Hierarchically electrospun nanofibers and their applications:A review

Electrospinning is a popular method for generating long and continuous nanofibers due to its simplicity and versatility.However,conventional electrospun products have weak strength and low availability,which restrict their functionality in complex applications.Hierarchical morphology introduces additional and distinctive structural layers onto electrospun fibers.This requires either an extra fabrication step or controlling electrospinning parameters to achieve the desired morphology.Hierarchical morphology can improve the properties of electrospun nanofibers while also mitigating the undesired characteristics.This review discusses the primary and secondary hierarchical structures of electrospun nanomaterials.Hierarchical structures were found to enhance the functionality of nanomaterials and improve pore connectivity and surface areas of electrospun nanofibers.A further advantage is the ability to impart multiple functionalities on nanostructures.With a better understanding of some of the dominant hierarchical structures,nanomaterials applications in drug delivery,tissue engineering,catalysis,and energy devices industries can be improved.

Electrospun gelatin/chitosan nanofibers containing curcumin for multifunctional food packaging

Recently,food grade nanofiber-based materials have received growing attentions in food packaging.In this work,novel active and intelligent packaging nanofibers based on gelatin/chitosan with curcumin(GA/CS/CUR)were developed via electrospinning technique.Effects of the incorporation of CUR content(0.1%-0.3%,m/m)on the microstructure and functional properties of the electrospun nanofibers were investigated.Morphological studies using scanning electron microscopy indicated that loading CUR can affect the average diameter of nanofiber mats,which remained around 160-180 nm.The addition of an appropriate level CUR(0.2%,m/m)led to a stronger intermolecular interaction,and thus enhanced the thermal stability and tensile strength of the obtained nanofibers.Meanwhile,the incorporation of CUR significantly improved antioxidant activity and the antimicrobial activity of GA/CS/CUR nanofibers.Moreover,the sensitivity of nanofibers to ammonia results indicated that GA/CS nanofibers containing 0.2%CUR(GA/CS/CURⅡ)presented high sensitivity of colorimetric behavior to ammonia(within 3 min).These results suggest GA/CS/CURⅡnanofibers has great potential as a multifunctional packaging to protect and monitor the freshness of proteinrich animal foods,such as meat and seafood.

Cardiac patches made of brown adipose-derived stem cell sheets and conductive electrospun nanofibers restore infarcted heart for ischemic myocardial infarction

Cell sheet engineering has been proven to be a promising strategy for cardiac remodeling post-myocardial infarction. However, insufficient mechanical strength and low cell retention lead to limited therapeutic efficiency. The thickness and area of artificial cardiac patches also affect their therapeutic efficiency. Cardiac patches prepared by combining cell sheets with electrospun nanofibers, which can be transplanted and sutured to the surface of the infarcted heart, promise to solve this problem. Here, we fabricated a novel cardiac patch by stacking brown adipose-derived stem cells (BADSCs) sheet layer by layer, and then they were combined with multi-walled carbon nanotubes (CNTs)-containing electrospun polycaprolactone/silk fibroin nanofibers (CPSN). The results demonstrated that BADSCs tended to generate myocardium-like structures seeded on CPSN. Compared with BADSCs suspension-containing electrospun nanofibers, the transplantation of the CPSN-BADSCs sheets (CNBS) cardiac patches exhibited accelerated angiogenesis and decreased inflammation in a rat myocardial infarction model. In addition, the CNBS cardiac patches could regulate macrophage polarization and promote gap junction remodeling, thus restoring cardiac functions. Overall, the hybrid cardiac patches made of electrospun nanofibers and cell sheets provide a novel solution to cardiac remodeling after ischemic myocardial infarction.

