High strength and biodegradable dielectric film with synergistic alignment of chitosan nanofibrous networks and BNNSs.

The development of biodegradable and robust dielectric capacitors with high breakdown strength and energy density are indispensable. Herein, the high strength chitosan/edge hydroxylated boron nitride nanosheets (BNNSs-OH) dielectric film was fabricated via combining the dual chemically-physically crosslinking and the drafting orientation strategy, which could induced BNNSs-OH and chitosan crosslinked network alignment within the film via covalent and hydrogen bonding interaction, leading to the comprehensive reinforcement of tensile strength from 126 to 240 MPa, the Eb from 448 to 584 MV m-1, the in-plane thermal conductivity from 1.46 to 5.95 W m-1 K-1 and energy storage density from 7.22 to 13.71 J cm-1, superior than the comprehensive evaluation of the reported polymer dielectrics. The dielectric film could be completely degraded in soil in 90 days, which opened a new path for the development of next-generation environment-friendly dielectrics with excellent mechanical and dielectric properties.

In situ synthesis of Ag/Ag2O-cellulose/chitosan nanocomposites via adjusting KOH concentration for improved photocatalytic and antibacterial applications.

This work proposed a facile way to construct cellulose/chitosan-loaded Ag/Ag2O nanocomposite films (ACC) from alkali/urea solution by increasing the content of alkali KOH in the solvent. The saturated alkali and hydroxyl groups of the cellulose and chitosan chains were accelerated to convert AgNO3 to Ag0. Ag2O served as nuclei to lower the energy barrier. The formation of Ag/Ag2O nanoparticles (NPs) endowed the cellulose bio-reduced Ag composites with multifunction and stronger photocatalytic activity. Ag/Ag2O NPs with the diameter of 139-360 nm were uniformly dispersed in the composite films, resulting in superior mechanical properties (64.6 MPa) and thermal stability. Almost 92 % of methyl orange was degraded under UV-irradiation within 40 min by ACC. After 3 runs of degradation, the photocatalytic abilities of ACC remained. Moreover, the films exhibited good antibacterial activities. The width of inhibition zones around ACC reached 9.2-12 mm and 8.6-10.4 mm for S. aureus and E. coli. The strategy provided a new avenue to construct multifunctional cellulose/chitosan materials for various applications, such as wastewater treatment, and electrocatalysis.

Recent progress in regenerated cellulose-based fibers from alkali/urea system via spinning process.

Cellulose as the most abundant renewable polymer displays great potential to substitute the petroleum-derived synthetic polymers. However, cellulose is difficult to be melted or dissolved, which greatly restricts its development and utilization. Herein, the "green" alkali/urea aqueous system for cellulose dissolution is briefly summarized by illustrating the dissolving mechanism. The comparison of cellulose fibers from different solvent is presented. In addition, the recent achievements for the efficient and "green" preparation of regenerated cellulose fibers from alkali/urea system are also summarized. By investigating the effects of experimental conditions and technical parameters on the structure and performance of regenerated cellulose fibers, the improved fiber mechanical properties and the decreased production costs are achieved. Moreover, the preparation and application of cellulose-based functional fibers from alkali/urea system are also reviewed, together with the urgent challenges and future development perspectives, which provide the novel approach for the high value-added development and utilization of cellulose fibers.

A new strategy to construct cellulose-chitosan films supporting Ag/Ag2O/ZnO heterostructures for high photocatalytic and antibacterial performance.

