Characterization of Association and Gelation of Pectin in Methanol−Water Mixtures

Chemical Composition and Rheological Properties of Seed Mucilages of Various Yellow- and Brown-Seeded Flax (Linum usitatissimum L.) Cultivars

When seeds sown in the soil become wet, their hulls secrete viscous matter that can retain water and thus support germination. Flaxseed mucilage (FSM) is an example of such a material and is attractive for food, cosmetic, and pharmaceutical applications due to its suitable rheological properties. FSM consists mainly of two polysaccharides, namely, arabinoxylan and rhamnogalacturonan I, and it also contains some proteins, minerals, and phenolic compounds. The genotype and the year of the flax harvest can significantly affect the composition and functional properties of FSM. In this work, FSM samples were isolated from flax seeds of different cultivars and harvest years, and their structural and rheological properties were compared using statistical methods. The samples showed significant variability in composition and rheological properties depending on the cultivar and storage time. It was found that the ratio of two polysaccharide fractions and the contribution of less-prevalent proteins are important factors determining the rheological parameters of FSM, characterizing the shear-thinning, thixotropic, and dynamic viscoelastic behavior of this material in aqueous solutions. The yield strength and the hysteresis loop were found to be associated with the contribution of the pectin fraction, which included homogalacturonan and rhamnogalacturonan I. In contrast, the shear-thinning and especially the dynamic viscoelastic properties depended on the arabinoxylan content. Proteins also affected the viscoelastic properties and maintained the elastic component of FSM in the solution. The above structural and rheological characteristics should be taken into account when considering effective applications for this material.

Hydrogels based on low-methoxyl amidated citrus pectin and flaxseed gum formulated with tripeptide glycyl-l-histidyl-l-lysine improve the healing of experimental cutting wounds in rats

Hydrogels based on natural and modified polysaccharides represent growing group of suitable matrices for the construction of effective wound healing materials. Bioactive tripeptide glycyl-l-histidyl-l-lysine and amino acid α-l-arginine are known to accelerate wound healing and skin repair. In this study, hydrogels based on low-methoxyl amidated citrus pectin or flaxseed gum were prepared and used for the transport of these healing agents to the experimental cutting wounds affected by extensive skin damage. Fourier-transform infrared spectroscopy, rheology, differential scanning calorimetry, scanning electron microscopy, swelling and release tests confirmed that these hydrogels differed in structure and physical properties. The cationic tripeptide was found to bind to carboxylic groups in LMA pectin, and the C3OH hydroxyl and ring oxygen O5 are involved in this interaction. The pectin hydrogel showed high viscosity and strong elastic properties, while the flaxseed gum hydrogel was characterised as a viscoelastic system of much lower viscosity. The former hydrogel released the drugs very slowly, while the latter hydrogel demonstrated zero order releasing kinetics optimal for drug delivery. In the in vivo wound healing testing on rats, both polysaccharide hydrogels improved the healing process mediated by the mentioned biomolecules. The tripeptide applied in the hydrogels showed significantly higher healing degree and lower healing time than in the control animals without treatment and when it was applied in an aqueous solution. Despite the absence of a synergistic effect, the mixture of the tripeptide and α-l-arginine in the hydrogels was also quite effective in wound healing. According to histological analysis, complete healing was achieved only when using the tripeptide in the flaxseed gum hydrogel. These observations might have an important prospect in clinical application of polysaccharide hydrogels.

Multi-scale pectin/polyphenol beads for non-fouling fluorescence tracking on soft matter under water

The smart polyphenol material could be designed to form two competitive interactions related to same one polyphenol molecule with different objects that could easily adhere to one surface through the weak interaction, and also could be entirely removed from the same surface by the strong interaction. In this study, the multi-scale pectin beads were fabricated by crosslinking with ions that could be acted as polyphenol loading agent through electrostatic force between the ions loading on the surface of pectin beads and polyphenol. The two effects on the size and appearance of pectin beads were detected. Because of the hydrogen bond between polyphenols loading on the beads and the surface of target, fluorescence-functionalized beads could easily adhere on target surfaces. Meanwhile, attributing to stronger electrostatic force between surface ions on beads and polyphenol, the thin membrane made of the beads can be entirely removed from the target surface to avoid the pollution of fluorescence probes.

Rheological and Mechanical Behavior of Silk Fibroin Reinforced Waterborne Polyurethane

Waterborne polyurethane (WPU) is a versatile and environment-friendly material with growing applications in both industry and academia. Silk fibroin (SF) is an attractive material known for its structural, biological and hemocompatible properties. The SF reinforced waterborne polyurethane (WPU) is a promising scaffold material for tissue engineering applications. In this work, we report synthesis and characterization of a novel nanocomposite using SF reinforced WPU. The rheological behaviors of WPU and WPU-SF dispersions with different solid contents were investigated with steady shear and dynamic oscillatory tests to evaluate the formation of the cross-linked gel structure. The average particle size and the zeta potential of WPU-SF dispersions with different SF content were examined at 25 °C to investigate the interaction between SF and WPU. FTIR, SEM, TEM and tensile testing were performed to study the effects of SF content on the structural morphology and mechanical properties of the resultant composite films. Experimental results revealed formation of gel network in the WPU dispersions at solid contents more than 17 wt %. The conjugate reaction between the WPU and SF as well as the hydrogen bond between them helped in dispersing the SF powder into the WPU matrix as small aggregates. Addition of SF to the WPU also improved the Young's modulus from 0.30 to 3.91 MPa, tensile strength from 0.56 to 8.94 MPa, and elongation at break from 1067% to 2480%, as SF was increased up to 5 wt %. Thus, significant strengthening and toughening can be achieved by introducing SF powder into the WPU formulations.

