Cross-linked Nanofibers Research Articles

Control release of mitochondria-targeted antioxidant by injectable self-assembling peptide hydrogel ameliorated persistent mitochondrial dysfunction and inflammation after acute kidney injury

Persistent mitochondrial injury occurs after acute kidney injury (AKI) and mitochondria-targeted antioxidant Mito-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) (MT) has shown benefits for AKI, but its efficiency is limited by short half-life and side effect in vivo. Self-assembling peptide (SAP) hydrogel is a robust platform for drug delivery. This study aims to develop an SAP-based carrier to slow release MT for enhancing its long-term therapeutic potency on AKI. The KLD with aspartic acid (KLDD) was designed. The microstructure and in vitro release of MT was assayed. The protective role of MT-loaded SAP (SAP-MT) hydrogel on renal mitochondrial injury, tubular apoptosis, and inflammation was evaluated in mice at five days after ischemia-reperfusion injury (IRI). Our results showed that KLDD could self-assemble into cross-linked nanofiber hydrogel and it had lower release rate than free MT and KLD hydrogel. Compared to IRI and free MT mice, SAP-MT mice exerted reduced renal mitochondria-produced ROS (mtROS) and improved mitochondrial biogenesis and architecture. Consequently, SAP-MT mice showed less renal tubular cell apoptosis, kidney injury marker kidney injury molecule-1 (Kim-1) expression, lower level of pro-inflammatory factors expression, and macrophages infiltration than those of IRI and free MT mice. This study suggested that SAP-MT ameliorated IRI due to its extended mitochondrial protection role than free MT and thus improved the long-term outcomes of AKI.

Crosslinked carbon nanofiber films with hierarchical pores as flexible electrodes for high performance supercapacitors

Flexible, cross-linked carbon nanofibers (CNFs) film with hierarchical micro-meso-macro-porous structure is prepared by carbonization of the elestrospun polyacrylonitrile (PAN)/NaN3 composite nanofiber mats. The gas liberation of NaN3 during the carbonization is responsible for the tuning of both specific surface area and the pore size distribution. In addition, the exothermal decomposition of NaN3 at the heating stage of carbonization leads to the melting of the PAN/NaN3 composite fibers, resulting in a cross-linked CNF structure. The CNF film with 5wt% NaN3 carbonized at 900°C (CNF-5-900) shows a high specific capacitance of 222.92Fg−1, nearly twice as high as that of the CNF film without NaN3 (CNF-0-900). It also shows an excellent capacitance retention ratio of 81.97% of its initial capacitance from 0.5A/g to 50A/g, much superior to the value of 51.02 % for CNF-0-900. Moreover, it has an excellent cycling stability with cycling retention ratio achieves 94.5% after 10,000 charge-discharge cycles. Coupled with its excellent mechanical stability (only 1.6% conductivity loss after bending of CNF-5-900 film at curvature radii (r)=2.5×10−3m for 10,000cycles) and facile fabrication process, the flexible, cross-linked CNF films with hierarchical micro-meso-macro-porous structure is a potential electrode materials and/or backbone to support other active materials for various application, including the flexible energy storage and electrocatalytic.

Robust fluorinated polyimide nanofibers membrane for high-performance lithium-ion batteries

A robust fluorinated polyimide (FPI) nanofibers membrane was prepared by an electrospinning technique and subsequent thermo-crosslinking process. Compared to pristine FPI nanofibers membrane, the thermally cross-linked FPI nanofibers membrane possesses considerable mechanical strength (i.e., 31.7MPa), small average pore size and narrow pore-size distribution and shows enhanced performance to prevent the growth and penetration of dendritic lithium, which is crucial to safe and reliable lithium-ion batteries. It is demonstrated that the FPI nanofibers membrane possesses admirable thermal stability and flame retardancy. The as-prepared pristine or thermally cross-linked FPI nanofibers membrane as a separator has greater electrolyte wettability, larger ionic conductivity, higher electrochemical oxidation limit, lower interfacial resistance, as compared to its non-fluorinated analogue nanofibers membrane and the commercial polyethylene (PE) separator. Moreover, compared with non-fluorinated PI analogue nanofibers membrane, the battery assembled with FPI nanofibers membrane with FPI binder exhibits enhanced cycle performance and rate capacity. And the electrochemical performances of the FPI-based battery are also better than the commercial battery fabricated by PE separator and polyvinylidene fluoride (PVDF) binder.

