Fig. 1. Graphical representation of the number of articles on electrospinning published worldwide for each year since 2000.

Fig. 2. Proportion of electrospinning papers published by countries in the world.

Fig. 3. Schematic of different electrospinning techniques. (A) The traditional electrospinning; (B) Coaxial electrospinning; (C) Emulsion electrospinning; (D) Dynamic water flow electrospinning.

Fig. 4. Diagram illustrating the double-spray electrospinning [22]. (a) The schematic of double-spray electrospinning. (b) A photograph of the receiving funnel. (c) A photograph of the process of nanoyarn formation and winding. (d) A photograph of yarn coil. (e) Scanning electron microscopy (SEM) images of a single nanoyarn.

Fig. 5. SEM of fibroblasts in a native tissue after freeze-drying [27].

Fig. 6. Schematic of how a scaffold structure affects cell adhesion and spreading [32]. (A), (B) Cells adhere in a flat morphology on the microporous and microfiber scaffolds, similar to that observed on flat surfaces. (C) Nanofibers have a greater surface area, and therefore adsorbed more protein, providing more adhesion sites for cell membrane receptors.

Fig. 7. Schematic of the fabrication of a scaffold for skin tissue engineering by a four-step process and the animal experiment to evaluate wound repair [44]. (1) 2D nanofibrous mats were fabricated via electrospinning. (2) A homogeneous short fiber solution was prepared by high-speed mechanical cutting. (3) The 3D scaffold was obtained after freeze-drying the solution. (4) The 3D scaffold was reinforced through heat treatment.

Fig. 8. Confocal microscopy images of human smooth muscle cells (hSMCs) and L929 murine fibroblasts after culturing for 5 days on the P(LLA-CL), 3: 1 and 1:1 composite scaffolds (A). Cell viability of hSMCs (B) and L929 cells (C) cultured for 1, 3, and 5 days [50].

Fig. 9. Process of fabricating the core (heparin)-shell (PC/SAB-MSN) fiber (left) [51]. Transmission electron microscope images of MSN (A) and core (heparin)-sheath (P(LLA-CL) and collagen with SAB-MSN) fiber (B), SEM of the nanofiber with MSN particle on the surface (C), SEM-EDS image of the fiber membrane (D).

Fig. 10. Fluorescence micrographs of (A-D) the bilayer vascular scaffold after implantation for 2 months and (E-H) the autologous vessel both after immunohistochemical staining of (A, E) DAPI for nuclei, (B, F) CD31 for endothelial cells, and (C, G) α-SMA for smooth muscle cells. (D, H) The corresponding merged fluorescence micrographs [53].

Fig. 11. A schematic showing how ideal NGCs are constructed by incorporating a diverse array of physical and biological cues into a neural scaffold with different configurations [56].

Fig. 12. Schematic of the graphene oxide-coated antheraea pernyi silk fibroin (ApF)/P(LLA-CL) scaffold preparation [63].

Fig. 13. Mechanism of nanofiber yarn fabrication and schematic of incorporating the nanofiber yarn into the NGC [65].

Fig. 14. Schematic of polypyrrole (Ppy)-coated PCL nanoyarn (NY) fabrication for the development of a conductive, filament-filled NGC [67].

Fig. 15. Schematic illustrating the fabrication of the electrospun 3D nanofiber sponges and the fabrication of a NGC by electrospinning [68].

Fig. 16. Schematic of 3D nanofibrous scaffold preparation incorporating nano-hydroxyapatite (nHA) and BMP-2 for testing in an in vivo, cranial defect regeneration model [76].

Fig. 17. Design of an scaffold containing MSN and alendronate (ALN) for the dual delivery of ALN and silicate to modulate bone resorption and formation for accelerating bone repair. The ALN pre-loaded within the MSNs is released from the nano?bers and inhibits the bone-resorption process by preventing GTP-related protein expression. The silicate produced by the hydrolysis of MSNs is released from the nano?bers and promotes the bone-forming process by improving vascularization and bone calci?cation [77].

