Hydrophobically Modified Xanthan: An Amphiphilic but Not Associative Polymer

Amidation of arabinoglucuronoxylans to modulate their flow behavior

Arabinoglucuronoxylans obtained from the exudate of Cercidium praecox (Brea gum) were subjected to an amidation reaction to modulate their flow behavior to obtain a product with similar behavior to gum Arabic. The amidation reaction of the uronic acids present in this exudate was studied using the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) system with the aim of maximizing product yield and minimizing by-product. An analysis of the significant factors involved in the reaction was carried out and a response surface methodology was conducted to optimize the stoichiometry of the reagents used. It was possible to obtain models for predicting the degree of amidation (DA) of arabinoglucuronoxylans and the formation of by-products. The formation of a secondary product derived from the amino acid β-alanine which has not been reported previously in the reaction with polysaccharides, was described. The flow behavior of an amidated product (DA = 52 %) was determined, showing a pseudoplastic behavior and a decreased Newtonian viscosity (η0 = 36.2 Pa s) at the lowest shear rate range with respect to native product solution (η0 = 115 Pa s). Amidated arabinoglucuronoxylans had a flow behavior more similar to that of gum Arabic.

An Innovative Methodology to Characterize, at the Molecular Scale, Interactions in Polysaccharide Aqueous Solutions

Characterizing molecular interactions at the microscopic level remains difficult and, therefore, represents a key target to better understand macromolecule and biomacromolecule behaviors in solution, alone, or in mixtures with others. Therefore, accurate characterization in liquid media, especially in aqueous solutions, without causing any perturbation of the system in which they are studied, is quite difficult. To this purpose, the present paper describes an innovative methodology based on fluorescence spectrophotometry. Two molecular fluorescent probes, namely 8-anilino-1-naphtalenesulfonic acid (ANS) and 2-benzofuryl-3-hydroxy-4(1H)-quinolone (3HQ-Bf), were selected to characterize, respectively, the dipole-dipole interactions and hydrophobic micro-domains, for the first one, and hydrogen bonding, for the second. As a support to study molecular interactions, xanthan, galactomannan, and corresponding mixtures of these substances which are well known to exhibit a synergy of interactions in well-defined mixture conditions were chosen. Once the methodology was set up, the existence of the three types of interactions in these systems was demonstrated, thus allowing the elucidation of the mechanisms of interactions at the molecular scale.

Modification of chicha gum: Antibacterial activity, ex vivo mucoadhesion, antioxidant activity and cellular viability

The aim of the present work was to modify the exuded gum of Sterculia striata tree by an amination reaction. The viscosity and zero potential of the chicha gum varied as a function of pH. The modification was confirmed by X-ray diffraction (XRD), infrared spectroscopy (FTIR), size exclusion chromatography (SEC), zeta potential, thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). Furthermore, the chemical modification changed the molar mass and surface charge of the chicha gum. In addition, the gums were used in tests for ex vivo mucoadhesion strength, antibacterial activity against the standard strain of Staphylococcus aureus (ATCC 25923), inhibitory activity of α-glucosidase, antioxidant capacity, and viability of Caco-2 cells. Through these tests, it was found that amination caused an increase in the mucoadhesive and inhibitory activity of chicha gum against the bacterium Staphylococcus aureus. In addition, the gums (pure and modified) showed antioxidant capacity and an inhibitory effect against the α-glucosidase enzyme and did not show cytotoxic potential.

Zwitterionic polymer modified xanthan gum with collagen II-binding capability for lubrication improvement and ROS scavenging

High friction of damaged cartilage requires long-acting lubricated additive, which can also effectively scavenge reactive oxidative species (ROS) produced by mechanically stimulated chondrocytes. In this study, xanthan gum (XG) was grafted by poly (sulfobetaine methacrylate) (PSBMA) (the [XG]/[SBMA] molar ratio is 1:5 or 1:10), forming nanoparticles and then conjugated with collagen II-binding peptide, finally obtaining CBPXGSB1/5 or CBPXGSB1/10. Therein, the CBPXGSB1/5 was chosen as optimal lubricated additive. The results show that hydrated effect of PSBMA side chains endows CBPXGSB1/5 with favorable lubrication property (COF is 0.063). Furthermore, the CBPXGSB1/5 combining lubrication property and specific binding capability together may achieve the long-acting lubrication for injured cartilage in medical field. The CBPXGSB1/5 also possesses antioxidation verified by DPPH assay and exhibits synergistically enhanced ROS (OH, O₂^- and H₂O₂) scavenging. Besides, cytotoxicity experiment demonstrates that CBPXGSB1/5 has good biocompatibility. Therefore, multifunctional CBPXGSB1/5 developed here may have promising application potential in osteoarthritis treatment.