Balanced energy density and power density: Asymmetric supercapacitor based on activated fullerene carbon soot anode and graphene-Co3O4 composite cathode

The enhancement of energy density at high power density is highly desired in design of supercapacitor, which relies on the electrochemically accessible electrode area, electrons/ions diffusion channels of electrodes and the device assembly manner. Herein, graphitized and porous fullerene carbon soot is used as matrix for preparation of activated carbon (denoted as a-FC). The high specific surface area, hierarchical pore sizes and moderate graphitization degree of a-FC enable balanced specific capacitance, rate capability and cycleability. Meanwhile, graphene-Co3O4 composite (GC) with cross-linked porous Co3O4 nanofibers array onto graphene sheet is hydrothermally deposited on Ni foam substrate. The pseudocapacitive GC electrode can offer superior capacitance (1935 F g−1 at 5 A g−1), rate capability (68% capacitance retaining ratio within 0.5–50 A g−1) and considerable cycleability (17% capacitance decline within 2000 charge-discharge cycles) comprehensively. Furthermore, the asymmetric supercapacitor based on the a-FC and GC electrodes delivers balanced energy density (50.3–20.9 Wh kg−1), power density (786–12128 W kg−1) and cycleability (77% initial capacitance maintaining ratio within 5000 charge-discharge cycles), highlighting the potential in efficient energy storage device.

The Preparation of Core–shell Structured Gelatin–chitosan Nanofibers for Biomedical Applications

In recently, electrospun nature fibers have been investigated as scaffolding materials for tissue engineering. In this study, The core-shell structured of nanofibers were prepared by coaxial electrospinning, where the natural polymer chitosan(CS) as shell and the highly spinnable gelatin(GEL) was used as core. In order to maintain the structure of the nanofibers that kept them in contact with aqueous medium. In this report, we used glutaraldehyde as the cross-linking agent for improving the water stability of the nanofibers. The results show that the as prepared core-shell structure and the cross-linked nanofibers exhibits better water stability.

Cross-linked poly(lactic acid)/dextran nanofibrous scaffolds with tunable hydrophilicity promoting differentiation of embryoid bodies

Poly(lactic acid) (PLA) and polysaccharide have been extensively studied for biomedical applications. However, the hydrophobicity of PLA makes it less desirable for cell adhesion, while dextran, a polysaccharide, is highly hydrophilic but its linear form is not very useful for tissue engineering because it readily dissolves in water. This study aimed to fabricate biodegradable cross-linked PLA-dextran nanofibrous scaffolds with tunable hydrophilicity and to test their effects on the attachment, differentiation and biological activities of mouse embryonic stem cells (ES cells). The cross-linked nanofibers of various compositions of PLA-g-dextran (10–88% dextran) were fabricated by grafting dextran onto PLA through maleic anhydride followed by co-axially reactive electrospinning with in situ photo-cross-linking of methacrylated dextran under UV irradiation. The results have shown that contact angles of electrospun PLA-g-dextran nanofibers decreased with increasing dextran content. The hydrophilic nanofibrous scaffolds containing 30% or 50% dextran can significantly enhance the attachment and differentiation of ES cells, which have demonstrated spontaneous contractions.

Photo-cross-linked Antibacterial Zein Nanofibers Fabricated by Reactive Electrospinning and its Effects against Streptococcus mutans

Native zein electrospun nanofibers have shown poor solvent resistance and low mechanical strength. Compared to other toxic cross-linkers, a safer method of stabilizing zein based fibers while retaining or with improved mechanical strength is needed to convert these materials for biomedical applications where culture media or body fluids may be present. We report here a method of fabricating non-toxic zein nanofibers using reactive electrospinning coupled with in situ photo-cross-linking. The cross-linked zein nanofibers exhibited significantly improved mechanical strength and sustained morphology against water and aqueous ethanol solution. This process doesn't require additional conventional cross-linking agents to form cross-linking network, which is advantageous for biomedical applications. Antimicrobial monomer with photo-reactive moiety was coupled with methacrylate zein nanofibers and showed strong inhibitory activity against cariogenic Streptococcus mutans. Cytotoxicity test with human gingival fibroblasts revealed high biocompatibility.

