Chitosan, xanthan and locust bean gum matrices crosslinked with β-cyclodextrin as green sorbents of aromatic compounds

Three different polysaccharides, xanthan gum, chitosan and locust bean gum, were crosslinked with or without β-cyclodextrin, using citric acid in different ratios, to create ‘green’ hydrogel matrices. The crosslinking of these polysaccharides was produced through an inexpensive and innocuous solvent-free synthesis process. A favorable swelling behavior of the hydrophilic matrices facilitates the sorption of the solutes tested. Interestingly, the amount of β-cyclodextrin groups is not the only factor to yield the best sorption capability for hydrophobic model molecules: polysaccharides themselves also influence the sorption depending on their characteristic functional groups, the conformation of their chains and, as mentioned above, their degrees of swelling. In order to ascertain the effect of the polysaccharides on the sorption capabilities of a model sorbate (1-naphthol), isotherms using a wide range of solute concentrations were analyzed, and the Hill equation yielded the best fitting results and provided some insight into the mechanisms of interaction

Non-covalent hydrogels of cyclodextrins and poloxamines for the controlled release of proteins

Different types of gels were prepared by combining poloxamines (Tetronic), i.e. poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) octablock star copolymers, and cyclodextrins (CD). Two different poloxamines with the same molecular weight (ca. 7000) but different molecular architectures were used. For each of their four diblock arms, direct Tetronic 904 presents PEO outer blocks while in reverse Tetronic 90R4 the hydrophilic PEO blocks are the inner ones. These gels were prepared by combining α-CD and poloxamine aqueous solutions. The physicochemical properties of these systems depend on several factors such as the structure of the block copolymers and the Tetronic/α-CD ratio. These gels were characterized using differential scanning calorimetry (DSC), viscometry and X-ray diffraction measurements. The 90R4 gels present a consistency that makes them suitable for sustained drug delivery. The resulting gels were easily eroded: these complexes were dismantled when placed in a large amount of water, so controlled release of entrapped large molecules such as proteins (Bovine Serum Albumin, BSA) is feasible and can be tuned by varying the copolymer/CD ratio

Self-assembled supramolecular gels of reverse poloxamers and cyclodextrins

A series of supramolecular aggregates were prepared using a poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) block copolymer and β- or α-cyclodextrins (CD). The combination of β-CD and the copolymer yields inclusion complexes (IC) with polypseudorotaxane structures. These are formed by complexation of the PPO blocks with β-CD molecules producing a powder precipitate with a certain crystallinity degree that can be evaluated by X-ray diffraction (XRD). In contrast, when combining α-CD with the block copolymer, the observed effect is an increase in the viscosity of the mixtures yielding fluid gels. Two cooperative effects come into play: the complexation of PEO blocks with α-CD and the hydrophobic interactions between PPO blocks in aqueous media. These two combined interactions lead to the formation of a macromolecular network. The resulting fluid gels were characterized using different techniques such as differential scanning calorimetry (DSC), viscometry and XRD measurements

Locust bean gum, a vegetable hydrocolloid with industrial and biopharmaceutical applications

Locust bean gum (LBG), a vegetable galactomannan extracted from carob tree seeds, is extensively used in the food industry as a thickening agent (E410). Its molecular conformation in aqueous solutions determines its solubility and rheological performance. LBG is an interesting polysaccharide also because of its synergistic behavior with other biopolymers (xanthan gum, carrageenan, etc.). In addition, this hydrocolloid is easily modified by derivatization or crosslinking. These LBG-related products, besides their applications in the food industry, can be used as encapsulation and drug delivery devices, packaging materials, batteries, and catalyst supports, among other biopharmaceutical and industrial uses. As the new derivatized or crosslinked polymers based on LBG are mainly biodegradable and non-toxic, the use of this polysaccharide (by itself or combined with other biopolymers) will contribute to generating greener products, considering the origin of raw materials used, the modification procedures selected and the final destination of the products

