pH-responsive, self-sculptured Mg/PLGA composite microfibers for accelerated revascularization and soft tissue regeneration

Biodegradable Mg/polymer composite fibers offer a promising therapeutic option for tissue injury because of bioactive Mg2+ and biomimetic microstructure. However, current studies are limited to the contribution of Mg2+ and the single microstructure. In this study, we designed Mg/poly (lactic-co-glycolic acid) (Mg/PLGA) composite microfibers that significantly enhanced angiogenesis and tissue regeneration synergistically by Mg2+ and self-sculptured microstructure, due to spontaneous in situ microphase separation in response to the weakly alkaline microenvironment. Our composite microfiber patch exhibited superior performance in the adhesion, spreading, and angiogenesis functions of human umbilical vein endothelial cells (HUVECs) due to the joint contribution of the hierarchically porous microstructure and Mg2+. Genomics and proteomics analyses revealed that the Mg/PLGA composite microfibers activated the cell focal adhesion and angiogenesis-related signaling pathways. Furthermore, the repair of typical soft tissue defects, including refractory urethral wounds and easily healed skin wounds, validated that our Mg/PLGA composite microfiber patch could provide favorable surface topography and ions microenvironment for tissue infiltration and accelerated revascularization. It could cause rapid urethral tissue regeneration and recovery of rabbit urethral function within 6 weeks and accelerate rat skin wound closure within 16 days. This work provides new insight into soft tissue regeneration through the bioactive alkaline substance/block copolymer composites interactions.

Effect of degree of substitution on the microphase separation and mechanical properties of cellooligosaccharide acetate-based elastomers

Thermoplastic elastomers (TPEs) have long been used in a wide range of industries. However, most existing TPEs are petroleum-derived polymers. To realize environmentally benign alternatives to conventional TPEs, cellulose acetate is a promising TPE hard segment because of its sufficient mechanical properties, availability from renewable sources, and biodegradability in natural environments. Because the degree of substitution (DS) of cellulose acetate governs a range of physical properties, it is a useful parameter for designing novel cellulose acetate-based TPEs. In this study, we synthesized cellulose acetate-based ABA-type triblock copolymers (AcCel_x-b-PDL-b-AcCel_x) containing a celloologosaccharide acetate hard A segment (AcCel_x, where x is the DS; x = 3.0, 2.6, and 2.3) and a poly(δ-decanolactone) (PDL) soft B segment. Small-angle X-ray scattering showed that decreasing the DS of AcCel_x-b-PDL-b-AcCel_x resulted in the formation of a more ordered microphase-separated structure. Owing to the microphase separation of the hard cellulosic and soft PDL segments, all the AcCel_x-b-PDL-b-AcCel_x samples exhibited elastomer-like properties. Moreover, the decrease in DS improved toughness and suppressed stress relaxation. Furthermore, preliminary biodegradation tests in an aqueous environment revealed that the decrease in DS endowed AcCel_x-b-PDL-b-AcCel_x with greater biodegradability potential. This work demonstrates the usefulness of cellulose acetate-based TPEs as next-generation sustainable materials.

Statistical Thermodynamics Approach for Intracellular Phase Separation

Phase separation is one of the fundamental processes to compartmentalize biomolecules in living cells. RNA-protein complexes (RNPs) often scaffold biomolecular condensates formed through phase separation. We here present a statistical thermodynamics approach to investigate intracellular phase separation. We first present the statistical thermodynamic theory of the liquid-liquid phase separation (LLPS) of two molecules (such as proteins and solvent molecules) and of a polymer solution (such as RNPs and solvent molecules). Condensates produced by LLPS show coarsening and/or coalescence to minimize their total surface area. In addition to the LLPS, there are other types of self-assembly, such as microphase separation, micellization, emulsification, and vesiculation, with which the growth of the assembly stops with optimal size and shape. We also describe a scaling theory of micelles of block copolymers, where their structures are analogous to the core-shell structure of paraspeckle nuclear bodies scaffolded by RNPs of NEAT1_2 long noncoding RNAs (lncRNAs) and RNA-binding proteins (RBPs). These theories treat the self-assembly of polymers in the thermodynamic equilibrium, where their concentrations and compositions do not change with time. In contrast, RNPs are produced according to the transcription of RNAs and are degraded with time. We therefore take into account the dynamical aspect of the production of RNPs in an extension of the theory of the self-assembly of soft matter. Finally, we discuss the structure of paraspeckles as an example to demonstrate that an approach combining experiment and theory is powerful to investigate the mechanism of intracellular phase separation.