Synergistic role of in-situ crosslinkable electrospun nanofiber/epoxy nanocomposite interlayers for superior laminated composites

Adopting a multi-scaled/hierarchical toughening approach, we have produced nanofiber-reinforced epoxy laminate composites with superior toughness as a consequence of built-in, thermally catalyzed cross-linking between the nanofiber and the epoxy matrix, in addition to the usual curing within the epoxy itself. The nanofiber composition of P(St-co-GMA)/TBA-PA is designed such that the cross-linking agent PA groups are catalyzed by the thermally stimulated TBA initiators and inherent epoxy-nanofiber interfacial quality is promoted for toughening purposes. These nanofibers are electrospun onto two forms of the same base epoxy—neat resin films and pre-preg plies containing unidirectional carbon fibers. The nanofiber/epoxy nanocomposite specimens are manufactured via an in-house hot-press film molding method. DSC analysis reveal an increase in exothermic curing enthalpy, consistent with cross-linking between the epoxide groups of the fiber and epoxy matrix occurring in-situ, i.e., triggered and advanced during the epoxy curing cycle. Analysis of the curing kinetics, following Ozawa-Flynn-Wall method, shows that the P(St-co-GMA)/TBA-PA nanofibers have a significant autocatalytic effect on the epoxy matrix curing. Increases in tensile strength (30%) and elastic modulus (8%) are measured compared to the un-reinforced epoxy specimens. Furthermore, end-notched flexure tests reveal a 95% increase in GIIC, due to the incorporation of a single P(St-co-GMA)/TBA-PA nanofiber interlayer into laminated carbon fiber-reinforced composite of (0)48 lay-up configuration. These results suggest that the self-initiated cross-linking between the nanofibers and surrounding epoxy matrix synergistically forms interlayer zones that contribute to toughening. Analysis of the fracture surfaces is presented to elaborate on the significant role of the proposed in-situ cross-linked nanofibers on the remarkable improvements in mechanical behavior of these nanocomposites and interlayered laminates.

Preparation and characterization of thermally crosslinked poly(vinyl alcohol)/feather keratin nanofiber scaffolds

Electrospun keratin nanofiber fabricated with non-toxic solvents and crosslinking reagents are promising scaffolds for tissue engineering applications. Keratin from chicken feathers was solubilized in aqueous alkaline conditions and electrospun using aqueous poly(vinyl alcohol)(PVA)/citric acid solution as electrospinning polymer aid. Keratin/PVA nanofibers were successfully prepared containing 10, 20 and 30% keratin to PVA mass ratio. The increase in keratin concentration from 0 to 20% resulted in decreased viscosity of keratin/PVA solutions leading to a reduction in the fiber diameter from 565nm in to 274nm. Further decrease in viscosity with 30% keratin resulted in beads-on-fiber type of morphology. Nanofibers were thermally cross-linked through esterification reaction between carbonyl groups in citric acid and hydroxyl groups in PVA. Cross-linked nanofibers maintained their morphology and pore structure after soaking in water. The incorporation of keratin in PVA nanofiber was confirmed by FTIR and XPS results. Proliferation of fibroblasts after 14days was higher in scaffolds containing 20% keratin which was attributed to the superior biological properties of keratin and higher surface area to volume ratio compared to 30% keratin/PVA scaffolds. Safer extraction, electrospinning and crosslinking conditions of keratin/PVA nanofiber are important for potential uses in tissue engineering.

