This paper describes the preparation of Ni/Pt/CNFs via electrospinning technology, carbonization process, and chemical reduction method. The structure and composition of Ni/Pt/CNFs were characterized with X-ray diffraction, Raman spectroscopy, nitrogen adsorption isotherms, and X-ray photoelectron spectroscopy. Meanwhile, the morphology was analyzed with scanning electron microscopy and transmission electron microscopy. The electrochemical performance was evaluated by oxygen reduction reaction (ORR), cyclic voltammetry and chronopotentiometry. The results indicated that Pt and Ni nanoparticles were completely reduced in the experimental process and homogeneously distributed on the nanofibers with the average diameters of 3.8 and 17.8 nm, respectively. In addition, the Ni50/Pt/CNFs catalyst showed excellent electrocatalytic performance for ORR and superior specific and mass activities for methanol oxidation (the maximum current density is ca. 10.9 mA cm–2) and exhibited a slightly slower current decay over time, better than the reference samples which indicated a higher tolerance to CO-like intermediates.

•Core–shell fibers enriched with Fe/S-N active sites for ORR.•Core–shell fibers prepared via electrospinning and photopolymerization.•The catalyst showed high catalytic activity.One-dimensional (1D) nanomaterials have gained attention in energy conversion, storage, and catalyst due to the unique physical and chemical properties. Electrospinning is a kind of simple, versatile, and cost-effective technology to fabricate 1D functional nanofibers. Herein, electrospun polyacrylonitrile (PAN), melamine, and ferric chloride hexahydrate (FeCl3·6H2O) composite nanofibers are used as template, and polythiophene (PT) are prepared by photopolymerization technology on the surface of electrospun nanofibers as shell part of fibers. Then, the core–shell nanofibers are pyrolyzed and converted into Fe–S/N–C nanofibers, which can be used as catalysts for ORR due to the metal and S-/N-codoped structure and unique 1D structure which provided facile pathways for efficient mass transport and charge transfer. The ORR electrocatalytic ability of Fe–S/N–C nanofibers is tested and present excellent property, especially in stability and methanol crossover. The electrocatalytic ability of sample is comparable to that of 20 wt% Pt/C benchmarks. These results offer an easy pathway for exploring metal-heteroatom-codoped carbon nanofibers applicable for ORR catalyst.Schematic illustration of the fabrication process of Fe–S/N–C nanofibers via electrospinning and photopolymerization.Download high-res image (152KB)Download full-size image

•PAN/PDMS core-shell nanofibers were fabricated by synchronous ptotopolymerization during electrospinning process.•Monomer migrated to the surface of polymer fluid jet to cause phase separation with the evaporation of solvent.•We applied UV irradiation in N2 atmosphere, which ensure that photopolymerization could be conducted completely.Different from the traditional method for fabricating core-shell structure nanofiber, the PAN/PDMS nanofibers with core-shell structure (PAN as the core layer and PDMS as the shell layer) have been illustrated, which combines with the synchronous photopolymerization during emulsion electrospinning process. The morphology and structure of as-fabricated PAN/PDMS nanofibers are characterized by SEM and TEM. The composition of PAN/PDMS nanofibers is characterized by FTIR, XPS, TG, and DTG, successfully. The photopolymerization process is characterized by UV–vis spectroscopy indirectly. The WCA tests show that it has good hydrophobicity, which makes it possible as functional material. Meanwhile, the most important thing is that the method provides a flexible design strategy of core-shell structure nanofibers.The fabrication process included three main stages. Firstly, microphase separation occurred at the tip of the needle with electrostatic stretching and solvent evaporation. Secondly, the photoinitiator on the surface of polymer fluid jet was decomposed to induce photopolymerization by UV irradiation. Finally, photopolymerization happened on the surface of polymer fluid jet to form PAN/PDMS core-shell structure nanofibers.Download high-res image (331KB)Download full-size image

•HA/CS core-shell nanofibers are prepared via electrospinning.•Electric field induces phase separation, and leads CS and HA migrate.•The nanofibers showed more controlled and sustained release.The core-shell polyelectrolyte complexes chitosan (CS)/hyaluronic acid (HA) nanofibers could be produced from electric field inducing phase separation during the progress of electrospinning. The morphology of core-shell nanofibers was supported using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence of CS on the shell of the nanofibers was also verified by X-ray photoelectron spectroscopy (XPS) analysis as further evidence of core-shell formation. In the electrospinning process, the protonated CS molecules migrated in the direction of the electric field, whereas the ionized HA molecules migrated in the opposite direction. Methylthiazolydiphenyl-tetrazolium bromide (MTT) assay was employed to investigate the toxic and cytocompatibility with the possible application for tissue engineering scaffolds. The drug release from core–shell nanofiber in vitro was investigated by UV spectrophotometry. The release profiles for core–shell nanofibers showed more controlled and sustained release. while fibroblasts cells could still adhere to and proliferate on the drug-loaded core–shell nanofiber membranes. The results implied that core-shell polyelectrolyte complexes CS/HA nanofibers encapsulating drugs have great potential in tissue engineering scaffolds.Download high-res image (159KB)Download full-size image

