# Poly(lactic acid)-Based Electrospun Fibrous Structures for Biomedical Applications
## 5 Engineering of PLA-Based Electrospun Structures for Biomedical Applications
### PLA-Based Electrospun Yarns  
Initial research on the electrospinningning of PLA for biomedical engineering has been centralized on the fabrication of randomly oriented fibrous webs which is suitable for wound dressings, tissue regeneration scaffolds, and drug carriers. Nevertheless, the low mechanical performance of such random fibrous webs has restricted their efficiency; hence, in addition to the optimized morphology and uniformity, it is a substantial challenge to develop PLA nanofibrous structures with improved mechanical functions [11]. In order to meet the requirements for particular loadbearing applications in biomedical engineering, in recent years, electrospinningning of aligned structures and yarns with improved mechanical features has received attention. Aiming to increase the adhesion and frictional forces between the fibers, and thus enhance their strength, twist was inserted into the fibrous bundle during the electrospinningning procedure [37]. The superior lateral interaction and cohesion between fibers in twisted yarns significantly improve their mechanical properties. Electrospun PLA yarns have recently attracted great attention and offered advanced applications as medical devices in the form of sutures and implants, artificial blood vessels, high-performance and functional fabrics, drug delivery carriers, and tissue scaffolding materials [8; 37; 38]. In recent years, a variety of electrospinningning technologies have been proposed by researchers to produce uniaxially aligned bundles and yarns. In several research works performed by [PERSON] and coworkers, a double-nozzle electrospinninging set-up has been applied to produce PLA-based twisted yarns for biomedical application. This set-up includes a high voltage power supply, two syringe nozzles, a neutral surface, and a take-up twister unit (Figure 8a). Using this device, a PLA fibrous structure in the form of continuous twisted yarn was electrospun (Figure 8b). Through a comprehensive study, they have investigated the effects of processing parameters (i.e., voltage, take-up rate, and distances) [38], twist level [45], and post-draw treatment [55] on the morphology, diameter, crystallinity, and mechanical features of electrospun PLA yarns. Finally, they concluded that the mechanical behavior of yarns was affected by the yarn geometry and characteristics of individual fibers in the yarn structure [8; 38; 45; 55]. In a recently published work, [PERSON] et al. [17], have suggested the same electrospinninging set-up to produce  
Figure 7: Different arrangements of fiber deposits produced via electrospinningning of PLA: (**a**) random. Reproduced with permission from [40] (License number: 5235950005044), (**b**) oriented, reproduced from an open access paper [4] distributed under the terms of the Creative Commons CC BY license, and (**c**) yarn, Reproduced with permission from [45] (License number: 5235871036609). PLA-based twisted yarns with a core-shell structure for suture application (Figure 8c). The investigations revealed that the electrospun core-shell drug-loaded yarn with desirable physical and mechanical properties can use as a suitable drug carrier for wound healing. Additionally, the loading efficiency of drug and release profile could versatility be controlled by tuning the structural characteristics of electrospun yarns as an effective tool for developing suture yarns with appropriate functions. [PERSON] et al. [16] produced electrospun core-shell yarns as surgical sutures, with PLLA core, and drug-loaded Poly-Lactic-co-Glycolic acid (PLGA) as a shell.