In Situ-Generated Heat-Resistant Hydrogen-Bonded Organic Framework for Remarkably Improving Both Flame Retardancy and Mechanical Properties of Epoxy Composites.

In this study, the heat-resistant hydrogen-bonded organic framework (HOF) material HOF-FJU-1 was synthesized via in situ generation and then used as flame retardants (FRs) to improve the flame retardancy of epoxy resin (EP). HOF-FJU-1 can maintain high crystallinity at 450 °C and thus function as a flame retardant in EP. The study found that HOF-FJU-1 facilitates the improvement of char formation in EP, thus inhibiting heat transfer and smoke release during combustion. For EP/HOF-FJU-1 composites, the in situ-generated HOF-FJU-1 can remarkably improve both the mechanical properties and the flame retardancy of EP. Furthermore, the in situ-generated HOF-FJU-1 has better fire safety than the ex situ-generated HOF-FJU-1 at the same filling content. Thermal degradation products and flame retardation mechanisms in the gas and condensed phases were further investigated. This work demonstrates that the in situ-generated HOF-FJU-1 is promising to be an excellent flame-retardant candidate.

Preparation of a novel functionalized magnesium-based curing agent as an intrinsic flame retardant for epoxy resin.

In this study, a novel organic-inorganic hybrid flame retardant 10-(1,4-dicarboxylic acid magnesium salt)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DMMH) was synthesized via neutralization and addition reaction of maleic acid, magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and subsequently used in an intrinsic flame retardant epoxy resin. The chemical structure and morphology of DMMH were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Further, the prepared DMMH was combined with ammonium polyphosphate (APP) to form an intumescent flame retardant system. The thermal stability and flame retardance were evaluated by thermogravimetric analysis (TG), UL-94 vertical burning test, limiting oxygen index (LOI) and cone calorimetry. It was observed that the addition of 1.7% DMMH and 5.3% APP led EP-7 to acquire UL-94 V-0 rating, with the limiting oxygen index of 26.0%. As compared with pure EP, the peak heat release rate, total heat release, smoke production rate and total smoke production of the sample was noted to decrease by 54.5%, 35.1%, 43.6% and 38.1%, respectively. In addition, the introduction of DMMH did not negatively impact the mechanical properties of the epoxy resin.

Preparation and anti-leakage properties of hydroxyethyl cellulose-g-poly (butyl acrylate-co-vinyl acetate) emulsion.

A hydroxyethyl cellulose-g-poly (butyl acrylate-co-vinyl acetate)(HEC-g-P (BA-co-VAc)) emulsion was synthesized by free radical emulsion polymerization method from hydroxyethyl cellulose (HEC), butyl acrylate (BA) and vinyl acetate (VAc) in the presence of emulsifier sodium dodecyl benzene sulfonate (SDBS). The structure, thermal stability and morphology of the emulsion were characterized by Fourier-transform infrared (FTIR), thermogravimetric analysis (TGA), transmission electron microscope (TEM) and other analytical techniques. The results proved that BA and VAc monomers had grafted with HEC. Its thermal stability was also significantly improved compared to HEC. Moreover, the prepared emulsion was evaluated to study the performance of preventing water leakage in soil. Compared with the published anti-leakage materials prepared by directly doping hydroxyethyl cellulose, the emulsion interacted with attapulgite to form a dense consolidation layer, which had better anti-leakage performance and water retention. Therefore, the material was more favorable for popularization and application in arid and semi-arid areas.

Arsenic accumulation and distribution in Pteris vittata fronds of different maturity: Impacts of soil As concentrations.

Arsenic (As) hyperaccumulator Pteris vittata is efficient in As uptake, translocation and accumulation, but the impacts of soil As concentrations on As accumulation and distribution in P. vittata are still unclear. The impacts of soil As (7.3, 63 and 228 mg kg-1) on plant growth and As accumulation in P. vittata after 6 months of growth were evaluated. Arsenic concentrations in the roots, midribs and pinna margin of P. vittata fronds of different maturity were determined by inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy coupled with an energy dispersive spectrometer (SEM-EDS). While moderate As level at As63 didn't impact P. vittata growth, higher As at As228 decreased plant biomass by 38%. Under As stress, more As was accumulated in the senescing fronds (47%) and mature fronds (11%) than the young fronds. In senescing fronds, As concentrations in pinna margin were 2.3 times that of the midribs, consistent with As-induced necrotic symptom. Arsenic distribution based on SEM-EDS analysis revealed good correlation between Si and As in the pinnae (r = 0.49). Our data showed that As accumulation in pinna margin caused necrosis and Si may have a potential role in As detoxification in P. vittata.

