# Poly(lactic acid)-Based Electrospun Fibrous Structures for Biomedical Applications
## 7 Electrospinning of PLA Stereocomplex Nanofibers  
The biocompatible, biodegradable, and non-toxic electrospun PLA fibers with desired thermomechanical properties are suitable materials to develop various medical devices; however, PLA-based nanofibrous structures have several limitations that considerably narrow their applications [11,12]. PLA is brittle with a low impact toughness, which is a hindrance in mechanically intensive applications, such as medical implants. It has a low thermal resistance and is hydrolytically sensitive which may restrict its function on prolonged operations in physiological media. Accordingly, the improvement of the physical and mechanical properties of PLA nanofibers is an essential matter for their ultimate functions [11,12,32,63,64]. Several research attempts have been performed to modify the PLA's physical limitation. Stereocomplexation, which was firstly reported by [PERSON] et al. in 1987 [65], has presented a suitable approach to control these restrictions. This strategy has attained increasing attention and offered a feasible procedure to design and develop the PLA-based biomaterials with specified and tunable features, such as degradation behavior, thermal stability, and mechanical properties [11,12]. Sc-PLA can be formed via crystallization of the mixture of enantiomers of PLLA and PDLA in solution or under melting conditions. In addition to the denser structure and higher melting temperature of the stereocomplex crystals than PLA homopolymers, the formation of stereocomplex also developed PLA-based materials with enhanced mechanical performance, thermal stability, and hydrolysis resistance [11,12,63,64]. Different research studies have focused on the fabrication of Sc-PLA fibers through the solution or melt spinning. Since, in the fibers spun via these methods, in addition to the stereocomplex crystallites, the homocrystallites also exist in the structure [11,12]. [PERSON] et al. [66] realized that the electrostatic forces during the electrospinning may facilitate the molecular chain orientation in the polymer and thus enhance the possibility for Sc crystallites growth and hinder the homocrystallites formation (Figure 10a) [67]. For the first time, [PERSON] and colleagues employed the electrospinning strategy to form the Sc-PLA crystallites in the nanofibers; in line with this, several research efforts have been performed to modify the PLA limitations by creating Sc crystallites in the PLA electrospun fibers. In comparison to homo-crystallized, Sc-PLA nanofibers exhibited distinguished characteristics likely lower degradation rate, improved mechanical performance, and enhanced thermal stabilities [68]. Electrospun Sc-PLA structures have been positively considered in the biomedical field as tissue engineering scaffolds, drug delivery matrices, among others [68]. In research works performed by [PERSON] et al., in order to provide the requirements for some loadbearing applications in biomedical engineering, the mechanical function of the nanofibrous structures has been improved. Their approach was to electrospun Sc-PLA-aligned structures in the form of twisted yarns (Figure 10b). Sc-PLA nanofibrous yarns prepared by electrospinningning of a blend solution of high molecular weight PLLA and PDLA and their characteristics compared with pure PLLA fibers [11; 12]. The results indicated that, upon heat treatment, stereocomplex crystals were completely formed in the Sc-PLA electrospun fibers, without any homocrystallites formation [11; 12]. The formation of Sc led to form fibers and yarns with smaller diameters and also narrower diameter distributions [11; 12; 64]; moreover, the thermal analysis revealed that the strong interaction between PLLA and PDLA chains enhanced the melting temperature of the Sc-PLA nanofibrous structures by around 56 \({}^{\circ}\)C compared to homopolymers (Figure 10d) [11; 12; 64]. The stereocomplexation phenomenon also affects the mechanical performance of the electrospun PLA structures.