Structural and Functional Design of Electrospun Nanofibers for Hemostasis and Wound Healing

Electrospun nanofibers have been extensively studied in the biomedical field,including the controlled release of drugs,bionics,cell scaffolds,hemostasis,wound healing,and tissue engineering because of their high porosity,large surface area-to-volume ratio,and programmable features.In recent years researchers have continuously broadened the structural design of electrospun nanofibers,which have evolved from one-dimensional to three-dimensional structures,in order to diversify their function.These properties enable nanofibers to structurally and functionally mimic natural extracellular matrix(ECM),thereby obtaining a favorable physiological microenvironment for both wound healing and hemostasis due to improved blood coagulation and concentration.A comprehensive review summarizing the recent research progress of the structural and functional design of electrospun nanofibers for hemostasis and wound healing,on the other hand,is lacking.This review summarizes electrospun nanofibers used for hemostasis and wound healing,with a focus on structural design and modification strategies.The wide application of electrospun nanofibers in hemostasis and wound healing is clarified using a special structural and innovative design for electrospinning.The advantages and limitations of electrospun nanofibers with various structural forms are also discussed,as are the main challenges and future development directions for the development of structurally specific electrospun nanofibers for hemostasis and wound healing.

Electrospun antibacterial nanofibers for wound dressings and tissue medicinal fields:A Review

Bacterial infections are a major cause of chronic infections.Thus,antibacterial material is an urgent need in clinics.Antibacterial nanofibers,with expansive surface area,enable efficient incorporation of antibacterial agents.Meanwhile,structure similar to the extracellular matrix can accelerate cell growth.Electrospinning,the most widely used technique to fabricate nanofiber,is often used in many biomedical applications including drug delivery,regenerative medicine,wound healing and so on.Thus,this review provides an overview of all recently published studies on the development of electrospun antibacterial nanofibers in wound dressings and tissue me-dicinal fields.This reviewer begins with a brief introduction of electrospinning process and then discusses electrospun fibers by incorporating various types of antimicrobial agents used as in wound dressings and tissue.Finally,we finish with conclusions and further perspectives on electrospun antibacterial nanofibers as 2D biomedicine materials.

Bimetallic ZIFs-derived electrospun carbon nanofiber membrane as bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

The recharged zinc-air battery(ZAB) has drawn significant attention owing to increasing requirement for energy conversion and storage devices.Fabricating the efficient bifunctional oxygen catalyst using a convenient strategy is vitally important for the rechargeable ZAB.In this study,the bimetallic ZIFs-containing electrospun(ES) carbon nanofibers membrane with hierarchically porous structure was prepared by coaxial electrospinning and carbonization process,which was expected to be a bifunctional electrocatalyst for ZABs.Owing to the formed dual single-atomic sites of Co-N_(4) and Zn-N_(4),the obtained ES-Co/ZnCNZIFexhibited the preferable performance toward oxygen reduction reaction(ORR) with E1/2of 0.857 V and JLof 5.52 mA cm^(-2),which were more than Pt/C.Meanwhile,it exhibited a marked oxygen evolution reaction(OER) property with overpotential of 462 mV due to the agglomerated metallic Co nanoparticles.Furthermore,the ZAB based on the ES-Co/Zn-CNZIFcarbon nanofibers membranes delivered peak power density of 215 mW cm^(-2),specific capacity of 802.6 mA h g^(-1),and exceptional cycling stability,far larger than Pt/C+RuO_(2)-based ZABs.A solid-state ZAB based on ES-Co/Zn-CNZIFshowed better flexibility and stability with different bending angles.

Electrospun Semiconductor-Based Nano-Heterostructures for Photocatalytic Energy Conversion and Environmental Remediation:Opportunities and Challenges

Harvesting solar energy to drive the semiconductor photocatalysis offers a promising tactic to address ever-growing challenges of both energy shortage and environmental pollution.Design and synthesis of nano-heterostructure photocatalysts with controllable components and morphologies are the key factors for achieving highly efficient photocatalytic processes.Onedimensional(1D)semiconductor nanofibers produced by electrospinning possess a large ratio of length to diameter,high ratio of surface to volume,small grain sizes,and high porosity,which are ideally suited for photocatalytic reactions from the viewpoint of structure advantage.After the secondary treatment of these nanofibers through the solvothermal,gas reduction,in situ doping,or assembly methods,the multi-component nanofibers with hierarchical nano-heterostructures can be obtained to further enhance their light absorption and charge carrier separation during the photocatalytic processes.In recent years,the electrospun semiconductorbased nano-heterostructures have become a“hot topic”in the fields of photocatalytic energy conversion and environmental remediation.This review article summarizes the recent progress in electrospinning synthesis of various kinds of high-performance semiconductor-based nano-heterostructure photocatalysts for H2 production,CO_(2) reduction,and decomposition of pollutants.The future perspectives of these materials are also discussed.