In this work, a bimetal-organic framework/graphene oxide with sandwich-type structure as a precursor is prepared by the solvent-thermal approach. A nanoporous reduced graphene oxide (rGO) nanosheets enriched with Fe, Co and N (Fe/Co-N) co-doped active sites is prepared followed by a high temperature carbonization and acid leaching (AL) process. When the molar ratio of Fe/Co is 0.40 before carbonization, the prepared sample exhibits optimized electrocatalytic activity (a high onset potential (0.98 V vs. RHE), half-wave potential (0.84 V vs. RHE), and a large limiting current density (-5.46 mA cm−2 at 0.21 V vs. RHE) as oxygen reduction reaction (ORR) electrocatalysts. Most importantly, the duration stability and methanol tolerance of the as-prepared sample are better than common commercial 20 wt% Pt/C under 0.10 M KOH alkaline condition. These results demonstrate the co-doping of bimetal Fe/Co and heteroatom N, excellent electrical conductivity of rGO and large surface area of nanoporous structure enhance the electrocatalytic activity. The successful synthesis of such nanoporous rGO nanosheets provides a facile way to explore a series of 2D non-precious metal electrocatalysts for energy conversion and storage devices.

•Chondroitin sulfate/polyvinyl alcohol nanofibres was prepared by electrospinning.•The nanofibres showed excellent cell compatibility in vitro.•The drug-loaded nanofibres used as a model for testing drug release.Composite nanofibres were prepared by electrospinning from a solution of chondroitin sulfate and polyvinyl alcohol. The chondroitin sulfate/polyvinyl alcohol (CS/PVA) mass ratios of 7/3 has a uniform and smooth morphology, and the average diameter of the nanofibres was 136 nm. Combretastatin A-4 phosphate was loaded on the nanofibres and used as a model for testing drug release from the nanofibres crosslinked with glutaric dialdehyde. The morphology and structure of the nanofibres was determined using scanning electron microscopy. In order to assess their possible application to tissue engineering scaffolds, the toxicity and cytocompatibility of the nanofibres were tested by methylthiazolydiphenyl-tetrazolium bromide assay.

In this study, we have fabricated of Polyacrylonitrile/Zeoliticimidazolate frameworks (PAN@ZIF-8) core–shell nanofibers by combining electrospinning techniques and the MOF synthesis method. In the first step, 2MI ligand was dispersed on PAN by using electrospinning, and then 2MI was made to coordinate Zn2+ ions derived from a zinc acetate solution. In the second step, the nanofiber mats were immersed in a ZIF-8 seed solution, and continuous and compact ZIF-8 was formed on the PAN surface by a second round of crystal growth. Analyses of XPS results and of SEM and TEM images revealed the core–shell structure of PAN@ZIF-8 nanofibers, and showed them to have a uniform nanoshell but a variety of crystal diameters. In addition, the core–shell PAN@ZIF-8 nanofibers were found to display unique properties such as a stable and flexible structure and an excellent gas adsorption capability. Our findings suggest that the core–shell PAN@ZIF-8 nanofiber mats may form a good filter material because of their gas absorption properties and because of the structural flexibility and stability of ZIF-8.

In the present study, PVP/Ag nanofibers with a core–shell structure have been successfully prepared by using the electrospinning technique under the action of electric field induction. PVP (polyvinyl pyrrolidone), as the functional template during electrospinning, plays an important role both as the reducing agent and as the capping agent. The structure and properties of the thus-obtained nanofibers have been investigated thoroughly through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have also been employed to analyze the coordination interactions and chemical states of the core–shell nanofiber surface. Moreover, a static simulation of an electric-field-induced experiment has been carried out and energy-dispersive X-ray analysis (EDS) has been performed to demonstrate the field-induced mechanism. The results prove the fact that the electric field plays an important role on the induction of silver migration and formation of core–shell nanofibers. On the other hand, UV-Vis spectrophotometry has been used to test the catalytic properties of the samples for the reduction of methylene blue (MB) by NaBH4, it shows that PVP/Ag core–shell nanofibers hold great potential in the field of catalysis.

