Poly(lactic acid) stereocomplexes: A decade of progress

Microfluidic Assembly of Degradable, Stereocomplexed Hydrogel Microparticles

Hydrogel microparticles (HMPs) have been investigated widely for their use in tissue engineering and drug delivery applications. However, translation of these highly tunable systems has been hindered by covalent cross-linking methods within microparticles. Stereocomplexation, a stereospecific form of physical cross-linking, provides a robust yet degradable alternative for creating translationally relevant HMPs. Herein, 4-arm polyethylene glycol (PEG) stars were used as macromolecular initiators from which oligomeric poly(l-lactic acid) (PLLA) was polymerized with a degree of polymerization (DPn) of 20 on each arm. Similarly, complementary propargyl-containing ABA cross-linkers with enantiomeric poly(d-lactic acid) (PDLA) segments (DPn = 20) on each arm. Droplets of these gel precursors were formed via a microfluidic organic-in-oil-in-water system where microparticles self-assembled via stereocomplexation and were stabilized after precipitation in deionized water. By varying the flow rate of the dispersed phase, well-defined microparticles with diameters of 33.7 ± 0.5, 62.4 ± 0.6, and 105.7 ± 0.8 μm were fabricated. Gelation due to stereocomplexation was confirmed via wide-angle X-ray scattering in which HMPs exhibited the signature diffraction pattern of stereocomplexed PLA at 2θ = 12.2, 21.2, 24.2°. Differential scanning calorimetry also confirmed stereocomplexation by the appearance of a crystallization exotherm (Tc = 37 °C) and a high-temperature endotherm (Tm = 159 °C) that does not appear in the homocrystallization of PLLA or the hydrogel precursors. Additionally, the propargyl handle present on the cross-linker allows for pre- or post-assembly thiol-yne "click" functionalization as demonstrated by the addition of thiol-containing fluorophores to the HMPs.

Insulin Extended Release from PLA-PEG Stereocomplex Nanoparticles

This report addresses the challenges of controlled drug delivery for peptide and protein therapeutics by introducing a novel approach of nano formulation fabricated in aqueous media applying stereo-interaction mechanism with poly(D-lactide)-polyethylene glycol (D-PLA-PEG). To overcome the inherent poor stability of peptide and protein therapeutics, stereocomplexation of the peptide, insulin, is applied, onto D-PLA-PEG in aqueous media. Nanoparticles of ≈400 nm are spontaneously formed when water-soluble D configured PLA-PEG diblock copolymer and L- configured insulin interlock into a stereocomplex, owing to their concave convex fitness. In vitro release of insulin from stereocomplex in phosphate buffer solution (PBS) pH 7.4 solution shows sustained release for 14 weeks. The therapeutic efficacy of the PLA-insulin stereocomplex nanoparticles are evaluated in diabetic Akita mice. Blood glucose levels and body weight are closely monitored for a period of 17 weeks, revealing a significant reduction in glucose levels of the Akita mice treated with insulin stereocomplex, as well as normal body weight gain. These findings suggest that the stereocomplex nanoparticles of insulin-D-PLA-PEG present a promising and effective sustained and extended release platform for insulin. Notably, the use of water-soluble D-PLA-PEG for stereocomplexation in water expands the applicability of this approach to fabricate controlled delivery systems for peptide and protein therapeutics.

Third-generation D-lactic acid production using red macroalgae Gelidium amansii by co-fermentation of galactose, glucose and xylose

Macroalgae biomass has been considered as a promising renewable feedstock for lactic acid production owing to its lignin-free, high carbohydrate content and high productivity. Herein, the D-lactic acid production from red macroalgae Gelidium amansii by Pediococcus acidilactici was investigated. The fermentable sugars in G. amansii acid-prehydrolysate were mainly galactose and glucose with a small amounts of xylose. P. acidilactici could simultaneously ferment the mixed sugars of galactose, glucose and xylose into D-lactic acid at high yield (0.90 g/g), without carbon catabolite repression (CCR). The assimilating pathways of these sugars in P. acidilactici were proposed based on the whole genome sequences. Simultaneous saccharification and co-fermentation (SSCF) of the pretreated and biodetoxified G. amansii was also conducted, a record high of D-lactic acid (41.4 g/L) from macroalgae biomass with the yield of 0.34 g/g dry feedstock was achieved. This study provided an important biorefinery strain for D-lactic acid production from macroalgae biomass.

Peptide and Protein Stereocomplexes

Stereocomplexation in peptides and proteins is a fascinating phenomenon arising from their inherent stereoisomerism. Peptides and proteins, with their three-dimensional helical structures, exhibit stereoselectivity and form intertwined complexes when complementary left- and right-handed structures are mixed together. Stereocomplexation provides an unprecedented opportunity to impart some valuable biological, chemical, and physical properties in peptide and protein polymeric platforms that can be employed in various applications such as catalysis and drug delivery and to improve the stability of these therapeutics. However, exploration of stereocomplexation in peptides and proteins remains limited. We report on a comprehensive understanding of stereocomplexation in peptides and proteins, compiling existing reports, discussing its implications, and highlighting its role in different applications, aiming to inspire further research and advancements in this direction.

Scalable manufacturing of an amide-based nucleating agent for transparency and high heat resistance of polylactic acid

The prevalent use of disposable plastic tableware presents notable environmental and health risks. An alternative, polylactic acid (PLA), often does not meet usage requirements due to its low crystallization rate. This research introduces an amide-based nucleating agent, BRE-T-100, developed through a straightforward method to enhance the heat resistance and crystallization rate of PLA. This study systematically investigates the impact of BRE-T-100 and other nucleating agents on the properties of PLA composites. The incorporation of 0.8 % BRE-T-100 increases the crystallization temperature of PLA from 109.6 °C to 131.9 °C. Further, the total crystallization time of PLA composites at 120 °C is reduced to <60 s, while maintaining good transparency. BRE-T-100 exhibits superior comprehensive properties compared to talcum, TMC-200, and TMC-300 and is nearly on par with LAK-301. Its application as a nucleating agent in PLA-based disposable tableware shows promise.