Blinking CsPbBr_(3) perovskite nanocrystals for the nanoscopic imaging of electrospun nanofibers

Blinking fluorophore perovskite nanocrystals (NCs) were employed to image the fine structure of the polystyrene (PS) electrospun fibers. The conditions of CsPbBr3 NCs embedded and dispersed into PS were investigated and optimized. The stochastic optical reconstruction microscopy is employed to visualize the fine structure of the resulted CsPbBr3@PS electrospun fibers at sub-diffraction limit. The determined resolution in the reconstructed nanoscopic image is around 25.5 nm, which is much narrower than that of conventional fluorescence image. The complex reticulation and multicompartment in bead sub-diffraction-limited structures of CsPbBr3@PS electrospun fibers were successfully mapped with the help of the stochastic blinking properties of CsPbBr3 NCs. This work demonstrated the potential applications of CsPbBr3 perovskite NCs in super-resolution fluorescence imaging to reconstruct the sub-diffraction-limited features of polymeric material.

Grapevine-like high entropy oxide composites boost high-performance lithium sulfur batteries as bifunctional interlayers

Lithium-sulfur batteries(LSBs)with high energy densities have been demonstrated the potential for energy-intensive demand applications.However,their commercial applicability is hampered by hysteretic electrode reaction kinetics and the shuttle effect of lithium polysulfides(LiPSs).In this work,an interlayer consisting of high-entropy metal oxide(Cu_(0.7)Fe_(0.6)Mn_(0.4)Ni_(0.6)Sn_(0.5))O_(4) grown on carbon nanofibers(HEO/CNFs)is designed for LSBs.The CNFs with highly porous networks provide transport pathways for Li^(+) and e^(-),as well as a physical sieve effect to limit LiPSs crossover.In particular,the grapevine-like HEO nanoparticles generate metal-sulfur bonds with LiPSs,efficiently anchoring active materials.The unique structure and function of the interlayer enable the LSBs with superior electrochemical performance,i.e.,the high specific capacity of 1381 mAh g^(-1) at 0.1 C and 561 mAh g^(-1) at 6 C.This work presents a facile strategy for exploiting high-performance LSBs.

Hierarchical structured CoP nanosheets/carbon nanofibers bifunctional eletrocatalyst for high-efficient overall water splitting

The design of efficient,stable,and economical electrocatalysts for oxygen and hydrogen evolution reaction(OER and HER)is a major challenge for overall water splitting.Herein,a hierarchical structured CoP/carbon nanofibers(CNFs)composite was successfully synthesized and its potential application as a high-efficiency bifunctional electrocatalyst for overall splitting water was evaluated.The synergetic effect of two-dimensional(2D)CoP nanosheets and on e-dimensi on al(1D)CNFs endowed the CoP/CNFs composites with abundant active sites and rapid electron and mass transport pathways,and thereby significantly improved the electrocatalytic performances.The optimized CoP/CNFs delivered a current density of 10 mA cm^(-2) at low overpotential of 325 mV for OER and 225 mV for HER.In the overall water splitting,CoP/CNFs achieved a low potential of 1.65 V at 10 mA cm^(-2).The facile strategy provided in the present work can facilitate the design and development of multifunctional non-noble metal catalysts for energy applications.