•PEO/HA core–shell nanofibers are prepared via electrospinning.•Electric field induces phase separation during the electrospinning.•Hyaluronic acid would move in the opposite direction.Core-shell structured PEO/HA nanofibers could be produced from electric field inducing phase separation during the electrospinning progress. Hyaluronic acid (HA) molecules could move along the opposite direction of the electric field under the electrostatic force, which induced phase separation from PEO to form the core layer of nanofibers. The morphology of core–shell nanofibers was supported using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermal analysis and X-ray diffraction (XRD) results showed that the fibers had good thermal stability and HA hindered the crystallization of the PEO. The presence of PEO on the surface was also verified by X-ray photoelectron spectroscopy (XPS) analysis as further evidence of core–shell formation during the process of electrospinning. Methylthiazolydiphenyl-tetrazolium bromide (MTT) assay was employed to investigate the toxic and cytocompatibility with the aim of demonstrating the possible application for tissue engineering scaffolds. Furthermore, In vitro cytotoxicity against fibroblasts cells culture demonstrated the nanofibers as scaffolds were biocompatible and nontoxic.

•Morphologies of CaCO3 were obtained by the co-effect of chitosan and positively charged monomers.•The effect of monomers on mineralization of CaCO3 was investigated.•The reason of monomers on mineralization of CaCO3 was analyzed.Amines monomers, N,N-dimethylaminoethyl methacrylate (DMAEMA), N,N-dimethylethanolamine (DMEA), 2-dimethylaminoethylamine (DMEDA) and N-methiyldiethanolamine (MDEA) were used to induce the formation of calcium carbonate (CaCO3) crystals on chitosan films, by using (NH4)2CO3 diffusion method at ambient temperature. The obtained CaCO3 particles were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The influence of reaction variables, such as the additive concentration and their types were also investigated on the products. The morphologies of CaCO3 crystals, inter-grown in cube-shape, were controlled by DMAEMA and DMEA. It was observed that the morphologies of CaCO3 changed from the cube grown arms to massive calcite with a hole on the face by increasing the concentrations of DMEDA and MDEA. While the precipitation grew on chitosan film without any organic additive, only single cube-shaped crystals were obtained. By these results the possible mechanisms can be proposed that electronic movement of the groups on the monomer effected ions configuration and molecules absorbed on the exposed surface, resulted the change of the surface energy, which caused the change in the morphology of CaCO3.

•Alginate/chitosan layer-by-layer composite coatings were prepared on titanium substrates via electrodeposition at room temperature•The thickness of the deposited chitosan layer and alginate was about 20 μm and 10 μm, respectively•Provides opportunities in the fabrication of functional coatings on titanium substrates.In this study, alginate/chitosan layer-by-layer composite coatings were prepared on titanium substrates via electrodeposition. The mechanism of anodic deposition of anionic alginate based on the pH decrease at the anode surface, while the pH increase at the cathode surface enabled the deposition of cationic chitosan coatings. The surface of coatings was characterized by using attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The properties of coatings were characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). Indirect in vitro cytotoxicity test showed that the extracts of coating had no significant effects on cell viability. Moreover, in vitro cytocompatibility test exhibited cell population and spreading tendency, suggesting that the coatings were non-toxic to L929 cells. However, the results revealed that alginate coating was more benefit for cells growing than chitosan coating. The results indicated that the proposed method could be used to fabricate alginate/chitosan layer-by-layer composite coatings on the titanium surface at room temperature and such composite coatings might have potential applications in tissue engineering scaffolds field.

•The HA fiber mats have been prepared via a facile approach – lyophilization.•The water-resistance property has been enhanced by cross-linked via EDC.•The degradation rate could be controlled by the cross-linking time with EDC.•The degradation rate was rapidly in PBS because of the strong ionic environments.The hyaluronic acid (HA) fibers scaffold with an extracellular matrix mimic structure has been prepared via lyophilization. The morphology of the HA fibers varying the concentration from 0.05 wt% to 0.15 wt% was characterized by scanning electron microscope (SEM). The diameter of HA fibers increased and the morphology changed from fiber to sheet-like structure as the concentration of HA solution increased. To enhance the water-resistance, the pure HA fiber membranes were chemical cross-linked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), and confirmed by fourier transform infrared (FT-IR) spectra. In vitro degradation behavior of cross-linked HA fiber membranes in both of water and PBS solutions was investigated, the physical properties were also studied by differential scanning calorimetry (DSC) and thermogravimetry (TG). The results showed that the bonding water capacity increased after crosslinking, and indicated that the crosslinked HA fibers could be used as scaffold in tissue engineering.