The industrial wastewater contaminants including dyes and bacteria have caused serious environmental pollutions. Herein, ternary Ag/Ag2O/ZnO heterostructure decorating cellulose-chitosan films were constructed via in situ synthesis. Cellulose and chitosan dissolved in alkali/urea solvent and regenerated in ethylene glycol to form cellulose/chitosan nanofiber network, which was an ideal supporter for ZnO and Ag nanoparticles and beneficial for recycle usage. The hydroxyl groups of cellulose and chitosan chains exposed and were utilized for the synthesis of Ag particles, as well as ZnO nanoparticles by biomineralization. The Ag/Ag2O/ZnO decorating cellulose/chitosan (AZ@CC) films exhibited excellent antibacterial activity against Staphylococcus aureus and Escherichia coli. The width of inhibition zones around AZ@CC films reached 10.0-19.6 mm and 12.4-15.0 mm for S. aureus and E. coli, respectively. Moreover, AZ@CC films exhibited good photocatalytic activity against methyl orange (MO), almost 97% degradation of methyl orange (MO) within 50 min was achieved with the assistance of AZ@CC film. Importantly, the nanocomposite films exhibited excellent tensile strength and thermal stability. This facile and eco-friendly approach provided a new route to utilize cellulose and chitosan advantages for constructing multifunctional materials.

Incorporation of Layered Rectorite into Biocompatible Core-Sheath Nanofibrous Mats for Sustained Drug Delivery.

Searching for drug carries with controlled release and good biocompatibility has always been one of the research hotspots and difficulties. Herein, core-sheath nanofibrous mats (NFs) consisting of biocompatible poly(ethylene oxide) (PEO, core) and poly(l-lactic acid) (PLLA, sheath) for drug delivery were fabricated via coaxial electrospinning strategy. The nontoxic layered silicate rectorite (REC) with 0.5-1 wt % amount was introduced in the sheath for sustained drug delivery. Layered REC could be intercalated with PLLA macromolecule chains, leading to the densified structure for loading and keeping doxorubicin hydrochloride (DOX) while reversibly capturing and releasing DOX to delay the drug migration due to its high cation activity. The addition of REC in NFs could delay the initial burst release of DOX and prolong the residence time from 12 to 96 h. Moreover, DOX-loaded core-sheath NFs had in vitro culture with strong antitumor activity, which was confirmed by cytotoxicity results and live and dead assay. HepG2 tumor-bearing xenograft further demonstrated the tumor-suppression effect and the excellent safety of the DOX-loaded core-sheath NFs in vivo. The constructed NFs as drug carriers showed great potential in the local treatment of solid tumors.

Recent Progress in High-Strength and Robust Regenerated Cellulose Materials.

High-strength petroleum-based materials like plastics have been widely used in various fields, but their nonbiodegradability has caused serious pollution problems. Cellulose, as the most abundant sustainable polymer, has a great chance to act as the ideal substitute for plastics due to its low cost, wide availability, biodegradability, etc. Herein, the recent achievements for developing cellulose "green" solvents and regenerated cellulose materials with high strength via the "bottom-up" route are presented. Cellulose can be regenerated to produce films/membranes, hydrogels/aerogels, filaments/fibers, microspheres/beads, bioplastics, etc., which show potential applications in textiles, biomedicine, energy storage, packaging, etc. Importantly, these cellulose-based materials can be biodegraded in soil and oceans, reducing environmental pollution. The cellulose solvents, dissolving mechanism, and strategies for constructing the regenerated cellulose functional materials with high strength and performances, together with the current achievements and urgent challenges are summarized, and some perspectives are also proposed. The near future will be an exciting era for high-strength biodegradable and renewable materials. The hope is that many environmentally friendly materials with good properties and low cost will be produced for commercial use, which will be beneficial for sustainable development in the world.

Controlled Co-delivery of Growth Factors through Layer-by-Layer Assembly of Core-Shell Nanofibers for Improving Bone Regeneration.

The regeneration of bone tissue is regulated by both osteogenic and angiogenic growth factors which are expressed in a coordinated cascade of events. The aim of this study was to create a dual growth factor-release system that allows for time-controlled release to facilitate bone regeneration. We fabricated core-shell SF/PCL/PVA nanofibrous mats using coaxial electrospinning and layer-by-layer (LBL) techniques, where bone morphogenetic protein 2 (BMP2) was incorporated into the core of the nanofibers and connective tissue growth factor (CTGF) was attached onto the surface. Our study confirmed the sustained release of BMP2 and a rapid release of CTGF. Both in vitro and in vivo experiments demonstrated improvements in bone tissue recovery with the dual-drug release system. In vivo studies showed improvement in bone regeneration by 43% compared with single BMP2 release systems. Time-controlled release enabled by the core-shell nanofiber assembly provides a promising strategy to facilitate bone healing.

