Coaxial electrospinning is a technique to create core-sheath or hollow electrospun micro- and nanofibers. While idea of coaxial spinning was already proposed by J.F. Cooley in 1900,1 the key initiating publication for the coaxial electrospinning as known today is considered to be the work of I. Loscertales in 2002. 2
A coaxial electrospinning setup enables two different solutions to be spun simultaneously (core and sheath/shell). These two solutions are processed through a coaxial nozzle, which has an inner and an outer orifice. The structure of the capillary allows the formation of fibers with one material surrounding the other.
In its basics, the buildup of the nozzle will be reflected in the fibers. Depending on the number of solutions connected to the spinneret and its conformation, it is possible to obtain more complex fiber shapes. Examples are triaxial electrospun fibers or fibers with different compartments.3,4 Changing the ratio between core and shell flow rates, varying solutions concentration as well as using standard electrospinning parameters such as voltage allows to adjust the thickness of the core and the shell fiber.5
An important application of this technique is drug delivery. The vast majority of drugs are non-spinnable by themselves. With coaxial electrospinning the drugs or proteins are loaded in the core whereas the sheath facilitates the spinning and protects the bioactive material. Selecting the shell material and/or its thickness allows to adjust the release rate, an important parameter to maximize the effect of the drug.6
Another application of the coaxial electrospinning is the production of reinforced fibers. For example polyurethane, can be used as core material to increase the mechanical properties of the mesh and collagen as shell around it to improve the biocompatibility and bioactivity of the scaffold.7
Furthermore coaxial electrospinnning facilitates the production of hollow fibers. Choosing a temporary core material, such as oil or a soluble material, which is removed in a second step, generates hollow fiber meshes.5,8 These hollow fibers can for example be employed as validation material in diffusion magnetic resonance imaging for brain analysis.5