Impact of solvent quality on the network strength and structure of alginate gels

The influence of the mixture of water and alcohols on the solubility and properties of alginate and its calcium-induced gels is of interest for the food, wound care and pharmaceutical industries. The solvent quality of water with increasing amounts of ethanol (0-20%) on alginate was studied using intrinsic viscosity. The effect of ethanol addition on the rheological and mechanical properties of calcium alginate gels was determined. Small-angle X-ray scattering and transmission electron microscopy were used to study the network structure. It is shown that the addition of ethanol up to 15% (wt) increases the extension of the alginate chain, which correlates with increased moduli and stress being required to fracture the gels. The extension of the polymer chain is reduced at 20% (wt) ethanol, which is followed by reduced moduli and stress at breakage of the gels. The network structure of gels at high ethanol concentrations (24%) is characterized by thick and poorly connected network strands.

Effect of salts on gelation and drug release profiles of methylcellulose-based ophthalmic thermo-reversible in situ gels

The poor bioavailability and therapeutic response exhibited by conventional ophthalmic solutions may be overcome by the use of thermo-reversible in situ gel. The purpose of this study was to examine the influence of different salts on the gelation, rheology and drug release of in situ gel based on methylcellulose. The gel temperature of 1% w/v methylcellulose (MC) was 60?C. It was found that 5?7% w/v sodium chloride (NaCl), 8?9% w/v potassium chloride (KCl), or 5% w/v sodium bicarbonate (NaHCO(3)) was capable of decreasing the gel temperature below physiological temperature, i.e. 37?C. Rheological studies indicated a large increase in viscosity at 37?C with the addition of salts in MC solutions. The duration of drug release from MC solution was 1.5?h. The significant observation was that the duration of drug release increased from 1.5?h to 3?5?h from salted MC solutions depending on the concentration and the type of salt. So, it can be concluded that the salted MC solutions were a better alternative than the MC solution to enhance the ocular bioavailability of the drug.

In situ crosslinkable hydrogel formed from a polysaccharide-based hydrogelator

In situ crosslinkable hydrogel formed from an amphiphilic amylopectin-based hydrogelator in aqueous solution was investigated with respect to its viscoelasticity, structure as well as protein encapsulation and release. Different from the physical hydrogel formed from an aqueous amylopectin system of sufficiently high concentration, such a hydrogel could be formed rapidly at room temperature and exhibit enhanced viscoelastic properties, mechanical strength, and shear thinning behavior. In addition, it has a more complex network structure with a higher fractal dimension due to intermolecular hydrophobic interactions and macromolecular chain entanglements. By circular dichroism analyses and in vitro release experiments, this hydrogel material was found to have a great potential as new matrix for the entrapment and sustained release of bovine serum albumin.

Influence of Water Content on the Self-Assembly of Metal−Organic Frameworks Based on Pyridine-3,5-dicarboxylate

A 0D discrete molecule [Co(3,5-pdc)(H2O)5].2H2O (1) was obtained in quantitative yield from the reaction of CoCl2.6H2O and pyridine-3,5-dicarboxylate (3,5-pdc) in pure water solvent at ambient temperature. While a 1D zigzag chain species, [{Co(3,5-pdc)(H2O)4}.H2O]n (2), was produced in a water-rich environment, a 2D layer compound, [Co(3,5-pdc)(H2O)2]n (3), with a 6(3) topology was generated under a water-reduced condition and a 2D sheet structure, [{Cu(3,5-pdc)(py)2}.H2O.EtOH]n (4), was formed under a water-poor condition. Compounds 1, 2, and 4 were characterized by single-crystal X-ray diffraction analysis. The 1D zigzag chain 2 shows a recoverable collapsing property. Compound 4 adopts a 2D sheet structure with a 4.8(2) topology, observed for the first time for the 3,5-pdc-related metal-organic frameworks. Water content was found to be an important factor in determining the topologies of the products in the self-assembly of divalent metal ions (Co2+, Cu2+) and pyridine-3,5-dicarboxylate under mild conditions.

Altering Associations in Aqueous Solutions of a Hydrophobically Modified Alginate in the Presence of β-Cyclodextrin Monomers

The formation of associative networks in semidilute aqueous solutions of hydrophobically modified alginate (HM-alginate) is dependent on intermolecular hydrophobic interactions. Addition of beta-cyclodextrin (beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. This results in a dramatic decrease in the viscoelastic response of the system and a more extended local structure of the polymer chains, as shown by small-angle neutron scattering (SANS) measurements. The zero-shear viscosity decreases about an order of magnitude when the beta-CD concentration is increased from 0 to 12 mm. The lifetime of the associative network decreases strongly with increasing levels of beta-CD addition. These findings clearly demonstrate that the hydrophobic association effect is efficiently reduced as the amount of beta-CD is increased. In the framework of drug delivery, this effect may be useful to improve the release of therapeutic molecules that can be entrapped in the polymer matrix.