By virtue of ultra-flexibility and non-inductive feature, fibrous electrode is an ideal platform for constructing wearable electronics and implantable electrodes for medical therapy. 2D nanofluidic channels with tailored ion transport dynamics enable minimized charge transfer resistance and efficient ion transport capability. Thus, combining the nanofluidic ion transport features and fibrous electrode advantages, 2D nanofluidic fiber electrode presents a series of extra advantages of unidirectional efficient ion transport and great biofriendliness. In this minireview, we first elaborate the architecture characteristics of the emerging 2D nanofluidic fibers and highlight the intriguing features, such as tunable interlayer spacing, efficient ion transport and modifiable channel surface. Conventional strategies for constructing 2D nanofluidic fibers have been systematically enumerated, including solvent volatilizing regulation, confinement triggered alignment, and flow-driven orientation. In addition, the promising applications of 2D nanofluidic fibers have been also summarized as well. Finally, we analyze the challenges and perspectives of fibrous 2D nanofluidic construction, ion transport mechanism study and potential application extension.
Electrospinning has drawn wide attention for its powerful capacity to produce ultrafine nanofibers (UNFs) from various materials. These UNFs demonstrated significantly enhanced performance, such as ultra-high surface area, more porosity and stronger mechanical properties. Here, we comprehensively review their basic principles, state-of-the-art methods and preponderant applications. We begin with a brief introduction to the refinement theory of polymer jets, followed by discussion of factors affecting fiber refinement. We then discuss the refining strategies from the aspects of solution properties, spinning parameters, auxiliary force and post-treatment. Afterward, we highlight the most relevant and recent applications associated with the remarkable features of UNFs, including filtration materials, supercapacitors, biomedical materials and other applications. At the end, we offer perspectives on the challenges, opportunities, and new directions for future development of electrospun UNFs.
Polymer nanofibers attract more and more attention from academia and industry continuously due to their desirable properties, including high specific surface area, high porosity, and numerous chemically-active surface groups on the fiber surface. Gas flow was widely adopted to fabricate nanofibers such as solution blown, melt blown, gas flow-assisted melt electrospinning, and bubble electrospinning. However, a comprehensive review covered the roles that gas flow played in fabricating nanofibers, and their mechanism has not been analysed yet. This review classifies the roles of gas flow into jet initialization, jet stretching, increasing production, surface modification, and inhibition of thermal degradation, to deepen the understanding of gas flow during nanofiber preparation. The mechanism of gas flows in the above fields is reviewed in detail.
As a potential electrochemical energy storage device, zinc–air batteries (ZABs) received considerable interest in the field of energy conversion and storage due to its high energy density and eco-friendliness. Nevertheless, the sluggish kinetics of the oxygen reduction and oxygen evolution reactions limit the commercial development of ZABs, so it is of great significance to develop efficient, low-cost and non-noble metal bifunctional catalysts. Electrospun one-dimensional nanofibers with unique properties such as high porosity and large surface area have great advantages on possessing more active sites, shortening the diffusion pathways for ions/electrons, and improving the kinetics via intercalation/de-intercalation processes, which endow them with promising application in the field of energy storage devices, especially ZABs. This review firstly introduces the electrospinning technique. Then, the oxygen reduction/evolution reaction triggered by electrospun nanofibers with self-supported structures are presented, followed by the application of electrospun nanofibers for liquid and flexible solid-state ZABs. Finally, the remaining challenges and research directions of ZABs based on electrospun nanofibers electrocatalysts are briefly discussed.
The surface morphology of micro- and nano- scale fiber determines its application to a great extent. At present, a variety of secondary morphology of microfibers and nanofibers, such as porous, wrinkle, groove and so on, have been prepared. Among them, grooved micro- and nano- fibers are attracting more and more attention because of their unique morphology and properties. In this paper, we review the literature on grooved fibers due to void-based elongation, wrinkle-based elongation, collapsed jet-based elongation and selective dissolution. By contrast, the method of phase separation is simpler and more commonly used than selective dissolution. What is more interesting is that the number and depth of grooves on the fiber surface can be well controlled by adjusting the experimental parameters, which greatly increases the research value and application fields of grooves micro-nano fibers. Grooved fibers can be made from a range of materials: polycaprolactone (PCL), polylactic acid (PLA), polystyrene (PS), cellulose acetate butyrate (CAB) and other polymers. The applications of grooved micro-nano fibers are discussed in detail, including peripheral nerve regeneration, water manipulation and energy conversion.