Arsenic-resistance mechanisms in bacterium Leclercia adecarboxylata strain As3-1: Biochemical and genomic analyses.

Microbial arsenic transformation is important in As biogeochemical cycles in the environment. In this study, a new As-resistant bacterial strain Leclercia adecarboxylata As3-1 was isolated and its associated mechanisms in As resistance and detoxification were evaluated based on genome sequencing and gene annotations. After subjecting strain As3-1 to medium containing arsenate (AsV), AsV reduction occurred and an AsV-enhanced bacterial growth was observed. Strain As3-1 lacked arsenite (AsIII) oxidation ability and displayed lower AsIII resistance than AsV, probably due to its higher AsIII accumulation. Polymerase chain reaction and phylogenetic analysis showed that strain As3-1 harbored a typical AsV reductase gene (arsC) on the plasmids. Genome sequencing and gene annotations identified four operons phoUpstBACS, arsHRBC, arsCRDABC and ttrRSBCA, with 8 additional genes outside the operons that might have involved in As resistance and detoxification in strain As3-1. These included 5 arsC genes explaining why strain As3-1 tolerated high AsV concentrations. Besides ArsC, TtrB, TtrC and TtrA proteins could also be involved in AsV reduction and consequent energy acquisition for bacterial growth. Our data provided a new example of diverse As-regulating systems and AsV-enhanced growth without ArrA in bacteria. The information helps to understand the role of As in selecting microbial systems that can transform and utilize As.

Efficient phosphate accumulation in the newly isolated Acinetobacter junii strain LH4.

Phosphate (PO43-) accumulation associated with bacteria contributes to efficient remediation of eutrophic waters and has attracted attention due to its low cost, high removal efficiency and environmental friendliness. In the present study, we isolated six strains from sludge with high concentrations of chemical oxygen demand, total nitrogen and total phosphorus levels. Among them, strain LH4 exhibited the greatest PO43- removal ability. Strain LH4 is typical of Acinetobacter junii based on physiological, biochemical, and molecular analyses and is a PO43--accumulating organism (PAO) based on toluidine blue staining. The strain grew quickly when subjected to aerobic medium after pre-incubation under anaerobic condition, with a maximum OD600 of 1.429 after 8 h and PO43- removal efficiency of 99%. Our data also indicated that this strain preferred utilizing the carbon (C) sources sodium formate and sodium acetate and the nitrogen (N) sources NH4Cl and (NH4)2SO4 over other compounds. To achieve optimal PO43- removal efficiency, a C:N ratio of 5:1, inoculation concentration of 3%, solution pH of 6, incubation temperature of 30 °C, and shaking speed of 100 rpm were recommended for A. junii strain LH4. By incubating this strain with different concentrations of PO43-, we calculated that its relative PO43- removal capacity ranged from 0.67 to 3.84 mg L-1 h-1, ranking in the top three among reported PAOs. Our study provided a new PO43--accumulating bacterial strain that holds promise for remediating eutrophic waters, and its potential for large-scale use warrants further investigation.

Insights into Bacterial Cellulose Biosynthesis from Different Carbon Sources and the Associated Biochemical Transformation Pathways in Komagataeibacter sp. W1.

