50th Anniversary Perspective: Advanced Polymer Fibers: High Performance and Ultrafine

Peptide-conjugated alginate fiber: A skeletal muscle regenerative scaffold

Biopolymeric fibers have garnered significant attention in biomedical applications due to their ability to promote tissue regeneration through aligned microstructures. Alginate (Alg) is commonly used to prepare wet-spun fibers through ionic interactions. However, ion-crosslinked Alg fibers present limitations in tissue regeneration due to their rapid degradation under physiological conditions and the absence of binding sites for bioactive molecules. In this study, oxidized methacrylated alginate (OMA) derivatives were synthesized to create Alg fibers crosslinked by both Ca2+ ions and photo-initiated covalent bonds. Moreover, aldehyde groups introduced on the oxidized chains facilitate covalent conjugation of bioactive molecules via Schiff base reactions. As a model bioactive factor, C domain peptide of insulin-like growth factor-1 (IGF-1C) was conjugated to fibers, and the resulting fibers (OMA-P) were evaluated for their potential in muscle regeneration. Cell experiments showed that OMA-P fibers promoted C2C12 myoblast proliferation and guided their oriented growth. In rat volume muscle loss (VML) models, OMA-P fibers significantly improved muscle regeneration compared to peptide-free OMA fibers and OMA-P sponges without aligned structure, because of the dual effects of axial guidance cue and bioactive peptide conjugation. This study presents a novel method for fabricating bioactive fibers, highlighting their potential as structured scaffolds for regenerative medicine.

Cellulose nanocrystal based electrospun nanofiber for biomedical applications-A review

Electrospinning has become a revolutionized technique for nanofiber fabrication by offering versatile procedures to precisely regulate the nanofibers' properties suitable for a wide range of advanced applications. Nanofibers are utilized as carriers for delivering medications and other health supplements as well as their ability to discharge their contents can be easily programmed and tailored in a specific manner, while serving as tissue engineering scaffolds or medical devices. Cellulose nanocrystals (CNC) are one of the most significant natural biopolymers incorporated as reinforcing agents for nanostructured fibrous frameworks. The integration of electrospinning technology and CNC offers a viable method for manufacturing nanostructured porous substances with favorable functionality, a high ratio of surface area to volume, a tunable crystal structure along with non-toxicity and cytocompatibility, outstanding mechanical properties, flexibility, sustainability, and biodegradable properties. This article offers a thorough summary of the latest progress in the application of CNC based electrospun nanofibers in various biomedical fields such as drug delivery, tissue engineering, and wound healing. It covers the techniques and parameters used for their fabrication, the different types of raw materials employed, and their application criteria. The review concludes by discussing the prospects and challenges in this rapidly evolving research domains.

Correlated Molecular Motion during Release of Residual Stress in Polymer Glassy Films

Correlated molecular motion during the process of residual stress release in polymer glassy films is studied at the single-molecule level. Using poly(n-butyl methacrylate) (PnBMA) and poly(vinyl acetate) (PVAc) as the model polymers, thin films fabricated by spin-casting without thermal annealing were chosen as samples for investigation. Single-molecule fluorescence defocused microscopy was used to track the rotational motion of the fluorescent probes doped inside the polymer films. Under the activation effect of residual stress at experimental temperatures, the rotational motions of individual probes are discovered to be correlated a few degrees below the glass transition temperature (Tg), by analyzing the cross-correlation function of the rotational trajectories of different probes. Detailed investigations into the dependence on residual stress strength, intermolecular distance, probe-polymer interaction, and molecular orientation have been conducted. The results have revealed that the physical mechanism of the motion correlation is the randomization process from the state with preferred molecular orientation and presumably the polymer chain stretching.

Metabolic engineering of Corynebacterium glutamicum: Unlocking its potential as a key cell factory platform for organic acid production

Corynebacterium glutamicum, a well-studied industrial model microorganism, has garnered widespread attention due to its ability for producing amino acids with a long history. In recent years, research efforts have been increasingly focused on exploring its potential for producing various organic acids beyond amino acids. Organic acids, which are characterized by their acidic functional groups, have diverse applications across industries such as food, agriculture, pharmaceuticals, and biobased materials. Leveraging advancements in metabolic engineering and synthetic biology, the metabolic pathways of C. glutamicum have been broadened to facilitate the production of numerous high-value organic acids. This review summarizes the recent progress in metabolic engineering for the production of both amino acids and other organic acids by C. glutamicum. Notably, these acids include, amino acids (lysine, isoleucine, and phenylalanine), TCA cycle-derived organic acids (succinic acid, α-ketoglutaric acid), aromatic organic acids (protocatechuate, 4-amino-3-hydroxybenzoic acid, anthranilate, and para-coumaric acid), and other organic acids (itaconic acid and cis, cis-muconic acid).