A 3D-Printed Scaffold for Repairing Bone Defects

The treatment of bone defects has always posed challenges in the field of orthopedics. Scaffolds, as a vital component of bone tissue engineering, offer significant advantages in the research and treatment of clinical bone defects. This study aims to provide an overview of how 3D printing technology is applied in the production of bone repair scaffolds. Depending on the materials used, the 3D-printed scaffolds can be classified into two types: single-component scaffolds and composite scaffolds. We have conducted a comprehensive analysis of material composition, the characteristics of 3D printing, performance, advantages, disadvantages, and applications for each scaffold type. Furthermore, based on the current research status and progress, we offer suggestions for future research in this area. In conclusion, this review acts as a valuable reference for advancing the research in the field of bone repair scaffolds.

Experimental evidence for immiscibility of enantiomeric polymers: Phase separation of high-molecular-weight poly(ʟ-lactide)/poly(ᴅ-lactide) blends and its impact on hindering stereocomplex crystallization

Although polymers tend not to mix, it remains challenging to characterize the immiscibility of enantiomeric poly(ʟ-lactide) (PLLA) and poly(ᴅ-lactide) (PDLA), particularly with equivalent and high molecular weight (high MW), which frustratingly disfavors the exclusive stereocomplexation. By introducing a random copolymer (PLC) of ʟ-lactide and caprolactone to form binary blends with PLLA and PDLA, the phase behavior of high-MW PLLA/PDLA blends was investigated mainly by using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). DSC results showed that PLLA/PLC blends exhibited a single glass transition temperature (Tg), which depended on the blending ratio and precisely corresponded with the theoretical values calculated from the Fox equation. In comparison, PDLA/PLC blends showed composition-dependent heat-capacity increment at two unchanged Tg values of pure PLC and PDLA. AFM observation revealed that PLC is completely miscible with PLLA at high MW but is immiscible with PDLA, logically suggesting immiscibility of high-MW PLLA and PDLA. Moreover, AFM results demonstrated that high-MW PLLA/PDLA blends exhibited spherical droplets in asymmetric blends and bicontinuous interpenetrating worm-like patterns in symmetric counterparts, showing distinct and well-defined interfaces, confirming the microphase separation. Additionally, different MWs fundamentally led to significant differences in miscibility, which consequently affected the crystallization behaviors of PLLA/PDLA blends. This work provides evidence for (im)miscibility and its crucial impact on the crystallization of PLLA/PDLA blends and has important implications for understanding the stereocomplexation of polymers.

The Effect of Stereocomplexation and Crystallinity on the Degradation of Polylactide Nanoparticles

Polymeric nanoparticles (PNPs) are frequently researched and used in drug delivery. The degradation of PNPs is highly dependent on various properties, such as polymer chemical structure, size, crystallinity, and melting temperature. Hence, a precise understanding of PNP degradation behavior is essential for optimizing the system. This study focused on enzymatic hydrolysis as a degradation mechanism by investigation of the degradation of PNP with various crystallinities. The aliphatic polyester polylactide ([C3H4O2]n, PLA) was used as two chiral forms, poly l-lactide (PlLA) and poly d-lactide (PdLA), and formed a unique crystalline stereocomplex (SC). PNPs were prepared via a nanoprecipitation method. In order to further control the crystallinity and melting temperatures of the SC, the polymer poly(3-ethylglycolide) [C6H8O4]n (PEtGly) was synthesized. Our investigation shows that the PNP degradation can be controlled by various chemical structures, crystallinity and stereocomplexation. The influence of proteinase K on PNP degradation was also discussed in this research. AFM did not reveal any changes within the first 24 h but indicated accelerated degradation after 7 days when higher EtGly content was present, implying that lower crystallinity renders the particles more susceptible to hydrolysis. QCM-D exhibited reduced enzyme adsorption and a slower degradation rate in SC-PNPs with lower EtGly contents and higher crystallinities. A more in-depth analysis of the degradation process unveiled that QCM-D detected rapid degradation from the outset, whereas AFM exhibited delayed changes of degradation. The knowledge gained in this work is useful for the design and creation of advanced PNPs with enhanced structures and properties.

Self-Reinforced PTLG Copolymer with Shish Kebab Structures and a Bionic Surface as Bioimplant Materials for Tissue Engineering Applications

Green and biodegradable materials with great mechanical properties and biocompatibility will offer new opportunities for next-generation high-performance biological materials. Herein, the novel oriented shish kebab crystals of a novel poly(trimethylene carbonate-lactide-glycolide) (PTLG) vascular stent are first reported to be successfully fabricated through a feasible solid-state drawing process to simultaneously enhance the mechanical performance and biocompatibility. The crystal structure of this self-reinforced vascular stent was transformed from spherulites to a shish kebab crystal, which indicates the mechanical interlocking effect and prevents the lamellae from slipping with a significant improvement of mechanical strength to 333 MPa. Meanwhile, it is different from typical biomedical polymers with smooth surface structures, and the as-obtained PTLG vascular stent exhibits a bionic surface morphology with a parallel micro groove and ridge structure. These ridges and grooves were attributed to the reorganization of cytoskeleton fiber bundles following the direction of blood flow shear stress. The structure and parameters of these morphologies were highly similar to the inner surface of blood vessels of the human, which facilitates cell adhesion growth to improve its proliferation, differentiation, and activity on the surface of PTLG.

Observation of Ferroelectric Lithography on Biodegradable PLA Films

Ferroelectric lithography, which can purposefully control and pattern ferroelectric domains in the micro-/nanometer scale, has extensive applications in data memories, field-effect transistors, race-track memory, tunneling barriers, and integrated biochemical sensors. In pursuit of mechanical flexibility and light weight, organic ferroelectric polymers such as poly(vinylidene fluoride) are developed; however, they still suffer from complicated stretching processes of film fabrication and poor degradability. These poor features severely hinder their applications. Here, the ferroelectric lithography on the biocompatible and biodegradable poly(lactic acid) (PLA) thin films at room temperature is demonstrated. The semicrystalline PLA thin film can be easily fabricated through the melt-casting method, and the desired domain structures can be precisely written according to the predefined patterns. Most importantly, the coercive voltage (Vc ) of PLA thin film is relatively low (lower than 30 V) and can be further reduced with the decrease of the film thickness. These intriguing behaviors combined with satisfying biodegradability make PLA thin film a desirable candidate for ferroelectric lithography and enable its future application in the field of bioelectronics and biomedicine. This work sheds light on further exploration of ferroelectric lithography on other polymer ferroelectrics as well as their application as nanostructured devices.