Fabrication of bi-layer scaffold of keratin nanofiber and gelatin-methacrylate hydrogel: Implications for skin graft

Bi-layer scaffold composed of human hair keratin/chitosan nanofiber mat and gelatin methacrylate (GelMA) hydrogel was fabricated by using electrospinning and photopolymerization techniques. To prepare the nanofiber layer, the blend solution of human hair keratin and chitosan (mixture ratio: 5/5) was electrospun using formic acid as a solvent in the presence of poly(ethylene glycol), followed by cross-linking with glutaraldehyde. The tensile strength of the human hair keratin/chitosan nanofiber mat was much higher than that of pure human hair keratin nanofiber mat. Meanwhile, the blend nanofiber mat was relatively more compatible with HaCaT cell proliferation and keratinocyte differentiation than the pure chitosan nanofiber mat. The bi-layer scaffold was prepared by photopolymerization of GelMA under the cross-linked nanofiber mat. To evaluate the feasibility as a skin graft, human fibroblast was encapsulated in the hydrogel layer and HaCaT cells were cultured on the nanofiber layer and they were co-cultured for 10days. As a result, the encapsulated fibroblasts proliferated in the hydrogel matrix and HaCaT cells formed a cell layer on the top of scaffold, mimicking dermis and epidermis of skin tissue.

Toughening of fibrous scaffolds by mobile mineral deposits.

Effective surgical repair of interfaces between tendon and bone remains an unmet clinical need, in part due to a lack of understanding of how toughness is achieved in the healthy tissue. Using combined synthesis, experiment, and modeling approaches, the current work supported the hypothesis that toughening of a fibrous scaffold arises from brittle mineral particles that crosslink the fibers, but only if the particles are free to slide relative to the fibers. In the case of the tendon-to-bone interface, this suggests that partially mineralized tissue between tendon and bone, with mobile mineral but relatively low stiffness, may serve as a compliant, energy-absorbing barrier that guards against injury. These results suggest an opportunity for fabrication of tough and strong fibrous scaffolds for tissue engineering applications.

Enhancement of nanoscale zero-valent iron immobilization onto electrospun polymeric nanofiber mats for groundwater remediation

Abstract A new approach that combines nanoscale zero-valent iron (nZVI) with electrospinning technology has been put forward to avoid nZVI agglomeration and a secondary pollution. In this study, to enhance the immobilization of nZVI particles onto the polyacrylic acid (PAA)/polyvinyl alcohol (PVA) electrospun nanofiber mat, mats (M1, M2 and M3) with different PAA/PVA mass ratios (1:1, 2:1 and 3:1) were tested for the immobilization of nZVI particles and their performance of removing contaminants. The results indicate that M3 immobilized the most nZVI particles (48.4 wt% on the mat, ∼2.5 times the figure for previous study) and had the highest removals to methylene blue and Cu(II) ions at 94% and 83.6% respectively, resulting from more free carboxylic groups available on the cross-linked nanofibers as well as a higher porosity into the mat. Therefore, increasing the PAA/PVA ratio is effective to boost the performance of nZVI–PAA/PVA electrospun nanofiber mat, which has a great potential for the application of nZVI-targeted contaminants remediation.

Assessing the Internal Structure of Cross-Linked Carbon Nanofibers by Chemical Methods

The structure of cross-linked carbon nanofibers of DNIPRO industrial carbon fabric produced by pyrolysis of hydrated cellulose is assessed, and their oxidation temperature (Tox = 923 ± 10 K) is found. Fractionated extraction of carbon (as CO2) in a purified oxygen flow is measured by coulometry of the extracted CO2 versus time at Tox. A selective chemical procedure for qualitative identification and determination of cross-linked carbon nanofibers in carbon nanomaterials of arbitrary composition is developed for the first time.