Advances in Electrospun Nanofiber Yarns

In order to increase the application area of nanofibers,electrospun nanofiber yarns have drawn attention of many researchers around the globe.Once the production method of nanofiber yarn is mature enough to be universally accepted,many new gates of applications will open to the world.In this review,different electrospinning techniques of electrospun nanofiber yarns are divided into needle electrospinning and needleless electrospinning.Considering yarn twist as an important mechanism,needle electrospinning technique is further categorized into mechanical,electrical and field flow twisting methods.Moreover,parameters influencing the mechanical properties of electrospun nanofiber yarns are investigated.Methods of improving mechanical properties of nanofiber yarns are addressed,including hot-water-bath treatment,addition of carbon nanotubes(CNTs)and introducing regulators.Finally,applications of electrospun nanofiber yarns in different fields of smart textile and bioengineering are summed-up.In summary,challenges encountered in the industrialization of nanofiber yarns and future prospects are anticipated.

Enhanced energy density in polyetherimide nanocomposite film at high temperature induced by electrospun BaZrTiO_(3) nanofibers

Polymer dielectrics which possess excellent dielectric properties such as high breakdown strength,flexibility,and facile processability are considered as promising materials for advanced electrostatic capacitors.However,most dielectric polymers have unsatisfactory energy storage performances at high-temperature environments.Here,polyetherimide(PEI) nanocomposite films contained with electrospun Ba(Zr_(0.79)Ti_(0.21))O_(3) nanofibers(BZTNFs) are fabricated by common solution casting method.The dielectric properties,especially the breakdown strength of the BZTNFs/PEI nanocomposites,are characterized,yet improvement is only in the small loading ones.The energy storage performance of the 0.5 vol% and1.0 vol% BZTNFs content nanocomposite is further investigated from 25 to 150℃.With the introduction of small loading BZTNFs,the dielectric permittivity and electric displacement of the nanocomposite are improved at all evaluated temperatures.The 1.0 vol% BZTNFs/PEI possesses a maximal discharged energy density of6.05 J·cm^(-3) with high efficiency of 94.9% at 25℃,then falls to 3.34 J·cm^(-3) with efficiency of 54.6% at 150℃ for the larger remnant displacement.Apparently,the relaxation ferroelectric nanofller of BZTNFs is much effective in increasing the dielectric permittivity of nanocomposite,but its capacity to restrict the migration of the charge carriers at high temperatures is weaker than that of the nanofillers with wider bandgap.The complementation of both kinds of the nanofillers probably provides an approach to available high-temperature dielectric films.

Electrospun Bi-decorated Bi_(x)Ti_(y)O_(z)/TiO_(2) flexible carbon nanofibers and their applications on degradating of organic pollutants under solar radiation

Presently,photocatalytic degradation has emerged as an attractive and efficient technology for wastewater treatment.In order to avoid hurdles,such as difficulty in the suspended photocatalyst segregation from the aqueous system and low reutilization rate,the strategy of immobilizing photocatalysts with electro-spun fibers has been widely studied.However,those methods usually require multi-step preparation and complex operations.Considering this,a novel metallic Bi-decorated flexible multiphase Bi_(x)Ti_(y)O_(z)/TiO_(2) electrospun carbon nanofibers(Bi/Bi_(x)Ti_(y)O_(z)-TiO_(2)/CNFs)with high photocatalytic efficiency,good mechanical property,good stability,easy separation,and recovery were synthesized via a one-step approach of pre-oxidation and carbonization treatment.The as-prepared Bi/Bi_(x)Ti_(y)O_(z)-TiO_(2)/CNFs with multiphase Bi_(x)Ti_(y)O_(z),anatase TiO_(2),and metallic Bi particles embedded not only enhance the harvest of light but also pro-vide more separation paths for photogenerated carriers,which improve photocatalytic efficiency greatly.The Bi/Bi_(x)Ti_(y)O_(z)-TiO_(2)/CNFs(S3)exhibited excellent photocatalytic performance and the degradation rate of 10 mg L^(-1) Rhodamine B(RhB)was up to 97%in only 30 min under simulated sunlight irradiation.Also,S3 exhibited stable activity during 5 cycles of experiments since the degradation rates remained at about 97%in 30 min.The mechanism of degradation of RhB by Bi/Bi_(x)Ti_(y)O_(z)-TiO_(2)/CNFs in the photocat-alytic process was also proposed based on active species trapping experiments.The work in this paper shows that Bi/Bi_(x)Ti_(y)O_(z)-TiO_(2)/CNFs are easy to prepare and have high photocatalytic ability and stability,thereby offering a new strategy in catalyst immobilization and wastewater treatment.

