Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

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

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

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Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Electrospun silk-BMP-2 scaffolds for bone tissue engineering.

This Review provides an overview of the synthesis of one-dimensional (1D) composite nanomaterials by electrospinning and their applications. After a brief description of the development of the electrospinning technique, the transformation of an inorganic nanocomponent or polymer into another kind of polymer or inorganic matrix is discussed in terms of the electrospinning process, including the direct-dispersed method, gas-solid reaction, in situ photoreduction, sol-gel method, emulsion electrospinning method, solvent evaporation, and coaxial electrospinning. In addition, various applications of such 1D composite nanomaterials are highlighted in terms of electronic and optical nanodevices, chemical and biological sensors, catalysis and electrocatalysis, superhydrophobic surfaces, environment, energy, and biomedical fields. An increasing number of investigations show that electrospinning has been not only a focus of academic study in the laboratory but is also being applied in a great many technological fields.

One-Dimensional Composite Nanomaterials: Synthesis by Electrospinning and Their Applications

Field-responsive superparamagnetic composite nanofibers by electrospinning

An inexpensive and versatile approach is reported for the synthesis of monodisperse magnetoresponsive rods of desired diameter, length, and magnetic susceptibility based on the confined alignment of magnetic beads in microchannels of selected channel height, followed by localized hydrolysis of sol-gel precursors within polyelectrolyte shells adsorbed on the beads. The layer-by-layer technique was used to coat the polystyrene beads with polyelectrolytes of alternating charge and with charged magnetic nanoparticles, and the polystyrene cores could be removed either by solvent dissolution or by calcination to form hollow-shelled chains. The reorientation dynamics of single and clustered chains following the application of an external magnetic field was evaluated theoretically, with favorable comparisons with the experimental data.

Rigid, superparamagnetic chains of permanently linked beads coated with magnetic nanoparticles. Synthesis and rotational dynamics under applied magnetic fields.

We have developed an efficient, one-step method to create magnetic nanowires consisting of permanently linked chains of magnetic beads of varying flexibility tethered to a patterned glass surface using simple amidation chemistry. The flexibility of the nanowire was governed by the molecular weight of the molecule used to covalently link the beads and its length by the height of the microchannel in which it was synthesized. The nanowire diameter was determined both by the bead size and by the number of beads adhering to each dot in the microstamped, patterned array. Longer nanowires can form loops attached at two points on the glass surface. Both single flexible chains and flexible loops can adopt different configurations (straight, hairpin, S-shaped, etc.) when subjected to magnetic fields, the configurations depending on the directions of these fields. Shorter, less flexible nanowires align with the field always and do not exhibit the more exotic configurations seen for long, flexible chains and loops. These magnetic nanowires can have potential use in microfluidic pumping and mixing processes and in microparticle manipulation.

Synthesis of Flexible Magnetic Nanowires of Permanently Linked Core−Shell Magnetic Beads Tethered to a Glass Surface Patterned by Microcontact Printing

Orientational dependence of apparent magnetic susceptibilities of superparamagnetic nanoparticles in planar structured arrays: Effect on magnetic moments of nanoparticle-coated core–shell magnetic beads

The effective stiffness of materials that are impregnated with magnetic nanoparticles can be modulated by magnetic fields if the nanoparticle Neel relaxation rates are slower than the characteristic deformation rates. A numerical analysis indicates that the deflection of magnetic dipoles against the applied magnetic field on deformation of the material provides the energy absorption necessary for the enhanced stiffness observed in drop ball impact tests. The penetration depth, fraction of the impact energy that is absorbed by the rotating dipoles, and the effective increase in stiffness are shown to depend uniquely on the ratio of the characteristic magnetic energy density relative to the elastic energy density, and on the shape of the impacting object.

Harpreet Singh

Papers

Field-responsive superparamagnetic composite nanofibers by electrospinning

Rigid, superparamagnetic chains of permanently linked beads coated with magnetic nanoparticles. Synthesis and rotational dynamics under applied magnetic fields.

Synthesis of Flexible Magnetic Nanowires of Permanently Linked Core−Shell Magnetic Beads Tethered to a Glass Surface Patterned by Microcontact Printing

Orientational dependence of apparent magnetic susceptibilities of superparamagnetic nanoparticles in planar structured arrays: Effect on magnetic moments of nanoparticle-coated core–shell magnetic beads

Tuning the Rate‐Dependent Stiffness of Materials by Exploiting Néel Relaxation of Magnetic Nanoparticles