Yarn-based strain sensors (YSSs) have shown great promising in the fabrication of wearable devices for their good comfortability and flexible designability. However, the false signals generated by the changes in the yarn structure of the YSSs are usually ignored. In this study, the generation, the characteristic, and the prediction of these signals were investigated. We recognized that these signals are composed of two negative pseudo peaks and a spurious resistance response plateau. These responses are found to have nothing in common with a true tensile strain, but be attributed to plastic deformation of the fibers. This is due to the fact that the deformation of YSSs exceeds the linear elastic range of the fibers. Although the use of pure elastic fibers can eliminate the spurious resistance response plateau, it will lead to an increase in the pseudo peak to the value compared with a true strain signal peak. Hence, a theoretical model was established to decouple the real signals from the false responses, ensuring the high sensing accuracy of YSSs for applications in wearable devices and artificial intelligence interfaces. This work provides an in-depth understanding of the response of the YSSs, which might provide inspiration and guidance in the design of high-accuracy fiber-based strain sensors.
To achieve dexterous motion controlling of robot, the sensors that function like human neurons for motion perception are essential. In this work, a silica microfiber probe-based optical neuron (MPON) for robot finger motion detection is proposed. The silica microfiber probe was fabricated by snapping a biconical silica optical microfiber that drawn from the standard optical fibre. Then it was embedded into thin polydimethylsiloxane (PDMS) to detect and recognize motions of robotic finger. Specifically, a PDMS-Teflon-Microfiber-Teflon-PDMS composite structure was prepared to protect the waveguide structure of silica microfiber probe and avoid the environmental pollution. With the help of this composite structure, the proposed MPON achieved the accurate measurement of bending angle with large range and fast response. The repeatability and stability of MPON were also investigated. Additionally, different finger motions were successfully distinguished through observing the output power variation of MPON. The proposed MPON could serve as the perceptron of robot hand, which could be applied in dexterous gesture control even human machine interaction.
Ultra-high molecular weight polyethylene (UHMWPE) membranes were prepared by 5 wt% UHMWPE/paraffin oil gels via thermally induced phase separation method and dried in air without significant collapse. The UHMWPE membranes were annealed at 110 °C for increasing the pores size in order to decrease the capillary forces. Furthermore, a new multiple stage extractant exchange drying (MSEED) technique was adopted to decrease the shrinkage of the UHMWPE membranes. Specifically, the paraffin oil was extracted by dichloromethane, then dichloromethane was replaced by ethanol, next ethanol could be exchanged to other liquid which is non-affinity with UHMWPE, for example water. UHMWPE membranes (annealing for 25 min) dried by dichloromethane-ethanol–water-air process have the lowest volume shrinkage of 16.5% and the porosity is as high as 88.29%. Moreover, compared with supercritical CO2 (SC-CO2) drying, atmospheric drying UHMWPE membranes have a lower pure water permeance, but a higher carbon particles rejection.
Electrochemical therapy emerged as a low-cost and effective method for tumor ablation. However, it has challenges such as the production of toxic byproducts and the use of rigid electrodes that damage soft tissues. Here, we report a new injectable and tissue-compatible fiber therapeutic electronics for safe and efficient tumor treatment. The design of aligned carbon nanotube (CNT) fiber as electrodes endowed the device with high softness and enabled mini-invasive implantation through injection. Under a mild voltage (1.2 V), the fiber device released hydroxyl ions to alter the local chemical environment of the tissues without additional toxic products/gases, leading to immediate death of tumor cells. The flexible fiber device could form stable interface with tissues and showed good biocompatibility after implantation for 30 days. The in vitro experimental results showed the fiber device could efficiently kill 90.9% of QGY-7703 cancer cells after a single treatment in a few minutes. The tumor-bearing animal models proved that the fiber therapeutic device could effectively inhibit the growth of tumor tissues, indicating it is a safe, effective, controllable and low-cost method for tumor therapy.
