Influence of Steric Hindrance Between Hydrogen Atoms of Linkage Groups and Adjacent Phenyls on Properties of Polyimide

A diamine monomer 4,4′-methylenedianiline（MDA） was introduced to modify the polyimide of pyromellitic dianhydride（PMDA） and 4,4′-oxydianiline（ODA） by polycondensation. A series of polyamic acids was synthesized from MDA and ODA of different molar ratios with PMDA of sum mole of moles of MDA and ODA, and polyimide films were obtained by thermal imidization. Polyimide（PI） films were characterized by tensile testing, dynamic mechanical analysis（DMA）, thermal gravimetry analysis（TGA）, Fourier transform infrared spectroscopy （FTIR）, wide X-ray diffraction（WAXD） and molecular simulation. With the increase of MDA content, the tensile strength and thermal decomposition temperature remained generally stable compared with those of PMDA/ODA polyimide. Unexpectedly, the glass transition temperature（Tg） and Young＇s modulus increased from 388.7 °C and 2.37 GPa to 408.3 °C and 5.74 GPa, respectively. The results of WAXD and molecular simulation indicate the steric hindrance among hydrogen atoms of the linkage groups and adjacent phenyls enhanced the properties of the polyimide modified with MDA.

Structural Optimization of Polyimide Foam via Composition with Hyperbranched Polymer Modified Fluorinated Carbon Nanotubes

The key to improve the foam’s performance is to optimize the cellular structure and its bulk-material composition.Here,the hyperbranched polymer modified fluorinated multi-walled carbon nanotube(HPMCNT-F)based on the nucleophilic reactions of MCNT-F was successfully prepared and used to composite with PI foams.The pristine MCNT shows a poor dispersity and weak interfacial interaction with PI matrix.While HPMCNT-F exhibits an excellent dispersity and effectively forms covalent/non-covalent interaction with PI matrix due to the surface-structure engineering,resulting in the enhancement of the PI bulk.Furthermore,HPMCNT-F works as a heterogeneous nucleation agent in PI foam to optimize the cellular structure.The enhancement of PI bulk and the optimizing of cellular structure result in the increase of compressive special strength of composite foam by 58.9%with a low loading of 1.6 wt%HPMCNT-F.Moreover,the hyperbranched polymers effectively prevent the thermal conduction among HPMCNT-F,and the isolated MCNTs effectively block thermal radiation through absorption and reflection the infrared waves.Thus,the thermal conductivity was reduced by 8.0%simultaneously.

Atom-economic synthesis of an oligomeric P/N-containing fire retardant towards fire-retarding and mechanically robust polylactide biocomposites

Renewable and biodegradable polylactide (PLA) has excellent mechanical strength but is highly flammable which restricts its practical applications. Many phosphorus/nitrogen (P/N)-based flame retardants are ef- fective in PLA, but their high addition loading usually decreases the mechanical strength of the PLA bulk. For polyphosphoramides, despite high fire-retardant efficiency, their chemical synthesis often generates chemical wastes as byproducts. Herein, we report an atom-economic and highly efficient oligomeric P/N fire retardant (APN) prepared using a mild Michael addition polymerization with no byproducts. Using only 3 wt% APN, the resulting PLA exhibits desired fire retardancy including a UL-94 V-0 rating and a limiting oxygen index of 37.6%. Furthermore, the toughness of the fire-retardant PLA increases by 85% compared to pure PLA, with both tensile strength and thermal stability preserved. This work offers an atom-economic strategy for synthesizing highly efficient P/N fire retardants for use in the creation of fire-resistant PLA with robust mechanical properties.

Fast synthesis of dopamine-coated Fe_3O_4 nanoparticles through ligand-exchange method

A fast approach was described for the synthesis of water-dispersible monodisperse dopamine-coated Fe304 nanoparticles （DA- Fe304） with uniform size and shape via ligand-exchange of oleic acid on Fe304 using only 2 min. The prepared DA-Fe304 nanoparticles were characterized by transmission electron microscopy, Fourier transform infrared spectrometry, and vibrating sample magnetometer. The results indicated that the resulting DA-Fe304 nanoparticles had an average diameter of about 19.2 nm. The magnetic saturation value of the prepared DA-Fe304 nanoparticles was determined to be 72.87 emu/g, which indicating a well- established superparamagnetic property.