Bio-Templated Aerogel Fibers: Heterogeneous Spinodal Architecting and In Situ Fibrillation of Thermoplastic Polyurethane-Silica on Nanostructured Cellulose Nanofiber Scaffold for Enhanced Thermomechanical Performance

This study addresses the inherent fragility and fractal limitations of traditional silica aerogels by developing a bio-templated aerogel fiber. Integrating cellulose nanofibers (CNFs), thermoplastic polyurethane (TPU), and silica aerogel (SA) in a dimethyl sulfoxide (DMSO) dispersion, a gel-spinning technique was employed to create aerogel fibers with superior thermomechanical performance. CNF also provided excellent rheological modification for successful spinnability, fast gelation, and fiber formation. The unique hierarchical structure of these fibers, formed through hot-stretching and surface modification, combined the superior mechanical strength and flexibility of TPU with the exceptional insulation properties of CNF and SA. The CNF network, encapsulated within the SA particles, formed a core-shell structure, axially aligned, that significantly enhances the thermal stability and mechanical performance of the fibers while maintaining a lightweight and porous architecture. Comprehensive morphological, thermal, and mechanical analyses were conducted to evaluate the properties of the developed aerogel fibers. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy verified the successful surface modification and grafting reactions on CNF, contributing to improved hydrophobicity and thermal insulation. Adjusting the CNF content allowed for tailoring of the thermomechanical characteristics, with a notable 294% increase in tensile strength from 5.3 to 15.6 MPa and an enhanced crystallization temperature from 106 to 119.97 °C. Furthermore, cyclic tensile and compression tests validated the durability and shape recovery capabilities of the aerogel fibers, making them promising candidates for high-performance applications in extreme environments. The thermal conductivity validated by experimental data further highlights the potential of CNF-based aerogel fibers as sustainable and multifunctional materials for advanced thermal insulation, mechanical reinforcement, and flexible structural applications.

Structural Rheology in the Development and Study of Complex Polymer Materials

The progress in polymer science and nanotechnology yields new colloidal and macromolecular objects and their combinations, which can be defined as complex polymer materials. The complexity may include a complicated composition and architecture of macromolecular chains, specific intermolecular interactions, an unusual phase behavior, and a structure of a multi-component polymer-containing material. Determination of a relation between the structure of a complex material, the structure and properties of its constituent elements, and the rheological properties of the material as a whole is the subject of structural rheology-a valuable tool for the development and study of novel materials. This work summarizes the author's structural-rheological studies of complex polymer materials for determining the conditions and rheo-manifestations of their micro- and nanostructuring. The complicated chemical composition of macromolecular chains and its role in polymer structuring via block segregation and cooperative hydrogen bonds in melt and solutions is considered using tri- and multiblock styrene/isoprene and vinyl acetate/vinyl alcohol copolymers. Specific molecular interactions are analyzed in solutions of cellulose; its acetate butyrate; a gelatin/carrageenan combination; and different acrylonitrile, oxadiazole, and benzimidazole copolymers. A homogeneous structuring may result from a conformational transition, a mesophase formation, or a macromolecular association caused by a complex chain composition or specific inter- and supramolecular interactions, which, however, may be masked by macromolecular entanglements when determining a rheological behavior. A heterogeneous structure formation implies a microscopic phase separation upon non-solvent addition, temperature change, or intense shear up to a macroscopic decomposition. Specific polymer/particle interactions have been examined using polyethylene oxide solutions, polyisobutylene melts, and cellulose gels containing solid particles of different nature, demonstrating the competition of macromolecular entanglements, interparticle interactions, and adsorption polymer/particle bonds in governing the rheological properties. Complex chain architecture has been considered using long-chain branched polybutylene-adipate-terephthalate and polyethylene melts, cross-linked sodium hyaluronate hydrogels, asphaltene solutions, and linear/highly-branched polydimethylsiloxane blends, showing that branching raises the viscosity and elasticity and can result in limited miscibility with linear isomonomer chains. Finally, some examples of composite adhesives, membranes, and greases as structured polymeric functional materials have been presented with the demonstration of the relation between their rheological and performance properties.

[Fe(NCMe)6](BF4)2 is a bifunctional catalyst for styrene aziridination by nitrene transfer and heterocycle expansion by subsequent dipolar insertion

