Multidimensional Control of Repeating Unit/Sequence/Topology for One-Step Synthesis of Block Polymers from Monomer Mixtures.

Synchronously and thoroughly adjusting the chemical structure difference between two blocks of the diblock copolymer is very useful for designing materials but difficult to achieve via self-switchable alternating copolymerization. Here, we report self-switchable alternating copolymerization from a mixture of two different cyclic anhydrides, epoxides, and oxetanes, where a simple alkali metal carboxylate catalyst switches between ring-opening alternating copolymerization (ROCOP) of cyclic anhydrides/epoxides and ROCOP of cyclic anhydrides/oxetanes, resulting in the formation of a perfect block tetrapolymer. By investigating the reactivity ratio of these comonomers, a reactivity gradient was established, enabling the precise synthesis of block copolymers with synchronous adjustment of each unit's chemical structure/sequence/topology. Consequently, a diblock tetrapolymer with two glass transition temperatures (Tg) can be easily produced by adjusting the difference in chemical structures between the two blocks.

Varying-coefficient semiparametric model averaging prediction.

Forecasting and predictive inference are fundamental data analysis tasks. Most studies employ parametric approaches making strong assumptions about the data generating process. On the other hand, while nonparametric models are applied, it is sometimes found in situations involving low signal to noise ratios or large numbers of covariates that their performance is unsatisfactory. We propose a new varying-coefficient semiparametric model averaging prediction (VC-SMAP) approach to analyze large data sets with abundant covariates. Performance of the procedure is investigated with numerical examples. Even though model averaging has been extensively investigated in the literature, very few authors have considered averaging a set of semiparametric models. Our proposed model averaging approach provides more flexibility than parametric methods, while being more stable and easily implemented than fully multivariate nonparametric varying-coefficient models. We supply numerical evidence to justify the effectiveness of our methodology.

Influence of HMW tail chains on the structural evolution of HDPE induced by second melt penetration.

It is widely accepted that the role of the high molecular weight (HMW) component is cooperative in shear-induced crystallization, owing to entanglements among long chains. However, this paper demonstrates that the HMW component has a novel effect on structural evolution during the process of multi-melt multi-injection molding (M3IM), organized as follows. First, the appropriate HDPE system with an incremental concentration of HMW tails was established. Second, the crystalline morphologies and orientation behaviors of the M3IM samples were characterized using a combination of scanning electron microscopy (SEM) and two-dimensional small angle X-ray scattering (2D-SAXS), and these suggested that the amount of shish-kebabs was not monotonically promoted with an increasing content of HMW tails but tended to reduce at a certain value. Third, in order to explain this phenomenon, the special temperature and shear profiles of M3IM were depicted subsequently, and finally the mechanism of hierarchical structure formation with the influence of various amounts of HMW tail chains was discussed, based on the classical rheological viewpoint.

Formation of various crystalline structures in a polypropylene/polycarbonate in situ microfibrillar blend during the melt second flow.

A strong shear flow was imposed on the melt of polycarbonate (PC) microfibrils with ß-nucleation agent reinforced isotactic polypropylene (iPP) during the melt second flow process, i.e. gas-assisted injection molding (GAIM). A special shell-core structure was formed in the iPP/PC microfibrils with ß-nucleation agent (PP/PC/ß-NA) composites. A lot of ß-transcrystalline and α-transcrystalline superstructures were observed in the skin and sub-skin regions, whereas ß-spherulite structures were formed in the gas channel region. There is no doubt that the distinct hierarchical structure has great potential to significantly improve the mechanical performance of the composites, and the experimental results verify this. The results of the mechanical performance testing show that the yield strength of the PP/PC/ß-NA composites reached 61.9 MPa, which is 19.7 MPa higher than that of the iPP parts molded by GAIM (G-iPP) (42.2 MPa). The tensile modulus of the PP/PC/ß-NA composites (3.3 GPa) increased by 135%, compared to that of G-iPP (1.4 GPa). The high content of ß-crystals improved the elongation at break of the composites compared to the iPP/PC microfibril (PP/PC) composites; the elongation at break of the PP/PC/ß-NA composites (13%) is over 3 times greater than that of the PP/PC composites (4%).

Strong shear-driven large scale formation of hybrid shish-kebab in carbon nanofiber reinforced polyethylene composites during the melt second flow.