Polyelectrolyte complex (PEC) membrane of cationic chitosan and anionic sodium alginate with fiber structure were prepared by freeze-drying method. Chitosan and sodium alginate were blended in different concentrations and frozen at different temperatures. Freeze-dried fiber membranes were extensively characterized for their inter-molecular interaction, the solution property, morphology and biocompatibility by using FTIR, XRD, zeta (ζ) potentials, SEM and cytotoxicity assay. The study of swelling property showed that PEC membrane with the fiber structure cross-linked with glutaraldehyde exhibited pH and ionic strength-dependent swelling in aqueous media, which might have a potential application in tissue engineering or drug controlled release. Furthermore, chitosan–sodium alginate samples showed better cell adhesion and proliferation than pure chitosan. The results indicated that two natural polyelectrolyte complex nanofibers were prepared by freeze-drying method and fitted for tissue engineering or as drug carriers.

The present work was focused on the preparation and characterization of polyelectrolyte complex (PEC) fibers based on the natural oppositely charged biopolymers, chitosan and sodium hyaluronate, via a freeze-drying method. The physical structure and chemical properties of the freeze-dried fibers were characterized by means of Fourier transform infrared spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The morphology, size, and surface structure of the freeze-dried PEC fibers were observed by means of scanning electron microscopy (SEM). An indirect in vitro cytotoxicity test showed the extracts of fibers had no significant effects on cell viability. Moreover, an in vitro cytocompatibility test exhibited cell population and spreading tendency, suggesting the fibers were non-toxic to L929 cells. All the results indicated that such freeze-dried PEC fibers might have potential applications in tissue engineering scaffolds.

The polyvinylpyrrolidone (PVP)/poly(vinylidene fluoride) (PVDF) core–shell nanofiber mats with superhydrophobic surface have been prepared via electrospinning its homogeneous blending solutions, and the formation of the core–shell structure was achieved by the thermal induced phase separation assisted with the low surface tension of PVDF. The electrospinnability of the blending solutions was also investigated by varying the blending ratio of the PVP and PVDF, and it enhanced with the increase of PVP content. SEM and TEM results showed that the fibers size was varied in the range of 100 nm–600 nm with smooth surface and core–shell structure. The composition of the shell layer was determined by the XPS analysis, and further confirmed by water contact angle (WCA) testing. As the fraction of PVDF exceeding PVP in the electrospinning solutions, the nanofiber mats showed superhydrophobic property with the WCA above 120°. It indicated that the PVDF was concentrated in the shell layer of the fibers. X-Ray diffraction (XRD) and attenuated total reflection infrared spectroscopy (ATR-IR) analysis indicated that the PVDF was aggregated with the β-phase crystallite as dominant crystallite. The nanofiber mats with the gas breathability and watertightness ability due to the porous structure and superhydrophobic would be potential applied in wound healing.

2-(3,4-Methylenedioxyphenyl)-4,6-bis-(trichloromethyl)-1,3,5-triazine as a visible light photo-initiator was used for creation of dental composite. UV-Vis absorption spectroscopy was applied to investigate photochemical behavior of initiator during the photochemical process. For the copolymerization of 2,2-bis-[4-(2-hydroxy-3-methacryloxypropoxy) phenyl] propane/triethylene glycol dimethacrylate (75/25 wt %) in the presence of photoinitiator the optimum cure rate was found; the cure rate increased with the increase in photoinitiator concentration. Compared to the commonly used tertiary amines, the camphorquinone/2-(3,4-methdioxyphenyl)-4,6-bis-(trichloromethyl)-1,3,5-triazine system reacted more quickly and the final conversion were higher than that of traditional camphorquinone/ethyl 4-N,N-dimethyl aminobenzoate system.

A water vapor induced phase separation (WVIPS) electrospinning process for the preparation of core–shell nanofibers with a single capillary is described. The PAN–PVP core–shell nanofibers were fabricated by WVIPS electrospinning a polyvinylpyrrolidone (PVP)–polyacrylonitrile (PAN) homogeneous solution. The solvent solubility parameter of the liquid electrospinning jets was altered by water vapor, which subsequently induced the phase separation before the solvent rapidly volatilized, and caused the formation of core–shell structured nanofibers. A scanning electron microscope (SEM) and transmission electron microscope (TEM) were applied to characterize the morphology. X-ray photoelectron spectroscopic analysis (XPS), water contact angle (CA) tests and thermogravimetry analysis (TGA) were used to confirm the composition of the fiber’s shell. The results of TGA also showed an improvement in the thermal stability of the fiber membranes.