Acrylic acid-grafted pre-plasma nanofibers for efficient removal of oil pollution from aquatic environment.

Oily wastewater is a worldwide problem threatening the environment and humans. High flux and low-energy consumption separation of oil and water is urgently required but still faces great challenges. In this study, nanofibrous membranes with superhydrophilic and underwater superoleophobic surfaces were fabricated by grafting acrylic acid onto plasma-treated electrospun polystyrene/polyacrylonitrile (PS/PAN) membranes. The morphologies, chemical compositions, mechanical and surface properties of the membranes were examined in detail. The water contact angles of the PS/PAN membranes were 137.4°, 130.1°, 119.5°, 88.1° and 80.2°, respectively, which decreased to 76.5°, 47.9°, 34.4°, 0° and 0° after grafting treatment, proving that the modification improved the surface hydrophilicity of the membranes due to the introduction of hydrophilic groups. In addition, a gravity-driven filtration device was utilized to investigate the oil/water separation potential of the membranes. The results indicated that the grafted PS/PAN membranes separated the layered oil/water mixtures with permeate flux up to 57509 L m-2 h-1, while high fluxes of 1390-6460 L m-2 h-1 for the separation of different oil-in-water emulsions. Importantly, the membranes still maintained high flux and efficiency even after several cycles of separation. Therefore, the reusable membranes can be expected to be potential cost-effective materials for oil/water treatment.

Layer-by-layer immobilization of amphoteric carboxymethyl chitosan onto biocompatible silk fibroin nanofibrous mats.

Novel antimicrobials with well biocompatibility are urgently needed for human public health protecting. Here, the silk fibroin (SF) nanofibrous mats coated with carboxymethyl chitosan (CMC), both extracted from natural polymers, were fabricated by combining electrospinning and electrostatic layer-by-layer (LBL) self-assembly techniques. The amphoteric CMC could be easily adsorbed on the surface of SF nanofibers due to the electrostatic interaction, which were a highly efficient and "green" route for the surface modification of SF mats. The mats after LBL procedure exhibited better hydrophilicity and stronger mechanical properties. The experimental results demonstrated that the LBL modified mats not only kept well biocompatibility but also obtained extremely enhanced antibacterial activity. More importantly, the mats displayed better bacterial inhibition with the increased CMC layers. LBL10 and LBL10.5 owned the antibacterial activity of more than 67% at the bacterial concentrations of 106 cfu ml-1 after 24 h cultivation, which implied that these novel natural polymer-based materials could be utilized as wound dressings for clinical skin and tissue regeneration, especially for infected wounds.

Efficient fabrication of reversible pH-induced carboxymethyl chitosan nanoparticles for antitumor drug delivery under weakly acidic microenvironment.

Searching for the carrier systems for drug controlled release under weakly acidic condition related to tumor environment has attracted a tremendous level of attention. In this study, amphiphilic carboxymethyl chitosan (CMC) was employed to fabricate nanoparticles (NPs) with an efficient and simple method by adjusting the pH values of CMC aqueous solutions. The prepared NPs could not only capture the doxorubicin hydrochloride (DOX) efficiently and alleviate the initial burst release, but also exhibit pH sensitivity under weakly acidic microenvironment for tumor therapy. Importantly, rectorite (REC) with lamellar structure could be intercalated with CMC chains to construct more compact structure and DOX could be captured in the interlayer of REC, which could contribute to heightening the encapsulation efficiency and loading capacity of DOX, as well as reducing the initial burst release and prolonging the therapeutic time. The NPs displayed the behavior of controlled DOX release at pH 4.5, which suggested that the intelligent colloids might be utilized in tumor therapy.

Incorporation of lysozyme-rectorite composites into chitosan films for antibacterial properties enhancement.