Tetracycline hydrochloride-loaded electrospun nanofibers mats based on PVA and chitosan for wound dressing

Fibrous mats built from biopolymer have been extensively explored for tissue engineering due mainly to their mimic structure to the extracellular matrix. The incorporation of drug in such scaffolds represents a growing interest for control drug delivery system in order to promote the tissue repair. In the present work, we present an experimental investigation of morphological, thermal, mechanical, drug release, antibacterial and cytotoxicity properties of electrospun PVA/Chitosan and PVA/Chitosan/Tetracycline hydrochloride (TCH) mats for wound dressing. Fibrous mats with cross-linked three-dimensional nanofibers were formed from the polymer blends. A uniform incorporation of drug was achieved along the nanofibers with not significant change on the morphological and thermal properties of the mats. Furthermore, the TCH release profile with a burst delivery during the first 2h allows an effective antibacterial activity on the Gram-negative Escherichia coli as well as on the Gram-positive Staphylococci epidermidis and Staphylococcus aureus. In vitro indirect MTT assay also showed that the developed drug-loaded nanofibrous scaffolds have good cytocompatibility, which was confirmed by scratch assay, indicating that the investigated scaffold may be used as antibacterial wound dressing for healing promotion.

Fabrication of PEDOT coated PVA-GO nanofiber for supercapacitor

Conducting nanofibers comprised of poly(vinyl alcohol) (PVA)-graphene oxide (GO) nanofiber coated with poly(3,4-ethylenedioxythiophene) (PEDOT) for supercapacitor application was prepared through integrated techniques i.e. electrospinning and electrodeposition. The formation of smooth cross-linking nanofibers without beads proved that GO has uniformly distributed into PVA with an average diameter of 117 ± 32 nm. Field emission scanning electron microscopy (FESEM) images revealed that cauliflower-like structure of PEDOT grew well on the surface of PVA-GO nanofibers with high porosity. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy proved the existence of PVA, GO, and PEDOT. PVA-GO/PEDOT nanocomposite showed the highest specific capacitance (224.27 F/g) compared to PEDOT (167.92 F/g) and PVA/PEDOT (182.73 F/g). PVA-GO/PEDOT nanocomposite exhibited 1.8 V wide operating potential windows which significantly can enhance its capacitive behaviour. PVA-GO/PEDOT nanocomposite has also demonstrated superior performance with the energy density and power density of 9.58 Wh/kg and 304.37 W/kg, respectively at 1.0 A/g current density. PVA-GO/PEDOT nanocomposite revealed the smallest resistance of charge transfer (Rct) and equivalent series resistance (ESR) indicating excellent charge propagation behaviour at the interfacial region. The composite exhibits a good capacity retention of 82.41% after 2000 CV cycles and further drops 11.27% after 5000 cycles caused by the swelling and shrinkage of the electrode material during the charging and discharging processes.

Novel electrospun nanofibers of modified gelatin-tyrosine in cartilage tissue engineering

In natural cartilage tissues, chondrocytes are linked to extracellular matrix (ECM) through cell-surface binding proteins. Surface modification of gelatin can provide a new generation of biopolymers and fibrous scaffolds with chemical, mechanical, and biological properties. In this study tyrosine protein and 1,2,3-triazole ring were utilized to functionalize gelatin without Cu catalyst. Their molecular structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (1HNMR). Chemical cross-linkers such as glutaraldehyde (GA) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysulfosuccinimide (NHS) were used to electrospin the modified gelatin. The modification of gelatin and cross-linking effects were confirmed by scanning electron microscopy (SEM), contact angle measurement, and mechanical tests. MTT assay using chondrocyte cells showed cell viability of electrospun modified gelatin scaffolds. In vitro cell culture studies showed that electrospun engineered protein scaffolds would support the attachment and growth of cells. The results also showed that cross-linked nanofibers with EDC/NHS could be considered excellent matrices in cell adhesion and proliferation before electrospinning process and their potential substrate in tissue engineering applications, especially in the field of cartilage engineering.

Improved genistein loading and release on electrospun chitosan nanofiber blends

Chitosan is a natural polysaccharide exhibiting excellent biocompatibility, biodegradability and nontoxicity, making Chitosan–based biomaterials ideal drug delivery systems and cell carriers for tissue engineering. The electrospinning technique, with optimized parameters, was used to fabricate chitosan/PVA as-spun mats. Field emission scanning electron microscopy (FESEM) was used to investigate the morphologies of the as-spun mats. We present a novel electrospun nanofiber-based drug delivery. In this system, genistein was loaded on nanofiber mats via three methods namely; passive loading, crosslinking after passive loading, and active loading. The way in which genistein was loaded significantly influenced its in-vitro drug release characteristics. The in-vitro release studies revealed that physical cross-linked nanofibers have a significantly delayed release demonstrating 21% progressive release after 30min and 69% after 24h, which is considered a superior drug delivery system compared to those reported before for genistein release.

