Beyond the Single-Nozzle: Coaxial Electrospinning Enables Innovative Nanofiber Chemistries, Geometries, and Applications.

With an ever increasing scientific, technological, and industrial interest in high surface area, porous nanofiber mats, electrospinning has emerged as a popular method to produce fibrous assemblies for use across biomedical, energy, and environmental applications. However, not all precursor solutions nor complex geometries can be easily fabricated using the traditional single-nozzle apparatus. Therefore, coaxial electrospinning, a modified version of electrospinning that features a concentrically aligned dual nozzle, has been developed. This review will first describe the mechanism of electrospinning two precursor solutions simultaneously and the operational parameters that need to be optimized to fabricate continuous fibers. Modifications that can be made to the coaxial electrospinning process, which enable the fabrication of uniform fibers with improved properties, as well as the fabrication of fibers that are hollow, functionalized, and from "nonspinnable precursors" will be discussed as a means of promoting the advantages of using a coaxial setup. Examples of how coaxially electrospun nanofibers are employed in diverse applications will be provided throughout this review. We conclude with a timely discussion about the current limitations and challenges of coaxial electrospinning.