The demand for designing antibacterial materials was quite substantial in packing and biomedical materials fields. Chitosan had a wide utilization to satisfy this demand. In this study, by incorporating lysozyme (LY) - rectorite (REC) into chitosan films, the ultimately obtained hybrid films can own the enhanced antibacterial properties and still remains good mechanical properties. Scanning electron microscopy (SEM) images revealed that LY and REC could be homogeneously distributed in the CS films. X-ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray analysis (EDX) results verified that the LY-REC incorporation process was successful. Small angle X-ray diffraction (SAXRD) and Fourier transform infrared (FT-IR) spectra revealed that some intercalation reactions occurred between CS chains and REC. The hydrophobic properties of the CS films were increased by the addition of LY and REC, determined by water contact angle measurement. In comparison with CS films, the mechanical properties of the composite films after adding LY-REC were reduced by 27.58%, but still maintained high tensile strength. Besides, the antibacterial properties of the films could be enhanced by introducing LY-REC. This method exhibited great application value in the food packaging fields.

Regulating the gaps between folds on the surface of silk fibroin membranes via LBL deposition for improving their biomedical properties.

Silk fibroin (SF) has become a promising biomaterial in guided bone regeneration (GBR). In an attempt to modify the size of the gaps on the surface of SF barrier membrane and improve its antibacterial activity, biological and mechanical properties, positively charged Lysozyme (LY)-Collagen Type-I (COL) composites and negatively charged SF were introduced to the negatively charged surface of SF substrates utilizing the electrostatic layer-by-layer (LBL) self-assembly technique. The morphology, chemical structures and element content of the LBL structured membranes were investigated. The results suggested that LY and COL were successfully assembled and the gaps between the folds on the surface of the membranes became smaller gradually with the increase of coated film numbers. Besides, the content of ß-sheets of the membranes increased after deposition, which indicated the improvement of their mechanical properties. Moreover, the results of the measurement of immobilized LY and antibacterial assay not only revealed that the enzymatic catalysis and antibacterial activity of the samples enhanced with the increase of coated bilayer numbers but also implied that LBL modified membranes had better antibacterial activity when LY-COL was on the outermost layer. Furthermore, CCK-8 assay certified both SF membrane and LBL structured membranes could facilitate cell growth and proliferation, and the introduction of COL could further promote this ability. Finally, cell attachment and morphology examination provided intuitional evidence that SF membrane and LBL modified membranes have excellent biocompatibility.

Rectorite-intercalated nanoparticles for improving controlled release of doxorubicin hydrochloride.

Controlled release of drugs has been widely researched in biomedical area. Nanoparticles (NPs) as ideal drug carriers are often used to facilitate improvements in the therapeutic index of drugs. In this study, natural polymers carboxymethyl chitosan (CMC) and lysozyme (LY) were mixed to prepare CMC-LY NPs by electrostatic self-assembly interactions. In addition, layered silicate rectorite (REC) was introduced into NPs to explore the effect on the encapsulation efficacy and controlled release of doxorubicin hydrochloride (DOX). It was confirmed that the average size of NPs increased with the addition of REC, and the interlayer distance of REC in NPs was enlarged because of the intercalation with polymer chains. Besides, the encapsulation efficiency and loading capacity of DOX in NPs increased markedly with the accretion of REC. The incorporation of REC into NPs could reduce the initial burst release and prolong the therapeutic time. Such results suggest that the REC-intercalated NPs are promising anticancer drug carriers for efficient cancer therapy.

Production of thick uniform-coating films containing rectorite on nanofibers through the use of an automated coating machine.

