Helical Fibers Research Articles

Chiral Fibers Formation Upon Assembly of Tetraphenylalanine Peptide Conjugated to a PNA Dimer.

Self‐assembly of biomolecules such as peptides, nucleic acids or their analogues affords supramolecular objects, exhibiting structures and physical properties dependent on the amino‐acid or nucleobase composition. Conjugation of the peptide diphenylalanine (FF) to peptide nucleic acids triggers formation of self‐assembled structures, mainly stabilized by interactions between FF. In this work we report formation of homogeneous chiral fibers upon self‐assembly of the hybrid composed of the tetraphenylalanine peptide (4F) conjugated to the PNA dimer adenine‐thymine (at). In this case nucleobases seem to play a key role in determining the morphology and chirality of the fibers. When the PNA “at” is replaced by guanine‐cytosine dimer “gc”, disordered structures are observed. Spectroscopic characterization of the self‐assembled hybrids, along with AFM and SEM studies is reported. Finally, a structural model consistent with the experimental evidence has also been obtained, showing how the building blocks of 4Fat arrange to give helical fibers.

Ultrasensitive refractometer based on helical long-period fiber grating near the dispersion turning point.

Precise and accurate measurements of the optical refractive index (RI) for liquids are increasingly finding applications in biochemistry and biomedicine. Here, we demonstrate a dual-resonance helical long-period fiber grating (HLPFG) near the dispersion turning point (DTP), which exhibits an ultrahigh RI sensitivity (∼25546 nm/RIU at ∼1.440). The achieved RI sensitivity is, to the best of our knowledge, more than one order of magnitude higher than a conventional HLPFG. The ultrahigh RI sensitivity can improve the RI measurement precision and accuracy significantly. Furthermore, ultralow wavelength shifts (nearly zero) with temperature and strain ranging from 20 to 100°C and 0 to 2226 µε, respectively, are also demonstrated for the proposed HLPFG, which may be a good candidate for developing new low-cross-talk sensors.

Water-in-Oil Emulsion Gels Stabilized by a Low-Molecular Weight Organogelator Derived from Dehydroabietic Acid.

High concentrations of surfactants or gelators are usually necessary to prepare emulsions gels with unusual physicochemical properties. This situation may be improved by innovating the aggregate morphology in systems. Herein, a rosin-based molecule is designed and synthesized using dehydroabietic acid as the starting material (denoted as R-Lys-R). The molecule acts as an effective organogelator and can gelate several hydrocarbon compounds with a minimum gelation concentration of 0.2% (w/v). Analysis using atomic force microscopy (AFM) and circular dichroism (CD) reveals that in n-decane, R-Lys-R forms left-handed helical fibers with a cross-sectional diameter of approximately 15 nm. The directional hydrogen bonding of the amide group is helpful to the formation of aggregates. At concentrations of R-Lys-R above 2%, water-in-oil emulsions are transformed into emulsion gels owing to the aptitude of R-Lys-R in gelating the oil phase. The concentrations of the emulsifier can be adjusted to obtain emulsion gels with different formulations. This work reveals the potential of rosin derivatives for the formation of small molecular weight organogels and provides a novel method for the utilization of natural resources in soft materials and home care products.

Chiral Asymmetric Polarizations Generated by Bioinspired Helical Carbon Fibers to Induce Broadband Microwave Absorption and Multispectral Photonic Manipulation

AbstractChirality, in which electromagnetic characteristic promotes asymmetric polarization, is expected to realize broadband absorption for microwave absorption materials (MAMs). Herein, inspired by the microstructure of nepenthes, a scalable approach is reported for fabricating hierarchical‐chiral helical carbon fibers with broadband microwave absorption as well as multispectral chiral manipulation. The chiral potential barriers are established by applying helically distributed stress to the fiber, which induce helical electric dipoles via positive and negative charges accumulated at the potential barriers. The states of polarization loss by Debye relaxation are 2, 3, and 4 in the samples with achirality, single‐chirality, and dual‐chirality, respectively; the polar vector of achiral electric dipoles is transformed into pseudovectors through chiral potential barriers to improve the synergistically magnetic loss, and the grade of chirality is quantified based on symmetry breaking theory. The single‐chiral fibers reach strongest absorption peak value of −30.67 dB at 2.96 GHz (carbon content is 50 wt%), and the dual‐chiral fibers achieve effective absorption bandwidth (RL ≤ −10 dB) of 8.8–18 GHz. In addition to microwaves, the chiral photonic manipulation plays a role in near‐ultraviolet and visible spectra. The present discovery points to a pathway for using chiral model to open up new microwave absorption mechanism and integrated application.