A review of the enzymatic, physical, and chemical modification techniques of xanthan gum

Xanthan gum (XG), a bacterial polysaccharide has numerous valuable characteristics in the food, biomedical, pharmaceuticals, and agriculture sector. However, XG has also its particular limitations such as its vulnerability to microbial contamination, inadequate mechanical and thermal stability, unusable viscosity, and poor water solubility. Therefore, XG's structure and conformation need to be modified enzymatically, chemically, or physically to improve its optimistic features and decrease the formation of crystals, increase antioxidant ability, and radical scavenging activity. We have found out different means to modify XG and elaborate the importance and significance of the modified structure of XG. In this review, different enzymes are reviewed for XG degradation, which modifies their structure from different points (main chain or side chain). This article also reviews various physical methods (ultrasound, shear, pressure, sonication, annealing, and heat treatments) based on prevailing publications to alter XG conformation and produce low molecular weight (LMW) and less viscous end-product. Moreover, some chemical means are also discussed that result in modified XG through crosslinking, grafting, acetylation, pyruvation, as well as by applying different chemical agents. Overall, the current progress on XG degradation is very auspicious to develop a new molecule with considerable uses, in various industries with future assessments.

Microwave-initiated rapid synthesis of phthalated cashew gum for drug delivery systems

Chemical modification of polysaccharides is an important approach for their transformation into customized matrices that suit different applications. Microwave irradiation (MW) has been used to catalyze chemical reactions. This study developed a method of MW-initiated synthesis for the production of phthalated cashew gum (Phat-CG). The structural characteristics and physicochemical properties of the modified biopolymers were investigated by FTIR, GPC, ¹H NMR, relaxometry, elemental analysis, thermal analysis, XRD, degree of substitution, and solubility. Phat-CG was used as a matrix for drug delivery systems using benznidazole (BNZ) as a model drug. BNZ is used in the pharmacotherapy of Chagas disease. The nanoparticles were characterized by size, PDI, zeta potential, AFM, and in vitro release. The nanoparticles had a size of 288.8 nm, PDI of 0.27, and zeta potential of -31.8 mV. The results showed that Phat-CG has interesting and promising properties as a new alternative for improving the treatment of Chagas disease.

Natural Hydrogels Applied in Photodynamic Therapy

Natural hydrogels are three-dimensional (3D) water-retaining materials with a skeleton consisting of natural polymers, their derivatives or mixtures. Natural hydrogels can provide sustained or controlled drug release and possess some unique properties of natural polymers, such as biodegradability, biocompatibility and some additional functions, such as CD44 targeting of hyaluronic acid. Natural hydrogels can be used with photosensitizers (PSs) in photodynamic therapy (PDT) to increase the range of applications. In the current review, the pertinent design variables are discussed along with a description of the categories of natural hydrogels available for PDT.

Poly(N-isopropylacrylamide) based thin microgel films for use in cell culture applications

Poly(N-isopropylacrylamide) (PNIPAm) is widely used to fabricate cell sheet surfaces for cell culturing, however copolymer and interpenetrated polymer networks based on PNIPAm have been rarely explored in the context of tissue engineering. Many complex and expensive techniques have been employed to produce PNIPAm-based films for cell culturing. Among them, spin coating has demonstrated to be a rapid fabrication process of thin layers with high reproducibility and uniformity. In this study, we introduce an innovative approach to produce anchored smart thin films both thermo- and electro-responsive, with the aim to integrate them in electronic devices and better control or mimic different environments for cells in vitro. Thin films were obtained by spin coating of colloidal solutions made by PNIPAm and PAAc nanogels. Anchoring the films to the substrates was obtained through heat treatment in the presence of dithiol molecules. From analyses carried out with AFM and XPS, the final samples exhibited a flat morphology and high stability to water washing. Viability tests with cells were finally carried out to demonstrate that this approach may represent a promising route to integrate those hydrogels films in electronic platforms for cell culture applications.

Xanthan Gum-Konjac Glucomannan Blend Hydrogel for Wound Healing

Hydrogels are considered to be the most ideal materials for the production of wound dressings since they display a three-dimensional structure that mimics the native extracellular matrix of skin as well as a high-water content, which confers a moist environment at the wound site. Until now, different polymers have been used, alone or blended, for the production of hydrogels aimed for this biomedical application. From the best of our knowledge, the application of a xanthan gum-konjac glucomannan blend has not been used for the production of wound dressings. Herein, a thermo-reversible hydrogel composed of xanthan gum-konjac glucomannan (at different concentrations (1% and 2% w/v) and ratios (50/50 and 60/40)) was produced and characterized. The obtained data emphasize the excellent physicochemical and biological properties of the produced hydrogels, which are suitable for their future application as wound dressings.

