Decoding the Pathway-Dependent Self-Assembly of Polymer-Grafted Nanoparticles by Ligand Crystallization

Functional metamaterials can be constructed by assembling nanoparticles (NPs) into well-ordered structures, which show fascinating properties at different length scales. Using polymer-grafted NPs (PGNPs) as a building block, flexible composite metamaterials can be obtained, of which the structure is significantly affected by the property of polymer ligands. Here, it is demonstrated that the crystallization of polymer ligands determines the assembly behavior of NPs and reveal a pathway-dependent self-assembly of PGNPs into different metastructures in solution. By changing the crystallization degree of polymer ligands, the arrangement structure of NPs can be tailored. When the polymer ligands highly crystallize, the PGNPs assemble into diamond-shaped platelets, in which the NPs arrange disorderedly. When the polymer ligands lowly crystallize, the PGNPs assemble into highly ordered 3D superlattices, in which the NPs pack into a body-centered-cubic structure. The structure transformation of PGNP assemblies can be achieved by thermal annealing to regulate the crystallization of polymer ligands. Interestingly, the diamond-shaped platelets remain "living" for seeded epitaxial growth of newly added crystalline species. This work demonstrates the effects of ligand crystallization on the crystallization of NP, providing new insights into the structure regulation of metamaterials.

Sizing down and functionalizing polylactide (PLA) resin for synthesis of PLA-based polyurethanes for use in biomedical applications

Alcoholysis is a promising approach for upcycling postconsumer polylactide (PLA) products into valuable constituents. In addition, an alcohol-acidolysis of PLA by multifunctional 2,2-bis(hydroxymethyl)propionic acid (DMPA) produces lactate oligomers with hydroxyl and carboxylic acid terminals. In this work, a process for sizing down commercial PLA resin to optimum medium-sized lactate oligomers is developed at a lower cost than a bottom-up synthesis from its monomer. The microwave-assisted reaction is conveniently conducted at 220-240 °C and pressure lower than 100 psi. The PLA resin was completely converted via alcohol-acidolysis reaction, with a product purification yield as high as 93%. The resulting products are characterized by FTIR, 2D-NMR, ¹H-NMR, GPC, DSC, and XRD spectroscopy. The effects of PLA: DMPA feed ratios and the incorporation of 1,4-butanediol (BDO) on the structures, properties, and particle formability of the alcohol-acidolyzed products are examined. The products from a ratio of 12:1, which possessed optimum size and structures, are used to synthesize PLA-based polyurethane (PUD) by reacting with 1,6-diisocyanatohexane (HDI). The resulting PUD is employed in encapsulating lavender essential oil (LO). Without using any surfactant, stable LO-loaded nanoparticles are prepared due to the copolymer's self-stabilizability from its carboxylate groups. The effect of the polymer: LO feed ratio (1.25-3.75: 1) on the physicochemical properties of the resulting nanoparticles, e.g., colloidal stability (zeta potential > -60 mV), hydrodynamic size (300-500 nm), encapsulation efficiency (80-88%), and in vitro release, are investigated. The LO-loaded nanoparticles show non-toxicity to fibroblast cells, with an IC₅₀ value higher than 2000 µg/mL. The products from this process have high potential as drug encapsulation templates in biomedical applications.

Electrospun strong, bioactive, and bioabsorbable silk fibroin/poly (L-lactic-acid) nanoyarns for constructing advanced nanotextile tissue scaffolds

Bio-textiles have aroused attractive attentions in tissue engineering and regenerative medicine, and developing robust, bio-absorbable, and extracellular matrix (ECM) fibril-mimicking nanofibrous textiles is urgently required for the renewal of existing microfibrous textile-based scaffolds and grafts. In this study, an integrated electrospinning system consisting of one nanoyarn-forming unit and one hot stretching unit is reported to fabricate silk fibroin (SF)/poly (L-lactic-acid) (PLLA) nanofibrous yarns (nanoyarns). The hot stretching process is demonstrated to significantly improve the fiber alignment, crystallinity, and mechanical properties of SF/PLLA nanoyarns, compared to the unstretched controls. For instance, the fiber alignment degree of hot stretched 50/50 SF/PLLA nanoyarn has increased by 25%, and the failure strength has increased by 246.5%, compared with the corresponding un-stretched control. Increasing the SF/PLLA mass ratio is found to significantly decrease the crystallinity and mechanical properties, but notably increase the degradation rate and surface hydrophilicity of SF/PLLA nanoyarns. Different SF/PLLA nanoyarns are further meticulously interwoven with warp and weft directions to obtain several nanofibrous woven textiles. The results from in vitro cell characterization and in vivo subcutaneous implantation show that increasing the SF/PLLA mass ratio significantly improves the biological properties and effectively reduces the inflammatory response of nanoyarn-constructed textiles. Overall, this study demonstrates that our SF/PLLA nanoyarns with controllable physical, mechanical and biological performances are fantastic candidates for the designing and development of advanced nanoarchitectured textile tissue scaffolds.

