Helical Nanofibers Research Articles

Design of a novel co‐electrospinning system with flat spinneret for producing helical nanofibers

ABSTRACTA kind of biomimetic fibers of helical structures at nanoscale has attracted increasing interest. In this study, a novel co‐electrospinning setup with a designed flat spinneret, used for the fabrication of helical nanofibers, is reported in this study. Poly(m‐phenylene isophthalamide) (Nomex) and Thermoplastic polyurethane (TPU) are chosen as the two components in co‐electrospinning. To display the efficiency for producing helical fibers, a generally used core–shell needle spinneret is used for comparison. The effect of the uniformity of electric field distribution created by these two types of spinnerets on the jet motion and the resultant helical fibers is developed, with systematical simulation and experimental research. The results showed that the co‐electrospinning system with the newly designed flat spinneret can produce helical nanofibers efficiently. Compared with the needle spinneret, the flat spinneret created more uniform electric field, leading to better morphology and structure of the resultant helical fibers. In addition, an approach to achieve the scale‐up of this co‐electrospinning system is developed. This novel design is expected to provide a promising method to fabricate nanofiber materials with helical structures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1496–1505

Formation of wavy carbon nanofibers and nanocoils via precursor constrained microbuckling

Flexible carbon nanosprings and wavy nanofibers can be used in micro and nanoelectromechanical system devices, deployable structures, flexible displays, energy storage, catalysis, nanocomposites and a multitude of other uses. A novel method to produce wavy and helical carbon nanofibers (CNFs) is presented here. The CNFs with controlled geometry were fabricated via pyrolysis of electrospun polyacrylonitrile (PAN) nanofibers as the precursor. The waviness/helicity of nanofibers was achieved by subjecting the precursor nanofibers to constraint buckling inside a thermally shrinking matrix. The much higher tendency of the matrix to shrink, compared to PAN nanofibers, was achieved by controlling the microstructure and crystallinity of the precursors. The formation of the wavy/helical geometry was explained quantitatively via mechanistic models, by minimizing the total mechanical energy stored in the PAN-matrix system during the matrix shrinkage. Despite its simplicity in considering elastic deformations only, the model provided reasonably quantitative matching with the experiments. Compared to existing methods in generating wavy/helical nanofibers, such as chemical vapor deposition growth methods, our method provides a more controllable geometry which is suitable for large scale production of aligned buckled CNFs.

Magnetic and Electric Control of Circularly Polarized Emission through Tuning Chirality-Generated Orbital Angular Momentum in Organic Helical Polymeric Nanofibers.

Circularly polarized light emission promotes the development of smart photonic materials for advanced applications in chiral sensing and information storage. The orbital angular momentum is a unique property for organic chiral helical materials. In this work, a type of organic chiral polymeric nanowires is designed with strong chirality induced orbital angular momentum. Under the stimulus of an external magnetic field of 600 mT, circularly polarized emission from the chiral polymeric nanowire becomes more pronounced, where the g factor increases from 0.21 to 0.3. The observed phenomena mainly originate from the chirality-dependent orbital angular momentum. Moreover, the orbital angular momentum in helical chiral nanowire structures can be suppressed by inhibiting electron transport in a helical way to diminish circularly polarized light emission at room temperature.

Helicity of perfluoroalkyl chains controlled by the self-assembly of the Ala-Ala dipeptides.

Four Ala-Ala dipeptides with a perfluoroalkyl chain at the N-terminal were synthesized. They were able to self-assemble into helical nanofibers and/or twisted nanobelts in a mixture of DMSO/H2 O. The handedness of nanofibers and nanobelts was controlled by the chirality of the alanine at the N-terminal. The stacking handedness of the phenylene groups and the helicity of the perfluoroalkyl chain were studied using circular dichroism spectroscopy and vibrational circular dichroism, respectively. The chirality of the alanine at N-terminal controlled the stacking handedness of the neighboring phenylene groups. Moreover, due to the low potential barrier between M- and P-helices of the perfluorocarbon chain, the handedness of the organic self-assemblies eventually controlled the helicity of the perfluorocarbon chain. X-ray diffraction indicated that a lamellar structure was formed by the dimers of the dipeptides.

Hybrid Soft Nanomaterials Composed of DNA Microspheres and Supramolecular Nanostructures of Semi-artificial Glycopeptides.

