Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Energy and environment will head the list of top global issues facing society for the next 50 years. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. The route toward these nano-objects is based primarily on electrospinning: a highly versatile method that allows the fabrication of continuous fibers with diameters down to a few nanometers. The mechanism responsible for the fiber formation mainly includes the Taylor Cone theory and flight-instability theory, which can be predicted theoretically and controlled experimentally. Moreover, the electrospinning has been applied to natural polymers, synthetic polymers, ceramics, and carbon. Fibers with complex architectures, such as ribbon fiber, porous fiber, core-shell fiber, or hollow fiber, can be produced by special electrospinning methods. It is also possible to produce nanofibrous membranes with designed aggregate structure including alignment, patterning, and two-dimensional nanonets. Finally, the brief analysis of nanofibers used for advanced energy and environmental applications in the past decade indicates that their impact has been realized well and is encouraging, and will continually represent a key technology to ensure sustainable energy and preserve our environment for the future.

Electrospun Nanofibers: Solving Global Issues

Advances in three-dimensional nanofibrous macrostructures via electrospinning

Nanofibres can be fabricated by various methods and perhaps electrospinning is the most facile route. In past years, electrospinning has been used as a synthesis technique and the fibres have been prepared from a variety of starting materials and show various properties. Recently, incorporating functional nanoparticles (NPs) with electrospun fibres has emerged as one of most exciting research topics in the field of electrospinning. When NPs are incorporated, on the one hand the NPs endow the electrospun fibres/mats novel or better performance, on the other hand the electrospun fibres/mats could preserve the NPs from corrosion and/or oxidation, especially for NPs with anisotropic structures. More importantly, electrospinning shows potential applications in self-assembly of nanoscale building blocks for generating new functions, and has some obvious advantages that are not available by other self-assembly methods, i.e., the obtained free-standing hybrid mats are usually flexible and with large area, which is favourable for their commercial applications. In this critical review, we will focus on the fabrication and applications of NPs-electrospun fibre composites and give an overview on this emerging field combining nanoparticles and electrospinning. Firstly, two main strategies for producing NPs-electrospun fibres will be discussed, i.e., one is preparing the NPs-electrospun fibres after electrospinning process that is usually combined with other post-processing methods, and the other is fabricating the composite nanofibres during the electrospinning process. In particular, the NPs in the latter method will be classified and introduced to show the assembling effect of electrospinning on NPs with different anisotropic structures. The subsequent section describes the applications of these NPs-electrospun fibre mats and nanocomposites, and finally a conclusion and perspectives of the future research in this emerging field is given.

Nanoparticles meet electrospinning: recent advances and future prospects

Hydrogels such as poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc) can be photopatterned to create a wide range of actuatable and self-folding microstructures. Mechanical motion is derived from the large and reversible swelling response of this cross-linked hydrogel in varying thermal or pH environments. This action is facilitated by their network structure and capacity for large strain. However, due to the low modulus of such hydrogels, they have limited gripping ability of relevance to surgical excision or robotic tasks such as pick-and-place. Using experiments and modeling, we design, fabricate, and characterize photopatterned, self-folding functional microgrippers that combine a swellable, photo-cross-linked pNIPAM-AAc soft-hydrogel with a nonswellable and stiff segmented polymer (polypropylene fumarate, PPF). We also show that we can embed iron oxide (Fe2O3) nanoparticles into the porous hydrogel layer, allowing the microgrippers to be responsive and remotely guided using magnetic fields. Usi...

http://pubs.acs.org/doi/pdf/10.1021/am508621s

Self-Folding Thermo-Magnetically Responsive Soft Microgrippers

The fabrication of tubular structures, with multiple cell types forming different layers of the tube walls, is described using a stress-induced rolling membrane (SIRM). Cell orientation inside the tubes can also be controlled by topographical contact guidance. These layered tubes precisely mimic blood vessels and many other tubular structures, suggesting that they may be of great use in tissue engineering.

A strategy for depositing different types of cells in three dimensions to mimic tubular structures in tissues.

We report a one-step method to fabricate necklace-like structures from zero-dimensional materials via electrospinning. PVA was used as polymer matrix for accomplishing necklace-like arrays of silica particles. We systemically investigated how the diameter of SiO(2) particles, the weight ratio of PVA to SiO(2), the voltage, and the relative content of PVA/SiO(2)/H(2)O influenced the morphology of electrospun fibers. SiO(2) particles with diameter of 143 nm tended to aggregate into bunches in the fibers, while 265 and 910 nm SiO(2) particles tended to align along the fibers one by one, resembling necklaces. The content of water in the PVA/SiO(2)/H(2)O solution showed critical influence on the diameter of fibers and consequently determined the morphology. Too thin solutions gave birth to blackberry-like structure; too condensed solution was too hard to eject from the orifice of the needle; when the ingredient was elaborately tailored, we obtained necklace-like structures. We believe that these results can serve as references to generating other complex structures involving polymers and particles via electrospinning and that these structures will be potentially useful in photoelectric devices, drug release, and optical components.

Fabrication of necklace-like structures via electrospinning.

A self-adjusting, blood vessel-mimicking, multilayered tubular structure with two polymers, poly(e-caprolactone) (PCL) and poly(dl-lactide-co-glycolide) (PLGA), can keep the shape of the scaffold during biodegradation The inner (PCL) layer of the tube can expand whereas the outer (PLGA) layers will shrink to maintain the stability of the shape and the inner space of the tubular shape both in vitro and in vivo over months This approach can be generally useful for making scaffolds that require the maintenance of a defined shape, based on FDA-approved materials

Self-Adjusting, Polymeric Multilayered Roll that can Keep the Shapes of the Blood Vessel Scaffolds during Biodegradation.

Electrospinning of poly(dimethylsiloxane)/poly(methyl methacrylate) nanofibrous membrane: fabrication and application in protein microarrays.

This report establishes an in vitro model on glass surfaces for patterning multiple types of cells to simulate cell-cell interactions in vivo. The model employs a microfluidic system and poly(ethylene glycol)-terminated oxysilane (PEG-oxysilane) to modify glass surfaces in order to resist cell adhesion. The system allows the selective confinement of different types of cells to realize complete confinement, partial confinement, and no confinement of three types of cells on glass surfaces. The model was applied to study intercellular interactions among human umbilical vein endothelial cells (HUVEC), PLA 801 C and PLA801 D cells.

Yu Jin

Papers

A strategy for depositing different types of cells in three dimensions to mimic tubular structures in tissues.

Fabrication of necklace-like structures via electrospinning.

Self-Adjusting, Polymeric Multilayered Roll that can Keep the Shapes of the Blood Vessel Scaffolds during Biodegradation.

Electrospinning of poly(dimethylsiloxane)/poly(methyl methacrylate) nanofibrous membrane: fabrication and application in protein microarrays.

In vitro model on glass surfaces for complex interactions between different types of cells.