# Fibers by Electrospinning and Their Emerging Applications in Bone Tissue Engineering
## 3 Mechanical Support  
Ideally, BTE scaffolds could not only mimic natural ECM, but also provide appropriate mechanical support for new bone formation. Polymeric materials are considered a promising candidate with mechanical properties similar to tissue for temporary support of bone regeneration. The electrospinningning technique has been employed to easily customize the scaffolds with special structures and mechanical properties by changing scaffold components and electrospinningning process. Figure 6: The illustration of building 3D electrospun fibrous scaffold via TISA and freeze drying [29; 56; 139]. One advantage of electrospinningning is that spinning solution can be easily customized. Electrospinning solutions can be easily mixed with nanomaterials for reinforcing resultant electrospun nanofibers, such as nanoparticles [51; 59; 100], nanosheets [32], etc. These nanomaterials are evenly dispersed in the electrospun matrix and the interface combination with matrix is established, which can effectively transfer the external force from the matrix. Moreover, several polymers with excellent mechanical properties have been utilized in electrospinningning solutions for BTE scaffolds. Polytetrafluoroethylene (PTFE) is known for its high fracture toughness [140], but its lack of spinnability remains a challenge. [PERSON] et al. [141] prepared a polyethylene oxide (PEO) solution containing PTFE dispersion for electrospinningning. The use of PEO effectively improved PTFE spinability and then PEO was removed by sintering process. Furthermore, previous studies reported that shape memory BTE scaffolds provided mechanical support while offering in situ mechanical stimulus for efficient bone regeneration [142]. For example, PLLA was used as a shape memory polymer and then modified to enhance its shape memory functionality [143; 144; 145]. [PERSON] et al. [85] fabricated PLLA electrospun BTE scaffold incorporated with PHBV for improvement of mechanical properties and shape memory functionality. Their study revealed that this improvement decreased the transition temperature of PLLA fibers owing to incorporated PHBV. Different electrospinningning methods have been explored for preparing BTE scaffolds for mechanical support. [PERSON] et al. fabricated core-sheath structured fibrous scaffolds by coaxial electrospinningning. Mechanical testing showed that the core-sheath scaffolds displayed better mechanical properties compared to those of single-component scaffolds [19]. In addition, core-sheath structure can also be obtained by double conjugate electrospinningning (Figure 7). Different from coaxial electrospun fibers, core-sheath yarns endowed with suitable mechanical properties for producing a fabric were generated by this method. [PERSON] et al. [107] developed PLA/tussah silk fibroin (TSF) nanofiber yarns by double conjugated electrospinning, and then the yarns were woven into multilayer fabrics as BTE scaffolds. Compression tests revealed that the multilayer fibrous fabric scaffolds showed significant superiority in compressive strength compared to the non-woven fibrous mats. Furthermore, [PERSON] et al. used the same method to prepare nanofiber yarns with different contents of HAP for fabrication of gradient woven fabric scaffolds [146]. Experimental results showed that the prepared scaffolds exhibited excellent mechanical properties while providing a mineral gradient graft for tendon-to-bone tissue interface regeneration. Figure 7: The illustration of core-sheath yarns endowed with suitable mechanical property for producing a fabric. The fiber web is drawn by an insulating rod placed in center of funnel, and then forms a fibrous cone which is twisted by rotating funnel to form continuous yarns [107]. Multilayer or hierarchical structure shows its potential of providing mechanical support for BTE. It is simple to prepare the scaffolds with hierarchical structure by folding electrospun mats several times [147] or bonding them layer by layer with adhesive [52].