Self-Stretchable Fiber Liquid Sensors Made with Bacterial Cellulose/Carbon Nanotubes for Smart Diapers.

Liquid sensors for detecting water and body fluids are crucial in daily water usage and health monitoring, but it is challenging to combine sensing performance with high tensile deformation and multifunctional applications. Here, a substrate-free, self-stretchable bacterial cellulose (BC)/carbon nanotube (CNT) helical fiber liquid sensor was prepared by the solution spinning and coiling process using BC as the water-sensitive matrix and CNTs as the active sensing materials. The BC/CNT (BCT) fiber sensor has a high stretch ratio of more than 1000% and a rapid response for a current change rate of 104% within 1 s, which is almost unaffected under washing and various stretching or knotting deformations. By combination of the BCT fiber, we can design smart diapers or water level detectors, which rapidly monitor the status of smart diapers or water level, and the monitoring result can be transferred on time through an alarm device or smartphone. In short, the scalable and continuous preparation of the self-stretchable BCT helical fiber will provide a capacious platform for the development of a wearable sensor applied in daily life (such as smart diapers, water level detection, etc.).

Spatial distribution and network morphology of epicardial, endocardial, interstitial, and Purkinje cell-associated elastin fibers in porcine left ventricle.

Cardiac extracellular matrices (ECM) play crucial functional roles in cardiac biomechanics. Previous studies have mainly focused on collagen, the major structural ECM in heart wall. The role of elastin in cardiac mechanics, however, is poorly understood. In this study, we investigated the spatial distribution and microstructural morphologies of cardiac elastin in porcine left ventricles. We demonstrated that the epicardial elastin network had location- and depth-dependency, and the overall epicardial elastin fiber mapping showed certain correlation with the helical heart muscle fiber architecture. When compared to the epicardial layer, the endocardial layer was thicker and has a higher elastin-collagen ratio and a denser elastin fiber network; moreover, the endocardial elastin fibers were finer and more wavy than the epicardial elastin fibers, all suggesting various interface mechanics. The myocardial interstitial elastin fibers co-exist with the perimysial collagen to bind the cardiomyocyte bundles; some of the interstitial elastin fibers showed a locally aligned, hinge-like structure to connect the adjacent cardiomyocyte bundles. This collagen-elastin combination reflects an optimal design in which the collagen provides mechanical strength and elastin fibers facilitate recoiling during systole. Moreover, cardiac elastin fibers, along with collagen network, closely associated with the Purkinje cells, indicating that this ECM association could be essential in organizing cardiac Purkinje cells into “fibrous” and “branching” morphologies and serving as a protective feature when Purkinje fibers experience large deformations in vivo. In short, our observations provide a structural basis for future in-depth biomechanical investigations and biomimicking of this long-overlooked cardiac ECM component.

Mutual Monomer Orientation To Bias the Supramolecular Polymerization of [6]Helicenes and the Resulting Circularly Polarized Light and Spin Filtering Properties.

