Ionogels: recent advances in design, material properties and emerging biomedical applications.

Ionic liquid (IL)-based gels (ionogels) have received considerable attention due to their unique advantages in ionic conductivity and their biphasic liquid-solid phase property. In ionogels, the negligibly volatile ionic liquid is retained in the interconnected 3D pore structure. On the basis of these physical features as well as the chemical properties of well-chosen ILs, there is emerging interest in the anti-bacterial and biocompatibility aspects. In this review, the recent achievements of ionogels for biomedical applications are summarized and discussed. Following a brief introduction of the various types of ILs and their key physicochemical and biological properties, the design strategies and fabrication methods of ionogels are presented by means of different confining networks. These sophisticated ionogels with diverse functions, aimed at biomedical applications, are further classified into several active domains, including wearable strain sensors, therapeutic delivery systems, wound healing and biochemical detections. Finally, the challenges and possible strategies for the design of future ionogels by integrating materials science with a biological interface are proposed.

Air-Tolerant Reversible Complexation Mediated Polymerization (RCMP) Using Aldehyde.

An air-tolerant reversible complexation mediated polymerization (RCMP) technique, which can be carried out without prior deoxygenation, is developed. The system contains a monomer, an alkyl iodide initiating dormant species, air (oxygen), an aldehyde, N-hydroxyphthalimide (NHPI), and a base. Oxygen is consumed via the NHPI-catalyzed conversion of the aldehyde (RCHO) to a carboxylic acid (RCOOH). The generated RCOOH is further converted to a carboxylate anion (RCOO- ) by the base. The RCOO- generated in situ works as an RCMP catalyst; the polymerization proceeds with the monomer, alkyl iodide dormant species, and RCOO- catalyst. Thus, the system is not only air-tolerant but also does not require additional RCMP catalysts, which is a notable feature of this system. (NHPI is used as an oxidation catalyst for converting RCHO to RCOOH.) This technique is amenable to methyl methacrylate, butyl methacrylate, benzyl methacrylate, 2-hydroxyethyl methacrylate, and styrene, yielding polymers with relatively low-dispersity (Mw /Mn  = 1.20-1.49), where Mw and Mn are the weight- and number-average molecular weights, respectively.

Solid-Phase Radical Polymerization of Halogen-Bond-Based Crystals and Applications to Pre-Shaped Polymer Materials.

Liquid vinyl monomers were converted into solid crystals via halogen bonding. They underwent solid-phase radical polymerizations through heating at 40 °C or ultraviolet photo-irradiation (365 nm). The X-ray crystallography analysis showed the high degree of monomer alignment in the crystals. The polymerizations of the solid monomer crystals yielded polymers with high molecular weights and relatively low dispersities because of the high degree of the monomer alignment in the crystal. As a unique application of this system, the crystalized monomers were assembled to pre-determined structures, followed by solid-phase polymerization, to obtain a two-layer polymer sheet and a three-dimensional house-shaped polymer material. The two-layer sheet contained a unique asymmetric pore structure and exhibited a solvent-responsive shape memory property and may find applications to asymmetric membranes and polymer actuators.

Metal-Free Fast Azidation by Using Tetrabutylammonium Azide: Effective Synthesis of Alkyl Azides and Well-Defined Azido-End Polymethacrylates.

An effective method to synthesize azido-end polymethacrylates from tetrabutylammonium azide (BNN3 ) in a nonpolar solvent (toluene) was developed. Several low-mass alkyl halides were reacted with BNN3 in toluene as model reactions and the rate constants of these reactions were determined, to confirm fast BNN3 azidation for tertiary and secondary halides. The end-group transformation of halide-end polymethacrylates was effective and nearly quantitative. Notably, the combination of organocatalyzed living (or reversible deactivation) radical polymerization and BNN3 azidation enabled the metal-free synthesis of azido-end polymethacrylates, including single-azido-end and multi-azido-end functional homopolymers and block copolymers. The rapid and quantitative reaction without the requirement for a large excess of BNN3 , metal-free and polar-solvent-free nature, and broad polymer scope are attractive features of this azidation.

