# Poly(lactic acid)-Based Electrospun Fibrous Structures for Biomedical Applications
## 5 Engineering of PLA-Based Electrospun Structures for Biomedical Applications
### Control of Morphology  
Commonly, research works are focused on determining the optimized electrospinningning conditions to fabricate PLA structures composed of uniform bead-less fibers with a cylindrical shape, and smooth surfaces (Figure 6b), while to fulfill the requirements of some specified applications, it is also necessary to obtain electrospun nanofibers with other morphologies [35]. By precise control of the electrospinningning parameters and applying spinnerets and collectors with specific shapes, nanofibers with diverse morphologies have been explored; for example, it is found that the drug release from electrospun fibers with flat ribbon morphology (Figure 6c) with higher surface area to volume ratio, may happen via diffusion from a shorter distance. In addition, the flat ribbon-like morphology limits the volume of entrapped air at the fiber-water interface, and thus influences the surface hydrophobicity which is important for their biological function in some applications like drug release, and cell adhesion and proliferation [4]. Generally, nanofibers fabricated by electrospinningning have a solid structure with a smooth surface. Since the fiber morphology changes to a porous state (Figure 6d,e), some fiber characteristics likely specific surface area, network porosity, and thus functional flexibility will enhance [4; 35]. For many biomedical applications, such as scaffolds for tissue engineering, wound dressing, and carriers for drug delivery, PLA-based fibers are electrospun purposefully to have porous morphology. The porous fibers can mimic the native ECM and the increased network porosity assists cell attachment and creates adequate space for cell penetration and thus improving their efficiency as tissue engineering scaffold. The network porosity of the electrospun matrices with tiny pores can increase hemostasis, and successfully preserve the wound site from bacterial permeation. The porosity of electrospun fibers may increase drug loading efficacy. Small pores and enhanced surface-to-volume ratio can also affect the release behavior from porous fibrous structures [4; 8; 36; 47]. Several types of research have been focused on electrospinningning of PLA fibers with porous morphology using a volatile solvent or solvent/non-solvent system [47; 49; 50; 51]. As mentioned in Section Solvent Systems by proper choice of solvent system, and within appropriate environmental conditions whereby porous fibers can be electrospun from PLA-based solutions. Figure 4c,d show SEM images of the nanofibers with porous surface morphology were fabricated by electrospinningning of PLA solutions in highly volatile solvents of CHCl\({}_{3}\) and DCM, respectively [35; 36; 37]. Solvent and non-solvent combination is another approach that has also been proposed to induce porosity in PLA fibers; for example, [PERSON] et al. [50] found that the addition of DMF to the PLA/DCM system led to forming fibers with porous morphology, and the same system for producing porous PLA fibers has been applied by [PERSON] et al. [52]. [PERSON] et al. [49] used 1-butanol (BuOH) as a non-solvent to create porosity on PLA fibers. In another research work, [PERSON] et al. [53] fabricated PLA porous fibers, by electrospinningning of PLA-DCM-hexane solution. However, the uniform and beadles' fibers are usually preferred to form, but bead-on-string nanofibers (Figure 6a,e), with versatility in the bead diameter, shape, and surface morphology, have been proposed as a potential for some specific applications. Electrospun fibers with beaded morphology can provide efficient encapsulation of biomolecules and a controlled release profile as a drug carrier for tissue engineering and wound dressing applications. The diameter of the formed beads affects the release behavior of the bead-on-string nanofibers [54].