We report on the synthesis and self-assembly of 2,15- and 4,13-disubstituted carbo[6]helicenes 1 and 2 bearing 3,4,5-tridodecyloxybenzamide groups. The self-assembly of these [6]helicenes is strongly influenced by the substitution pattern in the helicene core that affects the mutual orientation of the monomeric units in the aggregated form. Thus, the 2,15-substituted derivative 1 undergoes an isodesmic supramolecular polymerization forming globular nanoparticles that maintain circularly polarized light (CPL) with glum values as high as 2 × 10–2. Unlike carbo[6]helicene 1, the 4,13-substituted derivative 2 follows a cooperative mechanism generating helical one-dimensional fibers. As a result of this helical organization, [6]helicene 2 exhibits a unique modification in its ECD spectral pattern showing sign inversion at low energy, accompanied by a sign change of the CPL with glum values of 1.2 × 10–3, thus unveiling an example of CPL inversion upon supramolecular polymerization. These helical supramolecular structures with high chiroptical activity, when deposited on conductive surfaces, revealed highly efficient electron-spin filtering abilities, with electron spin polarizations up to 80% for 1 and 60% for 2, as measured by magnetic conducting atomic force microscopy.

Synthesis of inherently helical nanofibers: Effects of solidification of electrified jet during electrospinning

AbstractIn this paper, a helical fiber was fabricated through electrospinning by increasing the vapor pressure of the solvent, increasing the conductivity of the polymer solution and forming an uneven electrical field distribution around the jet. Fiber morphology during electrospinning of a dielectric polymer solution was observed to dramatically change from straight to helical due to rapid solidification of the jet as vapor pressure of the solvent increased. A similar effect was observed with conductive solutions prepared by adding large amounts of metal ion to the polymer solution. The addition of metal ion induced strong electrical stresses, causing the electrified jet to rapidly solidify in the early stage of electrospinning. Simulations revealed that the jet near the nozzle tip was subject to a strong electrical field due to increased charge density. The thickness of the emerging fiber was rapidly reduced with fast and simultaneous solidification, resulting in helical nanofibers. In addition, by using the asymmetric spinnerets, an uneven electric field distribution around jet was generated, maximizing the fiber curvature and increasing the helical fiber ratio.

Broadband edge filter based on a helical long-period fiber grating and its application to a power-interrogated torsion sensor

A broadband edge filter with linear dynamic ranges of 40 n m in wavelength and 93 % in transmission loss has been demonstrated both theoretically and experimentally, which is achieved by using a helical long-period fiber grating (HLPG) operating near the dispersion turning point (DTP) of the L P 1 , 10 mode. To take full advantage of the wide dynamic ranges, the fabricated edge filter has been successfully used as a power-interrogated torsion sensor, and the torsion responsivity presented is about 0.501 nm/(rad/m), which is higher than most conventional HLPG-based torsion sensors. The results indicate that the proposed edge filter may find applications in any other kinds of power-interrogated sensors as well.

High-Q-factor phase-shifted helical fiber Bragg grating by one-step femtosecond laser inscription for high-temperature sensing.

The phase-shifted fiber Bragg grating (FBG) plays an important role in optical communication and sensing due to its ultra-narrow 3-dB bandwidth. Here, we demonstrate the fabrication and thermal property of a high-quality (Q)-factor phase-shifted helical fiber Bragg grating (PS-HFBG). A single-mode fiber is twisted and then inscribed point-by-point with a third-order uniform FBG by a single round of laser irradiation. The grating is curved slightly into a helical shape after the torsion is released, generating a phase shift in the grating. With annealing treatment, the PS-HFBG responds very stably to temperature with a linear sensitivity of 15.24 pm/°C within the range from 100 to 1100°C. Moreover, the PS-HFBG peak tends to narrower for higher temperature and the minimum 3-dB bandwidth is as low as 32 pm, indicating the highest Q-factor of 4.91 × 104. In addition, the PS-HFBG shows a low strain sensitivity (0.896 pm/μ ε). The proposed device is very promising to be applied as a high-precision and stable high-temperature sensor.