Aqueous hybrid soft nanomaterials consisting of plural supramolecular architectures with a high degree of segregation (orthogonal coexistence) and precise hierarchy at the nano- and microscales, which are reminiscent of complex biomolecular systems, have attracted increasing attention. Remarkable progress has been witnessed in the construction of DNA nanostructures obtained by rational sequence design and supramolecular nanostructures of peptide derivatives through self-assembly under aqueous conditions. However, orthogonal self-assembly of DNA nanostructures and supramolecular nanostructures of peptide derivatives in a single medium has not yet been explored in detail. In this study, DNA microspheres, which can be obtained from three single-stranded DNAs, and three different supramolecular nanostructures (helical nanofibers, straight nanoribbons, and flowerlike microaggregates) of semi-artificial glycopeptides were simultaneously constructed in a single medium by a simple thermal annealing process, which gives rise to hybrid soft nanomaterials. Fluorescence imaging with selective staining of each supramolecular nanostructure uncovered the orthogonal coexistence of these structures with only marginal impact on their morphology. Additionally, the biostimuli-responsive degradation propensity of each supramolecular architecture is retained, and this may allow the construction of active soft nanomaterials exhibiting intelligent biofunctions.

Self-Assembled Dual Helical Nanofibers of Amphiphilic Perylene Diimides with Oligopeptide Substitution.

We designed an asymmetric amphiphilic perylene diimide (PDI) with the oligopeptide substituting one of the imides. The self-assembly mechanism of this PDI in different solvents was investigated. Right-handed "dual" helical nanofibers/nanowires with a uniform lateral dimension of ∼8 nm are constructively self-assembled. The long-term ordered degree within the nanofibers stems from the delicate balance between π-π stacking of the PDI rings and β-sheet-like hydrogen bond formed by the oligopeptide. The synergistic interplay between the hydrogen bond and π-π stacking rather than competition endows the nanofibers with the controllable longitudinal dimensions by different factors such as the concentration and solvents. The transition from the nanofibers to the small aggregates is also achieved by the addition of trifluoroacetic acid because of breakup of the hydrogen bonds, which is reversed by further addition of trimethylamine. The acid-base stimulation can be extended to different solvents as long as the existence of the unique hydrogen bonds.

Building carbon structures inside hollow carbon spheres

The synthesis and characterization of helical carbon nanofibers (CNFs) contained within a fully confined nanoreactor is described. In particular, hollow carbon spheres (od = ca. 310 nm; wall thickness ca. 20 nm) were infiltrated with Cu ions (1%) to produce CuO particles (<10 nm) and the CuO was converted to Cu particles at temperature of 300 °C. Acetylene was then used as a carbon source to grow helical CNFs within the hollow carbon spheres. The diameter and helicity of the CNFs was influenced by the Cu content within a hollow carbon sphere, the limited Cu sintering inside a sphere as well as the dimensions of the sphere. The procedures employed suggest that the philosophy of building other structures (and molecules) with any elements within confined nanoreactors is possible.

Design and preparation of a novel fluorescent naphthalimide derivative supramolecular self-assembly system and its bioimaging application

ABSTRACTA novel fluorescent naphthalimide derivative gelator (N-18) was designed and characterised which could form a stable gel in 1,4-dioxane/H2O (2/1, v/v), methyl sulfoxide (DMSO), ethanol/H2O (4/1, v/v), acetone/H2O (2/1, v/v) and methanol. The self-assembly process of molecule N-18 in the five solvents was carefully investigated by the field emission scanning electron microscope, UV-vis absorption spectra, fluorescence emission spectra, fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and water contact angle experiments. Different structures from microbelts to helical nanofibers were formed in the self-assembly process. Hydrogen bonding and π–π stacking interaction were the mainly driving forces for the formation of gel. At the same time, the hydrophobic surface with the contact angles of 133°–142° was observed on the xerogel films N-18 from the above five solvents. Interestingly, molecule N-18 could be applied in bioimaging in a living cell.