Cellulose is the most abundant and widely used biopolymer on earth and can be produced by both plants and micro-organisms. Among bacterial cellulose (BC)-producing bacteria, the strains in genus Komagataeibacter have attracted wide attention due to their particular ability in furthering BC production. Our previous study reported a new strain of genus Komagataeibacter from a vinegar factory. To evaluate its capacity for BC production from different carbon sources, the present study subjected the strain to media spiked with 2% acetate, ethanol, fructose, glucose, lactose, mannitol or sucrose. Then the BC productivity, BC characteristics and biochemical transformation pathways of various carbon sources were fully investigated. After 14 days of incubation, strain W1 produced 0.040⁻1.529 g L-1 BC, the highest yield being observed in fructose. Unlike BC yields, the morphology and microfibrils of BCs from different carbon sources were similar, with an average diameter of 35⁻50 nm. X-ray diffraction analysis showed that all membranes produced from various carbon sources had 1⁻3 typical diffraction peaks, and the highest crystallinity (i.e., 90%) was found for BC produced from mannitol. Similarly, several typical spectra bands obtained by Fourier transform infrared spectroscopy were similar for the BCs produced from different carbon sources, as was the Iα fraction. The genome annotation and Kyoto Encyclopedia of Genes and Genomes analysis revealed that the biochemical transformation pathways associated with the utilization of and BC production from fructose, glucose, glycerol, and mannitol were found in strain W1, but this was not the case for other carbon sources. Our data provides suggestions for further investigations of strain W1 to produce BC by using low molecular weight sugars and gives clues to understand how this strain produces BC based on metabolic pathway analysis.

The in vitro and in vivo biocompatibility evaluation of electrospun recombinant spider silk protein/PCL/gelatin for small caliber vascular tissue engineering scaffolds.

Recombinant spider silk protein (pNSR32) and gelatin (Gt) were demonstrated to enhance cytocompatibility of electrospun pNSR32/PCL/Gt scaffold. However, its potential pro-inflammatory effects and interactions with tissue and blood are unknown. In this study, the physicochemical properties and in vitro and in vivo biocompatibility of such scaffolds were evaluated. The results showed that the pNSR32/PCL/Gt scaffold possessed larger average fiber diameters, wider fiber diameter distribution and faster degradation rate than that of pNSR32/PCL and PCL scaffolds. The addition of pNSR32 and Gt had little influence on the hemolysis and plasma re-calcification time, but prolonged kinetic clotting time and reduced the platelet adhesion. The Il-6 and Tnf-α mRNA expression levels were up-regulated in macrophages seeded on the PCL and pNSR32/PCL scaffolds. The lowest release of IL-6 and TNF-α appeared in the pNSR32/PCL/Gt scaffold. Histological results revealed that the PCL and pNSR32/PCL scaffolds elicited severe host tissue responses after implantation, while prominent ingrowth of host cells were observed in the pNSR32/PCL and pNSR32/PCL/Gt scaffolds. The comet assay and bone marrow micronucleus test demonstrated that the pNSR32/PCL/Gt scaffold did not increase the frequency of DNA damage or bone marrow micronucleus. In short, this study confirmed that the pNSR32/PCL/Gt scaffold exhibited better blood and tissue compatibility than pNSR32/PCL and PCL scaffolds. No induction of genotoxicity and inflammatory factor releases makes the pNSR32/PCL/Gt scaffold a good candidate for engineering small diameter vascular tissue.

Studies on the use of recombinant spider silk protein/polyvinyl alcohol electrospinning membrane as wound dressing.

A series of wound membranes of polyvinyl alcohol and recombinant spider silk protein (pNSR16) was prepared by electrospinning. The membrane was analyzed by scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. The result showed that the three factors that affected average fiber diameter from high to low were, voltage, flow speed, and solidification distance; and the three factors that affected fiber uniformity from high to low were, flow speed, solidification distance, and voltage. The fibers adhered together after being dealt with alcohol. pNSR16 transformed from random coil into ß-sheet after being immersed in alcohol. Additionally, the porosity of the electrospun membrane was 84.85%, which was higher than that of cast membrane prepared with the same composition. Experiments of applying electrospun membranes as wound dressing for Sprague Dawley rat wound healing showed that it could promote wound healing and basic fibroblast growth factor expression.

Bacteria from the rhizosphere and tissues of As-hyperaccumulator Pteris vittata and their role in arsenic transformation.

