Thermoreversible gelation and scaling laws for graphene oxide-filled κ-carrageenan hydrogels

Eco-Friendly Extraction, Structure, and Gel Properties of ι-Carrageenan Extracted Using Ca(OH)2

An eco-friendly method for ι-carrageenan extraction from seaweed Eucheuma denticulatum through boiling and using a low concentration of Ca(OH)2 is reported. Compared to the traditional method of ι-carrageenan extraction using NaOH, the reported method using Ca(OH)2 had the advantages of using 93.3% less alkali and 86.8% less water, having a 25.0% shorter total extraction time, a 17.6% higher yield, and a 43.3% higher gel strength of the product. In addition, we evaluated the gel properties and structures of ι-carrageenan products extracted by Ca(OH)2 (Ca-IC) and NaOH (Na-IC). The Fourier transform infrared spectroscopy results showed that the structures of Ca-IC and Na-IC did not change remarkably. The results of the thermogravimetric analysis and differential scanning calorimetry showed that Ca-IC had the same thermal stability as Na-IC. The results of the textural analysis showed that Ca-IC had a higher hardness and better chewiness compared to Na-IC. Rheological results indicated that Ca-IC and Na-IC exhibited shear-thinning and non-Newtonian fluid properties, whereas the viscosity of Ca-IC was less than that of Na-IC. In conclusion, this new method of ι-carrageenan extraction using Ca-IC is markedly better and yields higher quality carrageenan than the conventional method of using Na-IC.

Functionalized Graphene Oxide-Reinforced Chitosan Hydrogel as Biomimetic Dressing for Wound Healing

A novel chitosan composite hydrogel by combining functionalized graphene oxide (CGO) is fabricated. The introduction of CGO significantly improves the mechanical property of CS hydrogel owing to the enhanced interaction between chitosan and CGO sheets. In comparison to the CS-GO composite hydrogel, the compressive stress of the CS-CGO composite hydrogel increases from 1.9 MPa at strain of 70.4% to 4.2 MPa at strain of 78.4%, the tensile stress and strain improve from 141.2 kPa and 134.6% to 300.2 kPa and 165.9%, respectively. An interconnected porous structure is formed in the CS-CGO composite hydrogel and the pore size decreases as the CGO loading increases, which is desirable in improving its mechanical property. Furthermore, the cytotoxicity tests indicate that the CS-CGO composite hydrogel possesses an excellent biocompatibility and can promote the adhesion and proliferation of fibroblasts. In vivo evaluation on full-thickness excision wounds in experimental rat shows that the CS-CGO composite hydrogel significantly accelerates wound healing, and the wound closure rate reaches up to 92.2% after 21 days. A feasible strategy to fabricate an enhanced chitosan composite hydrogel for application in wound healing is offered.

The assembly and antitumor activity of lycium barbarum polysaccharide-platinum-based conjugates

In this work, the new polysaccharide-platinum conjugates of 5-aminosalicylic acid modified lycium barbarum polysaccharide linking platinum compounds were designed in order to construct an anticancer metal drug delivery system. The multiple analysis methods were used to describe the chemical structure and physical properties of the polysaccharide-metal conjugates. The results showed that 5-aminosalicylic acid successfully acted as linker which was covalently bound between polysaccharide and platinum compound. The morphology and rheological properties of polysaccharide have been changed by the formation of conjugates, which exhibited certain inhibition specificity to A549 (human lung cancer cell line). The agarose gel electrophoresis and fluorescence microscopy results demonstrated that such conjugates promoted the unwinding of DNA and could significantly damage the nucleus of A549 cells. Cell cycle analyzing the Pt complex of conjugates could cause intracellular DNA damage and induced G2 phase arrest. So, polysaccharide-platinum conjugates might find a range of applications, for example in metal anticancer drug delivery.

Properties of a commercial κ-carrageenan food ingredient and its durable superabsorbent hydrogels

Physical kappa-carrageenan-based hydrogels are often prepared from dilute aqueous kappa-carrageenan (κ-carrageenan) solutions at the presence of metallic ions or by mixing these solutions with proteins and other polysaccharides. The κ-carrageenan hydrogels have been used for technological purposes; however, there are no reports about the properties of a commercial GENUGEL® κ-carrageenan produced by the CP Kelco. The flame atomic absorption spectrometry shows that the commercial κ-carrageenan comprises a high content of metallic ions (K⁺ = 216.1 g kg^-1, Na⁺ = 6.3 g kg^-1 and Ca²⁺ = 12.5 g kg^-1). The X-ray photoelectron spectroscopy (XPS) indicates the presence of sodium, calcium, and potassium atoms on the as-received κ-carrageenan and its physical hydrogel surfaces. XPS supports the occurrence of a low protein content onto the sample surfaces, as well. The metallic level (especially for K⁺) in the commercial κ-carrageenan plays an essential role in the preparation of durable hydrogels. These materials are prepared by cooling aqueous κ-carrageenan solutions at 4.0 and 5.0 wt%. The gelation temperature is determined by measuring G' &G″ as a function of the temperature. The gelation behavior depends on the κ-carrageenan concentration, as well as the metallic content in the commercial sample. Scanning electron microscopy shows that hydrogels have porous and smooth surfaces. The dried materials swell from 2400 to 3100%, while the disintegration/dissolution test confirms that the samples present high stability in distilled water throughout 14 days. These hydrogels are superabsorbent materials and can be applied in agriculture as soil conditioners.