Dynamic mechanical properties of elastomeric nanoparticle composites

The blends of two crosslinked polystyrene-b-polyisoprene (PS-b-PI) copolymers with homopolystyrene were investigated for their dynamic mechanical properties. Elastomeric block copolymer nanofibers utilized as filler were prepared by employing the phase separation property of a polystyrene-b-polyisoprene copolymer, which was then exposed to a crosslinking agent (S2Cl2) for cold vulcanization. The crosslinking density and morphology of nanofillers resulted in three elastomeric block copolymer nanofillers: fully cross-linked nanofiber (FCF), fully crosslinked multi-junctioned nanofiber (FCM), and partially crosslinked multi-junctioned sample (PCM). Uncrosslinked PS-PI block copolymer (UBC) was also studied as a comparison. Crosslinking density was calculated by measuring the change in intensity of the double bond peaks using FTIR spectroscopy. Thermo-mechanical properties and morphology of the blends were characterized by dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). DMA results show that modulus increases with increasing filler loading in the terminal region for both PS/FCM and PS/FCF systems and the increasing rate is related to crosslinking density. Open image in new window

Facile fabrication of cross-linked carbon nanofiber via directly carbonizing electrospun polyacrylonitrile nanofiber as high performance scaffold for supercapacitors

Cross-linked carbon nanofiber (CLCNF) was successfully prepared by directly carbonizing electrospun polyacrylonitrile (PAN) nanofiber. Comparing to non-cross-linked carbon nanofiber (NCLCNF) obtained via carbonizing of pre-oxidation PAN nanofiber, CLCNF shows better conductivity owing to its cross-linked structure. Then CLCNF was used as scaffold to support polyaniline (PANi) nanorods for supercapacitor electrode material. The hierarchical CLCNF/PANi composite displays a capacity of 206Cg−1 at 0.5Ag−1 with excellent rate capability (remains 49% even at 800Ag−1), which is much higher than that of NCLCNF/PANi composite (17%). More interestingly, supercapacitor device based on CLCNF/PANi composite achieves 75.3% capacity retention after 10000 charge-discharge cycles at 10Ag−1, suggesting excellent cycle stability. All these experimental results indicate that this method for fabricating CLCNF is a substantial advancement towards the practical applications of carbon nanofiber in energy conversion and storage field.

Effect of Morphology and Chemical Modification on Water Degradation Behavior of Polyvinyl Alcohol - Gelatin Blend

Polyvinyl Alcohol - Gelatin (PVAG) nanofibers were successfully synthesized using the electrospinning method. After synthesis, the degradation study of electrospun PVAG nanofibers was done using Quartz Crystal Microbalance submerged in distilled water at ambient conditions. Additional samples were prepared: PVAG film, and cross-linked PVAG nanofibers using 37% formaldehyde vapor, to analyze the effects of the morphology and chemical modification on the degradation property of PVAG blend. Results revealed significant differences in the degradation properties of different samples. PVAG film exhibited initial mass loss at the beginning but afterwards began to uptake water from the environment, achieving steady state value. PVAG nanofibers' behavior was in a continuous mass loss behavior in contrast to the film morphology, probably due to its large surface area exposed to the aqueous environment that readily solubilized PVA and gelatin components of the nanofibers. Analysis on the PVAG cross-linked nanofibers showed degradation profile comparable to a damped sinusoid function, achieving a pseudo steady-state profile after considerable time. Evidence from QCM studies show that morphology and chemical modification has an effect on the degradation property of PVAG, and further tuning of these effects could be utilized for functional use in tissue engineering, drug delivery systems, and other chemical and biomedical use.