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Polylactide (PLA) is among the most common biodegradable polymers, with applications in various fields, such as renewable and biomedical industries. PLA features poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) enantiomers, which form stereocomplex crystals through racemic blending. PLA emerged as a promising material owing to its sustainable, eco-friendly, and fully biodegradable properties. Nevertheless, PLA still has a low applicability for drug delivery as a carrier and scaffold. Stereocomplex PLA (sc-PLA) exhibits substantially improved mechanical and physical strength compared to the homopolymer, overcoming these limitations. Recently, numerous studies have reported the use of sc-PLA as a drug carrier through encapsulation of various drugs, proteins, and secondary molecules by various processes including micelle formation, self-assembly, emulsion, and inkjet printing. However, concerns such as low loading capacity, weak stability of hydrophilic contents, and non-sustainable release behavior remain. This review focuses on various strategies to overcome the current challenges of sc-PLA in drug delivery systems and biomedical applications in three critical fields, namely anti-cancer therapy, tissue engineering, and anti-microbial activity. Furthermore, the excellent potential of sc-PLA as a next-generation polymeric material is discussed.

Monofilaments such as those consisting of polyamide (PA), polydioxanone (PDS), and poly(vinylidene fluoride) (PVDF), have been commonly used in various industries. However, most are non-biodegradable, which is unfavorable for many biomedical applications. Although biodegradable polymers offer significant benefits, they are still limited by their weak mechanical properties, which is an obstacle for use as a biomaterial that requires high strength. To overcome the current limitations of biodegradable monofilaments, a novel solid-state drawing (SSD) process was designed to significantly improve the mechanical properties of both PA and poly(l-lactic acid) (PLLA) monofilaments in this study. Both PA and PLLA monofilaments exhibited more than two-fold increased tensile strength and a highly reduced thickness using SSD. In X-ray diffraction and scanning electron microscopy analyses, it was determined that SSD could not only promote the α-crystal phase, but also smoothen the surface of PLLA monofilaments. To apply SSD-monofilaments with superior properties to cardiovascular stents, a shaped-annealing (SA) process was designed as the follow-up process after SSD. Using this process, three types of vascular stents could be fabricated, composed of SSD-monofilaments: double-helix, single-spring and double-spring shaped stents. The annealing temperature was optimized at 80 °C to minimize the loss of mechanical and physical properties of SSD-monofilaments for secondary processing. All three types of vascular stents were tested according to ISO 25539-2. Consequently, it was confirmed that spring-shaped stents had good recovery rate values and a high compressive modulus. In conclusion, this study showed significantly improved mechanical properties of both tensile and compressive strength simultaneously and extended the potential for biomedical applications of monofilaments.

Most biomaterials composed of biodegradable polymers will contact either accidentally or consistently with blood and this commonly requires both good  mechanical strength and blood compatibility. Despite this demand, current processing methods still make it difficult and complex to simultaneously improve the two properties. To overcome present limitations, the aim of this work is to develop a solid-state drawing which is a novel method for blood-contact biomaterials that can simultaneously improve the two essential factors of mechanical strength and blood compatibility, as well as induce a micro-patterned surface. Solid-state drawn (SSD) poly(L-lactic acid) (PLLA) film significantly maximally increased tensile strength and elastic modulus about ninefold and sixfold, respectively, compared to undrawn film. Furthermore, it was determined that SSD-PLLA film had highly developed molecular orientation, higher crystallinity and surface hydrophobicity. Additionally, the SSD method could greatly reduce roughness of the surface and induce the formation of aligned valleys, forming microstructures on the film surface. The topographical cue delayed hydrolytic degradation and prevented damage on the surface by NaOH of alkali compounds are compared with undrawn film. In energy-dispersive x-ray spectroscopy analysis, the surface of SSD film treated by NaOH was not detected on any ions whereas undrawn film held foreign ions on surface defects. The hemolysis rate of SSD film was considerably decreased with an increase of draw ratio up to 0.2% maximally and SSD film has shown greatly lower platelet adhesion compared to undrawn film in blood-compatibility analysis. Interestingly, one-directional alignment of micro-valley structure on SSD film could promote initial adhesion of human umbilical vein endothelial cells (HUVEC) compared with undrawn film and guide the direction of HUVEC. In conclusion, the newly designed SSD method has shown potential for developing blood-contact biomaterials simply due to great mechanical properties, blood compatibility and an aligned micro-patterned surface.