The solvated iron(II) salt [Fe(NCMe)6](BF4)2 (Me = methyl) is shown to be a bifunctional catalyst with respect to aziridination of styrene. The salt serves as an active catalyst for nitrene transfer from PhINTs to styrene to form 2-phenyl-N-tosylaziridine (Ph = phenyl; Ts = tosyl, -S{O}2-p-C6H4Me). The iron(II) salt also acts as a Lewis acid in non-coordinating CH2Cl2 solution, to catalyze heterolytic CN bond cleavage of the aziridine and insertion of dipolarophiles. The 1,3-zwitterionic intermediate is presumably supported by interaction of the metal dication with the anion, and by resonance stabilization of the carbocation. Nucleophilic dipolarophiles then insert to give a five-membered heterocyclic ring. The result is a two-step cycloaddition, formally [2 + 1 + 2], that is typically regiospecific, but not stereospecific. This reaction mechanism was confirmed by conducting a series of one-step, [3 + 2] additions of unsaturated molecules into pre-formed 2-phenyl-N-tosylaziridine, also catalyzed by [Fe(NCMe)6](BF4)2. Relevant substrates include styrenes, carbonyl compounds and alkynes. These yield five-membered heterocylic rings, including pyrrolidines, oxazolidines and dihydropyrroles, respectively. The reaction scope appears limited only by the barrier to formation of the dipolar intermediate, and by the nucleophilicity of the captured dipolarophile. The bifunctionality of an inexpensive, earth-abundant and non-toxic catalyst suggests a general strategy for one-pot construction of heterocyclic rings, as demonstrated specifically for pyrrolidine ring formation.

Effect of Water-Soluble Polymers on the Rheology and Microstructure of Polymer-Modified Geopolymer Glass-Ceramics

This work explores the effects of rigid (0.1, 0.25, and 0.5 wt. %) and semi-flexible (0.5, 1.0, and 2.5 wt. %) all-aromatic polyelectrolyte reinforcements as rheological and morphological modifiers for preparing phosphate geopolymer glass-ceramic composites. Polymer-modified aluminosilicate-phosphate geopolymer resins were prepared by high-shear mixing of a metakaolin powder with 9M phosphoric acid and two all-aromatic, sulfonated polyamides. Polymer loadings between 0.5-2.5 wt. % exhibited gel-like behavior and an increase in the modulus of the geopolymer resin as a function of polymer concentration. The incorporation of a 0.5 wt. % rigid polymer resulted in a three-fold increase in viscosity relative to the control phosphate geopolymer resin. Hardening, dehydration, and crystallization of the geopolymer resins to glass-ceramics was achieved through mold casting, curing at 80 °C for 24 h, and a final heat treatment up to 260 °C. Scanning electron microscopy revealed a decrease in microstructure porosity in the range of 0.78 μm to 0.31 μm for geopolymer plaques containing loadings of 0.5 wt. % rigid polymer. Nano-porosity values of the composites were measured between 10-40 nm using nitrogen adsorption (Brunauer-Emmett-Teller method) and transmission electron microscopy. Nanoindentation studies revealed geopolymer composites with Young's modulus values of 15-24 GPa and hardness values of 1-2 GPa, suggesting an increase in modulus and hardness with polymer incorporation. Additional structural and chemical analyses were performed via thermal gravimetric analysis, Fourier transform infrared radiation, X-ray diffraction, and energy dispersive spectroscopy. This work provides a fundamental understanding of the processing, microstructure, and mechanical behavior of water-soluble, high-performance polyelectrolyte-reinforced geopolymer composites.

Precise Fabrication and Manipulation of Individual Polymer Nanofibers

Polymer nanofibers hold promise in a wide range of applications owing to their diverse properties, flexibility, and cost effectiveness. In this study, we introduce a polymer nanofiber drawing process in a scanning electron microscope and focused ion beam (SEM/FIB) instrument with in situ observation. We employed a nanometer-sharp tungsten needle and prepolymer microcapsules to enable nanofiber drawing in a vacuum environment. This method produces individual polymer nanofibers with diameters as small as ∼500 nm and lengths extending to millimeters, yielding nanofibers with an aspect ratio of 2000:1. The attachment to the tungsten manipulator ensures accurate transfer of the polymer nanofiber to diverse substrate types as well as fabrication of assembled structures. Our findings provide valuable insights into ultrafine polymer fiber drawing, paving the way for high-precision manipulation and assembly of polymer nanofibers.

Robust and Flame-Retardant Zylon Aerogel Fibers for Wearable Thermal Insulation and Sensing in Harsh Environment

The exceptional lightweight, highly porous, and insulating properties of aerogel fibers make them ideal for thermal insulation. However, current aerogel fibers face limitations due to their low resistance to harsh environments and a lack of intelligent responses. Herein, a universal strategy for creating polymer aerogel fibers using crosslinked nanofiber building blocks is proposed. This approach combines controlled proton absorption gelation spinning with a heat-induced crosslinking process. As a proof-of-concept, Zylon aerogel fibers that exhibited robust thermal stability (up to 650 °C), high flame retardancy (limiting oxygen index of 54.2%), and extreme chemical resistance are designed and synthesized. These fibers possess high porosity (98.6%), high breaking strength (8.6 MPa), and low thermal conductivity (0.036 W m-1 K-1 ). These aerogel fibers can be knotted or woven into textiles, utilized in harsh environments (-196-400 °C), and demonstrate sensitive self-powered sensing capabilities. This method of developing aerogel fibers expands the applications of high-performance polymer fibers and holds great potential for future applications in wearable smart protective fabrics.