Xanthan gum derivatives: review of synthesis, properties and diverse applications

Natural polysaccharides are well known for their biocompatibility, non-toxicity and biodegradability. These properties are also inherent to xanthan gum (XG), a microbial polysaccharide. This biomaterial has been extensively investigated as matrices for tablets, nanoparticles, microparticles, hydrogels, buccal/transdermal patches, tissue engineering scaffolds with different degrees of success. However, the native XG has its own limitations with regards to its susceptibility to microbial contamination, unusable viscosity, poor thermal and mechanical stability, and inadequate water solubility. Chemical modification can circumvent these limitations and tailor the properties of virgin XG to fulfill the unmet needs of drug delivery, tissue engineering, oil drilling and other applications. This review illustrates the process of chemical modification and/crosslinking of XG via etherification, esterification, acetalation, amidation, and oxidation. This review further describes the tailor-made properties of novel XG derivatives and their potential application in diverse fields. The physicomechanical modification and its impact on the properties of XG are also discussed. Overall, the recent developments on XG derivatives are very promising to progress further with polysaccharide research.

Due to presence of hydroxy and carboxy functional groups, xanthan gum is amenable to various chemical modification for producing derivatives such as carboxymethyl xanthan and carboxymethyl hydroxypropyl xanthan with desirable properties for end use.

Synthesis, characterization and evaluation of deacetylated xanthan derivatives as new excipients in the formulation of chitosan-based polyelectrolytes for the sustained release of tramadol

This paper addressed the application of deacetylated xanthan (XGDS) and chitosan (CTS) as a mixture blend forming hydrophilic matrices for Tramadol (TD) sustained release tablets. XGDSs derivatives were obtained by alkaline treatment of xanthan gum (XG) with various degrees of deacetylation (DD). The obtained products were characterized in terms of structural, thermal and physicochemical properties. Different tablet formulations containing CTS/XGDSs were prepared by direct compression method and compared to CTS/XG tablets. Flow properties of powder mixtures and pharmaceutical characteristics were evaluated. The dissolution test of TD was realized under simulated gastric and intestinal conditions to achieve drug release more than 24 h. All developed tablets were found conforming to standard evaluation tests. It was shown that CTS/XGDSs matrices ensure a slower release of TD in comparison with CTS/XG based formulations. Meanwhile, increasing DD resulted in a decrease of drug release. In addition, TD release from XGDS matrices was faster at pH (6.8) than at acidic pH (1.2). The matrix tablets based on CTS/XGDS4 (DD = 98.08%) were selected as the best candidates compared to the other systems in prolonging drug release. The optimal formulation was found to release 99.99% of TD after 24 h following a non-Fickian type.

Oral Administration of Salecan-Based Hydrogels for Controlled Insulin Delivery

We present an improved type of food gum (salecan) based hydrogels for oral delivery of insulin. Structural hydrogel formation was assessed with Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. We found that the hydrogel modulus, morphology, and swelling properties can be controlled by varying the salecan dose during hydrogel formation. Insulin was introduced into the hydrogel using a swelling-diffusion approach and then further used a drug prototype. In vitro insulin release profiles demonstrated that the release of entrapped insulin was suppressed in acidic conditions but markedly increased at neutral pH. Cell viability and toxicity tests revealed that the salecan hydrogel constructs were biocompatible. Oral administration of insulin-loaded salecan hydrogels in diabetic rats resulted in a sustained decrease of fasting plasma glucose levels over 6 h postadministration. For nondiabetic animals, the relative pharmacological bioavailability of insulin was significantly larger (6.24%, p < 0.05) for insulin-loaded hydrogels compared to free insulin. These results encourage further development of salecan-based hydrogels as vehicles for controlled insulin delivery following oral administration.