Remarkably enhanced stereocomplex crystallization of high-molar-mass enantiomeric polylactide blends by adding double-grafted copolymers

Stereocomplex (SC) crystallization can prominently improve the physico-chemical properties of poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends, yielding a novel polylactide (PLA) material. However, the predominant formation of SC crystals in the melt-processing of high-molar-mass (high-MW, >100 kg/mol) enantiomeric PLA blends remains a huge challenge due to the competition between SC crystallization and homocrystallization. Herein, double-grafted copolymer having both PLLA and PDLA side chain has been designed and synthesized as an efficient crystallization promoter for the harvest of SC crystals in the high-MW PLLA/PDLA blends. The results show that, with the addition of such a copolymer, the blends can preferentially crystallize into SC crystals in both isothermal and non-isothermal conditions. Promisingly, the SC crystals can be exclusively formed by adding only small amounts (e.g., 0.5 wt%) of the copolymer, without the formation of any homocrystals. This interesting observation can be interpreted by the crucial role of the unique copolymer in suppressing the phase separation of the opposite PLA enantiomers upon melting as an efficient compatibilizer and then encouraging the generation of alternatingly arranged PLLA/PDLA chain clusters favored for SC nucleation and crystal growth. These findings provide new inspiration for the development of high-performance PLA with desirable SC crystallizability.

Ring Opening Polymerization of Six- and Eight-Membered Racemic Cyclic Esters for Biodegradable Materials

The low percentage of recyclability of the polymeric materials obtained by olefin transition metal (TM) polymerization catalysis has increased the interest in their substitution with more eco-friendly materials with reliable physical and mechanical properties. Among the variety of known biodegradable polymers, linear aliphatic polyesters produced by ring-opening polymerization (ROP) of cyclic esters occupy a prominent position. The polymer properties are highly dependent on the macromolecule microstructure, and the control of stereoselectivity is necessary for providing materials with precise and finely tuned properties. In this review, we aim to outline the main synthetic routes, the physical properties and also the applications of three commercially available biodegradable materials: Polylactic acid (PLA), Poly(Lactic-co-Glycolic Acid) (PLGA), and Poly(3-hydroxybutyrate) (P3HB), all of three easily accessible via ROP. In this framework, understanding the origin of enantioselectivity and the factors that determine it is then crucial for the development of materials with suitable thermal and mechanical properties.

Theoretical and experimental studies on sulfasalazine interactions with poly (lactic acid): Impact of hydrogen bonding and charge transfer interactions on molecular structure, electronic and optical properties

The interaction between sulfasalazine (SSZ) through different functional groups and poly (lactic acid) (PLA) in the chloroform phase was investigated in this study using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The binding energy and thermodynamic parameters show that the hydrogen double bond interaction between SSZ and PLA in state I (-0.71 eV) is stronger than in states II (-0.64 eV) and III (-0.51 eV). The SSZ and PLA interaction results in an enhanced dipole moment, greater solubility, and more negative values for Gibbs free energy (ΔGsolv) and energy gap (Eg). Considerable changes in absorption peaks of SSZ and PLA indicate surface adsorption of the drug (SSZ) into the carrier (PLA) in UV-Vis spectra. Theoretical UV-Vis analysis demonstrates SSZ interaction with PLA happens in the ultraviolet region with a maximum absorption peak at 380 nm, which is close to experimental UV-Vis analysis. The experimental spectra showed minimal variations in the maximum absorption wavelength, with respect to theoretical calculations. The presence of SSZ was found to cause a modification in the structure of PLA, as evidenced by both experimental and theoretical Infrared (IR) spectra.

Influence of polylactide coating stereochemistry on mechanical and in vitro degradation properties of porous bioactive glass scaffolds for bone regeneration

The mechanical properties of polylactide stereocomplexes (PLA SC) have been primarily studied through tensile testing, with inconsistent results, and the compressive properties of PLA SC compared to homocrystalline or amorphous PLA remain poorly understood. In this study, we coated porous bioactive glass 13-93 scaffolds with amorphous, homocrystalline, or stereocomplex PLA to investigate their mechanical and degradation properties before and after immersion in simulated body fluid. The glass scaffolds had interconnected pores and an average porosity of 76%. The PLA coatings, which were 10-100 μm thick and approximately 3% of the glass scaffold mass, covered the glass to a large extent. The compressive strength and toughness of all PLA-coated scaffolds were significantly higher than those of uncoated scaffolds, with approximately a fourfold increase before immersion and a twofold increase after immersion. The compressive strength and toughness of PLA SC-coated scaffolds were similar to those of scaffolds with homocrystalline PLA coating, and significantly higher than for scaffolds with amorphous PLA coating. All PLA coatings moderated the initial pH increase caused by the glass, which could benefit surrounding cells and bone tissue in vivo after implantation.

Enhancing the tribological performance of PLA-based biocomposites reinforced with graphene oxide

Poly(lactic acid) (PLA) reinforced with graphene has gained substantial interest as a biomaterial, where the tribological and mechanical behavior of PLA/graphene composites are major concerns. This study aims to develop PLA-based biocomposites reinforced with graphene oxide (GO) that have enhanced tribological capabilities. First, homogenous dispersions of GO and GO treated with the anionic surfactant dioctyl sulfosuccinate sodium salt (AOT) were retained. Then, poly(L-lactic acid) (PLLA) biopolymer and PLLA/GO, PLLA/GO(AOT), PLA/GO(AOT), and PLLA/polyethylene glycol (PEG)/GO biocomposite samples were produced via hot pressing, and their tribological behavior was examined in detail. The worn surface characteristics were examined using scanning electron microscopy (SEM), 3D confocal microscopy, and atomic force microscopy (AFM). Results showed that GO reinforcement considerably affected the sliding wear behavior of PLA. Contrary to anticipated, surface treatment of GO does not improve the PLLA/GO wear resistance; rather, it increases the wear rate. PEG positively affects the sliding wear performance of PLLA/GO. PLLA/GO and PLLA/PEG/GO biocomposites exhibited the lowest wear rate at normal loads of 5 and 8 N, respectively, which was decreased by about 50% compared to unreinforced PLLA samples. With the addition of GO, the wear mechanisms of the PLA-based biocomposites changed from adhesive wear to abrasive wear. These findings might increase the applicability of PLA-based biocomposites where tribological performance is the main concern, such as biodegradable implants for load-bearing bone fractures or scaffolds, opening up new opportunities for their use.

