Figure 7.

(a) Basic electrospinning setup. A programmable syringe pump is used to infuse a polymer solution, emulsion, or melt through an electrically conductive spinneret (e.g., a metallic needle), to which a high voltage (usually 5–20 kV) is applied. The accumulation of electrical charges in the polymer droplets at the tip of the spinneret leads to repulsive forces that eventually result in the formation of a cone shape, the Taylor cone (b), which is followed by the ejection of the liquid. While the majority of electrospinning studies report the use of a positive voltage at the nozzle, negative voltages can be applied instead (see ref. [284]). The jet is then accelerated towards a grounded or oppositely charged collector, the solvent is evaporated, and dry fibres are deposited. When a monoaxial (single-channel) spinneret is used, blend fibres are formed. Core-shell fibres can be produced using coaxial electrospinning (c), with the help of a coaxial spinneret (d) in which an inner solution (core), usually containing an active pharmaceutical ingredient, is enveloped by an outer solution (shell). The organisation of the deposited fibres can be controlled using different collector architectures: a flat collector (e) will generate randomly deposited fibres, while a cylindrical mandrel (f) rotating at high speeds will result in highly aligned fibres. The Taylor cone schematic representation in (b) was adapted from [285] with permission from Elsevier. Copyright © 2020, Elsevier B.V. The scanning electron microscopy (SEM) images in (e,f) were adapted from [275] with permission from Elsevier. Copyright © 2015, Elsevier Inc.