Fig. 18. Electrospun silk fibroin nanofibrous scaffolds engineered with two-stage hydroxyapatite (HA) particle functionalization. These scaffolds were found to support the osteogenic differentiation of genetically-modified human adipose-derived mesenchymal stem cells after 21 days in vitro and enhance mineralized bone formation and collagen deposition in vivo in a critical-sized calvarial bone defect after 8 weeks [79].

Fig. 19. Macroscopic images (a, d, and g) of the cartilage joints from the non-treated group, group treated with the non-functionalized scaffold (3DS-1), and the group treated with the hyaluronic acid-functionalized scaffold (3DS-2) at 12 weeks after surgery. Histological analysis of the cartilage defect area from the three groups, stained with Safranin O-fast green (b, e, and h) and H&E (c, f, and i), indicate that the functionalized scaffold enhanced repair. Arrows and dotted lines indicated the defect sites. OC: original cartilage tissue. RC: repaired cartilage tissue [83].

Fig. 20. Schematic of various electrospun fiber scaffolds [84]. (a) Traditional fiber scaffold-electrospun fiber membrane. (b) 3D fibrous scaffold constructed by dispersed Electrospun, short fibers via freeze-shaping. (c) The synthetic steps of a 3D-printed fiber-based scaffold.

Fig. 21. Water-induced shape memory of 3D printed scaffolds made from an ink containing electrospun nanofibers [84]. (a) Square scaffold. (b) In a wet state, a tubular-shaped scaffold was obtained by folding the opposite angle of the square, and the scaffold was freeze-dried to maintain its deformed shape. (c) Shape recovery process of square scaffold after absorption of water for 12 s. (d) Square scaffold completely recovered its original shape within 20 s of water absorption. (e) Rectangular scaffold. (f) Wet scaffold was folded into a wave shape and freeze-dried to maintain its shape. (g) Shape recovery process of rectangular scaffold after water absorption for 12 s. (h) Rectangular scaffold completely recovered its original shape within 30 s of water absorption.

Fig. 22. Fabrication and characterization of collagen control scaffolds and bi-layered scaffolds of electrospun PLA and collagen [82]. The fabrication process of collagen scaffolds (A) and bi-layered scaffolds (B) and their microstructures.

Fig. 23. Macroscopic images of the cartilage joints from three groups at 6 (upper panel) and 12 (lower panel) weeks after surgery [82]. (A, D) Non-treated group, (B, E) collagen control group, and (C, F) bi-layered scaffold group.

Fig. 24. (A) Composite scaffold preparation. Dual electrospinning was employed to fabricate a scaffold containing PCL and methacrylated gelatin (mGLT) fibers (Insert 1). The dry scaffold was wetted with an aqueous photo-initiator solution (Insert 2) and then photo-crosslinked by visible light to retain the gelatin (Insert 3). (B) Scaffold sheets were wetted, stacked, and exposed to visible light for crosslink formation between adjacent scaffold layers to create a complex multi-layered structure [90].

Fig. 25. Schematic representation of electrospinning setup and hierarchical assembling of continuous aligned nanofiber threads (CANT). (A) Continuous electrospinning system to produce CANT; (B) CANT as the elementary unit of the 3D assembly, mimicking the collagen fibers in native tendon; (C) Yarns composed of twisted CANT represent tendon fascicles: i) Yarn 6, ii) Yarn 9, and iii) Yarn 12; (D) Braided 3D scaffold produced using Yarns; (E) Weaving process using Yarns: (i) arrays of 1 mm pins, (ii) Yarns weaving, and (iii) final 3D Woven scaffold. Both textile scaffolds represent the tendon unit [92].

Fig. 26. Schematic showing the structure of a native bone-tendon insertion site and fabrication of an aligned gradient platform with immobilized PDGF-BB that could mimic the bone-tendon insertion site [96].

Fig. 27. Schematic illustration of the application of the double-layer membrane. (a and b) The nanofibrous membrane is placed at the site of tendon-to-bone insertion. (c) The structure and composition of the scaffold mimic the normal fibrocartilage enthesis. (d) Illustration of hydroxyapatite (HA) growth on PLLA fibers [97].