Mechanical properties and microstructure characterization of natural rubber reinforced by helical carbon nanofibers

Reinforcement of natural rubber (NR) was achieved by a novel kind of carbon filler, helical carbon nanofibers (HCNFs). The good interface bonding between HCNFs and NR matrix was confirmed by the analysis of transmission electron microscopy, scanning electron microscopy and dynamic mechanical analyzer. The tensile and dynamic mechanical properties of HCNFs/NR nanocomposites with the filler loading of 1–5 phr were studied. When the filler loading is 5 phr, HCNFs/NR nanocomposites have a significant enhancement in the modulus at 300% strain (464% and 163% higher than pure NR and N330/NR, respectively), storage modulus (83.5% and 82% higher than pure NR and N330/NR, respectively) at 0 °C, with a small decrease in elongation at break. The unique carbon coil structure and abundant surface oxygen-containing functional groups of HCNFs play a critical role in the formation of good interface bonding between HCNFs and NR matrix. This work can provide guidance for the development of HCNFs filled rubber materials with excellent mechanical properties.

Construction of helical nanofibers from cellulose acetate and a flexible component

A combination of Cellulose Acetate and an appropriate flexible polymer component was applied to construct a kind of new hierarchical nanofibers of three-dimensional helical structure with porous core. The morphology and structure of as-spun fibers were observed with the help of Optical Microscope, Field Emission Scanning Electron Microscope and Transmission Electron Microscopy. The polymer structure and intrinsic property that would affect the formation of helical structure were studied by means of differential scanning calorimetry and Fourier Transformation Infrared Spectroscopy. To explain the formation of helical structure, mechanical behavior of the polymer components in the process of the formation of helical structure was studied. Longitudinal stress difference between the components under the electric field is simulated for further verification. The obtained hierarchical structure displays an efficient oil sorption capacity and is expected to be a promising candidate for various applications, especially for sorption and filtration materials.

Helical nanofiber yarn enabling highly stretchable engineered microtissue

Development of microtissues that possess mechanical properties mimicking those of native stretchable tissues, such as muscle and tendon, is in high demand for tissue engineering and regenerative medicine. However, regardless of the significant advances in synthetic biomaterials, it remains challenging to fabricate living microtissue with high stretchability because application of large strains to microtissues can damage the cells by rupturing their structures. Inspired by the hierarchical helical structure of native fibrous tissues and its behavior of nonaffine deformation, we develop a highly stretchable and tough microtissue fiber made up of a hierarchical helix yarn scaffold, scaling from nanometers to millimeters, that can overcome this limitation. This microtissue can be stretched up to 15 times its initial length and has a toughness of 57 GJ m-3 More importantly, cells grown on this scaffold maintain high viability, even under severe cyclic strains (up to 600%) that can be attributed to the nonaffine deformation under large strains, mimicking native biopolymer scaffolds. Furthermore, as proof of principle, we demonstrate that the nanotopography of the helical nanofiber yarn is able to induce cytoskeletal alignment and nuclear elongation, which promote myogenic differentiation of mesenchymal stem cells by triggering nuclear translocation of transcriptional coactivator with PDZ-binding motif (TAZ). The highly stretchable microtissues we develop here will facilitate a variety of tissue engineering applications and the development of engineered living systems.

Glycyrrhizic acid based self-assembled helical nanostructures as scaffolds for asymmetric Diels-Alder reaction

Glycyrrhizic acid (GA), as a traditional herbal, can self-assemble into helical nanofiber in the water. The formed helical nanostructures can be employed as scaffolds for asymmetric Diels-Alder reaction. Through co-assembling with a series of achiral copper-ligands, the chirality of GA helical nanostructures can be transferred to catalytic site, and resulted assemblies showed moderated enantioselectivity toward catalysis of Diels-Alder reaction.

Tuning the Handedness: Role of Chiral Component in Peptide-Appended Bolaamphiphile-Based Coassembled Hydrogels.