The formation of a hybrid shish-kebab (HSK) structure with different degrees of lamellar orientations was first observed in the solution crystallization of polyethylene (PE) in the presence of carbon nanofibers (CNFs). In this study, PE crystal lamellae were periodically decorated on the surface of CNFs and were aligned approximately perpendicular to the long axes of the CNFs, forming aligned hybrid shish-kebab nanostructures. More importantly, the fascinating structure was directly formed in all regions of the injection molded bars of HDPE/CNF composites, via a gas-assisted injection molding (GAIM), instead of the shell-core structure. In the GAIM process, an intense shear was imposed onto the melt during the melt second flow and drove PE chains to orient along the axes of the CNFs. Then the entropy penalty for PE chains deposited on the CNF surface was drastically decreased. Although the attractive van der Waals interactions were weak, the oriented PE chains could successfully adsorb on the CNF surface due to the decrease of the entropy penalty, therewith the underlayer coating was formed along the axis based on a two-dimensional mode for early nucleation on the CNF surface. Subsequently, subglobules appeared on the ordered structure, which could be regarded as the crystal nucleus. Finally, the oriented PE chains began to epitaxially grow from the subglobules with a folded-chain shape to decrease the polymer surface energy and grew perpendicular to the CNFs long axis, abiding by the "soft epitaxy" crystallization mechanism regardless of strict lattice matching.

Low-dimensional confounder adjustment and high-dimensional penalized estimation for survival analysis.

High-throughput profiling is now common in biomedical research. In this paper we consider the layout of an etiology study composed of a failure time response, and gene expression measurements. In current practice, a widely adopted approach is to select genes according to a preliminary marginal screening and a follow-up penalized regression for model building. Confounders, including for example clinical risk factors and environmental exposures, usually exist and need to be properly accounted for. We propose covariate-adjusted screening and variable selection procedures under the accelerated failure time model. While penalizing the high-dimensional coefficients to achieve parsimonious model forms, our procedure also properly adjust the low-dimensional confounder effects to achieve more accurate estimation of regression coefficients. We establish the asymptotic properties of our proposed methods and carry out simulation studies to assess the finite sample performance. Our methods are illustrated with a real gene expression data analysis where proper adjustment of confounders produces more meaningful results.

Surface Modification of PEEKs with Cyclic Peptides to Support Endothelialization and Antithrombogenicity.

Synthetic polymers are often utilized in the creation of vascular devices, and need to possess specific qualities to prevent thrombosis. Traditional strategies for this include surface modification of vascular devices through covalent attachment of substrates such as heparin, antiplatelet agents, thrombolytic agents, or hydrophilic polymers. One promising prosthetic material is polyether ether ketone (PEEK), which is utilized in various FDA-approved medical devices, including vascular and endovascular prostheses. We hypothesized that surface modification of biologically inert PEEK can help improve its endothelial cell affinity and reduce its thrombogenic potential. To evaluate this, we developed an effective surface-modification approach with unique cyclic peptides, such as CCHGGVRLYC and CCREDVC. We treated the PEEK surface with ammonia plasma, which introduced amine groups onto the PEEK surface. Subsequently, we were able to conjugate these peptides to the plasma-modified PEEKs. We observed that cyclic CCHGGVRLYC conjugated on prosthetic PEEK not only supported endothelialization, but minimized platelet adhesion and activation. This technology can be potentially applied for in vivo vascular and endovascular protheses to enhance their utility and patency.

Extracellular Vesicles Derived from Glioma Stem Cells Affect Glycometabolic Reprogramming of Glioma Cells Through the miR-10b-5p/PTEN/PI3K/Akt Pathway.