De novo biosynthesis of 2-hydroxyterephthalic acid, the monomer for high-performance hydroxyl modified PBO fiber, by enzymatic Kolbe-Schmitt reaction with CO2 fixation

BACKGROUND

High-performance poly(p-phenylenebenzobisoxazole) (PBO) fiber, with excellent mechanical properties (stiffness, strength, and toughness), high thermal stability combined and light weight, are widely employed in automotive and aerospace composites, body armor and sports goods. Hydroxyl modified PBO (HPBO) fiber shows better photostability and interfacial shear strength. 2-Hydroxyterephthalic acid (2-HTA), the monomer for the HPBO fiber, is usually synthesized by chemical method, which has poor space selectivity and high energy consumption. The enzymatic Kolbe-Schmitt reaction, which carboxylates phenolic substrates to generate hydroxybenzoic acids with bicarbonate/CO2, was applied in de novo biosynthesis of 2-HTA with CO2 fixation.

RESULTS

The biosynthesis of 2-HTA was achieved by the innovative application of hydroxybenzoic acid (de)carboxylases to carboxylation of 3-hydroxybenzoic acid (3-HBA) at the para-position of the benzene carboxyl group, known as enzymatic Kolbe-Schmitt reaction. 2,3-Dihydroxybenzoic acid decarboxylase from Aspergillus oryzae (2,3-DHBD_Ao) were expressed in recombinant E. coli and showed highest activity. The yield of 2-HTA was 108.97 ± 2.21 μg/L/mg protein in the whole-cell catalysis. In addition, two amino acid substitutions, F27G and T62A, proved to be of great help in improving 2,3-DHBD activity. The double site mutation F27G/T62A increased the production of 2-HTA in the whole-cell catalysis by 24.7-fold, reaching 2.69 ± 0.029 mg/L/mg protein. Moreover, de novo biosynthetic pathway of 2-HTA was constructed by co-expression of 2,3-DHBD_Ao and 3-hydroxybenzoate synthase Hyg5 in S. cerevisiae S288C with Ura3, Aro7 and Trp3 knockout. The engineered strain synthesized 45.40 ± 0.28 μg/L 2-HTA at 36 h in the CO2 environment.

CONCLUSIONS

De novo synthesis of 2-HTA has been achieved, using glucose as a raw material to generate shikimic acid, chorismic acid, and 3-HBA, and finally 2-HTA. We demonstrate the strong potential of hydroxybenzoate (de)carboxylase to produce terephthalic acid and its derivatives with CO2 fixation.

A 4-hydroxybenzoate 3-hydroxylase mutant enables 4-amino-3-hydroxybenzoic acid production from glucose in Corynebacterium glutamicum

BACKGROUND

Microbial production of aromatic chemicals is an attractive method for obtaining high-performance materials from biomass resources. A non-proteinogenic amino acid, 4-amino-3-hydroxybenzoic acid (4,3-AHBA), is expected to be a precursor of highly functional polybenzoxazole polymers; however, methods for its microbial production have not been reported. In this study, we attempted to produce 4,3-AHBA from glucose by introducing 3-hydroxylation of 4-aminobenzoic acid (4-ABA) into the metabolic pathway of an industrially relevant bacterium, Corynebacterium glutamicum.

RESULTS

Six different 4-hydroxybenzoate 3-hydroxylases (PHBHs) were heterologously expressed in C. glutamicum strains, which were then screened for the production of 4,3-AHBA by culturing with glucose as a carbon source. The highest concentration of 4,3-AHBA was detected in the strain expressing PHBH from Caulobacter vibrioides (CvPHBH). A combination of site-directed mutagenesis in the active site and random mutagenesis via laccase-mediated colorimetric assay allowed us to obtain CvPHBH mutants that enhanced 4,3-AHBA productivity under deep-well plate culture conditions. The recombinant C. glutamicum strain expressing CvPHBHM106A/T294S and having an enhanced 4-ABA biosynthetic pathway produced 13.5 g/L (88 mM) 4,3-AHBA and 0.059 g/L (0.43 mM) precursor 4-ABA in fed-batch culture using a nutrient-rich medium. The culture of this strain in the chemically defined CGXII medium yielded 9.8 C-mol% of 4,3-AHBA from glucose, corresponding to 12.8% of the theoretical maximum yield (76.8 C-mol%) calculated using a genome-scale metabolic model of C. glutamicum.

CONCLUSIONS

Identification of PHBH mutants that could efficiently catalyze the 3-hydroxylation of 4-ABA in C. glutamicum allowed us to construct an artificial biosynthetic pathway capable of producing 4,3-AHBA on a gram-scale using glucose as the carbon source. These findings will contribute to a better understanding of enzyme-catalyzed regioselective hydroxylation of aromatic chemicals and to the diversification of biomass-derived precursors for high-performance materials.