Ultrathin FeS nanosheets with high chemodynamic activity for sensitive colorimetric detection of H_(2)O_(2) and glutathione

Iron chalcogenides have attracted great interest as potential substitutes of nature enzymes in the colorimetric biological sensing due to their unique chemodynamic characteristics.Herein,we report the preparation of ultrathin Fe S nanosheets(NSs)by a simple one-pot hydrothermal method and the prepared Fe S NSs exhibit strong Fenton-reaction activity to catalyze hydrogen peroxide(H_(2)O_(2))for generation of hydroxyl radical(^(·)OH).Based on the chromogenic reaction of resultant^(·)OH with 3,3,5,5-tetramethylbenzidine(TMB),we develop colorimetric biosensors for highly sensitive detection of H_(2)O_(2)and glutathione(GSH).The fabricated biosensors show wide linear ranges for the detection of H_(2)O_(2)(5–150μmol/L)and GSH(5–50μmol/L).Their detection limits for H_(2)O_(2)and GSH reach as low as0.19μmol/L and 0.14μmol/L,respectively.The experimental results of sensing intracellular H_(2)O_(2)and GSH demonstrate that this colorimetric method can realize the accurate detection of H_(2)O_(2)and GSH in normal cells(L02 and 3T3)and cancer cells(MCF-7 and He La).Our results have demonstrated that the synthesized Fe S NSs is a promising material to construct colorimetric biosensors for the sensitive detection of H_(2)O_(2)and GSH,holding great promising for medical diagnosis in cancer therapy.

Preparation and Characterization of Chitosan Composite Membranes Crosslinked by Carboxyl-capped Poly(ethylene glycol)

In this study a series of chemically crosslinked chitosan/poly（ethylene glycol） （CS/PEG） composite membranes were prepared with PEG as a crosslinking reagent other than an additional blend. First, carboxyl-eapped poly（ethylene glycol） （HOOC-PEG-COOH） was synthesized. Dense CS/PEG composite membranes were then prepared by casting/evaporation of CS and HOOC-PEG-COOH mixture in acetic acid solution. Chitosan was chemically crosslinked due to the amidation between the carboxyl in HOOC-PEG-COOH and the amino in chitosan under heating, as confirmed by FTIR analysis. The hydrophilicity, water-resistance and mechanical properties of pure and crosslinked chitosan membranes were characterized, respectively. The results of water contact angle and water absorption showed that the hydrophilicity of chitosan membranes could be significantly improved, while no significant difference of weight loss between pure chitosan membranes and crosslinked ones was detected, indicating that composite membranes with amidation crosslinking possess excellent water resistanance ability. Moreover, the tensile strength of chitosan membranes could be significantly enhanced with the addition of certain amount of HOOC-PEG-COOH crosslinker, while the elongation at break didn＇t degrade at the same time. Additionally, the results of swelling behaviors in water at different pH suggested that the composite membranes were pH sensitive.

DYNAMICS OF α AND α' RELAXATION IN LAYERED SILICATE/POLYSTYRENE NANOCOMPOSITES STUDIED BY ANELASTIC SPECTROSCOPY

The dynamics of polymer chains in layered silicate/polystyrene nanocomposites was studied by anelastic spectroscopy. Two thermal activated peaks （or and α＇ peaks） appeared when the specimens were heated to a high temperature and they were related to glass transition and liquid-liquid transition, respectively. The activation energy was calculated based on Arrhenius equation and it showed that the activation energy of glass transition （Eg） is much higher than that of liquid-liquid transition （EH）. Furthermore, the most interesting result for the activation energy was that there were two contrary trends for Eg and Ell, Eg decreased and Ell increased with the addition of clay platelets. The fragile parameter was analyzed and the variation of fragile parameters for the two transitions was also contrary to each other with the addition of clay platelets. All the results indicated that the confinement effect of clay platelets on the dynamics of polymer chain was scale dependent, and perhaps, the two transitions were produced by different mechanisms.

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal(PSLC)film is a relatively novel electro-optical material,which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal.In this paper,the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation.The effects of liquid crystal concentration,curing time,monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated.The results show that the transmittance in the OFF state(TOFF)increased with the liquid crystal concentration,but the driving voltage decreased.TOFF was also influenced by the curing time.Furthermore,when polyimide was used as alignment layer,the films prepared from the bifunctional monomer shows a higher TOFF,while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks.