Modulating Barrier Properties of Stereocomplex Polylactide: The Polymorphism Mechanism and Its Relationship with Rigid Amorphous Fraction

The barrier properties of semicrystalline polymers are crucial for their performance and their use as packaging materials. This work uncovers the mechanism of polymorphism modification (α, α' and stereocomplex-crystals) and its combined effect on the oxygen and water vapor barrier properties of semicrystalline stereocomplex polylactide (SCPLA). A polymorphic selective filler-type nucleator was employed to eliminate the temperature effect on the development of polymorphism and rigid amorphous fraction (RAF), allowing correlations of barrier properties with different crystal forms and RAF combinations under the same amorphous composition (SCPLA). The oxygen and water vapor barrier performances strongly correlated with crystallinity and crystal form but were not monotonically related to the RAF quantity. The study proposes that the chain conformation of intermediate phases between the crystalline and amorphous phases differs with the associated crystal forms, thereby leading to different RAF "qualities" and contributing to different gas diffusion and solubility coefficients of the amorphous regions. RAF's per unit excess free volume may be varied with crystal forms, for instance: α' ≫ SC > α. Therefore, SCPLA with α' crystals exhibited high oxygen and water vapor permeabilities. Those with high SC and α crystals showed similar barrier behaviors governed by Henry's law dissolution and followed a linear "two-phase" relationship with total crystallinity.

Hexagonal Phase Formation and Crystalline Structural Transition in Long-Spaced Aliphatic Polyesters with Side Groups

Side substitution is an effective method for the chemical modification and functionalization of linear polyesters. The presence of side groups can have a profound effect on the crystalline structure and phase transition of semicrystalline polyesters. Herein, we synthesized the long-spaced polyesters with -OH and -CH3 side groups and various methylene segment lengths and studied the effects of the side groups on the crystal polymorph and phase transition of substituted polyesters. The substituted polyesters grow in the thermally stable phase (form I) at a higher temperature. However, the polyesters crystallize in a metastable hexagonal phase (form II) with trans chain conformation at a lower temperature. The metastable form II transforms into the more stable form I during long-time annealing or upon heating; this phase transition is accompanied by chain tilting and crystal lamellar thickening. This study has elucidated the critical role of side groups in the polymorphic crystallization and phase transition of linear polyesters.

VEGF combined with DAPT promotes tissue regeneration and remodeling in vascular grafts

Previous research on tissue-engineered blood vessels (TEBVs) has mainly focused on the intima or adventitia unilaterally, neglecting the equal importance of both layers. Meanwhile, the efficacy of grafts modified with vascular endothelial growth factor (VEGF) merely has been limited. Here, we developed a small-diameter graft that can gradually release VEGF and γ secretase inhibitor IX (DAPT) to enhance tissue regeneration and remodeling in both the intima and adventitia. In vitro, experiments revealed that the combination of VEGF and DAPT had superior pro-proliferation and pro-migration effects on endothelial cells. In vivo, the sustained release of VEGF and DAPT from the grafts resulted in improved regeneration and remodeling. Specifically, in the intima, faster endothelialization and regeneration of smooth muscle cells led to higher patency rates and better remodeling. In the adventitia, a higher density of neovascularization, M2 macrophages and fibroblasts promoted cellular ingrowth and replacement of the implant with autologous neo-tissue. Furthermore, western blot analysis confirmed that the regenerated ECs were functional and the effect of DAPT was associated with increased expression of vascular endothelial growth factor receptor 2. Our study demonstrated that the sustained release of VEGF and DAPT from the graft can effectively promote tissue regeneration and remodeling in both the intima and adventitia. This development has the potential to significantly accelerate the clinical application of small-diameter TEBVs.

Stereocomplex-Driven Morphological Transition of Coil-Rod-Coil Poly(lactic acid)-Based Cylindrical Nanoparticles

The stereocomplexation of poly(lactic acid) (PLA) enantiomers opens up an avenue for the formation of new materials with enhanced performance, specifically regarding their mechanical and thermal resistance and resistance to hydrolysis. Despite these useful features, the study of the stereocomplexation between block copolymers based on PLA in solution is limited, and a comprehensive understanding of this phenomenon is urgently needed. Herein, triblock copolymers of poly(N-hydroxyethyl acrylamide) and PL(or D)LA in which PLA was midblock (PHEAAmy-b-PL(D)LAx-b-PHEAAmy) were synthesized and assembled into cylindrical micelles via crystallization-driven self-assembly . The stereocomplexation between enantiomeric micelles facilitates the morphological transition, and the transformation process was investigated in detail by varying the aging temperature, block composition, and solvent. It was found that the solubility of the copolymers played a vital role in determining the occurrence and the speed of the chain exchange between the micelles and the unimers, which thereafter has a significant impact on the shape transition. These results lead to a deeper understanding of the stereocomplex-driven morphological transition process and provide valuable guidance for further optimization of the transition under physiological conditions as a new category of stimuli-responsive systems for biomedical applications.

Recent advances in enantioselective ring-opening polymerization and copolymerization

Precisely controlling macromolecular stereochemistry and sequences is a powerful strategy for manipulating polymer properties. Controlled synthetic routes to prepare degradable polyester, polycarbonate, and polyether are of recent interest due to the need for sustainable materials as alternatives to petrochemical-based polyolefins. Enantioselective ring-opening polymerization and ring-opening copolymerization of racemic monomers offer access to stereoregular polymers, specifically enantiopure polymers that form stereocomplexes with improved physicochemical and mechanical properties. Here, we highlight the state-of-the-art of this polymerization chemistry that can produce microstructure-defined polymers. In particular, the structures and performances of various homogeneous enantioselective catalysts are presented. Trends and future challenges of such chemistry are discussed.