Polymer Dispersity Control by Organocatalyzed Living Radical Polymerization.

Molecular weight distribution of polymers, termed dispersity (D), is a fundamental parameter for determining polymer material properties. This paper reports a novel approach for controlling D by exploiting a temperature-selective radical generation in organocatalyzed living radical polymerization. The polymers with tailored D were synthesized in a batch system without the assistance of an external pump. A unique aspect of this approach is that D was tuneable from 1.11 to 1.50 in any segment in diblock, triblock, and multiblock copolymers and in any form of star and brush polymer without segmental or topological restriction. This approach is amenable to various monomers and free from metals and thus attractive for applications. The approach also generated polymer brushes on surfaces with tailored D. An interesting finding was that the polymer brushes exhibited unique interaction with external molecules, depending on the D value.

Facile Fabrication of Concentrated Polymer Brushes with Complex Patterning by Photocontrolled Organocatalyzed Living Radical Polymerization.

Photocontrolled surface-initiated reversible complexation mediated polymerization (photo-SI-RCMP) was successfully applied to fabricate concentrated polymer brushes with complex patterning structures. Positive-type patterned polymer brushes were obtained by photo-SI-RCMP under visible light (550(±50) nm) using photomasks. A particularly interesting finding was that negative-type patterned polymer brushes were also obtainable in a facile manner. A nonspecial UV light (250-385 nm) enabled the preparation of pre-patterned initiator surfaces in a remarkably short time (1 min), leading to negative-type patterned polymer brushes. Based on this unique selectivity between visible and UV light, the combination of two patterning techniques enabled the preparation of complex patterned brushes, including diblock copolymers, binary polymers, and functional binary polymers, without multistep immobilization of one or more initiators on the surfaces.

Temperature-Selective Dual Radical Generation from Alkyl Diiodide: Applications to Synthesis of Asymmetric CABC Multi-Block Copolymers and Their Unique Assembly Structures.

Temperature-selective radical generation from a newly designed alkyl diiodide (I-R2 -R1 -I) was studied. R1 -I and I-R2 had different reactivities for generating alkyl radicals in the presence of a tetraoctylammonium iodide (ONI) catalyst. Taking advantage of the temperature selectivity, we used the alkyl diiodide as a dual initiator in ONI-catalyzed living radical polymerization to uniquely synthesize CABC non-symmetric multi-block copolymers. Because of their non-symmetric structure, CABC multi-block copolymers form unique assemblies, that is, Janus-type particles with hetero-segment coronas and flower-like particles with hetero-segment petals.

Solvent-Selective Reactions of Alkyl Iodide with Sodium Azide for Radical Generation and Azide Substitution and Their Application to One-Pot Synthesis of Chain-End-Functionalized Polymers.

Herein, a new reaction of an alkyl iodide (R-I) with an azide anion (N3-) to reversibly generate the corresponding alkyl radical (R•) is reported. Via this new reaction, N3- was used as an efficient catalyst in living radical polymerization, yielding a well-defined polymer-iodide. A particularly interesting finding was the solvent selectivity of this reaction; namely, R-I and N3- generated R• in nonpolar solvents, while the substitution product R-N3 was generated in polar solvents. Exploiting this unique solvent selectivity, a one-pot synthesis of polymer-N3 was attained. N3- was first used as a catalyst for living radical polymerization in a nonpolar solvent to produce a polymer-iodide and was subsequently used as a substitution agent in a polar solvent by simply adding the polar solvent, thereby transforming the polymer-iodide to polymer-N3 in one pot. This one-pot synthesis was further applied to obtain N3-chain-end-functionalized polymer brushes on the surface, uniquely controlling the N3 coverage (number density). Using the chain-end N3, the obtained linear and brush polymers were connected to functional molecules via an azide-alkyne click reaction. The attractive features of this system include facile operation, access to unique polymer designs, and no requirement for using excess NaN3. In addition to N3-, thiocyanate (-SCN) and cyanate (-OCN) anions were also studied.