Combining electrospinning with hot drawing process to fabricate high performance poly (L-lactic acid) nanofiber yarns for advanced nanostructured bio-textiles

Fiber constructed yarns are the elementary building blocks for the generation of implantable biotextiles, and there are always needs for designing and developing new types of yarns to improve the properties of biotextile implants. In the present study, we aim to develop novel nanofiber yarns (NYs) by combining nanostructure that more closely mimic the extracellular matrix fibrils of native tissues with biodegradability, strong mechanical properties and great textile processibility. A novel electrospinning system which integrates yarn formation with hot drawing process was developed to fabricate poly(L-lactic acid) (PLLA) NYs. Compared to the PLLA NYs without hot drawing, the thermally drawn PLLA NYs presented superbly-orientated fibrous structure and notably enhanced crystallinity. Importantly, they possessed admirable mechanical performances, which matched and even exceeded the commercial PLLA microfiber yarns (MYs). The thermally drawn PLLA NYs were also demonstrated to notably promote the adhesion, alignment, proliferation, and tenogenic differentiation of human adipose derived mesenchymal stem cells (hADMSCs) compared to the PLLA NYs without hot drawing. The thermally drawn PLLA NYs were further processed into various nanofibrous tissue scaffolds with defined structures and adjustable mechanical and biological properties using textile braiding and weaving technologies, demonstrating the feasibility and versatility of thermally drawn PLLA NYs for textile-forming utilization. The hADMSCs cultured on PLLA NY-based textiles presented enhanced attachment and proliferation capacities than those cultured on PLLA MY-based textiles. This work presents a facile technique to manufacture high performance PLLA NYs, which opens up opportunities to generate advanced nanostructured biotextiles for surgical implant applications.

Poly(Glycerol Succinate) as an Eco-Friendly Component of PLLA and PLCL Fibres towards Medical Applications

This study was conducted as a first step in obtaining eco-friendly fibres for medical applications using a synthesised oligomer poly(glycerol succinate) (PGSu) as an additive for synthetic poly(L-lactic acid) (PLLA) and poly (L-lactide-co-caprolactone) (PLCL). The effects of the oligomer on the structure formation, morphology, crystallisation behaviour, and mechanical properties of electrospun bicomponent fibres were investigated. Nonwovens were investigated by means of scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and mechanical testing. The molecular structure of PLLA fibres is influenced by the presence of PGSu mainly acting as an enhancer of molecular orientation. In the case of semicrystalline PLCL, chain mobility was enhanced by the presence of PGSu molecules, and the crystallinity of bicomponent fibres increased in relation to that of pure PLCL. The mechanical properties of bicomponent fibres were influenced by the level of PGSu present and the extent of crystal formation of the main component. An in vitro study conducted using L929 cells confirmed the biocompatible character of all bicomponent fibres.

Pressure induced crystallization and in situ simultaneous SAXS/WAXS investigations on structure transitions

A phase diagram of PLLA crystal structures as a function of crystallization temperature (T_c) and pressure (P_c).

Aminolysis of Various Aliphatic Polyesters in a Form of Nanofibers and Films

Surface functionalization of polymer scaffolds is a method used to improve interactions of materials with cells. A frequently used method for polyesters is aminolysis reaction, which introduces free amine groups on the surface. In this study, nanofibrous scaffolds and films of three different polyesters-polycaprolactone (PCL), poly(lactide-co-caprolactone) (PLCL), and poly(l-lactide) (PLLA) were subjected to this type of surface modification under the same conditions. Efficiency of aminolysis was evaluated on the basis of ninhydrin tests and ATR-FTIR spectroscopy. Also, impact of this treatment on the mechanical properties, crystallinity, and wettability of polyesters was compared and discussed from the perspective of aminolysis efficiency. It was shown that aminolysis is less efficient in the case of nanofibers, particularly for PCL nanofibers. Our hypothesis based on the fundamentals of classical high speed spinning process is that the lower efficiency of aminolysis in the case of nanofibers is associated with the radial distribution of crystallinity of electrospun fiber with more crystalline skin, strongly inhibiting the reaction. Moreover, the water contact angle results demonstrate that the effect of free amino groups on wettability is very different depending on the type and the form of polymer. The results of this study can help to understand fundamentals of aminolysis-based surface modification.