Combined Effect of Poly(lactic acid)-Grafted Maleic Anhydride Compatibilizer and Halloysite Nanotubes on Morphology and Properties of Polylactide/Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Blends

Given the global challenge of plastic pollution, the development of new bioplastics to replace conventional polymers has become a priority. It is therefore essential to achieve a balance in the performances of biopolymers in order to improve their commercial availability. In this topic, this study aims to investigate the morphology and properties of poly(lactic acid) (PLA)/ poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) (at a ratio of 75/25 (w/w)) blends reinforced with halloysite nanotubes (HNTs) and compatibilized with poly(lactic acid)-grafted maleic anhydride (PLA-g-MA). HNTs and PLA-g-MA were added to the polymer blend at 5 and 10 wt.%, respectively, and everything was processed via melt compounding. A scanning electron microscopy (SEM) analysis shows that HNTs are preferentially localized in PHBHHx nodules rather than in the PLA matrix due to its higher wettability. When HNTs are combined with PLA-g-MA, a finer and a more homogeneous morphology is observed, resulting in a reduction in the size of PHBHHx nodules. The presence of HNTs in the polymer blend improves the impact strength from 12.7 to 20.9 kJ/mm2. Further, with the addition of PLA-g-MA to PLA/PHBHHX/HNT nanocomposites, the tensile strength, elongation at break, and impact strength all improve significantly, rising from roughly 42 MPa, 14.5%, and 20.9 kJ/mm2 to nearly 46 MPa, 18.2%, and 31.2 kJ/mm2, respectively. This is consistent with the data obtained via dynamic mechanical analysis (DMA). The thermal stability of the compatibilized blend reinforced with HNTs is also improved compared to the non-compatibilized one. Overall, this study highlights the effectiveness of combining HNTs and PLA-g-AM for the properties enhancement of PLA/PHBHHx blends.

A Versatile Disorder-to-Order Technology to Upgrade Polymers into High-Performance Bioinspired Materials

Biodegradable polymer as traditional material has been widely used in the medical and tissue engineering fields, but there is a great limitation as to its inferior mechanical performance for repairing load-bearing tissues. Thus, it is highly desirable to develop a novel technology to fabricate high-performance biodegradable polymers. Herein, inspired by the bone's superstructure, a versatile disorder-to-order technology (VDOT) is proposed to manufacture a high-strength and high-elastic modulus stereo-composite self-reinforced polymer fiber. The mean tensile strength (336.1 MPa) and elastic modulus (4.1 GPa) of the self-reinforced polylactic acid (PLA) fiber are 5.2 and 2.1 times their counterparts of the traditional PLA fiber prepared by the existing spinning method. Moreover, the polymer fibers have the best ability of strength retention during degradation. Interestingly, the fiber tensile strength is even higher than those of bone (200 MPa) and some medical metals (e.g., Al and Mg). Based on all-polymeric raw materials, the VDOT endows bioinspired polymers with improved strength, elastic modulus, and degradation-controlled mechanical maintenance, making it a versatile update technology for the massive industrial production of high-performance biomedical polymers.

Peptide Stereocomplexation Orchestrates Supramolecular Assembly of Hydrogel Biomaterials

Stereocomplexation, or specific interactions among complementary stereoregular macromolecules, is burgeoning as an increasingly impactful design tool, exerting exquisite control of material structure and properties. Since stereocomplexation of polymers produces remarkable transformations in mechanics, morphology, and degradation, we sought to leverage stereocomplexation to tune these properties in peptide-based biomaterials. We found that blending the pentapeptides l- and d-KYFIL triggers dual mechanical and morphological transformations from stiff fibrous hydrogels into less stiff networks of plates, starkly contrasting prior reports that blending l- and d-peptides produces stiffer fibrous hydrogels than the individual constituents. The morphological transformation of KYFIL in phosphate-buffered saline from fibers that entangle into hydrogels to plates that cannot entangle explains the accompanying mechanical transformation. Moreover, the blends shield l-KYFIL from proteolytic degradation, producing materials with comparable proteolytic stability to d-KYFIL but with distinct 2D plate morphologies that in biomaterials may promote unique therapeutic release profiles and cell behavior. To confirm that these morphological, mechanical, and stability changes arise from differences in molecular packing as in polymer stereocomplexation, we acquired X-ray diffraction patterns, which showed l- and d-KYFIL to be amorphous and their blends to be crystalline. Stereocomplexation is particularly apparent in pure water, where l- and d-KYFIL are soluble random coils, and their blends form β-sheets and gel within minutes. Our results highlight the role of molecular details, such as peptide sequence, in determining the material properties resulting from stereocomplexation. Looking forward, the ability of stereocomplexation to orchestrate supramolecular assembly and tune application-critical properties champions stereochemistry as a compelling design consideration.

The Preparation of Superhydrophobic Polylactic Acid Membrane with Adjustable Pore Size by Freeze Solidification Phase Separation Method for Oil-Water Separation

An environmentally friendly pore size-controlled, superhydrophobic polylactic acid (PLA) membrane was successfully prepared by a simpler freeze solidification phase separation method (FSPS) and solution impregnation, which has application prospects in the field of oil-water separation. The pore size and structure of the membrane were adjusted by different solvent ratios and solution impregnation ratios. The PLA-FSPS membrane after solution impregnation (S-PLA-FSPS) had the characteristics of uniform pore size, superhydrophobicity and super lipophilicity, its surface roughness Ra was 338 nm, and the contact angle to water was 151°. The S-PLA-FSPS membrane was used for the oil-water separation. The membrane oil flux reached 16,084 L·m^-2·h^-1, and the water separation efficiency was 99.7%, which was much higher than that of other oil-water separation materials. In addition, the S-PLA-FSPS membrane could also be applied for the adsorption and removal of oil slicks and underwater heavy oil. The S-PLA-FSPS membrane has great application potential in the field of oil-water separation.

Simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid production facilitates D-lactide synthesis

D-lactide is the precursor of poly(D-lactide) (PDLA) or stereo-complex with poly(L-lactide) (PLLA). Lignocellulosic biomass provides the essential feedstock option to synthesize D-lactic acid and D-lactide. The residual sugars in D-lactic acid fermentation broth significantly blocks the D-lactide synthesis. This study showed a simultaneous and rate-coordinated conversion of lignocellulose derived glucose, xylose, arabinose, mannose, and galactose into D-lactic acid by adaptively evolved Pediococcus acidilactici ZY271 by simultaneous saccharification and co-fermentation (SSCF) of wheat straw. The produced D-lactic acid achieved minimum residual sugars (∼1.7 g/L), high chirality (∼99.1%) and high titer (∼128 g/L). A dry acid pretreatment eliminated the wastewater stream generation and the biodetoxification by fungus Amorphotheca resinae ZN1 removed the inhibitors from the pretreatment. The removal of the sugar residues and inhibitor impurities in D-lactic acid production from lignocellulose strongly facilitated the D-lactide synthesis. This study filled the gap in cellulosic D-lactide production from lignocellulose-derived D-lactic acid.

A New Self-Healing Degradable Copolymer Based on Polylactide and Poly(p-dioxanone)

In this paper, the copolymerization of poly (p-dioxanone) (PPDO) and polylactide (PLA) was carried out via a Diels-Alder reaction to obtain a new biodegradable copolymer with self-healing abilities. By altering the molecular weights of PPDO and PLA precursors, a series of copolymers (DA2300, DA3200, DA4700 and DA5500) with various chain segment lengths were created. After verifying the structure and molecular weight by 1H NMR, FT-IR and GPC, the crystallization behavior, self-healing properties and degradation properties of the copolymers were evaluated by DSC, POM, XRD, rheological measurements and enzymatic degradation. The results show that copolymerization based on the DA reaction effectively avoids the phase separation of PPDO and PLA. Among the products, DA4700 showed a better crystallization performance than PLA, and the half-crystallization time was 2.8 min. Compared to PPDO, the heat resistance of the DA copolymers was improved and the Tm increased from 93 °C to 103 °C. Significantly, the rheological data also confirmed that the copolymer was self-healing and showed obvious self-repairing properties after simple tempering. In addition, an enzyme degradation experiment showed that the DA copolymer can be degraded by a certain amount, with the degradation rate lying between those of PPDO and PLA.

Electrically conductive crystalline polylactide nonwovens obtained by electrospinning and modification with multiwall carbon nanotubes

Polylactide nonwovens were electrospun from solutions and then crystallized, one in the α-form, and another, S-PLA made of poly(l-lactide) and poly(d-lactide) 1:1 blend, in scPLA crystals with high melting temperature, close to 220 °C. To make the nonwovens electrically conductive, they were coated with multiwall carbon nanotubes (MWCNT) by padding with an aqueous dispersion of MWCNT or dip-coating in this dispersion. The electrical conductivity evidenced the formation of the electrically conductive MWCNT network on the fiber surfaces. Depending on the coating method, the surface resistivity (R_s) of S-PLA nonwoven of 1.0 kΩ/sq. and 0.09 kΩ/sq. was reached. To study the effect of surface roughness, before the modification the nonwovens were etched with sodium hydroxide, which additionally made them hydrophilic. The effect of etching depended on the coating method and led to an increase or decrease of R_s, in the case of padding or dip-coating, respectively. All MWCNT-modified nonwovens, unetched and etched, were hydrophobic with water contact angles of 138-144°. Scanning electron microscopy corroborated the presence of MWCNT on the fiber surfaces. The impedance spectroscopy confirmed the dominant role of the network of MWCNT direct contacts on the electrical properties of MWCNT-modified nonwovens in a broad frequency range.

Stereocomplexed microparticles loaded with Salvia cadmica Boiss. extracts for enhancement of immune response towards Helicobacter pylori

Controlled delivery of therapeutic substance gives numerous advantages (prevents degradation, improves uptake, sustains concentration, lowers side effects). To encapsulate Salvia cadmica extracts (root or aerial part), enriched with polyphenols with immunomodulatory activity, in stereocomplexed microparticles (sc-PLA), for using them to enhance the immune response towards gastric pathogen Helicobacter pylori. Microparticles were made of biodegradable poly(lactic acid) (PLA) and poly(D-lactic acid) (PDLA). Their stereocomplexation was used to form microspheres and enhance the stability of the obtained particles in acidic/basic pH. The release of Salvia cadmica extracts was done in different pH (5.5, 7.4 and 8.0). The obtained polymers are safe in vitro and in vivo (guinea pig model). The sc-PLA microparticles release of S. cadmica extracts in pH 5.5, 7.4, and 8.0. S. cadmica extracts enhanced the phagocytic activity of guinea pig bone marrow-derived macrophages, which was diminished by H. pylori, and neutralized H. pylori driven enhanced production of tumor necrosis factor (TNF)-α and interleukin (IL)-10. The sc-PLA encapsulated S. cadmica extracts can be recommended for further in vivo study in guinea pigs infected with H. pylori to confirm their ability to improve an immune response towards this pathogen.

Crystallization of Star-Shaped Poly(l-lactide)s with Arm Chains Aligned in the Same Direction in Two-Dimensional Crystals in a Langmuir Monolayer

Polylactide (PLA) crystallizes to form extended-chain crystals in a Langmuir monolayer because crystallization is accelerated on the water surface. This is a unique situation where chain packing can be analyzed by simply measuring the lamellar thickness. Herein, star-shaped poly(l-lactide)s (PLLAs) with 2-12 arms were synthesized through the polymerization of l-lactide with various polyols as initiators, and their crystallization behavior in a monolayer was studied via atomic force microscopy. The PLLAs comprising 2-4 arms crystallized with all arms aligned in the same direction and being folded at the central polyol unit. Meanwhile, the PLLAs comprising 6 and 12 arms crystallized with both halves of the arms extended from the center to the opposite directions, most likely due to the steric hindrance of the crowded arms. Considering that the PLLAs crystallized from a once-formed condensed amorphous state during compression, they have a strong tendency to crystallize with the arms aligned in the same direction. The crystallization rate of star-shaped PLAs is known to reduce compared with that of a linear PLA even if the number of arms is as few as 2. This should be closely related to the unique crystallization behavior of the star-shaped PLLAs with the arms aligned in the same direction.