Chirality is the intrinsic property of a molecule that can be tuned by the change in chirality of a molecule or by the addition of a chiral component as an external stimulus. An l-leucine-based dipeptide-appended succinic acid-based bolaamphiphile coassembled with d-tartaric acid to form supramolecular right-handed nanostructured hydrogel, whereas l-tartaric acid coassembled to form supramolecular left-handed nanostructured hydrogel. Scanning electron microscopy and transmission electron microscopy experiments revealed the right- and left-handed helical nanofibers that are responsible for the formation of supramolecular nanostructured hydrogels. The synergistic chiral effect of l-leucine in peptide bolaamphiphile and d/l-tartaric acid plays a significant role in bicomponent gelation with helical nanofibers. The first two amino acids attached to both sides of succinic acid moiety act as a tuning button for supramolecular chirality of amino acids/peptides attached with succinic acid-based bolaamphiphiles. The second amino acid plays the role of modulating supramolecular chirality if the first two amino acids act neutrally to the chirality of bolaamphiphiles, which was confirmed by circular dichroism spectroscopy.

Enantiomeric helical TiO2 nanofibers modulate different peptide assemblies and subsequent cellular behaviors.

The effect of the morphological chirality of inorganic TiO2 nanofibers on peptide assembly and cellular behaviors was investigated. Model peptide insulin maintains its native structure and served as a growth factor for promoting proliferation and differentiation of PC12 cells on the surface of right-handed TiO2. In contrast, insulin forms amyloid fibrils and loses its bioactivity on the left-handed TiO2.

Aromatic Motifs Dictate Nanohelix Handedness of Tripeptides.

Self-assembly of peptides and amyloid fibrils offers an appealing approach for creating chiral nanostructures, which has promising applications in the fields of biology and materials science. Although numerous self-assembled chiral materials have been designed, the precise control of their twisting tendency and their handedness is still a challenge. Herein, we report the self-assembly of chiral nanostructures with precisely tailored architectures by changing the amino acid sequences of the peptides. We designed a series of self-assembling tripeptides bearing different l-amino acid sequences. The peptide with l-Phe-l-Phe sequence preferred to self-assemble into left-handed nanohelices, while with l-Phe-l-Trp right-handed nanohelices would be formed. Moreover, the diameter of the self-assembled nanohelices could be tailored by changing the terminal amino acids (His, Arg, Ser, Glu, and Asp). Circular dichroism (CD) and molecular dynamics simulations (MDSs) revealed that both of the right- and left-handed nanohelices formed by the tripeptides showed negative Cotton effects in the peptide adsorption region but exhibited nearly opposite CD Cotton effects in the aromatic regions. These results indicated that the handedness of the self-assembled helical nanofibers was not only determined by the chirality of the peptide backbone but also closely related to the aromatic stacking, hydrogen bonding and steric interactions induced by the side chains. The findings deepen our understanding on the chiral self-assembly of peptide and offer opportunities for the creation of highly functional chiral nanomaterials.

Carbon Nanofibers: A New Adsorbent for Copper Removal from Wastewater

This research describes the adsorption of Cu2+ onto a helical ribbon carbon nanofiber. The characterization of carbon nanofiber by zeta potential showed an isoelectronic pH of 1.9. The influence of different adsorption factors, such as stirring speed, temperature, pH, adsorbent concentration, etc., on the Cu2+ adsorption capacity have been evaluated. The pH has a great influence on Cu2+ adsorption, with the maximum adsorption capacity reached at a pH of 10. The experimental data fit well to pseudo-second order kinetic and Langmuir isotherm models (qm = 8.80 mg·g−1) at T = 298 K and pH = 4. The Cu2+ adsorption could be explained by the particle diffusion model. Results showed that carbon nanofiber could be successfully used for the elimination of Cu2+ from wastewater.

Handedness switch of synthesized helical polyaniline nanofibers featuring the use of a single enantiomeric acid and aniline oligomers

The polymerization of aniline (AN) was assisted with an oligomer that possessed two amino end groups (2AO) in the presence of a single enantiomeric acid, (1S)-(+)-10-camphorsulfonic acid ((S)CSA). The reaction produced helical polyaniline (PANI) nanofibers with the opposite helical sense due to the concentration changes of (S)CSA in the polymerization system. The similar dependence of the circular dichroism (CD) signal on the (S)CSA concentration was also observed in the oxidization of the oligomer 2AO by ammonium persulfate (APS) in the presence of (S)CSA. In addition, under a certain (S)CSA concentration, the 2AO-assisted polymerization at low and high temperatures also produced the PANI fibers with the opposite helical sense. It is likely that these result from the different interaction modes of (S)CSA with the 2AO at different (S)CSA concentration. As a consequence, the oxidized 2AO (oligomer seeds) with different chirality in the early stage of the polymerization control the helicity of the resulting PANI nanofibers.