Microfluidic fabrication of calcium alginate helical microfibers for highly stretchable wound dressing

AbstractDue to suitable biocompatibility and biodegradability, natural polymers have a wide range of applications in the biomedical field, but the defects of mechanical properties limit their performance in some practical scenarios. Here, the microfluidic method was used to spin alginate into helical fibers, and then the gaps of packed microfibers were filled with polyacrylamide (PAM) to obtain a calcium alginate/PAM composite polymer membrane. Compared with pure calcium alginate, this composite film greatly improved the flexibility and stretchability, and could be stretched up to 14 times of its original length, and not deform significantly under 300% strain for 8 cycles. It also had good transparency and skin adhesion, further guaranteeing the application potential in the field of wound dressings. The loading and release experiments showed that the calcium alginate fibers maintained a dense morphology, and could achieve higher loading efficiency and more controllable release than pure PAM. Above all, this film has great application potential in joint wound dressings, especially when loading with antibacterial substances or healing‐promoting drugs is needed. In addition, our research of achieving substantial optimization of elasticity and stretchability through the introduction of helical shape also has certain reference significance for other natural polymers limited by mechanical properties.

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

All Fiber-Optic Immunosensors Based on Elliptical Core Helical Intermediate-Period Fiber Grating with Low-Sensitivity to Environmental Disturbances.

An all fiber-optic immunosensor based on elliptical core helical intermediate-period fiber grating (E-HIPFG) is proposed for the specific detection of human immunoglobulin G (human IgG). E-HIPFGs are all-fiber transducers that do not include any additional coating materials or fiber architectures, simplifying the fabrication process and promising the stability of the E-HIPFG biosensor. For human IgG recognition, the surface of an E-HIPFG is functionalized by goat anti-human IgG. The functionalized E-HIPFG is tested by human IgG solutions with a concentration range of 10–100 μg/mL and shows a high sensitivity of 0.018 nm/(μg/mL) and a limit of detection (LOD) of 4.7 μg/mL. Notably, the functionalized E-HIPFG biosensor is found to be insensitive to environmental disturbances, with a temperature sensitivity of 2.6 pm/°C, a strain sensitivity of 1.2 pm/με, and a torsion sensitivity of −23.566 nm/(rad/mm). The results demonstrate the considerable properties of the immunosensor, with high resistance to environmental perturbations, indicating significant potential for applications in mobile biosensors and compact devices.

Rod and Helical Organic Fiber Structures Revealing Lamellar and Rosette Ordering Pathways in Self-Assembly of Barbiturate Oligothiophene Derivatives

Rod and Helical Organic Fiber Structures Revealing Lamellar and Rosette Ordering Pathways in Self-Assembly of Barbiturate Oligothiophene Derivatives

Helical Fiber Strain Sensors Based on Triboelectric Nanogenerators for Self-Powered Human Respiratory Monitoring.

Respiration is a major vital sign, which can be used for early illness diagnosis and physiological monitoring. Wearable respiratory sensors present an exciting opportunity to monitor human respiratory behaviors in a real-time, noninvasive, and comfortable way. Among them, fiber-shaped triboelectric nanogenerators (FS-TENGs) are attractive for their comfort and high degree of freedom. However, the single-electrode FS-TENGs cannot respond to their own tensile strains, and the coaxial double-electrode FS-TENGs show low sensitivity to strain due to structural limitations. Here, a type of helical fiber strain sensor (HFSS) is developed, which can respond to tiny tensile strains. In addition, a smart wearable real-time respiratory monitoring system is developed based on the HFSSs, which can measure some key breathing parameters for disease prevention and medical diagnosis. An intelligent alarm can automatically call a preset mobile phone for help in response to respiratory behavior changes. This work provides an effective helical structure for fabricating highly sensitive strain sensors based on FS-TENGs and develops wearable self-powered real-time respiratory monitoring systems.

Hysteresis Nanoarchitectonics with Chiral Gel Fibers and Achiral Gold Nanospheres for Reversible Chiral Inversion.

Intelligent control over the handedness of circular dichroism (CD) is of special significance in self-organized biological and artificial systems. Herein, we report a chiral organic molecule (R1) containing a disulfide unit self-assembles into M-type helical fibers gels, which undergoes chirality inversion by incorporating gold nanospheres due to the formation of Au-S bonds between R1 and gold nanospheres. Upon heating at 80 °C, the aggregation of gold nanospheres results in a disappearance of the Au-S bond, allowing the reversible switching back to M-type helical fibers. The original chirality of M-type fibers could also be retained by adding anisotropic gold nanorods. A series of characterization methods, involving CD, Raman, Infrared spectroscopy, electric microscopy, and small-angle X-ray scattering (SAXS) measurements were used to investigate the mechanism of chiral evolutions. Our results provide a facile way of fabricating hysteresis nanoarchitectonics to achieve dynamic supramolecular chirality using inorganic metallic nanoparticles.

