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Bacillus thuringiensis (Bt) and transgenic crops carrying cry genes are widely used in the management of lepidopteran and coleopteran pests. However, almost none of the Cry toxins have insecticidal properties against sap-sucking insects, such as planthoppers, leafhoppers and aphids. To understand the low insecticidal activity of Cry1Ac toxin on sap-sucking insects, we investigated two critical steps in the Bt-intoxication cascade: the proteolytic processing of Cry1Ac toxin by gut proteases, and the binding of Cry1Ac to brush border membrane vesicles (BBMV) of Nilaparvata lugens. Proteolytic processing of Cry1Ac protoxin by N. lugens gut proteases resulted in an ∼65 kDa product, similar to the expected size of the trypsin-activated Cry1Ac toxin. In addition, activation of cysteine proteases in N. lugens gut increased the efficiency of proteolytic activities in the processing of Cry1Ac. However, feeding N. lugens nymphs with either Cry1Ac protoxin or trypsin-activated Cry1Ac toxin resulted in low mortalities. The LC50 of Cry1Ac protoxin and trypsin-activated Cry1Ac was 198.92 and 450.18 μg/mL, respectively. In vitro binding analysis of BBMV with the pre-activated Cry1Ac showed that Cry1Ac toxin could specifically bind to the BBMV. However, binding competition with 500-fold molar excess GalNAc (N-acetyl-d-galactosamine) suggested that the binding was not mediated by GalNAc-like glycoproteins. These results indicate that Cry1Ac toxin could be successfully processed by the treatment of N. lugens gut proteases. However, the binding of Cry1Ac toxin to the midgut brush border membrane was not mediated by GalNAc-like glycoprotein. This may be responsible for the low susceptibility of N. lugens to Cry1Ac. [ABSTRACT FROM AUTHOR]

The ability to accurately predict the rheological behavior of the blends of two incompatible polymers is critical to the polymer industry. The constitutive modeling of incompatible polymer blends requires understanding the structure and dynamics of the blends across different length scales. The polydispersity of chain length at the molecular level and nonuniformity of flow field due to dispersed domains at the mesoscopic level present significant challenges to this industrially relevant problem. This work proposes a modeling framework for linear and nonlinear rheology of industrial incompatible polymer blends with sea-island morphology. For the individual components, we adopt the Rolie-Double-Poly model and generate the relaxation spectrum from an optimized molecular weight distribution. We derive a new mixing rule without empirical parameters from the flow field analysis inside and outside the droplets. The phase interface, modeled by an ellipsoidal model, contributes to the apparent rheology only at low shear rates. Our modeling approach is verified by the shear and extensional rheology of eight polymer blends with a broad range of viscosity ratios (0.01–100). We also show that the model has the ability to predict the nonlinear rheological behaviors of incompatible polymer blends with known molecular weight distributions and phase morphology. [ABSTRACT FROM AUTHOR]

A facile one-pot method was designed and used to synthesize alginate (SA) noncovalently functionalized amino-graphene oxide, A-aGO, which possesses an excellent dispersibility in water. Subsequently, A-aGO was added to an aqueous solution of alginate and the gelation behavior of A-aGO/SA in water was studied by rheology when calcium chloride (CaCl 2 ) was used as a physical crosslinking agent. The presence of A-aGO promoted the sol–gel transition of alginate, where the critical gel concentration of CaCl 2 (c g ) decreased and the critical gel strength S g increased with increasing A-aGO content, even though the critical relaxation exponent n was almost constant. A schematic diagram was proposed, which is able to describe the change in the junctions of gel network with increasing A-aGO content, and further interpreted the rheological scaling law at the gel point. In the stable gel state, the plateau modulus G e of A-aGO/SA hydrogels at a fixed concentration of Ca 2+ ions depended on A-aGO content according to a parabola equation, G e = 831.1 + 11740.4 w − 6448.6w 2 , where w is the weight percentage of A-aGO relative to alginate. The FESEM images further verified a porous microstructure of A-aGO/SA gels, and the pore size decreased and the pore density increased with A-aGO due to the increased junction density at a higher A-aGO content. [ABSTRACT FROM AUTHOR]

This work aims to study how three kinds of nanofillers: graphene oxide (GO), ammonia functionalized graphene oxide (AGO), and triethoxylpropylaminosilane functionalized silica, can affect stability and mechanical strength of sodium alginate (SA) composite films. The filler/sodium alginate (SA) solutions were first studied by rheology to reveal effects of various fillers on zero shear viscosity η 0 . SA composite films were then prepared by a solution mixing-evaporation method. The structure, morphology and properties of SA composite films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), contact angle and mechanical testing. Compared to GO and silica, the presence of AGO significantly improved the interaction between AGO and SA, which led to the increase in stability and mechanical strength of the resulting SA composite films. The tensile strength and elongation at break of AGO/SA composite film at 3 wt% AGO loading were increased by 114.9% and 194.4%, respectively, in contrast to pure SA film. Furthermore, the stability of AGO/SA composite films at high temperatures and in a wet environment were better than that of silica/SA and GO/SA composite films. [ABSTRACT FROM AUTHOR]