2D conjugated microporous polyacetylenes synthesized via halogen-bond-assisted radical solid-phase polymerization for high-performance metal-ion absorbents.

The paper reports the first free-radical solid-phase polymerization (SPP) of acetylenes. Acetylene monomers were co-crystalized using halogen bonding, and the obtained cocrystals were polymerized. Notably, because of the alignment of acetylene monomers in the cocrystals, the adjacent C≡C groups were close enough to undergo radical polymerization effectively, enabling the radically low-reactive acetylene monomers to generate high-molecular-weight polyacetylenes that are unattainable in solution-phase radical polymerizations. Furthermore, the SPP of a crosslinkable diacetylene monomer yielded networked two-dimensional conjugated microporous polymers (2D CMPs), where 2D porous polyacetylene nanosheets were cumulated in layer-by-layer manners. Because of the porous structures, the obtained 2D CMPs worked as highly efficient and selective adsorbents of lithium (Li+) and boronium (B3+) ions, adsorbing up to 312 mg of Li+ (31.2 wt%) and 196 mg of B3+ (19.6 wt%) per 1 g of CMP. This Li+ adsorption capacity is the highest ever record in the area of Li+ adsorption.

Surface antimicrobial functionalization with polymers: fabrication, mechanisms and applications.

Undesirable adhesion of microbes such as bacteria, fungi and viruses onto surfaces affects many industries such as marine, food, textile, and healthcare. In particular in healthcare and food packaging, the effects of unwanted microbial contamination can be life-threatening. With the current global COVID-19 pandemic, interest in the development of surfaces with superior anti-viral and anti-bacterial activities has multiplied. Polymers carrying anti-microbial properties are extensively used to functionalize material surfaces to inactivate infection-causing and biocide-resistant microbes including COVID-19. This review aims to introduce the fabrication of polymer-based antimicrobial surfaces through physical and chemical modifications, followed by the discussion of the inactivation mechanisms of conventional biocidal agents and new-generation antimicrobial macromolecules in polymer-modified antimicrobial surfaces. The advanced applications of polymer-based antimicrobial surfaces on personal protective equipment against COVID-19, food packaging materials, biomedical devices, marine vessels and textiles are also summarized to express the research trend in academia and industry.

Flexible polymeric patch based nanotherapeutics against non-cancer therapy.

Flexible polymeric patches find widespread applications in biomedicine because of their biological and tunable features including excellent patient compliance, superior biocompatibility and biodegradation, as well as high loading capability and permeability of drug. Such polymeric patches are classified into microneedles (MNs), hydrogel, microcapsule, microsphere and fiber depending on the formed morphology. The combination of nanomaterials with polymeric patches allows for improved advantages of increased curative efficacy and lowered systemic toxicity, promoting on-demand and regulated drug administration, thus providing the great potential to their clinic translation. In this review, the category of flexible polymeric patches that are utilized to integrate with nanomaterials is briefly presented and their advantages in bioapplications are further discussed. The applications of nanomaterials embedded polymeric patches in non-cancerous diseases were also systematically reviewed, including diabetes therapy, wound healing, dermatological disease therapy, bone regeneration, cardiac repair, hair repair, obesity therapy and some immune disease therapy. Alternatively, the limitations, latest challenges and future perspectives of such biomedical therapeutic devices are addressed.

Polyelectrolyte Hydrogels for Tissue Engineering and Regenerative Medicine.