OBJECTIVE: Glioma is one of the most prevalently diagnosed types of primary malignant brain tumors. Glioma stem cells (GSCs) are crucial in glioma recurrence. This study aims to elucidate the mechanism by which extracellular vehicles (EVs) derived from GSCs modulate glycometabolic reprogramming in glioma. METHODS: Xenograft mouse models and cell models of glioma were established and treated with GSC-EVs. Additionally, levels and activities of PFK1, LDHA, and FASN were assessed to evaluate the effect of GSC-EVs on glycometabolic reprogramming in glioma. Glioma cell proliferation, invasion, and migration were evaluated using MTT, EdU, Colony formation, and Transwell assays. miR-10b-5p expression was determined, with its target gene PTEN and downstream pathway PI3K/Akt evaluated. The involvement of miR-10b-5p and the PI3K/Akt pathway in the effect of GSC-EVs on glycometabolic reprogramming was tested through joint experiments. RESULTS: GSC-EVs facilitated glycometabolic reprogramming in glioma mice, along with enhancing glucose uptake, lactate level, and adenosine monophosphate-to-adenosine triphosphate ratio. Moreover, GSC-EV treatment potentiated glioma cell proliferation, invasion, and migration, reinforced cell resistance to temozolomide, and raised levels and activities of PFK1, LDHA, and FASN. miR-10b-5p was highly-expressed in GSC-EV-treated glioma cells while being carried into glioma cells by GSC-EVs. miR-10b-5p targeted PTEN and activated the PI3K/Akt pathway, hence stimulating glycometabolic reprogramming. CONCLUSION: GSC-EVs target PTEN and activate the PI3K/Akt pathway through carrying miR-10b-5p, subsequently accelerating glycometabolic reprogramming in glioma, which might provide new insights into glioma treatment.

Genomic evolution of island birds from the view of the Swinhoe's pheasant (Lophura swinhoii).

Island endemic birds account for the majority of extinct vertebrates in the past few centuries. To date, the evolutionary characteristics of island endemic bird's is poorly known. In this research, we de novo assembled a high-quality chromosome-level reference genome for the Swinhoe's pheasant, which is a typical endemic island bird. Results of collinearity tests suggest rapid ancient chromosome rearrangement that may have contributed to the initial species radiation within Phasianidae, and a role for the insertions of CR1 transposable elements in rearranging chromosomes in Phasianidae. During the evolution of the Swinhoe's pheasant, natural selection positively selected genes involved in fecundity and body size functions, at both the species and population levels, which reflect genetic variation associated with island adaptation. We further tested for variation in population genomic traits between the Swinhoe's pheasant and its phylogenetically closely related mainland relative the silver pheasant, and found higher levels of genetic drift and inbreeding in the Swinhoe's pheasant genome. Divergent demographic histories of insular and mainland bird species during the last glacial period may reflect the differing impact of insular and continental climates on the evolution of species. Our research interprets the natural history and population genetic characteristics of the insular endemic bird the Swinhoe's pheasant, at a genome-wide scale, provides a broader perspective on insular speciation, and adaptive evolution and contributes to the genetic conservation of island endemic birds.

One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture.

Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

Mechanical Property and Structure of Polypropylene/Aluminum Alloy Hybrid Prepared via Ultrasound-Assisted Hot-Pressing Technology.

The polypropylene/aluminum alloy hybrid was prepared via an ultrasonic-assisted hot-pressing technology (UAHPT). The mechanical property and structure of the UAHPT processed polypropylene/aluminum alloy hybrid were explored by the tensile shear test, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Prior to obtaining the UAHPT processed hybrid, the microporous structures were prepared by the anodic oxidation in a phosphoric acid solution in which the polypropylene (PP) melt flowed into and formed the micro mechanical interlocking structure at the interface of polypropylene/aluminum alloy. The effects of bonding temperature, pressing pressure, ultrasonic amplitude, and ultrasonic time on the bonding properties of the hybrids were investigated via orthogonal experiment. The UAHPT processed hybrid was strengthened and the maximal tensile shear strength reached up to 22.43 MPa for the polypropylene/aluminum alloy hybrid prepared at the optimum vibration processing parameters.

Influence of Diameter on the Templated Crystallization of Polyethylene/Carbon Material Fiber Composites under Intense Shear Flow.

In this study, carbon fibers (CFs) and carbon nanofibers (CNFs) were introduced into polyethylene (PE) and intensive shear flow was imposed on the melt during the melt second flow caused by gas penetrating the melt during the gas-assisted injection molding (GAIM). The effect of fiber diameter on crystalline morphologies of obtained composites was deeply studied. The results revealed the fact that no matter whether CFs or CNFs were introduced into the PE matrix or not, the orientation degree of PE lamellae would increase during the melt second flow. Hybrid shish-kebab structures were difficult to be formed in GAIM CF/PE composites and only a few oriented PE lamellae overgrew on the local surface of CFs. However for GAIM CNF/PE composites, the formation of hybrid shish-kebab structures was clearly observed in the entire thickness. The structural diversity was mainly ascribed to the difference of CF diameter, showing obvious size-dependent effect.