Concentration-independent mechanics and structure of hagfish slime

The defense mechanism of hagfish slime is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a concentrated material into a comparably "infinite" sea of water to form a dilute, sticky, cohesive elastic gel. This raises questions about the robustness of gel formation and rheological properties across a range of concentrations, which we study here for the first time. Across a nearly 100-fold change in concentration, we discover that the gel has similar viscoelastic time-dependent properties with constant power-law exponent (α=0.18±0.01), constant relative damping tanδ=G^''/G^'≈0.2-0.3, and varying overall stiffness that scales linearly with the concentration (∼c^0.99±0.05). The power-law viscoelasticity (fit by a fractional Kelvin-Voigt model) is persistent at all concentrations with nearly constant fractal dimension. This is unlike other materials and suggests that the underlying material structure of slime remains self-similar irrespective of concentration. This interpretation is consistent with our microscopy studies of the fiber network. We derive a structure-rheology model to test the hypothesis that the origins of ultra-soft elasticity are based on bending of the fibers. The model predictions show an excellent agreement with the experiments. Our findings illustrate the unusual and robust properties of slime which may be vital in its physiological use and provide inspiration for the design of new engineered materials.

STATEMENT OF SIGNIFICANCE

Hagfish produce a unique gel-like material to defend themselves against predator attacks. The successful use of the defense gel is remarkable considering that hagfish cannot control the concentration of the resulting gel directly; they simply exude a small quantity of biomaterial which then expands by a factor of 10,000 (by volume) into an "infinite" sea of water. This raises questions about the robustness of gel formation and properties across a range of concentrations. This study provides the first ever understanding of the mechanics of hagfish slime over a very wide range of concentration. We discover that some viscoelastic properties of slime are remarkably constant regardless of its concentration. Such a characteristic is uncommon in most known materials.

Effects of Mixing Ratio and pH on the Electrostatic Interactions of Hydrolyzed Alaska Pollock Protein and κ-Carrageenan

In order to widen the application of Alaska Pollock salt-soluble protein and improve the properties of κ-carrageenan (KC), we evaluated whether the electrostatic interaction between KC and hydrolyzed protein (HP) improved the solubility of salt-soluble proteins and assessed acid hydrolysis-induced changes in the viscosity of KC. Moreover, we determined the effects of pH, KC, and HP mixing weight ratio (R, from 1:8 to 8:1) on the properties of mixtures. ζ-Potential results demonstrated that there were electrostatic interactions between KC and HP. Results of solution transmission and precipitation diagram analysis demonstrated that increasing the ratio of KC in KC-HP mixtures expanded the pH range of HP water solubility and prevented HP from precipitating, even at pH values around the pI. The highest viscosity of the solution measured by rheology analysis occurred at pH 3.5, and the ratio of KC:HP (R) was 1:1. These findings suggested that Alaska Pollock protein could be modified appropriately for use in acidic solutions and semisolid foods; moreover, KC-HPs have a potential application as thickeners in acid condition.

PRACTICAL APPLICATION

These findings suggested that Alaska Pollock protein could be modified appropriately for use in acidic solutions and semisolid foods and that KC-HP may have applications as a new acid thickener.

High Performances of Artificial Nacre-Like Graphene Oxide-Carrageenan Bio-Nanocomposite Films

This study was inspired by the unique multi-scale and multi-level ‘brick-and-mortar’ (B&M) structure of nacre layers. We prepared the B&M, environmentally-friendly graphene oxide-carrageenan (GO-Car) nanocomposite films using the following steps. A natural polyhydroxy polymer, carrageenan, was absorbed on the surface of monolayer GO nanosheets through hydrogen-bond interactions. Following this, a GO-Car hybridized film was produced through a natural drying process. We conducted structural characterization in addition to analyzing mechanical properties and cytotoxicity of the films. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses showed that the nanocomposite films had a similar morphology and structure to nacre. Furthermore, the results from Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Thermogravimetric (TG/DTG) were used to explain the GO-Car interaction. Analysis from static mechanical testers showed that GO-Car had enhanced Young’s modulus, maximum tensile strength and breaking elongation compared to pure GO. The GO-Car nanocomposite films, containing 5% wt. of Car, was able to reach a tensile strength of 117 MPa. The biocompatibility was demonstrated using a RAW264.7 cell test, with no significant alteration found in cellular morphology and cytotoxicity. The preparation process for GO-Car films is simple and requires little time, with GO-Car films also having favorable biocompatibility and mechanical properties. These advantages make GO-Car nanocomposite films promising materials in replacing traditional petroleum-based plastics and tissue engineering-oriented support materials.