Arsenic (As)-resistant bacteria are abundant in the rhizosphere and tissues of As-hyperaccumulator Pteris vittata. However, little is known about their roles in As transformation and As uptake in P. vittata. In this study, the impacts of P. vittata tissue extracts with or without surface sterilization on As transformation in solutions containing 100 µg L-1 AsIII or AsV were investigated. After 48 h incubation, the sterilized and unsterilized root extracts resulted in 45% and 73% oxidation of AsIII, indicating a role of both rhizobacteria and endobacteria. In contrast, AsV reduction was only found in rhizome and frond extracts at 3.7-24% of AsV. A total of 37 strains were isolated from the tissue extracts, which are classified into 18 species based on morphology and 16S rRNA. Phylogenic analysis showed that ∼44% isolates were Firmicutes and others were Proteobacteria except for one strain belonging to Bacteroidetes. While most endobacteria were Firmicutes, most rhizobacteria were Proteobacteria. All isolated bacteria belonged to AsV reducers except for an As-sensitive strain and one AsIII- oxidizer PVR-YHB6-1. Since As transformation was not observed in solutions after filtrating or boiling, we concluded that both rhizobacteria and endobacteria were involved in As transformation in the rhizosphere and tissues of P. vittata.

A novel Bruch's membrane-mimetic electrospun substrate scaffold for human retinal pigment epithelium cells.

Various artificial membranes have been used as scaffolds for retinal pigment epithelium cells (RPE) for monolayer reconstruction, however, long-term cell viability and functionality are still largely unknown. This study aimed to construct an ultrathin porous nanofibrous film to mimic Bruch's membrane, and in particular to investigate human RPE cell responses to the resultant substrates. An ultrathin porous nanofibrous membrane was fabricated by using regenerated wild Antheraea pernyi silk fibroin (RWSF), polycaprolactone (PCL) and gelatin (Gt) and displayed a thickness of 3-5 µm, with a high porosity and an average fiber diameter of 166 ± 85 nm. Human RPE cells seeded on the RWSF/PCL/Gt membranes showed a higher cell growth rate (p < 0.05), and a typical expression pattern of RPE signature genes, with reduced expression of inflammatory mediators. With long-term cultivation on the substrates, RPE cells exhibited characteristic polygonal morphology and development of apical microvilli. Immunocytochemisty demonstrated RPE-specific expression profiles in cells after 12-weeks of co-culture on RWSF/PCL/Gt membranes. Interestingly, the cells on the RWSF/PCL/Gt membranes functionally secreted polarized PEDF and phagocytosed labeled porcine POS. Furthermore, RWSF/PCL/Gt membranes transplanted subsclerally exhibited excellent biocompatibility without any evidence of inflammation or rejection. In conclusion, we established a novel RWSF-based substrate for growth of RPE cells with excellent cytocompatibility in vitro and biocompatibility in vivo for potential use as a prosthetic Bruch's membrane for RPE transplantation.

Development of nanofibrous scaffolds for vascular tissue engineering.

Small-diameter vascular grafts can easily lead to thrombosis and intimal hyperplasia. So the rate of the long-term patency is not satisfactory. Scaffolds that can support the growth of cells and remain stable and passable in vivo are in great demand. Vascular scaffolds were fabricated by electrospinning RGD-recombinant spider silk protein (pNSR32), polycaprolactone (PCL) and chitosan (CS). In addition, the cytocompatibility, the stability and the patency of scaffolds in vivo were studied. The results demonstrated that Sprague-Dawley rat aortic endothelial cells (SDRAECs) could highly enhanced adhesion and proliferation, together with increasing stress of fiber formation, and intensive biological function (the expression of PECAM-1 and vWF, the secretion of NO), in the pNSR32/PCL/CS scaffolds, compared with in the pNSR32/PCL and PCL scaffolds. The cell cycle studies of SDRAECs also revealed that the scaffolds promoted the cells to enter the stage of divisional proliferation. Furthermore, pNSR32/PCL/CS scaffolds could support the growth of cells under physiologic conditions and are able to maintain the structural integrity and patency for at least 8 weeks in a SD rat abdominal aortic defect model.

Cytocompatibility of electrospun nanofiber tubular scaffolds for small diameter tissue engineering blood vessels.