Polyelectrolyte hydrogels are emerging materials for tissue engineering and regenerative medicine applications due to their tunable biochemical properties, electrical conductivity, biocompatibility and similar network structure to the extracellular matrix in mammalian bodies. In this review, representative polyelectrolyte hydrogels carrying anionic, cationic, ampholytic, zwitterionic and ionic liquid moieties are systemically cataloged to express their chemical structures and preparation strategies. Recent advance of polyelectrolyte hydrogels in tissue engineering and regenerative medicine for drug delivery, skin healing, bone regeneration, cardiac tissue repair and anti-biofouling coating are also highlighted. Eventually, the outlook and challenges of polyelectrolyte hydrogels and their biomedical material applications are also discussed to offer future directions.

One Reagent with Two Functions: Simultaneous Living Radical Polymerization and Chain-End Substitution for Tailoring Polymer Dispersity.

The molecular weight distribution of polymer, termed dispersity (D), is a fundamental parameter that determines polymer properties. Sodium azide (NaN3) functions as a catalyst in organocatalyzed living radical polymerization when the reaction medium is nonpolar. In contrast, NaN3 can act as a nucleophile when the reaction medium is polar. In this paper, we report an efficient approach to dispersity control by exploiting the dual functions of NaN3 under the varied solvent polarity. Simultaneous polymerization and chain-end substitution allowed us to tune the D values of various polymethacrylates and poly(butyl acrylate). Notably, the D value could be tuned to a wide range approximately from 1.2 to 2.0 for polymethacrylates and to 3.8 for poly(butyl acrylate). This approach afforded polymer brushes on surfaces with tailored D values. An interesting finding was that the polymer brushes exhibited a unique interaction with external molecules, depending on the D value.

Microscopically tuning the graphene oxide framework for membrane separations: a review.

Membrane-based separations have been widely applied in gas, water and organic solvent purifications to reduce energy consumption and minimize environmental pollution. In recent years, graphene oxide (GO) membranes have attracted increasing attention due to their self-assembly ability and excellent stability. In this review, publications within the last 3 years on microscopically tuning the GO framework are summarized and reviewed. Various materials, including organic molecules, polymers, inorganic particles, ions and 2D materials, have been deployed to intercalate with GO nanosheets. Due to the varied interlayer spacing and packing structure, the developed GO composites exhibit enhanced stabilities and separation performances. In addition, designing horizontal GO membranes and functionalizing GO nanosheets have also been reported to improve the performance. This review sheds light on the techniques to microscopically tune the GO framework and the resulting macroscopic changes in membrane properties and performances.

Current Research Trends and Perspectives on Solid-State Nanomaterials in Hydrogen Storage.

Hydrogen energy, with environment amicable, renewable, efficiency, and cost-effective advantages, is the future mainstream substitution of fossil-based fuel. However, the extremely low volumetric density gives rise to the main challenge in hydrogen storage, and therefore, exploring effective storage techniques is key hurdles that need to be crossed to accomplish the sustainable hydrogen economy. Hydrogen physically or chemically stored into nanomaterials in the solid-state is a desirable prospect for effective large-scale hydrogen storage, which has exhibited great potentials for applications in both reversible onboard storage and regenerable off-board storage applications. Its attractive points include safe, compact, light, reversibility, and efficiently produce sufficient pure hydrogen fuel under the mild condition. This review comprehensively gathers the state-of-art solid-state hydrogen storage technologies using nanostructured materials, involving nanoporous carbon materials, metal-organic frameworks, covalent organic frameworks, porous aromatic frameworks, nanoporous organic polymers, and nanoscale hydrides. It describes significant advances achieved so far, and main barriers need to be surmounted to approach practical applications, as well as offers a perspective for sustainable energy research.

Multistimuli Responsive Reversible Cross-Linking-Decross-Linking of Concentrated Polymer Brushes.