Fabricating strong and tough aramid fibers by small addition of carbon nanotubes

Synthetic high-performance fibers present excellent mechanical properties and promising applications in the impact protection field. However, fabricating fibers with high strength and high toughness is challenging due to their intrinsic conflicts. Herein, we report a simultaneous improvement in strength, toughness, and modulus of heterocyclic aramid fibers by 26%, 66%, and 13%, respectively, via polymerizing a small amount (0.05 wt%) of short aminated single-walled carbon nanotubes (SWNTs), achieving a tensile strength of 6.44 ± 0.11 GPa, a toughness of 184.0 ± 11.4 MJ m^-3, and a Young's modulus of 141.7 ± 4.0 GPa. Mechanism analyses reveal that short aminated SWNTs improve the crystallinity and orientation degree by affecting the structures of heterocyclic aramid chains around SWNTs, and in situ polymerization increases the interfacial interaction therein to promote stress transfer and suppress strain localization. These two effects account for the simultaneous improvement in strength and toughness.

Photoinduced Radical Persistent Luminescence in Semialiphatic Polyimide System with Temperature and Humidity Resistance

Organic persistent luminescence (pL) systems with photoresponsive dynamic features have valuable applications in the fields of data encryption, anticounterfeiting, and bioimaging. Photoinduced radical luminescent materials have a unique luminous mechanism with the potential to achieve dynamic pL. It is extremely challenging to obtain radical pL under ambient conditions; on account of it, it is unstable in air. Herein, a new semialiphatic polyimide-based polymer (A0) is developed, which can achieve dynamic pL through reversible conversion of radical under photoexcitation. A "joint-donor-spacer-acceptor" molecular design strategy is applied to effectively modulate the intramolecular charge-transfer and charge-transfer complex interactions, resulting in effective protection of the radical generated under photoirradiation. Meanwhile, polyimide-based polymers of A1-A4 are obtained by doping different amine-containing fluorescent dyes to modulate the dynamic afterglow color from green to red via the triplet to singlet Förster resonance energy-transfer pathway. Notably, benefiting from the structural characteristics of the polyimide-based polymer, A0-A4 have excellent processability, thermal stability, and mechanical properties and can be applied directly in extreme environments such as high temperatures and humidity.

Mechanically Strong and Thermally Insulating Polyimide Aerogel Fibers Reinforced by Prefabricated Long Polyimide Fibers

Aerogel fibers inherit the merits of aerogel and fibrous materials, such as high porosity and satisfactory knittability, demonstrating great potential as thermal protective materials applied in harsh environments. Nevertheless, the inferior mechanical property resulting from the porous structure immensely hampers the practical application of aerogel fibers. Herein, we develop robust and thermally insulating long polyimide fiber-reinforced polyimide composite aerogel fibers (LPF-PAFs). The porous crosslinked polyimide aerogel as the sheath endows LPF-PAFs with good thermal insulation performance, while the long polyimide fibers as the core provide LPF-PAFs with superior mechanical strength. Due to the introduction of the high-strength long polyimide fibers to undertake significant stress, LPF-PAFs display outstanding strength surpassing 150 MPa without obvious mechanical performance degeneration in a wide range of temperatures from -100 to 300 °C. Moreover, the textile woven by LPF-PAFs exhibits a superior thermal insulation ability and stability to cotton textile at 200 and -100 °C, indicating its potential application in thermal protective clothing under extreme environments.

Effect of Nano-SiO2 on Different Stages of UHMWPE/HDPE Fiber Preparation via Melt Spinning

Ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blend with lower viscosity is more suitable for melt spinning compared to pure UHMWPE; however, the mechanical property of the blend fiber is hard to dramatically improve (the maximum tensile strength of 998.27 MPa). Herein, different content modified-nano-SiO₂ is incorporated to UHMWPE/HDPE blend fiber. After adding 0.5 wt% nano-SiO₂, the tensile strength and initial modulus of UHMWPE/HDPE/nano-SiO₂ fiber are increased to 1211 MPa and 12.81 GPa, respectively, 21.57% and 43.32% higher than that of UHMWPE/HDPE fiber. Meanwhile, the influence of the nano-SiO₂ content on the performance for as-spun filament and fiber are emphatically analyzed. The crystallinity and molecular chain orientation of as-spun filament reduces with the addition of nano-SiO₂. On the contrary, for fiber, the addition of nano-SiO₂ promoted the crystallinity, molecular chain orientation and grain refinement more obvious at a lower content. Furthermore, the possible action mechanism of nano-SiO₂ in the as-spun filament extrusion and fiber hot drawing stage is explained.