Survivin (BIRC5) regulates bladder fibrosis in a rat model of partial bladder outlet obstruction

To the Editor:Fibrosis is a long duration wound healing process triggered by complex cellular and molecular responses that contributes to tissue or organ reconstruction.[1]Bladder fibrosis is initiated by pathological pressure such as hydrostatic pressure,stretching force,and fluid shear stress.Increased pressure leads to a bladder inflammatory microenvironment,smooth muscle hypertrophy,and fibrosis.

Flame-retardant Coating by Alternate Assembly of Poly(vinylphosphonic acid) and Polyethylenimine for Ramie Fabrics

A novel intumescent flame retardant coating, consisting of poly（vinylphosphonic acid） （PVPA） as the acid source and branched polyethylenimine （BPEI） as the blowing agent, was constructed on the surface of ramie fabrics by alternate assembly to remarkably improve the flame retardancy of ramie. The PVPA/BPEI coating on the surface of individual fibers of ramie fabric pyrolyzes to form protective char layer upon heating/burning and improves the flame retardancy of ramie. Thermogravimetric analysis reveals that the PVPA/BPEI-coated ramie fabrics left as much as 25.8 wt% residue at 600 ~C, while the control （uncoated） fabric left less than 1.4 wt% residue. Vertical flame test shows that all PVPA/BPEI-coated fabrics have shorter after-flame time, and the residues well preserved the original weave structure and fiber morphology, whereas, the uncoated fabric left only ashes. Microscale combustion calorimetry shows that the PVPA/BPEI coatings greatly reduce the total heat release by as much as 66% and the heat release capacity by 76%, relative to those of the uncoated fabric.

Soft overcomes the hard:Flexible materials adapt to cell adhesion to promote cell mechanotransduction

Cell behaviors and functions show distinct contrast in different mechanical microenvironment.Numerous materials with varied rigidity have been developed to mimic the interactions between cells and their surroundings.However,the conventional static materials cannot fully capture the dynamic alterations at the bio-interface,especially for the molecular motion and the local mechanical changes in nanoscale.As an alternative,flexible materials have great potential to sense and adapt to mechanical changes in such complex microenvironment.The flexible materials could promote the cellular mechanosensing by dynamically adjusting their local mechanics,topography and ligand presentation to adapt to intracellular force generation.This process enables the cells to exhibit comparable or even higher level of mechanotransduction and the downstream‘hard’phenotypes compared to the conventional stiff or rigid ones.Here,we highlight the relevant studies regarding the development of such adaptive materials to mediate cell behaviors across the rigidity limitation on soft substrates.The concept of‘soft overcomes the hard’will guide the future development and application of biological materials.

Perylene Diimide-Based Oligomers and Polymers for Organic Optoelectronics

CONSPECTUS:Perylene diimide(PDI)as a classical dye has some advantages,such as structural diversity,tunable optical and electronic properties,strong light absorption,high electron affinity,and good electron-transporting properties and stability.The PDI-based oligomers and polymers are good candidates for n-type semiconductors in organic electronics and photonic devices.A polymer solar cell(PSC)that converts sunlight into electricity is a promising renewable and clean energy technology and has some superiorities,such as simple preparation and being lightweight,low cost,semitransparent,and flexible.For a long time,fullerene derivatives(e.g.,PCBM)have been the most important electron acceptors used in the active layer of PSCs.However,PCBM suffers from some disadvantages,for example,weak absorption,a large amount of energy loss,and unstable morphology.Compared to PCBM,PDI-based materials present some advantages:intense visible-light absorption;lowest unoccupied molecular orbital(LUMO)energy levels can be modulated to achieve a suitable charge separation driving force and high open-circuit voltage(V_(OC));and the molecular configuration can be adjusted to achieve morphology stability.Thus,PDI-based oligomers and polymers are widely used as electron acceptors in the active layer of PSCs.In addition,PDI-based oligomers and polymers are widely used as n-type semiconductors in other electronic and photonic devices,such as organic field-effect transistors(OFETs),light-emitting diodes,lasers,optical switches,and photodetectors.