Controlling Supramolecular Chirality in Multicomponent Self-Assembled Systems.

Chirality exists as a ubiquitous phenomenon in nature, from molecular level l-amino acids, d-sugar, secondary structures of proteins, DNA, RNA, and nanoscale helices to macroscopic conch and even galaxy. The aggregation of molecular building blocks with or without chiral centers might bring about asymmetric spatial stacking, which further results in the appearance of nonsymmetry in extended scales like helical nanofibers. This phenomenon, known as supramolecular chirality, is an important branch of supramolecular and self-assembly chemistry, which relates intimately with biomimetics, asymmetric catalysis, and designing chiroptic advanced materials. One of the important research focuses among supramolecular chirality is about rational manipulation of chirality amplification and handedness, presenting a profound influence on the performance of resulting soft materials such as circularly polarized luminescence and cell adhesion on hydrogels. The control over supramolecular chirality normally relies on two factors, i.e., thermodynamic and kinetic variables dependent on molecular structural parameters and environmental contributions, respectively. Supramolecular chirality in two or more component-based systems places an emphasis on thermodynamic control as it occurs from either integrated coassembly or separated self-sorting, which is more sophisticated than that of single component systems. Thus, the study on supramolecular chirality in multicomponent systems could mimic complicated biosystems, allowing for better understanding about the origin of natural chirality and extended applications as biomimetics. To date, the exploration of supramolecular chirality in multicomponent systems is restricted on both fundamental and application aspects when compared to more matured single component systems. Over the past few years, we have carried out systematic studies on several systems expressing supramolecular chirality from chiral amplification or symmetry breaking. We emphasized more the thermodynamic control by introducing a second component to form noncovalent bonding like hydrogen bonding or coordination interactions. In this Account, we would specifically discuss rational manipulation of the occurrence, transfer, and inversion of supramolecular chirality by taking several of the latest representative examples. In the multicomponent systems, in addition to the building blocks with chiral centers, the second or third components could be structural analogues and achiral small molecules such as bipyridines, melamine, metal ions, inorganic nanomaterials, and even solvents. These second or third components are able to incorporate during the aggregation to form coassembly via noncovalent bonds, influencing spatial arrangements of building blocks within various dimensions from vesicles and nanofibers to organic/inorganic hybrids. Other than chirality, morphology, stimulus responsiveness, and properties could also be well tailored by controlling interactions between different components.

Controlling Supramolecular Chirality of Two-Component Hydrogels by J- and H-Aggregation of Building Blocks.

While manipulating the helicity of nanostructures is a challenging task, it attracts great research interest on account of its crucial role in better understanding the formation mechanisms of helical systems. For the supramolecular chirality in self-assembly systems, one challenge is how to understand the origin of supramolecular chirality and inherent helicity information on nanostructures regulated by functionality-oriented stacking modes (such as J- and H-aggregation) of building blocks. Herein, two-component hydrogels were prepared by phenylalanine-based enantiomers and achiral bis(pyridinyl) derivatives, where helical nanofibers with inverse handedness as well as controllable helical pitch and diameter were readily obtained through stoichiometric coassembly of these building blocks. The helix inversion was achieved by the transition between the J- and H-aggregation of bis(pyridinyl) derivatives, which was collectively confirmed by circular dichroism, scanning electron microscopy, Fourier transform infrared spectroscopy, and single X-ray crystallography. Interestingly, the helical coassemblies with opposite handedness could be obtained not only from the enantiomeric building blocks but also from the chiral monomers with the same configurational chirality by exchanging achiral additives. This work provides insight into the origin and helicity inversion of supramolecular chirality in molecular self-assembly systems and may shine light on the precise fabrication of chiral nanostructures for potential applications in smart display devices, optoelectronics, and biological systems.

The Cooperative Effect of Both Molecular and Supramolecular Chirality on Cell Adhesion

AbstractAlthough helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd–even effect of methylene units from homochiral l‐phenylalanine derivative during assembly. An increase in cell adhesion on left‐handed nanofibers and weak influence of cell behaviors on right‐handed nanofibers are observed, even though both were derived from l‐phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left‐ and right‐handed nanofibers derived from d‐phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.