In the present work, novel cellulose (C)/Antarctic krill protein (AKP) composite fibers with a multiple cross-linking network were prepared using glutaraldehyde (GA) as cross-linking agent to improve the fiber's properties. The structure and properties of fibers were characterized by different techniques including FTIR, NMR, XRD, SAXS, SEM and electronic single yarn strength tester, etc. The results indicate that the reaction of GA with C and AKP separately forms a multiple cross-linking network. The C/AKP composite fibers with a multiple cross-linking network has stronger crystallization ability, higher orientation degree and deeper trench than C/AKP composite fibers. The breaking stress and wet strength of composite fibers reaches the maximum of 1.04 cN/dtex and 0.55 cN/dtex at GA content of 0.2 wt%. And the fatigue and tensile properties, hygroscopicity and moisture retention of C/AKP composite fibers has been improved. The development of C/AKP composite fibers with a multiple cross-linking network could be a promising candidate for biomedicine applications.
Macroscopic assembly of graphene sheets has renovated the preparation of neat carbonaceous fibers with integrating high performance and superior functionalities, beyond the pyrolysis of conventional polymeric precursors. To date, graphene microfibers by the liquid crystalline wet-spinning method have been established. However, how to reliably prepare continuous neat graphene nanofibers remains unknown. Here, we present the electrospinning of neat graphene nanofibers enabled by modulating colossally extensional flow state of graphene oxide liquid crystals. We use polymer with mega molecular weight as transient additives to realize the colossal extensional flow and electrospinning. The neat graphene nanofibers feature high electronic quality and crystallinity and exhibit high electrical conductivity of 2.02 × 106 S/m that is to be comparable with single crystal graphite whisker. The electrospinning of graphene nanofibers was extended to prepare large-area fabric with high flexibility and superior specific electrical/thermal conductivities. The electrospinning of graphene nanofibers opens the door to nanofibers of rich two-dimensional sheets and the neat graphene nanofibers may grow to be a new species after conventional carbonaceous nanofibers and whiskers in broad functional applications.
Electrospinning of neat graphene nanofibers is realized by achieving the colossal extension flow of GO dispersion with the assistance of mega polymer. Neat graphene nanofibers and fabrics show good continuity, high crystallinity, excellent conductivity and thermal conductivity, having great potentials in extensive applications.
The molecular weight of ultra-high molecular weight polyethylene (UHMWPE) fibers is severely decreased compared with raw materials due to high temperature and strong shearing in the dissolving process. In this study, we reported a novel method to assist the dissolving of UHMWPE in paraffin oil without severe degradation in order to improve the tensile strength of resultant fibers. UHMWPE fibers with relatively high molecular weight and more excellent disentanglement effect were prepared by gel-spinning with UHMWPE suspension treated with supercritical carbon dioxide (SC-CO2). The dynamic thermomechanical, mechanical and crystalline properties of UHMWPE extracted fibers and drawn fibers were researched comprehensively. UHMWPE extracted fibers obtained after SC-CO2 treatment display a higher molecular weight. More importantly, it is clear that the disentanglement of UHMWPE gel fibers gained by processing SC-CO2 has been significantly promoted compared with that without SC-CO2 treatment from dynamic thermomechanical and rheological results, which could also be demonstrated from the cross-sectional morphology of UHMWPE extracted fibers. Furthermore, the tensile strength of UHMWPE fibers prepared through SC-CO2 treating is able to attain 30.11 cN/dtex, increased by 10.3% in comparison to UHMWPE fibers gained without assistance of SC-CO2. Beyond that, the thermal behavior and crystallization performance of UHMWPE extracted fibers and drawn fibers acquired by way of SC-CO2 treatment have also been enhanced.
Biphasic drug release is a popular advanced drug controlled release profile that has been drawing increasing attention from many fields. Electrospun nanofibers and their derivatives can be act as a strong platform for developing biphasic release dosage forms. In this study, a modified coaxial electrospinning was implemented, in which little molecule solutions that contain a drug ibuprofen (IBU) and polyethylene glycol (PEG) were exploited as a sheath fluid to surround the core solutions composed of polymer ethyl cellulose (EC) and IBU. The prepared nanofiber-based structural hybrids, i.e., engineered spindles-on-a-string (SOS) products, were successfully created and subjected to a series of characterizations. Scanning electron microscopy and transmission electron microscopy results showed the engineered SOS structures. IBU and the carriers EC and PEG had good compatibility, as suggested by X-ray diffraction and Fourier transform infrared spectroscopy assessments. In vitro dissolution tests verified that the SOS products were able to provide a typical biphasic release profile, releasing 40% of the loaded IBU within 1 h in an immediate manner in the first phase, and the rest of the IBU in a sustained manner in the second phase. A combined mechanism of erosion and diffusion is proposed for manipulating the IBU molecule release behaviors.