Clustered piperidinium-functionalized poly(terphenylene) anion exchange membranes with well-developed conductive nanochannels

Anion exchange membrane fuel cells (AEMFCs) attract considerable attention owing to their high-power density and potential utilization of cheap non-noble metal catalysts. However, anion exchange membranes (AEMs) still face the problems of low conductivity, poor dimensional and chemical stability. To address these issues, AEMs with clustered piperidinium groups and ether-bond-free poly(terphenylene) backbone (3QPAP-x, x = 0.3, 0.4, and 0.5) were designed. Transmission electron microscope results show that the clustered ionic groups are responsible for fabricating well-developed conductive nanochannels and restraining the swelling behavior of the membranes. 3QPAP-0.4 and 3QPAP-0.5 AEMs exhibit higher conductivity (117.5 mS cm^-1, 80 °C) and lower swelling ratio than that of commercial FAA-3-50 (80.4 mS cm^-1, 80 °C). The conductivity of 3QPAP-0.5 only decreased by 10.4% after treating with 1 M NaOH at 80 °C for 720 h. The Hofmann elimination degradation of the cationic groups is restrained by the long flexible alkyl chain between cations. Based on the high performance of 3QPAP-0.5, an H₂-O₂-type AEMFC reaches 291.2 mW cm^-2 (60 °C), which demonstrates that the as-prepared AEMs are promising for application in fuel cells.

Microphase separation of stimuli-responsive interpenetrating network microgels investigated by scattering methods

Polymer stimuli-responsive microgels find their use in various applications. The knowledge of its internal structure is of importance for further improvement and expanding the scope. Interpenetrating network (IPN) microgels may possess a remarkable feature of strongly non-uniform inner architecture, even microphase separation, in conditions of a selective solvent. In this research, we, for the first time, use a combination of static light scattering (SLS) and small-angle X-ray scattering (SAXS) techniques to collect the structure factors of aqueous dispersions of poly(N-isopropylacrylamide)-polyacrylic acid IPN microgels on the broad scale ofqvalues. We study the influence of solvent quality on microgel conformations and show that in a selective solvent, such a system undergoes microphase separation: the sub-network in a poor solvent conditions forms dense small aggregates inside the large swollen sub-network in a good solvent. We propose the microstructured sphere model for the IPN microgel structure factor interpretation and perform additional analysis and verification through coarse-grained molecular dynamics computer simulations.

One-pot synthesis of unique skin-tissue-bone structured porous carbons for enhanced supercapacitor performance

Introduction of hierarchical porous structure and heteroatom in porous carbons are always effective approaches to improve the capacitive performance for supercapacitor. However, it is still a challenge to achieve the desired structure characteristics by a convenient one-step synthesis. Herein, C₁₆mimPF₆, an ionic liquid, was introduced in the self-assembly process of poly-benzoxazine to obtain a unique skin-tissue-bone structured hierarchical porous carbon with homogeneous N, P co-doping after carbonization. As the key component, C₁₆mimPF₆ works not only as a structure-directing agent to form a hierarchical structure through microphase separation mechanism, thereby promoting the transfer of ion and electron, but also as a heteroatom precursor to contribute an additional pseudocapacitance by doping phosphorus atoms on carbon matrix. The obtained porous carbon displays a high gravimetric capacitance (C_g) of 209 F g^-1 (especially in the carbons prepared without corrosive activation step), a good volumetric capacitance (C_v) of 132 F cm^-3 and an excellent area-normalized capacitance (C_a) of 35 μF cm^-2. Overall, this work opens a new way to design the polymer-derived carbons with easy heteroatoms doping and hierarchical porous structure.