Core–shell structure nanofibers of sodium alginate/poly(ethylene oxide) were prepared via electrospinning their dispersions in water solution. The core–shell structure morphology of the obtained nanofibers was viewed under scanning electron microscope (SEM) and transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) analysis was used to further quantify the chemical composition of the core–shell composite SA/PEO nanofibers surface in detail. Furthermore, one-step cross-linking method through being immersed in CaCl2 solution was investigated to improve the anti-water property of the electrospun nanofibers mats in order to facilitate their practical applications as tissue engineering scaffolds, and the changes of the structural of nanofibers before and after cross-linking was characterized by Fourier transform infrared (FT-IR). Indirect cytotoxicity assessment indicated that SA/PEO nanofibers membrane was nontoxic to the fibroblasts cells, and cell culture suggested that SA/PEO nanofibers tended to promote fibroblasts cells attachment and proliferation. It was assumed that the nanofibers membrane of electrospun SA/PEO could be used for tissue engineering scaffolds.Highlights► Core–shell structure nanofibers of sodium alginate/poly(ethylene oxide) were prepared via electrospinning their dispersions in water solution. ► One-step cross-linking method through CaCl2 solution was investigated to improve the anti-water property of electrospun nanofibers. ► The potential use of the as-spun core–shell nanofibers could be as a scaffolding material for tissue engineering.

Fluoride compounds could migrate to the surface in a blending solution because of their low surface energy. In order to prepare a photo-sensitive nanofiber, a diphenyl-ketone photoinitiator with a fluorinated aliphatic chain was synthesized, and its structure was characterized using 1H NMR and 19F NMR, UV–vis absorbance spectroscopy, and fourier transform infrared (FT-IR). A blending solution of polyacrylonitrile (PAN) and photoinitiator containing fluorine with dimethylformamide (DMF) as the solvent was electrospun to prepare a photo-sensitive nanofiber. The photo-sensitive nanofiber was used to fabricate a polymer brush grafted on the nanofiber by initiating the polymerization of tripropylene glycol diacrylate (TPGDA) and hydroxyethyl acrylate (HEA) monomers via UV irradiation. The distribution of the photoinitiator on the surface of the nanofibers before and after photopolymerization was measured using UV–vis absorbance spectroscopy. The kinetics of the photopolymerization of TPGDA and HEA monomers on the surface of the nanofibers was studied using real-time infrared spectroscopy (RT-IR). The size and morphology of the nanofibers were investigated using scanning electron microscopy (SEM). The internal core–shell structure and the surface composition of nanofibers were further studied using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-infrared spectroscopy (ATR-IR). It was suggested that the photoinitiator on the nanofiber surface could cause the polymerization of the TPGDA and HEA monomers under UV irradiation. The solubility of the nanofibers polymerized with TPGDA on the surface was also investigated in water, DMF and acetone. The experimental results indicated that the nanofiber was enriched with the photoinitiator on its surface and that the nanofiber had potential for application in the preparation of functional core–shell nanofibers.

pH-sensitive drug loaded core shell fibers were fabricated by a combination of electrospinning and UV photo-polymerization. Combretastatin A4 (CA4) was selected as the model drug loaded in PLA to test the pH-sensitivity property of the core shell fibers. The morphology of the fibers was studied by scanning electron microscopy (SEM), and the core shell structure of the fibers was confirmed by transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The drug release assay was tested via the UV–vis spectrophotometer, and the pH-sensitivity of core shell fibers was tested by drug release assay under pH 5.0 and 7.4.Porous fibers from electrospinning PLA.Download full-size image

The objective of this work is to demonstrate the feasibility of preparation of core-shell nanofibers by electrospinning combined with in situ UV photopolymerization. The thiol-ene monomer with Si atom and the initiator can migrate to the surface with the evaporation of the solvent during the process of electrospinning, which caused phase separation due to the great migration ability of small molecule and low surface energy. Then photo induced polymerization and cross-linking reaction took place simultaneously during the electrospinning process, which formed shell of the nanofibers. The morphology and structure of electrospun nanofibers were investigated by SEM and TEM. The composition of the shell layer was determined by ATR-IR and XPS. Moreover, the nanofiber mats were tested by WCA test, and the hydrophobic ability of PVP nanofibers was improved because of the protection of the shell layer with Si atom. The most important thing is that the technology which combined electrospinning with in situ photopolymerization provides a simple method for preparation of core-shell nanofibers.Download high-res image (131KB)Download full-size image