When an efficient automated coating machine is used to process layer-by-layer (LBL) deposited nanofibrous mats, it causes an obvious planar effect on the surface of the mats, which can be eliminated through ultimate immersion. During this process, chitosan (CS) - rectorite (REC) intercalated composite films are built on the surface of cellulose acetate (CA) nanofibrous mats by a coating machine. Then, the immersion process is utilized to allow positively charged CS or CS-REC intercalated composites to uniformly assemble on the surface of negatively charged CA nanofibers. An investigation into the morphology of the resultant scaffolds confirms that the uniquely small pore size, high specific surface area and typically three-dimensional (3D) structure of nanofibrous mats remain present. The results of Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicate that it is feasible to assemble nanofibrous mats using a coating machine. The intercalated structure of CS-REC is confirmed by the results of small-angle X-ray diffraction (SAXRD) and wide-angle X-ray diffraction (WAXRD). The results of the cell experiment and antibacterial test demonstrate that the addition of REC not only has little impact on the cytocompatibility of the mats but also enhances their ability to inhibit bacteria.

Antimicrobial application of nanofibrous mats self-assembled with chitosan and epigallocatechin gallate.

Cellulose electrospun nanofibrous mats coated with bilayers of chitosan (CS) and epigallocatechin gallate (EGCG) or with bilayers of CS-rectorite (REC) composite (CS-REC) and EGCG were fabricated via layer-by-layer (LBL) self-assembly technique. LBL-structured cellulose nanofibers still maintained three-dimension fiber structure according to the observation from scanning electron microscopy images. The average diameter of nanofibers were enlarged with the addition of REC. X-ray photoelectron spectroscopy results confirmed the deposition of CS and CS-REC onto the corresponding mats. The tensile strength and rate of elongation at break of LBL-structured nanofibers had no difference from those of uncoated nanofibers. The encapsulation efficiency and loading capacity of nanofibers were enhanced in the presence of REC. In addition the in-vitro cumulative release profiles of EGCG indicate that the addition of REC delayed the release of EGCG. Antimicrobial assay demonstrated the inhibitory effects of CS and EGCG on the growth of Staphylococcus aureus. Meanwhile the CS-REC composites improved the antimicrobial effects of CS and EGCG by adsorption of bacteria to the surface of REC then enhancement of exposure of bacteria to EGCG and the matrix of CS.

Fabrication of rectorite-contained nanoparticles for drug delivery with a green and one-step synthesis method.

The composite nanoparticles (NPs) consisted of quaternized chitosan (QC)/bovine serum albumin (BSA)/rectorite (REC) were prepared successfully just by adding BSA solution into QC-REC nanocomposites solution via electrostatic interactions. The average diameter of NPs increased with the accretion of REC, which was demonstrated with dynamic laser scattering (DLS) and transmission electron microscopy (TEM). The results of small angle X-ray diffraction (SAXRD) and selected area electron diffraction (SAED) demonstrated that the intercalated structure of REC was enlarged with the addition of REC. Besides, it can was proved that the interaction had occurred between QC and REC in NPs with fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). In addition, doxorubicin (DOX) was used to investigate the entrapment efficiency and release pattern in NPs. It turned out to be that the addition of REC could increase the encapsulation efficiency (EE) and loading capacity (LC). The results also exhibited that the drug release in simulated gastric fluid reduced apparently with the addition of REC, which could ensure more DOX released in intestines.

Layer-by-layer immobilization of quaternized carboxymethyl chitosan/organic rectorite and alginate onto nanofibrous mats and their antibacterial application.

Quaternized carboxymethyl chitosan (QCM-chitosan) and organic rectorite (OREC) immobilized nanofibrous mats are fabricated via layer-by-layer (LBL) technique in a self-assembly manner. The negatively charged cellulose nanofibrous mats hydrolyzed from electrospun cellulose acetate (CEL) mats are alternately modified with the positively charged QCM-chitosan and OREC intercalated composites and the negatively charged sodium alginate (ALG) via LBL technique. The morphology and antibacterial activity of the resultant mats are studied by changing the number of deposition bilayers, the compositions of dipping solutions and outermost layer. X-ray photoelectron spectroscopy results imply that QCM-chitosan and OREC are coated on cellulose mats. Besides, wide angle X-ray diffraction and small angle X-ray diffraction are applied to investigate the crystalline of the composite mats and the interlayer distance of OREC, respectively. The antibacterial activity of the mats increases with the incorporation of OREC into LBL films.