Polylactic Acid/Polyaniline Nanofibers Subjected to Pre- and Post-Electrospinning Plasma Treatments for Refined Scaffold-Based Nerve Tissue Engineering Applications

Composite biopolymer/conducting polymer scaffolds, such as polylactic acid (PLA)/ polyaniline (PAni) nanofibers, have emerged as popular alternative scaffolds in the electrical-sensitive nerve tissue engineering (TE). Although mimicking the extracellular matrix geometry, such scaffolds are highly hydrophobic and usually present an inhomogeneous morphology with massive beads that impede nerve cell-material interactions. Therefore, the present study launches an exclusive combinatorial strategy merging successive pre- and post-electrospinning plasma treatments to cope with these issues. Firstly, an atmospheric pressure plasma jet (APPJ) treatment was applied on PLA and PLA/PAni solutions prior to electrospinning, enhancing their viscosity and conductivity. These liquid property changes largely eliminated the beaded structures on the nanofibers, leading to uniform and nicely elongated fibers having average diameters between 170 and 230 nm. After electrospinning, the conceived scaffolds were subjected to a N₂ dielectric barrier discharge (DBD) treatment, which significantly increased their surface wettability as illustrated by large decreases in water contact angles for values above 125° to values below 25°. X-ray photoelectron spectroscopy (XPS) analyses revealed that 3.3% of nitrogen was implanted on the nanofibers surface in the form of C-N and N-C=O functionalities upon DBD treatment. Finally, after seeding pheochromocytoma (PC-12) cells on the scaffolds, a greatly enhanced cell adhesion and a more dispersive cell distribution were detected on the DBD-treated samples. Interestingly, when the APPJ treatment was additionally performed, the extension of a high number of long neurites was spotted leading to the formation of a neuronal network between PC-12 cell clusters. In addition, the presence of conducting PAni in the scaffolds further promoted the behavior of PC-12 cells as illustrated by more than a 40% increase in the neurite density without any external electrical stimulation. As such, this work presents a new strategy combining different plasma-assisted biofabrication techniques of conducting nanofibers to create promising scaffolds for electrical-sensitive TE applications.

Scalable production of ultrafine polyaniline fibres for tactile organic electrochemical transistors

The development of continuous conducting polymer fibres is essential for applications ranging from advanced fibrous devices to frontier fabric electronics. The use of continuous conducting polymer fibres requires a small diameter to maximize their electroactive surface, microstructural orientation, and mechanical strength. However, regularly used wet spinning techniques have rarely achieved this goal due primarily to the insufficient slenderization of rapidly solidified conducting polymer molecules in poor solvents. Here we report a good solvent exchange strategy to wet spin the ultrafine polyaniline fibres. The slow diffusion between good solvents distinctly decreases the viscosity of protofibers, which undergo an impressive drawing ratio. The continuously collected polyaniline fibres have a previously unattained diameter below 5 µm, high energy and charge storage capacities, and favorable mechanical performance. We demonstrated an ultrathin all-solid organic electrochemical transistor based on ultrafine polyaniline fibres, which operated as a tactile sensor detecting pressure and friction forces at different levels.

General Suspended Printing Strategy toward Programmatically Spatial Kevlar Aerogels

Aerogels represent a kind of nanoporous solid with immense importance for a plethora of diverse applications. However, on-demand conformal shaping capacity remains extremely challenging due to the strength unfavorable during aerogel processing. Herein, a universal microgel-directed suspended printing (MSP) strategy is developed for fabricating various mesoporous aerogels with spatially stereoscopic structures on-demand. As a proof-of-concept demonstration, through the rational design of the used microgel matrix and favorable printing of the Kevlar nanofiber inks, the Kevlar aerogels with arbitrary spatial structure have been fabricated, demonstrating excellent printability and programmability under a high-speed printing mode (up to 167 mm s^-1). Furthermore, the custom-tailored Kevlar aerogel insulator possessing superior thermal insulation attribute has ensured normal discharge capacity of the drone even under a harsh environment (-30 °C). Finally, various types of spatial 3D aerogel architectures, including organic (cellulose, alginate, chitosan), inorganic (graphene, MXene, silica), and inorganic-organic (graphene/cellulose, MXene/alginate, silica/chitosan) hybrid aerogels, have been successfully fabricated, suggesting the universality of the MSP strategy. The strategy reported here proposes an alternative for the development of various customized aerogels and stimulates the inspiration to truly arbitrary architectures for wider applications.

DLC-Coated Ferroelectric Membranes as Vascular Patches: Physico-Chemical Properties and Biocompatibility

In this paper, the results on the fabrication of ferroelectric membranes as vascular patches with modified surfaces are presented. For the modification of a membrane surface contacting blood, DLC coating was deposited using the pulsed vacuum arc deposition technique. The physico-chemical properties and cytotoxicity of the membranes modified under various conditions were studied. It was found that DLC coatings do not affect membrane microstructure, preserving its crystal structure as well as its high strength and elongation. It was revealed that an increase in the capacitor storage voltage results in the rise in sp²- and sp-hybridized carbon concentration, which makes it possible to control the chemical structure and surface energy of the modified surface. The experiments with 3T3L1 fibroblasts showed no toxic effects of the materials extracts.