Preparation of levodopa-loaded crystalsomes through thermally induced crystallization reverses functional deficits in Parkinsonian mice

The prepared levodopa loaded crystalsomes are nanoscale crystals and controlling levodopa release which improving MPTP-induced behavioral impairments and pathological features of mice.

Stereocomplex-affected crystallization behaviour of PDLA in PDLA/PLDLA blends

In the presence of SC crystals, the spherulite growth rate of PDLA decreased, whereas its overall crystallization rate increased.

Effect of Dicumyl Peroxide on a Poly(lactic acid) (PLA)/Poly(butylene succinate) (PBS)/Functionalized Chitosan-Based Nanobiocomposite for Packaging: A Reactive Extrusion Study

Nanobiocomposites with balanced mechanical characteristics are fabricated from poly(lactic acid) (PLA)/poly(butylene succinate) (PBS)blend at a weight ratio of 80/20 in association with varying concentrations of functionalized chitosan (FCH) through reactive extrusion at a temperature of 185 °C. The combined effect of FCH and dicumyl peroxide (DCP) showed insignificant change in tensile strength with a remarkable increase in % elongation at break (∼45%) values. Addition of DCP also caused increase in the molecular weight (M _w ∼ 22%) of the PLA/PBS/1DFCH nanobiocomposite, which is attributed to the cross-linking/branching effect of FCH on the polymers. The interfacial polymer-filler adhesion is also improved, which is observed from the field-emission scanning electron microscopy images of PLA/PBS/1DFCH. For PLA/PBS/1DFCH, the crystallization rate and nucleation density of PLA are increased because of cross-linked/branched structures are developed, which acted as nucleating sites. Therefore, the present work facilitates a simple extrusion processing with a combination of balanced thermal and mechanical properties, improved hydrophobicity (∼27%), and UV-C-blocking efficiency, which draw the possibility for the utilization of the ecofriendly nanobiocomposite in the packing of UV-sensitive materials on a commercial level.

Unexpected Effect of Electrode Architecture on High-Performance Lithium-Sulfur Batteries

In the past years, considerable efforts have been devoted to the deliberate synthesis of nanosulfur in various hosts with sophisticated structures to improve the performance of lithium-sulfur batteries (LSBs) and reveal the structure-property relationship. It is taken for granted that these elaborate sulfur nanostructures are well maintained in the ultimate electrode after the traditional mixing and coating method. Herein, we, for the first time, reveal the unexpected sulfur structure deterioration in nanosulfur/graphene composites during the electrode preparation using the traditional method because of the long-term neglected dissolution-recrystallization effect of sulfur in solvents. Consequently, compared with binder-free three-dimensional graphene/sulfur electrodes, the milled graphene/sulfur electrodes exhibit much worse electrochemical performance. On the basis of this, we further propose a facile and universal graphene oxide-assisted assembly method to avoid the dissolution-recrystallization of sulfur, by which binder-free three-dimensional ethylenediamine-functionalized graphene/sulfur (3DEFGS) electrodes have been successfully prepared. The 3DEFGS electrodes with a high areal sulfur loading of ∼6 mg cm^-2 exhibit an ultrahigh initial capacity of 1394 mA h g^-1 at 0.1 C, an excellent rate performance with a capacity of 796 mA h g^-1 at 4 C, and superior long-term cycling stability (885 mA h g^-1 after 500 cycles at 1 C), which are among the best performances achieved by all reported LSB cathodes with high areal sulfur loadings.

Stereocomplex poly(lactic acid) nanoparticles crystallized through nanoporous membranes and application as nucleating agent

Stereocomplex crystallization of poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) was performed by flowing their blended solution through nano-channels of porous membranes.

Effects of extrusion draw ratio on the morphology, structure and mechanical properties of poly(l-lactic acid) fabricated using solid state ram extrusion

The utilization of an SSRE technique induced highly oriented PLLA.