Polylactide (PLA) is one of the most commonly used biodegradable polymers for various fields such as biomedical and renewable industries. This material must undergo molding processes to achieve the desired shape in the final manufactured product, which are typically thermal- or solvent-based. Unfortunately, the mechanical and thermal properties of PLA, such as the strength and crystallinity, are inevitably damaged during the molding process due to the slow crystallization rate. To overcome this limitation, a simple, novel, one-pot, self-accelerating method for the in situ self-nucleating (ISN) polymerization of l-lactide is developed. This strategy results in the simultaneous polymerization and self-nucleation of l-lactide crystallites upon addition of a self-nucleating agent. The results show that ISN-PLA experiences an acceleration effect on the crystallization with stereocomplex polylactide (sc-PLA) as the nucleating agent and has enhanced mechanical and thermal properties, despite repetitive thermal processing. The ISN polymerization of l-lactide can save considerable time and cost by using the one-pot process composed of both polymerization and self-nucleation. This study suggests a novel strategy for manufacturing industrial products with high strength and crystallinity based on PLA as a promising biopolymer.

Polylactide (PLA) is a eco‐friendly and biodegradable material that can be synthesized from renewable resources. PLA features poly(d‐lactic acid) (PDLA) and poly(l‐lactic acid) (PLLA) enantiomers. Supercritical fluid (SCF) technology is a very promising method for the stereocomplexation between PDLA and PLLA enantiomers. This study acquires stereocomplex (sc‐)PLA particles with diverse sizes and behaviors by controlling the experimental conditions. Various parameters including polymer concentration, reaction temperature, stirring speed, pressure reducing speed, and final temperature were controlled to adjust size and behavior of sc‐PLA particles. Additionally, we analyzed the effect of subsequent processing following SCF (such as homogenization, mechanical stirring, and sonication) on the size and morphological behavior of sc‐PLA particles. Finally, the mechanical strengths of different PLA composites featuring different sc‐PLA filler sizes were determined. The mechanical strength of PLA composites was significantly improved when using smaller filler sizes. POLYM. ENG. SCI., 58:1193–1200, 2018. © 2017 Society of Plastics Engineers

Biodegradable polymer polylactide (PLA) can form stereocomplex crystals through racemic blending between poly(Llactide) (PLLA) and poly(D-lactide) (PDLA). This stereocomplexation could lead to substantially improved mechanical and physical strengths for PLA. Various methods for preparing stereocomplex PLA (sc-PLA) have been studied, e.g., solution blending, melt blending, and supercritical fluid (SCF) technology. However, current methods inevitably have various drawbacks including poor efficiency, usability, and low stereocomplexation reaction speeds. Thus, the aim of this study is to develop a novel strategy using oil-in-water (O/W) emulsion blending to overcome the current limitations of stereocomplexation. Our results indicate that the developed strategy can considerably improve the efficiency and accessibility of stereocomplex crystal formation compared to conventional methods such as solution blending and SCF technology. The O/W emulsion blending method exhibits a stereocomplexation efficiency of up to nearly 99%. Additionally, the sc-PLA produced by O/W emulsion blending can act as filler in PLA composites, leading to improvement of their mechanical properties. In addition, a cancer drug such as fluorouracil (5-FU) could be infiltrated into sc-PLA during stereocomplexation induced by O/W emulsion blending. Furthermore, sc-PLA with 5-FU prepared by the novel method could be added for ISN-polymerization in order to give both a nucleating effect and an anticancer effect. It suggests that sc-PLA prepared by our novel method could act as a stable carrier for secondary molecules as well as nucleating agents.

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