Poly(furfuryl methacrylate) (PFMA) brushes were cross-linked using bismaleimide cross-linkers via the Diels-Alder (DA) reaction at 70 °C, generating cross-linked PFMA brushes (PFMA brush gels). The cross-linked PFMA brushes were decross-linked at 110 °C via the retro-Diels-Alder (rDA) reaction, offering the temperature-responsive reversible PFMA brush gels. The wettability of the brush was tunable by cross-linking and decross-linking. The use of a disulfide containing bismaleimide as a cross-linker gave the S-S bond at the cross-linking point. The S-S bond was cleaved upon thermal or photo stimulus and regenerated through oxidative stimulus, offering another reversible decross-linking/cross-linking pathway of the PFMA brush gel. The use of photo stimulus together with photomasks further offered patterned brushes with the cross-linked and decross-linked domains. The combination of the DA/rDA reactions and the reversible S-S bond cleavage provided multistimuli-responsive brush gels for switching the surface properties in unique manners. The reversible cross-linking, multiresponsiveness, access to patterned structures, and metal-free synthetic procedure are attractive features in the present approach for creating smart functional surfaces.

Effective Synthesis of Patterned Polymer Brushes with Tailored Multiple Graft Densities.

This paper reports an effective method to prepare patterned polymer brushes on surfaces with tailored graft densities. High-density (concentrated), moderate-density (semidiluted), and low-density (diluted) polymer brushes were fabricated in patterned manners, offering defined three-dimensional patterned structures. This method uses a middle/near-UV (≥250 nm) lamp and needs only a short time (≤10 min) to fabricate prepatterns of the initiator, in sharp contrast to the previous high-energy lithography and time-consuming processes. The obtained patterned brush served as a molecular (protein) repellent/adsorptive interface based on a graft-density-dependent size-exclusion effect. This method is facile and accessible to wide ranges of tunable density and pattern shapes, which are attractive for extensive use.

Biocompatible Choline Iodide Catalysts for Green Living Radical Polymerization of Functional Polymers.

Herein, nontoxic and metabolizable choline iodide analogues, including choline iodide, acetylcholine iodide, and butyrylcholine iodide, were successfully utilized as novel catalysts for "green" living radical polymerization (LRP). Through the combination of several green solvents (ethyl lactate, ethanol, and water), this green LRP process yielded low-polydispersity hydrophobic, hydrophilic, zwitterionic, and water-soluble biocompatible polymethacrylates and polyacrylates with high monomer conversions. Well-defined hydrophobic-hydrophilic and hydrophilic-hydrophilic block copolymers were also synthesized. The accessibility to a range of polymer designs is an attractive feature of this polymerization. The use of nontoxic choline iodide catalysts as well as green polymerization conditions can contribute to sustainable polymer chemistry.

Photo-selective chain end transformation of polyacrylate-iodide using cysteamine and its application to facile single-step preparation of patterned polymer brushes.

Cysteamine, which is an inexpensive and non-toxic aminothiol, was successfully employed as a photo-selective chain end transformation agent of iodo-terminated polymer chains (polymer-I). Polymer-I was selectively transformed to hydrogen-terminated (polymer-H) and thiol-terminated (polymer-SH) polymers with and without UV irradiation, respectively. This method is applicable to acrylate polymers. This photo-selective reaction offered a single-step preparation of patterned polymer brushes with SH and H chain end functionalities as a unique application.

Synthesis of Highly Reactive Polymer Nitrile N-Oxides for Effective Solvent-Free Grafting.

A one-pot synthesis of polymer nitrile N-oxides was achieved via the Michael addition of living polymer anions derived from vinyl monomers to commercially available trans-ß-nitrostyrene and subsequent dehydration with concd H2SO4. The polymer nitrile N-oxides are effective as grafting agents in catalyst- and solvent-free 1,3-dipolar cycloadditions to unsaturated-bond-containing polymers with high conversion and exhibit higher reactivity compared to that of nitrile N-oxides prepared from 1,1-diphenylnitroethene. Application to the preparation of a functional glass surface was demonstrated using PtBMA nitrile N-oxide as a grafting agent.