Modified β-cyclodextrin microspheres towards the application in intumescent fire resistance and smoke-suppressing of bio-based poly(L-lactic acid)

In this work, the β-cyclodextrin (β-CD) was modified by a phosphazene compound to prepare a novel amorphous derivate (β-CDCP), which was combined with the ammonium polyphosphate (APP) as a synergistic flame retardant (FR) of the bio-based poly(L-lactic acid) (PLA). The effects of the APP/β-CDCP on the thermal stability, combustion behavior, pyrolysis process, fire resistance performance and crystallizability of the PLA were investigated comprehensively and in depth by thermogravimetric (TG) analysis, limited oxygen index (LOI) analysis, UL-94 test, cone calorimetry measurement, TG-infrared (TG-IR), scanning electron microscopy-energy dispersive spectrometer, Raman spectroscopy, pyrolysis-gas chromatography/mass spectrometry and differential scanning calorimetry. The PLA/5%APP/10%β-CDCP showed a highest LOI of 33.2 %, passed V-0 rating and exhibited self-extinguish phenomenon in the UL-94 test. Also, it presented a lowest peak of heat release rate, total heat release, peak of smoke production rate and total smoke release, and a highest char yield treated by cone calorimetry analysis. In addition, the 5%APP/10%β-CDCP shortened significantly crystallization time and enhanced crystallization rate of the PLA. Gas phase and intumescent condensed phase fire proofing mechanisms are proposed to elucidate enhanced fire resistance in this system in detail.

A Versatile Step-Growth Polymerization Route to Functional Polyesters from an Activated Diester Monomer

This work describes a versatile and efficient condensation polymerization route to aliphatic polyesters by organo-catalyzed (4-dimethylaminopyridine) transesterification reactions between an activated pentafluorophenyl-diester of adipic acid and structurally different diols. By introducing "monofunctional impurity" or "stoichiometric imbalance," this methodology can afford well-defined end-functionalized polyesters with predictable molecular weights and narrow dispersity under mild conditions without any necessity for the removal of the byproducts to accelerate the polymerization reaction, which remains a major challenge in conventional polyester synthesis with non-activated diesters. Wide substrate scope with structurally different monomers and the synthesis of block copolymers by chain extension following either ring-opening polymerization or controlled radical polymerization have been successfully demonstrated. Some of the polyesters synthesized by this newly introduced approach show high thermal stability, crystallinity, and enzymatic degradation in aqueous environments.

Multi-Level Information Encryption/Decryption of Fluorescent Hydrogels Based on Spatially Programmed Crystal Phases

The growing urgence of information protection promotes continuously the development of information-encryption technique. To date, hydrogels have become an emerging candidate for advanced information-encryption materials, because of their unique stimulus responsiveness. However, current methods to design multi-level information-encrypted hydrogels usually need sophisticated chemistry or experimental setup. Herein, a novel strategy is reported to fabricate hydrogels with multi-level information encryption/decryption functions through spatially programming the polymorphic crystal phases. As homocrystalline and stereocomplex crystal phases in fluorescent hydrogels have different solvent stabilities, the transparency and fluorescence of the hydrogels can be regulated, thereby enabling the multi-level encryption/decryption processes. Moreover, the structural origins behind these processes are discussed. It is believe that this work will inspire future research on developing advanced information-encryption materials upon programming the polymer crystal structure.

Surface-Compartmentalized Micelles by Stereocomplex-Driven Self-Assembly

The unique corona structure of surface-compartmentalized micelles (Janus micelles, patchy micelles) opens highly relevant applications, e.g. as efficient particulate surfactants for emulsion stabilization or compatibilization of polymer blends. Here, stereocomplex-driven self-assembly (SCDSA) as a facile route to micelles with a semicrystalline stereocomplex (SC) core and a patch-like microphase separated corona, employing diblock copolymers with enantiomeric poly(L-lactide)/poly(D-lactide) blocks and highly incompatible corona-forming blocks (polystyrene (PS), poly(tert-butyl methacrylate)) is introduced. The spherical patchy SC micelles feature a narrow size distribution and show a compartmentalized, shamrock-like corona structure. Compared to SC micelles with a homogeneous PS corona the patchy micelles have a significantly higher interfacial activity attributable to the synergistic combination of an amphiphilic corona with the Pickering effect of nanoparticles. The patchy micelles are successfully employed in the stabilization of emulsions, underlining their application potential.

The proteins derived from platelet-rich plasma improve the endothelialization and vascularization of small diameter vascular grafts

Vascular transplantation has become an ideal substitute for heart and peripheral vascular bypass therapy and tissue-engineered vascular grafts (TEVGs) present an attractive potential solution for vascular surgery. However, small diameter (Ф < 6 mm) vascular do not have ideal TEVGs for clinical use. Platelet-rich plasma (PRP), a key source of bioactive molecules, has been confirmed to promote tissue repair and regeneration. In this study, we prepared PRP-loaded TEVGs (PRP-TEVGs) by electrospinning, investigated the characterization of TEVGs, and verified the effect of PRP-TEVGs in vivo and in vitro experiments. The results suggested that PRP-TEVGs had good biocompatibility, released growth factors stably, promoted cell proliferation and migration significantly, up-regulated the expression of endothelial NO synthase (eNOS) in functional vascular endothelial cells (VECs), and maintained the stability of the endothelial structure. In vivo experiments suggest that PRP can promote rapid endothelialization and reconstruction of TEVGs. Overall, this finding indicated that PRP could promote the rapid vascular endothelialization of small-diameter TEVGs by improving contractile vascular smooth muscle cells (VSMCs) regeneration, and maintaining the integrity and functionality of VECs.