The effect of calcium cations (Ca 2+ ) on thermoreversible gelation properties, microstructure, and scaling behavior of κ-carrageenan in aqueous solution was studied by micro-differential scanning calorimetry (micro-DSC), field emission scanning electron microscopy (FESEM) and rheology. It was found that κ-carrageenan molecules self-associated into fibrils, and the diameter and number of fibrils increased with increasing Ca 2+ ion concentration. The formation and melting of κ-carrageenan hydrogel was thermally reversible and extremely sensitive to Ca 2+ ions. The viscoelastic property at the gel point was examined using the Winter-Chambon criterion to obtain the critical relaxation exponent n and the critical gel strength S g . n and S g were found to decrease and increase with increasing Ca 2+ ion concentration respectively. The normalized gel strength, S g /Ca 2+ , was not independent of Ca 2+ ion concentration, suggesting a strong effect of Ca 2+ ions on both size and density of junctions formed during gelation. A schematic diagram has been proposed to explain how Ca 2+ ions could facilitate the coil-helix transition, leading to the formation of more aggregates acting as junctions. [ABSTRACT FROM AUTHOR]

The effects of graphene oxide (GO) and ammonia functionalized graphene oxide (AGO) on microstructure, thermoreversible and critical gelation properties of κ-carrageenan in aqueous solution were studied by micro-differential scanning calorimetry (micro-DSC), field emission scanning electron microscopy (FESEM) and rheology. The presence of GO or AGO was able to decrease the gel formation and melting temperatures and reduce gel strength. The effect of AGO was more evident than that of GO. It was observed by FESEM that κ-carrageenan gel was induced by the formation of a fibrillar network, and fibrillar size and density decreased with increasing GO or AGO content. The viscoelastic properties at the gel point were examined using the Winter-Chambon criterion to obtain the critical relaxation exponent n and the critical gel strength S g . n increased but S g decreased with increasing GO or AGO content. The more obvious increase in n and decrease in S g were observed in the AGO/κ-carrageenan solution, which further demonstrated the stronger weakening effect of AGO. A schematic diagram has been proposed to explain the effect of AGO on the gelation of κ-carrageenan, where AGO sheets attracted a number of κ-carrageenan chains through hydrogen bonding and electrostatic interaction between sulfate groups of κ-carrageenan and amine groups of AGO. As a result, the number of free κ-carrageenan chains in solution decreased and the coil-helix transition and aggregation of helices of κ-carrageenan were affected negatively. [ABSTRACT FROM AUTHOR]

Summary Proteins are promising therapeutics with several design challenges, such as their inherent immunogenicity due to their exogenous source or short circulation time. The common solution to such issues is the chemical conjugation of the amphiphilic polymer poly(ethylene glycol) (PEG), a process known as PEGylation. However, several studies demonstrated a decrease in protein bioactivity or an increase in the presence of specific antibodies post PEGylation, highlighting the importance of an alternative strategy. Here we compare the performance of a superhydrophilic zwitterionic polymer in protecting an immunogenic protein to PEG in (i) the maintenance of enzyme activity and stability post modification, (ii) mitigation of the antibody response elicited by the polymer and any subsequent effect on pharmacokinetics, and (iii) minimization of host response toward the underlying protein. In contrast to PEG, zwitterionic conjugation decreases host antibody response without sacrificing bioactivity or generating polymer-specific antibodies. [ABSTRACT FROM AUTHOR]

The gelation of alginate in aqueous solution was studied as a function of Ca 2+ concentration. At each given concentration of alginate, a critical gel concentration c g ,  Ca 2 + , was successfully determined for the first time using the Winter–Chambon criterion. The critical gel concentration c g ,  Ca 2 + was found to increase linearly with alginate concentration. At the same time, the critical relaxation exponent n decreased and the critical gel strength S g increased linearly with alginate concentration. An improved egg-box model was proposed to describe the change in gel junction and gel network. In the stable gel state, the plateau modulus G e of alginate gel depended on Ca 2+ concentration according to a power-law scaling, G e = kɛ 1.5 , where ɛ is the relative distance of a gelling variable (Ca 2+ concentration in this case) from the gel point ( c g ,  Ca 2 + ). The FESEM images verified the microstructure of alginate gel in which alginate chains associated into fibrils in the presence of Ca 2+ ions. The fibrillar diameter and network density increased with increasing Ca 2+ ion concentration while alginate concentration had a weak influence on fibrillar diameter. [ABSTRACT FROM AUTHOR]