Femtosecond laser inscribed helical long period fiber grating for exciting orbital angular momentum.

A method employing femtosecond lasers to inscribe helical long period fiber grating (HLPFG) for exciting orbital angular momentum (OAM) of light is experimentally demonstrated. In this method, the refractive index modulation (RIM) of HLPFG is realized by three-dimensional translation of a fiber without rotation, indicating better stability, repeatability and flexibility. The coupling efficiency can be customized by varying the radius of the helical RIM, except laser energy. The characteristics of phase and polarization purity of the coupled modes in HLPFGs are studied. Results show that HLPFGs can directly excite OAM modes, the polarization state and helical phase of the mode can be adjusted independently, and the purity is the highest at resonant wavelength, over 91%.

Coiled‐Coil Helical Nano‐Assemblies: Shape Persistent, Thixotropic, and Tunable Chiroptical Properties

AbstractHere, we studied the self‐assembly and chiroptical properties of four C2‐symmetric molecules bearing terephthaloyl (TLF−C4 and TLF−C12) and benzene‐1,4‐dicarbonyl core (BLF−C4 and BLF−C12). β‐turn in the aggregates of TLF−C4 and TLF−C12 was found irrespective of the amount of water as anti‐solvent in methanol (MeOH). Interestingly, chiroptical properties can be switched from β‐turn to twisted β‐sheet secondary structure in BLF−C4 and BLF−C12 beyond a certain amount of water in MeOH. Detailed studies suggested lamellar arrangement of the TLF−C4 gelators with a β‐turn led to the formation of right‐handed coiled‐coil helical fibers. However, left‐handed coiled‐coil twisted fibers were formed by lamellar packing (twisted β‐sheet) of BLF−C4. In addition, TLF−C12 gel in methylcyclohexane (MCH) revealed shape persistent gelation. Rapid dynamic equilibrium between association and dissociation of non‐covalent interactions in BLF−C12 gel in MCH resulted in thixotropic and, in turn, injectable behavior.

Centrifugal Assembly of Helical Bijel Fibers for pH Responsive Composite Hydrogels.

In microfluidics, centrifugal forces are important for centrifugal microfluidic chips and curved microchannels. Here, an unrecognized use of the centrifugal effect in microfluidics is introduced. The assembly of helical soft matter fibers in a rotating microcapillary is investigated. During assembly, the fibers undergo phase separation, generating particle stabilized bicontinuous interfacially jammed emulsions gels. This process is accompanied by a transition of the fiber density over time. As a result, the direction of the centrifugal force in the rotating microcapillary changes. The authors analyze this effect systematically with high-speed video microscopy and complementary computer simulations. The resulting understanding enables the control of the helical fiber assembly into microropes. These microropes can be converted into pH responsive hydrogels that swell and shrink with potential applications in tissue engineering, soft robotics, controlled release, and sensing. More generally, the knowledge gained from this work shows that centrifugal forces potentially enable directed self-assembly or separation of colloids, biological cells, and emulsions in microfluidics.

Tunable Spun Fiber Constructs in Biomedicine: Influence of Processing Parameters in the Fibers' Architecture.

Electrospinning and wet-spinning have been recognized as two of the most efficient and promising techniques for producing polymeric fibrous constructs for a wide range of applications, including optics, electronics, food industry and biomedical applications. They have gained considerable attention in the past few decades because of their unique features and tunable architectures that can mimic desirable biological features, responding more effectively to local demands. In this review, various fiber architectures and configurations, varying from monolayer and core-shell fibers to tri-axial, porous, multilayer, side-by-side and helical fibers, are discussed, highlighting the influence of processing parameters in the final constructs. Additionally, the envisaged biomedical purposes for the examined fiber architectures, mainly focused on drug delivery and tissue engineering applications, are explored at great length.