Читать книгу Poly(lactic acid) - Группа авторов - Страница 122

Several processing techniques such as electrospinning [29, 84] and melt spinning [85] have gained enormous recognition for developing sc‐PLA fibers with improved stereocomplexation [86–88). Often, targeted biomedical applications require a controlled hierarchy, which may be possible by selectively modifying the surface of nanofibers [89]. One such method reported by Xie et al. is the combined use of electrospinning and a controlled polymerization technique for designing PLA nanofiber shish kebabs. The sc‐PLA nanofibers produced by electrospinning are used as the shish where the secondary polymer (hc‐PLA or sc‐PLA) is decorated to form a kebab lamella. The soft epitaxy mechanism possibly leads to the formation of shish kebab structures where the sc‐PLA nanofibers (shish) serve as the nucleating sites for kebab lamellae [25]. Such controlled mechanisms are of substantial importance when functionalizing the surface of nanofibers required for intended applications. Furthermore, the functionalization of sc‐PLA using cyclodextrins has facilitated their use as pollutant absorbers and drug carriers [90]. The exclusive formation of sc‐PLA has been achieved during electrospinning along with its functionalization, where the sub‐micrometer dispersion of nanofillers, namely polyhedral oligomeric silsesquioxanes (POSS), has been established. The functionalized sc‐PLA retains the capability of forming pure stereocomplex upon annealing [91]. Nevertheless, efforts have also been made to tune the hydrolytic degradation of sc‐PLA by tailoring the backbone architecture. Stereocomplexation between PLLA and PDLA oligomers has been reported, where the polymer architecture and the end groups altered the hydrolytic degradation rate [92]. Namely, the linear sc architecture having alcoholic end groups exhibited an increased degree of stereocomplexation with higher hydrolytic stability. In contrast, for the polymer with carboxyl chain ends, the degradation was accelerated due to the lower degree of stereocomplexation. The use of sc‐PLA has also been explored in textiles and membranes for oil–water separation. The modification of PLA nonwoven fabric by the formation of sc crystals has been reported by Zhu et al., where the sc crystal phase increased the surface roughness, as well as imparted oleophilicity to the fabric. The modification of the surface by sc‐PLA increased the oil absorption capability by 30–40% [93], which can be repeatedly used for the same purpose. The sc‐PLA, being brittle in nature, is limited to only specific applications. When exploring sc‐PLA for tissue engineering applications, elasticity is often required for the scaffold materials to serve physiological functions [94, 95]. This may be made possible by using toughness modifiers [96, 97]. For example, poly(butylene adipate‐co‐terephthalate) (PBAT) may be regarded as a toughness modifier when loaded into the matrix of PLA to increase elongation and processability [98]. The sc‐PLA/PBAT scaffolds with high porosity have been prepared by Kang et al. by non‐solvent phase separation [99]. The sc‐PLA‐based scaffolds led to a uniform porous structure (as compared to PLLA‐ or PDLA‐based scaffolds) having a wall thickness of ~1 μm, which may be due to the intermolecular forces between the enantiomeric PLA chains. The sc‐PLA/PBAT scaffolds are capable of supporting the adhesion of fibroblast cells, which in turn accounts for its biocompatible nature.