Construction of Electrospun Organic/Inorganic Hybrid Nanofibers for Drug Delivery and Tissue Engineering Applications

Electrospun nanofibers hold a great potential in biomedical applications due to their advantages of large specific surface area,good biocompatibility,easy fabrication and surface modification.In particular,organic/inorganic hybrid nanofibers exhibit enhanced mechanical properties and long-term sustained release or controlled release profile of encapsulated drugs,which enables hybrid nanofibers to serve as desired platform for drug delivery and tissue engineering applications.This review summarizes the recent progresses in the preparation,performances and applications of hybrid nanofibers as drug delivery vectors for antibacterial and antitumor therapy,and as nanofibrous scaffolds for bone tissue engineering or other types of tissue engineering applications.Nanofibers doped with various types of inorganic nanoparticles(e.g.,halloysite,laponite®,nano-hydroxyapatite,attapulgite,carbon nanotubes,and graphene,etc.)are introduced and summarized in detail.Future perspectives are also briefly discussed.

Folic Acid Modified Electrospun Poly(vinyl alcohol)/Polyethyleneimine Nanofibers for Cancer Cell Capture Applications

Capture and detection of metastatic cancer cells are crucial for diagnosis and treatment of malignant neoplasm. Here, we report the use of folic acid （FA） modified electrospun poly（vinyl alcohol） （PVA）/polyethyleneimine （PEI） nanofibers for cancer cell capture applications. Electrospun PVA/PEI nanofibers crosslinked by glutaraldehyde vapor were modified with FA via a poly（ethylene glycol） （PEG） spacer, followed by acetylation of the fiber surface PEI amines. The formed FA-modified nanofibers were well characterized. The morphology of the electrospun PVA/PEI nanofibers is smooth and uniform despite the surface modification. In addition, the FA-modified nanofibers display good hemocompatibility as confirmed by hemolysis assay. Importantly, the developed FA-modified nanofibers are able to specifically capture cancer cells overexpressing FA receptors, which were validated by quantitative cell counting assay and qualitative confocal microscopy analysis. The developed FA-modified PVA/PEI nanofibers may be used for capturing circulating tumor cells for cancer diagnosis applications.

Controlled Release of Doxorubicin from Electrospun MWCNTs/PLGA Hybrid Nanofibers

In this study, multiwalled carbon nanotubes （MWCNTs） were used to encapsulate a model anticancer drug, doxorubicin （Dox）. Then, the drug-loaded MWCNTs （Dox/MWCNTs） with an optimized drug encapsulation percentage were mixed with poly（lactide-co-glycolide） （PLGA） polymer solution for subsequent electrospinning to form drug-loaded composite nanofibrous mats. The structure, morphology, and mechanical properties of the formed electrospun Dox/PLGA, MWCNTs/PLGA, and Dox/MWCNTs/PLGA composite nanofibrous mats were characterized using scanning electron microscopy （SEM）, Fourier transform infrared spectroscopy, and tensile testing. In vitro viability assay and SEM morphology observation of mouse fibroblast cells cultured onto the MWCNTs/PLGA fibrous scaffolds demonstrate that the developed MWCNTs/PLGA composite nanofibers are cytocompatible. The incorporation of Dox-loaded MWCNTs within the PLGA nanofibers is able to improve the mechanical durability and maintain the three-dimensional structure of the nanofibrous mats. More importantly, our results indicate that this double-container drug delivery system （both PLGA polymer and MWCNTs are drug carriers） is beneficial to avoid the burst release of the drug and able to release the antitumor drug Dox in a sustained manner for 42 days. The developed composite electrospun nanofibrous drug delivery system may be used as therapeutic scaffold materials for post-operative local chemotherapy.

