract: Radical photopolymerization of acrylate was carried out without a degassing process under conditions suitable for UV-curable coatings and UV-curable adhesives. We examined the differences in the resulting polymer structures obtained from the coating and adhesive by employing the same formulation. 2,2-Dimethoxy-2-phenylacetophenone was employed as a photoinitiator. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products. On the other hand, the UV-curable adhesive yielded a multitude of polymers that were terminated by disproportionation. In the latter case, some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group as the terminal group. We examined the differences between the resulting polymer structures in the cases of a coating and an adhesive employing the same formulation. The UV-curable coating yielded polymers terminated by either a hydroxyl group or a terminal carbonyl group as the main products, suggesting that bimolecular termination was strongly inhibited by oxygen. On the other hand, the UV-curable adhesive yielded a multitude of disproportionation products, whereas some polymers underwent hydrogen abstraction from the polymer backbone, resulting in β-scission of the midchain radical to generate polymers with an α-substituted acryloyl group.

Robust hydrogel–bioceramics composite and its osteoconductive properties

Abstract: Due to the soft and wet characteristics of hydrogels that acquire high mechanical strength by toughening strategies, tough and robust hydrogels are attractive as next-generation structural biomaterials, especially for the substitution of soft connective tissues such as cartilage, tendons, and ligaments. Firm fixation of the gels to bone in vivo is an indispensable technology in clinical applications. However, since the surface of the hydrogel is very watery, current medical adhesives cannot fix the gels at all. In this review, first, the double network (DN) strategy, a universal method to toughen hydrogels, is presented. Second, by combining hydroxyapatite (HAp) of a main bony inorganic component with a high-strength DN gel, a biocompatible adhesion method accompanied by spontaneous osteogenesis penetration into the gel matrix is introduced. In addition, the HAp-gel composite can be used as a simplified model of bone tissues because of their similarity in terms of components. Third, HAp formation spatially confined by the polymer network of gel is shown as a model of the earliest stage of biomineralization in vivo. These studies on biomineral–hydrogel composites have great potential to contribute not only basic research on osteogenesis mechanisms but also clinical applications of tough hydrogels. Double network (DN) gel - hydroxyapatite (HAp) composite achieves robust fixation to bone tissue accompanied by spontaneous osteogenesis penetration into the gel matrix. In addition, the HAp-DN gel composite can be used as a simplified model of bone tissues because of their similarity in terms of components. The HAp orientation is regulated by the anisotropy of the polymer network of gel, implying that the collagen matrix is oriented in the earliest stage of biomineralization in vivo.

Extended-chain crystallization and stereocomplex formation of polylactides in a Langmuir monolayer

Abstract: Polylactide (PLA) forms an extended-chain crystal (ECC) in a Langmuir monolayer. Therefore, the chain packings in crystals can be identified by simply evaluating the crystal sizes. Initially, we confirmed ECC formation and found that the lamella thicknesses were proportional to the molecular weight, although they were ~80% of the thickness expected for the chain conformation. Atomic force microscopy images indicated that the chains were tilted counterclockwise and clockwise for poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), respectively, in the lamella and that the length along the chain direction was in good agreement with the length expected for the chain conformation. A mixture of a high-molecular-weight (HMW) PDLA and a low-molecular-weight (LMW) PDLA was found to crystallize sequentially to form macroscopically separated crystals, although the individual crystalline behavior was almost the same according to the surface pressure–area isotherms. Furthermore, we studied the stereocomplex (SC) formation and found that the SC also formed as an extended-chain SC (ECSC), molecular structure of which was successfully visualized. A mixture of an HMW-PLLA and an LMW-PDLA was found to form an SC, the size of which was determined by the extended LMW-PDLA chains, and the HMW-PLLA chains were predicted to be folded and packed in the SC. Polylactide (PLA) formed an extended-chain crystal (ECC) and an extended-chain stereocomplex (ECSC) in Langmuir monolayers. Therefore, the chain packings in crystals and SCs could be identified by simply evaluating their sizes. A mixture of a high-molecular-weight (HMW) PDLA and a low-molecular-weight (LMW) PDLA was found to crystallize separately, while a mixture of an HMW-PLLA and an LMW-PDLA was found to form an SC composed of the extended LMW-PDLA chains and the folded HMW-PLLA chains. Furthermore, the molecular structure of SC was successfully visualized at the molecular level by AFM.

Synthesis of sequence-controlled polymers via sequential multicomponent reactions and interconvertible hybrid copolymerizations

Abstract: Synthesizing artificial polymers with precise sequence structures, such as their biological analogues, is a serious challenge and of great importance in polymer science. Recently, step-growth polymerization and chain growth polymerization have been the main synthesis methods for preparing artificial sequence-regulated polymers. However, it is difficult to obtain sequence-controlled polymers with sufficient molecular diversity via step-growth polymerization; on the other hand, chain-growth polymerization generally requires laborious repetitive monomer feeding. In this focus review, the sequential multicomponent reactions for preparing periodic sequence-controlled polymers with sufficient molecular diversity and complexity and the interconvertible hybrid copolymerizations producing hybrid multiblock copolymers rapidly in one pot are highlighted. We have developed sequential multicomponent reaction and interconvertible hybrid copolymerization methods to prepare sequence-controlled polymers. The sequential multicomponent reaction combines more than two different multicomponent reactions in one pot to prepare periodic sequence˗controlled polymers with sufficient molecular diversity. The interconvertible hybrid copolymerization method uses trithiocarbonate compounds to combine radical polymerization of vinyl monomers and anionic ring-opening polymerization of thiirane monomers, resulting in hybrid multiblock sequence-regulated polymers.