Polyimide Aerogel Fibers with Superior Flame Resistance, Strength, Hydrophobicity, and Flexibility Made via a Universal Sol-Gel Confined Transition Strategy

Aerogel fibers with ultrahigh porosity, large specific surface area, and ultralow density have shown increasing interest due to being considered as the next generation thermal insulation fibers. However, it is still a great challenge to fabricate arbitrary aerogel fibers via the traditional wet-spinning approach due to the obvious conflict between the static sol-gel transition of the aerogel bulks and the dynamic wet-spinning process of aerogel fibers. Herein, a sol-gel confined transition (SGCT) strategy was developed for fabricating various mesoporous aerogel fibers, in which the aerogel precursor solution was first driven by the surface tension into the capillary tubes, then the gel fibers were easily formed in the confined space after static sol-gel process, and finally the mesoporous aerogel fibers were obtained via the supercritical CO₂ drying process. As a typical case, the polyimide (PI) aerogel fiber prepared via the SGCT approach has exhibited a large specific surface area (up to 364 m²/g), outstanding mechanical property (with elastic modulus of 123 MPa), superior hydrophobicity (with contact angle of 153°), and excellent flexibility (with curvature radius of 200 μm). Therefore, the aerogel woven fabric made from PI aerogel fibers has possessed an excellent thermal insulation performance in a wide temperature window, even under the harsh environment. Besides, arbitrary kinds of aerogel fibers, including organic aerogel fibers, inorganic aerogel fibers, and organic-inorganic hybrid aerogel fibers, have been fabricated successfully, suggesting the universality of the SGCT strategy, which not only provides a way for developing aerogel fibers with different components but also plays an irreplaceable role in promoting the upgrading of the fiber fields.

Critical conditions for organic thread cutting under electric fields

Conditions for triggering the cutting of organic samples under an AC electric field are investigated in a microchannel to explore the strategy for organic sample manipulation. Based on the nature of triggering and developing instability at liquid interfaces, in combination with an equivalent electric circuit model, a novel electric capillary number method is proposed as a comprehensive critical condition for the cutting. We uncover the physics behind cutting and non-cutting of an organic thread for different electric frequencies, electric properties of fluid, and width of the organic thread. The critical time required and the critical cutting position are studied to offer guidelines for accurate cutting. Higher electric frequency and higher permittivity of the aqueous phase surrounding the organic phase can reduce the voltage required for cutting. In summary, the newly defined electric capillary number is proved to be a comprehensive criterion for determining the cutting phenomena, which is capable of considering the interfacial tension, the electric permittivity and the electric field strength applied. The results offer applicable references for achieving efficient and accurate cutting of organic samples in practical applications.

Boron dipyrromethene (BODIPY) in polymer chemistry

The present review provides both a summary and outlook on the exciting field of BODIPYs in polymer chemistry.

Electrohydrodynamics of droplets and jets in multiphase microsystems

Electrohydrodynamics is among the most promising techniques for manipulating liquids in microsystems. The electric stress actuates, generates, and coalesces droplets of small sizes; it also accelerates, focuses, and controls the motion of fine jets. In this review, the current understanding of dynamic regimes of electrically driven drops and jets in multiphase microsystems is summarized. The experimental description and underlying mechanism of force interplay and instabilities are discussed. Conditions for controlled transitions among different regimes are also provided. Emerging new phenomena either due to special interfacial properties or geometric confinement are emphasized, and simple scaling arguments proposed in the literature are introduced. The review provides useful perspectives for investigations involving electrically driven droplets and jets.

Vapor phase processing: a novel approach for fabricating functional hybrid materials

Materials science is nowadays facing challenges in optimizing properties of materials which are needed for numerous technological applications and include, but are not limited to, mechanics, electronics, optics, etc. The key issue is that for emerging applications materials are needed which incorporate certain properties from polymers or biopolymers and metals or ceramics at the same time, thus fabrication of functional hybrid materials becomes inevitable. Routes for the synthesis of functional hybrid materials can be manifold. Among the explored routes vapor phase processing is a rather novel approach which opts for compatibility with many existing industrial processes. This topical review summarizes the most important approaches and achievements in the synthesis of functional hybrid materials through vapor phase routes with the goal to fabricate suitable hybrid materials for future mechanical, electronic, optical or biomedical applications. Most of the approaches rely on atomic layer deposition (ALD) and techniques related to this process, including molecular layer deposition (MLD) and vapor phase infiltration (VPI), or variations of chemical vapor deposition (CVD). The thus fabricated hybrid materials or nanocomposites often show exceptional physical or chemical properties, which result from synergies of the hybridized materials families. Even though the research in this field is still in its infancy, the initial results encourage further development and promise great application potential in a large variety of applications fields such as flexible electronics, energy conversion or storage, functional textile, and many more.