Neurogenic differentiation of human umbilical cord mesenchymal stem cells on aligned electrospun polypyrrole/ polylactide composite nanofibers with electrical stimulation

Adult central nervous system （CNS） tissue has a limited capacity to recover after trauma or disease. Recent medical cell therapy using polymeric biomaterial- loaded stem cells with the capability of differentiation to specific neural population has directed focuses toward the recovery of CNS. Fibers that can provide topographical, biochemical and electrical cues would be attractive for directing the differentiation of stem cells into electro-responsive cells such as neuronal cells. Here we report on the fabrication of an electrospun polypyrrole/polylactide composite nanofiber film that direct or determine the fate of mesenchymal stem cells （MSCs）, via combination of aligned surface topography, and electrical stimulation （ES）. The surface morphology, mechanical properties and electric properties of the film were characterized. Comparing with that on random surface film, expression of neurofilament-lowest and nestin of human umbilical cord mesenchymal stem cells （huMSCs） cultured on film with aligned surface topography and ES were obviously enhanced. These results suggest that aligned topography combining with ES facilitates the neurogenic differentiation of huMSCs and the aligned conductive film can act as a potential nerve scaffold.

Nanofibrous Scaffold Containing Osteoblast-Derived Extracellular Matrix for the Proliferation of Bone Marrow Mesenchymal Stem Cells

Extracellular matrix( ECM) plays a prominent role in establishing and maintaining an appropriate microenvironment for tissue regeneration. The aims of this study were to construct a tissue engineered scaffold by reconstituting osteoblast cell-derived ECM( O-ECM) on the electrospun nanofibrous scaffold,and further to evaluate its subsequent application for promoting the proliferation of bone marrow mesenchymal stem cells( BMSCs). To engineer a biomimetic scaffold, calvarial osteoblasts and electrospun poly-llactic acid( PLLA) nanofibers were prepared and subjected to decellularize for O-ECM deposition. To evaluate and characterize the O-ECM/PLLA scaffold, the morphology was examined and several specific mark proteins of osteoblasts matrix were evaluated.Furthermore,the cell counting kit-8( CCK-8) assay was used to detect the proliferation of the BMSCs cultivated on the O-ECM/PLLA scaffold. The results indicated O-ECM/PLLA scaffold was loaded with Collagen I, Fibronectin, and Laminin, as the composition of the marrow ECM. After decellularization,O-ECM deposition was observed in O-ECM/PLLA scaffold. Moreover,the O-ECM/PLLA scaffold could significantly enhance the proliferation of BMSCs,suggesting better cytocompatibility compared to the other groups tested. Taken together,a biomimetic scaffold based on the joint use of O-ECM and PLLA biomaterials,which represents a promising approach to bone tissue engineering, facilitates the expansion of BMSCs in vitro.

Biofabrication of aligned structures that guide cell orientation and applications in tissue engineering

The organized alignment of cells in various tissues plays a significant role in the maintenance of specific functions.To induce such an alignment,ideal scaffolds should simulate the characteristics and morphologies of natural tissues.Aligned structures that guide cell orientation are used to facilitate tissue regeneration and repair.We here review how various aligned structures are fabricated,including aligned electrospun nanofibers,aligned porous or channeled structures,micropatterns and combinations thereof,and their application in nerve,skeletal muscle,tendon,and tubular dentin regeneration.The future use of aligned structures in tissue engineering is also discussed.

Engineering of electrospun nanofiber scaffolds for repairing brain injury

Patients with brain injury can suffer disability and accompanying complications.Current clinical treatments have significant limitations to successful repair due to the complexity of the pathological processes and the inhibitory microenvironment that follows brain injury.Here,we conclude recent research progresses in engineering strate-gies based on electrospun nanofibers for promoting neural repair and functional recovery after brain injury.Firstly,we introduce the main pathological mechanisms of current brain injuries,pointing out the prospect of the application of electrospun nanofiber scaffolds compared to current clinical treatment strategies.We then discuss the repair strategies combining the structure and the morphology of nanofiber scaffolds with load therapeutic factors such as cells,drugs and growth factors.All of these strategies show potential for improving the repair of brain injury.Finally,we point out the challenges facing the effective treatment of brain injury,aiming to provide insights into the development of repairing scaffolds for brain function recovery from the perspective of clinical treatment.