The Advancement of Biodegradable Polyesters as Delivery Systems for Camptothecin and Its Analogues-A Status Report

Camptothecin (CPT) has demonstrated antitumor activity in lung, ovarian, breast, pancreas, and stomach cancers. However, this drug, like many other potent anticancer agents, is extremely water-insoluble. Furthermore, pharmacology studies have revealed that prolonged schedules must be administered continuously. For these reasons, several of its water-soluble analogues, prodrugs, and macromolecular conjugates have been synthesized, and various formulation approaches have been investigated. Biodegradable polyesters have gained popularity in cancer treatment in recent years. A number of biodegradable polymeric drug delivery systems (DDSs), designed for localized and systemic administration of therapeutic agents, as well as tumor-targeting macromolecules, have entered clinical trials, demonstrating the importance of biodegradable polyesters in cancer therapy. Biodegradable polyester-based DDSs have the potential to deliver the payload to the target while also increasing drug availability at intended site. The systemic toxicity and serious side-effects associated with conventional cancer therapies can be significantly reduced with targeted polymeric systems. This review elaborates on the use of biodegradable polyesters in the delivery of CPT and its analogues. The design of various DDSs based on biodegradable polyesters has been described, with the drug either adsorbed on the polymer's surface or encapsulated within its macrostructure, as well as those in which a hydrolyzed chemical bond is formed between the active substance and the polymer chain. The data related to the type of DDSs, the kind of linkage, and the details of in vitro and in vivo studies are included.

Enhanced cellulosic d-lactic acid production from sugarcane bagasse by pre-fermentation of water-soluble carbohydrates before acid pretreatment

After several rounds of milling process for sugars extraction from sugarcane, certain amounts of water-soluble carbohydrates (WSC) still remain in sugarcane bagasse. It is a bottleneck to utilize WSC in sugarcane bagasse biorefinery, since these sugars are easily degraded into inhibitors during pretreatment. Herein, a simple pre-fermentation step before pretreatment was conducted, and 98 % of WSC in bagasse was fermented into d-lactic acid. The obtained d-lactic acid was stably preserved in bagasse and 5-hydroxymethylfurfural (HMF) generation was sharply reduced from 46.0 mg/g to 6.2 mg/g of dry bagasse, after dilute acid pretreatment. Consequently, a higher d-lactic acid titer (57.0 g/L vs 33.2 g/L) was achieved from the whole slurry of the undetoxified and pretreated sugarcane bagasse by one-pot simultaneous saccharification and co-fermentation (SSCF), with the overall yield of 0.58 g/g dry bagasse. This study gave an efficient strategy for enhancing lactic acid production using the lignocellulosic waste from sugar industry.

Scalable Preparation of Complete Stereo-Complexation Polylactic Acid Fiber and Its Hydrolysis Resistance

Due to their high sensitivity to temperature and humidity, the applications of polylactic acid (PLA) products are limited. The stereo-complexation (SC) formed by poly(L-lactic acid) (PLLA) and its enantiomer poly(D-lactic acid) (PDLA) can effectively improve the heat resistance and hydrolysis resistance of PLA products. In this work, the blended melt-spinning process of PLLA/PDLA was carried out using a polyester fiber production line to obtain PLA fiber with a complete SC structure. The effects of high-temperature tension heat-setting on the crystalline structure, thermal properties, mechanical properties, and hydrolysis resistance were discussed. The results indicated that when the tension heat-setting temperature reached 190 °C, the fiber achieved an almost complete SC structure, and its melting point was 222.5 °C. An accelerated hydrolysis experiment in a 95 °C water bath proved that the SC crystallites had better hydrolysis resistance than homocrystallization (HC). The monofilament strength retention rate of SC−190 fiber reached as high as 78.5% after hydrolysis for 24 h, which was significantly improved compared with PLLA/PDLA drawn fiber.

One-pot d-lactic acid production using undetoxified acid-pretreated corncob slurry by an adapted Pediococcus acidilactici

Inhibitor tolerance is still a bottleneck for lactic acid bacteria in lignocellulose biorefinery, while it is hard to obtain one engineered strain with strong tolerance to all inhibitors. Herein, a robust adapted d-lactic acid producing strain Pediococcus acidilactici XH11 was obtained by 111 days' long-term adaptive evolution in undetoxified corncob prehydrolysates. The adapted strain had higher inhibitors tolerance compared to the parental strain, primarily due to its increased conversion capacities of four typical aldehyde inhibitors (furfural, HMF, vanillin, and 4-hydroxybenzaldehyde). One-pot simultaneous saccharification and co-fermentation was successfully achieved using the whole slurry of acid-pretreated corncob without solid-liquid separation and detoxification, by applying the adapted P. acidilactici XH11. Finally, 61.9 g/L of d-lactic acid was generated after 96 h' fermentation (xylose conversion of 89.9 %) with the overall yield of 0.48 g/g dry corncob. This study gave an important option for screening of industrial strains in cellulosic lactic acid production processes.

Enhancement in Crystallizability of Poly(L-Lactide) Using Stereocomplex-Polylactide Powder as a Nucleating Agent

High-molecular-weight poly(L-lactide) (HMW-PLLA) is a promising candidate for use as a bioplastic because of its biodegradability and compostability. However, the applications of HMW-PLLA have been limited due to its poor crystallizability. In this work, stereocomplex polylactide (scPLA) powder was prepared by precipitation of a low-molecular-weight poly(L-lactide)/poly(D-lactide) (LMW-PLLA/LMW-PDLA) blend solution and investigated for use as a fully-biodegradable nucleating agent for HMW-PLLA compared to LMW-PLLA powder. The obtained LMW-PLLA and scPLA powders with a nearly spherical shape showed complete homo- and stereocomplex crystallites, respectively. HMW-PLLA/LMW-PLLA powder and HMW-PLLA/scPLA powder blends were prepared by melt blending. The LMW-PLLA powder was homogeneously melted in the HMW-PLLA matrices, whereas the scPLA powder had good phase compatibility and was well-dispersed in the HMW-PLLA matrices, as detected by scanning electron microscopy (SEM). It was shown that the enthalpies of crystallization (ΔHc) upon cooling scans for HMW-PLLA largely increased and the half crystallization time (t1/2) dramatically decreased as the scPLA powder content increased; however, the LMW-PLLA powder did not exhibit the same behavior, as determined by differential scanning calorimetry (DSC). The crystallinity content of the HMW-PLLA/scPLA powder blends significantly increased as the scPLA powder content increased, as determined by DSC and X-ray diffractometry (XRD). In conclusion, the fully biodegradable scPLA powder showed good potential for use as an effective nucleating agent to improve the crystallization properties of the HMW-PLLA bioplastic.