Bifunctional Peptide-Polymer Conjugate-Based Fibers via a One-Pot Tandem Disulfide Reduction Coupled to a Thio-Bromo "Click" Reaction

In view of the potential applications of fibers in material sciences and biomedicine, an effective synthetic strategy is described to construct peptide-based bifunctional polymeric conjugates for supramolecular self-association in solution. A direct coupling method of an α-acyl-brominated peptide Phe-Phe-Phe-Phe (FFFF) with a disulfide-bridged polymeric scaffold of poly(ethylene glycol) (PEG) (M n,GPC = 8700 g mol-1, Đ = 2.02) is reported to readily prepare the bi-headed conjugate FFFF-PEG-FFFF (M n,GPC = 3800 g mol-1, Đ = 1.10) via a one-pot, tandem disulfide reduction (based on tris(2-carboxyethyl)phosphine hydrochloride (TCEP)) coupled to a thio-bromo "click" reaction. The conjugate was investigated via transmission electron microscopy to exploit supramolecular fibril formation and solvent-dependent structuring into macroscale fibers via fibril-fibril interactions and interfibril cross-linking-induced bundling. Circular dichroism spectroscopic analysis is further performed to investigate β-sheet motifs in such fibrous scaffolds. Overall, this synthetic approach opens an attractive approach for a simplified synthesis of PEG-containing peptide conjugates.

Gravity Drawing of Micro- and Nanofibers for Additive Manufacturing of Well-Organized 3D-Nanostructured Scaffolds

This work introduces a gravity fiber drawing (GFD) method of making single filament nanofibers from polymer solutions and precise alignment of the fibers in 3D scaffolds. This method is advantageous for nanofiber 3D alignment in contrast to other known methods. GFD provides a technology for the fabrication of freestanding filament nanofibers of well-controlled diameter, draw ratio, and 3D organization with controllable spacing and angular orientation between nanofibers. The GFD method is capable of fabricating complex 3D scaffolds combining fibers with different diameters, chemical compositions, mechanical properties, angular orientations, and multilayer structures in the same construct. The scaffold porosity can be as high as 99% to secure transport of nutrients and space for cell infiltration and differentiation in tissue engineering and 3D cell culture applications.

Organic Liquid Impregnation Behavior into Nanofibrous Membranes: Quantitative Analysis of the Effects of Structural Parameters

This paper reports the effects of structural parameters on organic liquid impregnation behavior into nanofibrous (NF) polymer membranes. The NF membranes were prepared from organic liquidphilic polymers, poly(amide-imide)s (PAIs), by electrospinning. The impregnation velocity of the organic liquid, ethylmethylcarbonate, into the as-spun PAI NF membranes with diameters ranging from 400 to 900 nm was approximately 10-20 times higher than that into commercial cellulose nonwoven membranes. Our theoretical analyses based on the Kozeny-Carman equation and multivariate statistics clearly indicate that in addition to the porosity of the membranes, the variation in fiber diameter as well as the average fiber diameter is a crucial factor for controlling the liquid impregnation behavior.

Segmental Rearrangements Relax Stresses in Nonequilibrated Polymer Films

We probed the relaxation of preparation-induced residual stresses in nonequilibrated polymer films through dewetting experiments. While we observed fast relaxations at temperatures close to or below the glass transition, at elevated temperatures these relaxation times were orders of magnitude longer than the reptation time. Intriguingly, applying appropriate scaling of preparation conditions allowed us to present all relaxation times, including published data, from various complementary experiments on a single master curve exhibiting an Arrhenius-type behavior. The corresponding activation energy (75 ± 10 kJ/mol) is similar to values obtained for the relaxation of segments in polystyrene. The observed long relaxation times suggest that residual stresses, a consequence of nonequilibrium conformations inherited from preparation, relax via concerted rearrangements of many segments.

Dynamic Strengthening of Carbon Nanotube Fibers under Extreme Mechanical Impulses

A monofilament fiber spun from individual carbon nanotubes is an arbitrarily long ensemble of weakly interacting, aligned, discrete nanoparticles. Despite the structural resemblance of carbon nanotube monofilament fibers to crystalline polymeric fibers, very little is known about their dynamic collective mechanics, which arise from van der Waals interactions among the individual carbon nanotubes. Using ultrafast stroboscopic microscopy, we study the collective dynamics of carbon nanotube fibers and compare them directly with nylon, Kevlar, and aluminum monofilament fibers under the same supersonic impact conditions. The in situ dynamics and kinetic parameters of the fibers show that the kinetic energy absorption characteristics of the carbon nanotube fibers surpass all other fibers. This study provides insight into the strain-rate-dependent strengthening mechanics of an ensemble of nanomaterials for the development of high-performance fibers used in body armor and other protective nanomaterials possessing exceptional stability in various harsh environments.