Microtubule Assists Actomyosin to Regulate Cell Nuclear Mechanics and Chromatin Accessibility

Cellular behaviors and functions can be regulated by mechanical cues from microenvironments,which are transmitted to nucleus through the physical connections of cytoskeletons in the cells.How these physical connections determine transcriptional activity were not clearly known.The actomyosin,which generates intracellular traction force,has been recognized to control the nuclear morphology.Here,we have revealed that microtubule,the stiffest cytoskeleton,is also involved in the process of nuclear morphology alteration.The microtubule negatively regulates the actomyosin-induced nuclear invaginations but not the nuclear wrinkles.Moreover,these nuclear shape changes are proven to mediate the chromatin remodeling,which essentially mediates cell gene expression and phenotype determination.The actomyosin disruption leads to the loss of chromatin accessibility,which can be partly recovered by microtubule interference through nuclear shape control.This finding answers the question of how mechanical cues regulate chromatin accessibility and cell behaviors.It also provides new insights into cell mechanotransduction and nuclear mechanics.

Understanding the interplay between cell force and cell adhesion processes

Cells,wrapped among their neighbors and surrounding extracellular matrix(ECM),form cell-cell adhesions and cell-ECM adhesions.Extracellular biophysical cues exert a far-reaching influence on a sweeping of cell behaviors,including signal transduction,gene expression,and fate determination.Cell-cell adhesions mediated by inter-cellular adhesion molecules bridge the membranes of adjacent cells through either heterophilic or homophilic adhesive interactions,playing a critical part in multicellular structural maintenance and,therefore,a foundation for multicellular organisms.Cell-ECM adhesions are derived from the interaction between cell adhesion receptors and multi-adhesive matrix proteins to ensure cell and tissue cohesion.Whereas cells not only unilaterally respond to certain cues from extracellular environment but can also alter the physicochemical profiles of the externalities and hence hold important implications for clinical applications.The essential function of cell adhesions has cre-ated tremendous interests in developing methods for measuring and studying cell adhesion properties,namely,cellular force.Here,we describe the collection of cell adhesive inputs on cellular signaling cascades and the“crosstalk”between cell-cell adhesions and cell-ECM adhesions.Furthermore,we provide the summary of the current methods to measure such cell adhesive forces.

Recent advances in fire-retardant carbon-based polymeric nanocomposites through fighting free radicals

Polymeric materials are ubiquitously utilized in modern society and continuously improve quality of life.Unfortunately,most of them suffer from intrinsic flammability,significantly limiting their practical applications.Fundamentally,free-radical reaction is a critical“trigger”for their thermal pyrolysis and following combustion process regardless of the anaerobic thermal pyrolysis in the condensed phase or aerobic combustion of polymers in the gaseous phase.The addition of free radical scavengers represents a promising and effective means to enhance the fire safety of polymeric materials.This review aims to offer a state-of-the-art overview on the creation of fire-retardant polymeric nanocomposites by adding fire retardants with an ability to trap free radicals.Their specific modes of action(condensed-phase action,gaseous-phase action,and dual-phases action)and performances in some typical polymers are reviewed and discussed in detail.Following this,some key challenges associated with these free-radical capturers are discussed,and design strategies are also proposed.This review provides some insights into the modes of action of free radical capturing agents and paves the avenue for the design of advanced fire-retardant polymeric nanocomposites for expanded real-world applications in industries.

Recent advances in fire-retardant rigid polyurethane foam

Driven by global environmental concerns,many efforts have been made to develop halogen-free flame retardants for rigid polyurethane foam(RPUF).These environmentally benign flame retardants are mainly divided into(i)reactive,(ii)additive,and(iii)coating types.The last decade has witnessed great progress of these three strategies,which enhance the fire safety of RPUF and maintain even improve the thermal insulation properties.This comprehensive review focuses on the up-to-date design of the reactive,additive,and coating flame retardants,and their effects on flame retardancy and thermal conductivity of RPUF.Moreover,the practical applications of the as-prepared flame-retardant RPUFs are highlighted.Finally,key challenges associated with these three kinds of flame retardants are discussed and future research opportunities are also proposed.

A cell retrievable strategy for harvesting extracellular matrix as active biointerface

Extracellular matrix(ECM) provides a variety of physical and chemical cues for cells. Here, a very simple and smart method is developed to glue living cells away for harvesting their ECMs. The obtained ECM coatings show less cell fragment residues comparing with those obtained by the traditional cell lysis. The glued cell sheets can even be re-cultured and reused after transferring to new environment. This moderate way well maintains the activity of the ECM proteins, which can promote cell adhesion and growth.Strikingly, the ECM coatings acquired from different functional cells can guide stem cell differentiation,which is attributed to the natural physical and biochemical cues on ECM coatings. Consequently, this method provides a substantial progress for preparing natural ECM coatings and shows promising potential in regenerative medicine and other related fields of biomedical engineering.