Multiscale Surface-Attached Hydrogel Thin Films with Tailored Architecture

A facile route for the fabrication of surface-attached hydrogel thin films with well-controlled chemistry and tailored architecture on wide range of thickness from nanometers to micrometers is reported. The synthesis, which consists in cross-linking and grafting the preformed and ene-reactive polymer chains through thiol-ene click chemistry, has the main advantage of being well-controlled without the addition of initiators. As thiol-ene click reaction can be selectively activated by UV-irradiation (in addition to thermal heating), micropatterned hydrogel films are easily synthesized. The versatility of our approach is illustrated by the possibility to fabricate various chemical polymer networks, like stimuli-responsive hydrogels, on various solid substrates, such as silicon wafers, glass, and gold surfaces. Another attractive feature is the development of new complex hydrogel films with targeted architecture. The fabrication of various architectures for polymer films is demonstrated: multilayer hydrogel films in which single-networks are stacked one onto the other, interpenetrating networks films with mixture of two networks in the same layer, and nanocomposite hydrogel films where nanoparticles are stably trapped inside the mesh of the network. Thanks to its simplicity and its versatility this novel approach to surface-attached hydrogel films should have a strong impact in the area of polymer coatings.

Novel associative nanoparticles grafted with hydrophobically modified zwitterionic polymer brushes for the rheological control of aqueous polymer gel fluids

Novel associative nanoparticles (ANPs) are synthesized by grafting poly(2-methacryloyloxyethyl phosphorylcholine-co-stearyl methacrylate) polymer brushes on silica nanoparticles by using surface-mediated living radical polymerization.

Submicrometric Films of Surface-Attached Polymer Network with Temperature-Responsive Properties

Temperature-responsive properties of surface-attached poly(N-isopropylacrylamide) (PNIPAM) network films with well-controlled chemistry are investigated. The synthesis consists of cross-linking and grafting preformed ene-reactive polymer chains through thiol-ene click chemistry. The formation of surface-attached and cross-linked polymer films has the advantage of being well-controlled without any caution of no-oxygen atmosphere or addition of initiators. PNIPAM hydrogel films with same cross-link density are synthesized on a wide range of thickness, from nanometers to micrometers. The swelling-collapse transition with temperature is studied by using ellipsometry, neutron reflectivity, and atomic force microscopy as complementary surface-probing techniques. Sharp and high amplitude temperature-induced phase transition is observed for all submicrometric PNIPAM hydrogel films. For temperature above LCST, surface-attached PNIPAM hydrogels collapse similarly but without complete expulsion of water. For temperature below LCST, the swelling of PNIPAM hydrogels depends on the film thickness. It is shown that the swelling is strongly affected by the surface attachment for ultrathin films below ∼150 nm. For thicker films above 150 nm (to micrometers), surface-attached polymer networks with the same cross-link density swell equally. The density profile of the hydrogel films in the direction normal to the substrate is confronted with in-plane topography of the free surface. It results that the free interface width is much larger than the roughness of the hydrogel film, suggesting pendant chains at the free surface.

Injectable thermo-responsive hydrogel composed of xanthan gum and methylcellulose double networks with shear-thinning property

Injectable hydrogel precursor solution was prepared by physical blend of xanthan gum (XG) and methylcellulose (MC) in aqueous solution. Due to the formation of XG network composed of XG double helical strand structure, XG/MC blend was a high viscous solution with good shear-thinning property at room temperature. When the temperature was changed from 23 to 37 °C, thermo-responsive MC network formed, which caused XG/MC blend solution to gelate. The gelation time and storage modulus of the blend can be tuned by XG and/or MC concentrations. Both in vitro and in vivo investigations revealed that the blend solution immediately recovered its high viscosity and rapidly formed hydrogel at body temperature after injection using a syringe. In vivo biocompatibility and biodegradability of the hydrogel were validated by implantation of the hydrogel in rats. In vitro investigation demonstrated that XG/MC blend is a promising injectable hydrogel material for long-term drug delivery.

Injectable shear-thinning xanthan gum hydrogel reinforced by mussel-inspired secondary crosslinking

With a xanthan gum double helical strand network and dopamine-mediated crosslinking network, hydrogels possess injectable properties and enhanced mechanical strength.

Synthesis and evaluation of a novel hydrophobically associating polymer based on acrylamide for enhanced oil recovery

A novel polymerizable hydrophobic monomer 1-(4-dodecyloxy-phenyl)-propenone (DPP) was synthesized by esterification, Frise rearrangement and Williamson etherification; then, the obtained DPP was copolymerized with 2-(acrylamido)-dodecanesulfonic acid (AMC

Conformational transition of a non-associative fluorinated amphiphile in aqueous solution

A non-associative fluorinated amphiphile was synthesized. Instead of self-association at high concentrations, this amphiphile undergoes conformational transition in which the hydrophilic tails wrap around the fluorocarbon core to shield it from water, bearing certain similarity to protein folding in a crowded environment.