Self-assembly of copper-free maltoheptaose-block-polystyrene nanostructured thin films in real and reciprocal space

The promising carbohydrate-based block copolymer maltoheptaose-block-polystyrene (MH-b-PS) has been used for high-performance memory transistors and next generation nanolithography. In order to realize the potential of MH-b-PS especially in microelectronic applications, we firstly improved its synthetic method for obtaining large amount of copper-free MH-b-PS. The main improvement relies on the removal of the residual copper catalyst by using a chelating resin. Then, the microphase separation of copper-free MH-b-PS in both thin film and bulk states under different solvent vapor annealing conditions were investigated comprehensively and compared with our previous report by using both real-space and reciprocal-space techniques. A phase transition of MH-b-PS from hexagonal close-packed horizontal cylinders to face-centered cubic were observed when increasing the amount of tetrahydrofuran in the mixture annealing solvent of tetrahydrofuran and H₂O. More details about self-assembled MH-b-PS nanostructures were analyzed by comparing grazing incidence small angle X-ray scattering patterns with corresponding atomic force microscopy phase images.

Fabrication of Ordered Nanopattern by using ABC Triblock Copolymer with Salt in Toluene

Ordered nanopatterns of triblock copolymer polystyrene-block-poly(2-vinylpyridine)-block- poly (ethylene oxide)(PS-b-P2VP-b-PEO) have been achieved by the addition of lithium chloride (LiCl). The morphological and structural evolution of PS-b-P2VP-b-PEO/LiCl thin films were systematically investigated by varying different experimental parameters, including the treatment for polymer solution after the addition of LiCl, the time scale of ultrasonic treatment and the molar ratio of Li⁺ ions to the total number of oxygen atoms (O) in PEO block and the nitrogen atoms (N) in P2VP block. When toluene was used as the solvent for LiCl, ordered nanopattern with cylinders or nanostripes could be obtained after spin-coating. The mechanism of nanopattern transformation was related to the loading of LiCl in different microdomains.

Facile access to cytocompatible multicompartment micelles with adjustable Janus-cores from A-block-B-graft-C terpolymers prepared by combination of ROP and ATRP

The architecture of hydrophobic segments can determine the specific morphology of multicompartment micelles (MCMs) that are generated from aqueous assembly of amphiphilic terpolymers. In this study, we aimed to design and generate poly(ɛ-caprolactone)-based multicompartment micelles with adjustable Janus-cores. Well-defined terpolymers with a novel A-block-B-graft-C architecture composed of biologically compatible polymers, methoxy poly(ethylene glycol) (PEG), poly(ɛ-caprolactone) (PCL) and poly(2-(perfluorobutyl)ethyl methacrylate) (PPFEMA), were prepared by the stepwise use of ring-opening polymerization and atom transfer radical polymerization. Characterization of the obtained terpolymers was carried out by (1)H NMR and gel permeation chromatography. Results from differential scanning calorimetry and X-ray diffraction studies indicated that within the terpolymer structure, the PCL segments are in the crystalline state, while fluorocarbon segments belong to the amorphous domains. Due to the thermodynamic incompatibility of PCL and PPFEMA, MCMs could be obtained upon aqueous self-assembly of the terpolymer. The well-segregated Janus-cores with adjustable compartment balance were revealed by transmission electron microscopy. In vitro cell viability assays further demonstrated an excellent cytocompatibility of the MCMs both in mouse embryonic fibroblasts (3T3) and human acute monocytic leukemia (THP-1) cells.

Local demixion in plasticized polylactide probed by electron spin resonance

Improving the barrier properties to gas and organic compounds of biosourced polyesters, such as polylactides (PLAs), by increasing their crystallinity has been suggested by several authors. This paper investigates the risk of microphase separation for a technological approach that would involve a plasticization of PLA, to further its crystallization kinetics, with common plasticizers: Acetyl tributyl citrate (ATBC) and Poly(ethylene glycol) (PEG). Overplasticization effects following microphase separation were monitored along the film thickness by exposing dynamically thermo-compressed films to nitroxide spin-probes. The method enabled a scan of the local polymer mobility for different concentration profiles in spin-probes, with in particular a maximum moving continuously in time towards the geometric center. The results were interpreted as excess local temperatures that would give similar ESR spectra motion in the bulk. It was shown that measured excess temperatures could be related to local shifts in the glass transition temperature along the film thickness.