A tubular scaffold was fabricated by using electrospun polymer solution blends of pNSR32 (recombinant spider silk protein), PCL (polycaprolactone) and Gt (gelatin). The physicochemical properties and cytocompatibility of these scaffolds were investigated. Afterwards, the pNSR32/PCL/Gt tubular scaffold (inner diameter=3mm) showed high porosity of 86.2 ± 2.9%, pore size of 2423 ± 979nm and average fibre diameter of 166 ± 85nm. Water uptake and contact angle of the scaffolds reached 112.0 ± 4.4% and 45.7 ± 13.7°, respectively. SDRAECs (Sprague Dawley Rat Aortic Endothelial Cells) grew and proliferated well and phenotype could be maintained on the composite scaffolds after they had been cultured on the composite scaffolds for 7 days. Compared with pure PCL scaffolds a greater density of viable cells was seen on the composites, especially the pNSR32/PCL/Gt scaffolds.

[Preliminary study on polyvinyl alcohol/wild antheraea pernyi silk fibroin as nanofiber scaffolds for tissue engineered tendon].

OBJECTIVE: To investigate the cellular compatibility of polyvinyl alcohol (PVA)/wild antheraea pernyi silk fibroin (WSF), and to explore the feasibility for tendon tissue engineering scaffold in vitro. METHODS: The solutions of WSF (11%), PVA (11%), and PVA/WSF (11%) were prepared with 98% formic acid (mass fraction) at a mass ratio of 9:1. The electro spinning membranes of WSF, PVA, and PVA/WSF were prepared by electrostatic spinning apparatus. The morphologies of scaffolds were evaluated using scanning electronic microscope (SEM). The tendon cells were isolated from tail tendon of 3-day-old Sprague Dawley rats in vitro. The experiment was performed using the 3rd generation cells. The tendon cells (1 x 10(6)/mL) were cocultured with PVA and PVA/WSF electro spinning film, respectively, and MTT test was used to assess the cell adhesion rate 4, 12 hours after coculture. The tendon cells were cultured in PVA and PVA/WSF extraction medium of different concentration (1, 1/2, and 1/4), respectively; and the absorbance (A) values were detected at 1, 3, 5, and 7 days to evaluate the cytotoxicity. The composite of tendon cells and the PVA or PVA/WSF scaffold were observed by HE staining at 7 days and characterized by SEM at 1, 3, 5, and 7 days. RESULTS: The solution of WSF could not be used to electro spin; and the solution of PVA and PVA/WSF could be electrospun. After coculture of tendon and PVA or PVA/WSF electro spinning membranes, the cell adhesion rates were 26.9% +/- 0.4% and 87.0% +/- 1.0%, respectively for 4 hours, showing significant difference (t = 100.400, P = 0.000); the cell adhesion rates were 35.2% +/- 0.6% and 110.0% +/- 1.7%, respectively for 12 hours, showing significant difference (t = 42.500, P = 0.000). The cytotoxicity of PVA/WSF was less significantly than that of PVA (P < 0.05) and significant difference was observed between 1/2 PVA and 1/4 PVA (P < 0.05). HE staining and SEM images showed that the tendon cells could adhere to PVA and PVA/WSF scaffolds, but that the cells grew better in PVA/WSF scaffold than in PVA scaffold in vitro. CONCLUSION: PVA/WSF electro spinning membrane scaffold has good cell compatibility, and it is expected to be an ideal scaffold of tendon tissue engineering.

[Application of electrostatic spinning technology in nano-structured polymer scaffold].

OBJECTIVE: To review the latest development in the research on the application of the electrostatic spinning technology in preparation of the nanometer high polymer scaffold. METHODS: The related articles published at home and abroad during the recent years were extensively reviewed and comprehensively analyzed. RESULTS: Micro/nano-structure and space topology on the surfaces of the scaffold materials, especially the weaving structure, were considered to have an important effect on the cell adhesion, proliferation, directional growth, and biological activation. The electrospun scaffold was reported to have a resemblance to the structure of the extracellular matrix and could be used as a promising scaffold for the tissue engineering application. The electrospun scaffolds were applied to the cartilage, bone, blood vessel, heart, and nerve tissue engineering fields. CONCLUSION: The nano-structured polymer scaffold can support the cell adhesion, proliferation, location, and differentiation, and this kind of scaffold has a considerable value in the tissue engineering field.