(Central) a typical apparatus for needle electrospinning and (outer) images of electrospun nanofibers with various morphologies, (a) beaded fiber [3], (b) round fiber [4], (c) fiber with a porous surface [5], (d) grooved fiber [6], (e) ribbon [7], (f) multichannel fiber [8], (g) side-by-side fiber [9, 10], (h) crimped fiber [9, 11], (i) hollow fiber [12], and (j) core-sheath fiber [13]. (a–f) are prepared by conventional needle electrospinning, and (g–j) are electrospun mainly by a special needle spinneret.