Phase behavior of reverse poloxamers and poloxamines in water

The phase behavior of two types of poly(ethylene oxide)/ poly(propylene oxide) (PEO/PPO) copolymers in aqueous solutions was studied by light scattering, viscometry and infrared spectroscopy. Both the reverse poloxamer (Pluronic 10R5) and the star type poloxamine (Tetronic 90R4) have practically the same PEO/PPO ratio with their hydrophobic blocks (PPO) located in the outer part. The temperature-composition phase diagrams show that both 10R5 and 90R4 tend to form aggregates in water. Up to four different phases can be detected in the case of Tetronic 90R4 for each temperature: unimers, random networks, micellar networks and macrophase separation. Viscometric and infrared measurements complemented the results obtained by light scattering and visual inspection

Síntesis y caracterización de polímeros de ciclodextrina. Aplicación a la liberación de fármacos

Cyclodextrins (CD) are cyclic oligosaccharides which have been widely employed for pharmaceutical applications. CD based hydrogels have been synthesized by the crosslinking reaction with epichlorohydrin using αCD, ßCD, γCD, and 50:50 mixtures of α/ßCD and ß/γCD, at different synthesis temperatures. These gels have been characterized by measuring their swelling capacity, mechanical behavior, thermal properties and pore size distribution. The hydrogels synthesized at higher temperatures present a higher swelling capacity, due to the self-polymerization of epichlorohydrin, yielding a more expanded reticular structure with pores of higher diameter. Mechanical assays show that a lower synthesis temperature leads to stronger and harder polymers, according with a lower swelling capacity. Polymers containing different CD types and synthesized at the same temperature present similar reticular structures. In order to investigate the sorption capacity of these hydrogels toward different solutes, five model molecules have been selected: phenol, 3-nitrophenol, 4-nitrophenol, 1-naphthol, and the antiinflamatory drug diflunisal. The amounts sorbed have been related to the different affinities of CDs to the solutes. Drug delivery of two antiinflammatory (naproxen and nabumetone) and two antifungal drugs (naftifine and terbinafine) from ßCD polymer discs has been investigated. Drug release kinetics were carried out at physiological conditions of pH and temperature, and kinetic and diffusion constants were calculated. The drug release followed a simple Fickian diffusion mechanism for all the model drugs. Also, diffusion coefficients were calculated according to the simplified Higuchi model. Naproxen was also used to perform release assays from polymers containing different CDs. The βCD polymer showed the highest amount of drug loaded and the lowest one corresponds to the polymer containing αCD, in agreement with the affinities for naproxen of the corresponding cyclodextrins. It can be inferred that a simple Fickian diffusion mechanism occurs, except for the mixed polymers at pH 1.2 (anomalous transport) and in the case αCDP at pH 7.0 (burst phenomenon). Furthermore, the diffusion and relaxation contributions have been determined for the mixed polymers in order to achieve progress in the design of new polymer matrices according to the structure of the selected drugs

Solventless crosslinking of chitosan, xanthan, and locust bean gum networks functionalized with beta-Cyclodextrin

The incorporation of cyclodextrins into polymeric crosslinked gels of hydrophilic nature can be useful for promoting the sorption of hydrophobic molecules and/or modulating the release of active principles. The covalent addition of these excipients to the matrix integrates their solubilizing effect that can contribute to increase the capacity of retention of hydrophobic substances. In this study, three diverse polysaccharides, chitosan, xanthan gum, and locust bean gum, were crosslinked with or withoutβ-cyclodextrin, using citric acid in different ratios, to create hydrogel matrices. Through a green synthetic path, the efficient production of soluble and insoluble (hydrogel) networks functionalized with β-cyclodextrin was achieved by means of a solventless procedure. The characterization of their chemical composition, swelling in water, and their sorption and release behavior were also carried out in this work

Interpenetrated polymer networks of Poly(β-cyclodextrin) and Polyvinylpyrrolidone with synergistic and selective sorption capacities

Interpenetrating polymer network (IPN) hydrogels were synthesised using β-cyclodextrin (β-CD) and N-vynil-2-pyrrolidone (NVP) crosslinked with epichlorohydrin and divinylbenzene, respectively, and prepared by four different procedures: simultaneous, sequential, hybrid and a novel one named hybrid-sequential. The IPNs prepared have been characterised by infrared spectroscopy and thermal analysis. The equilibrium swelling in water and the sorption of model substances into the IPNs have also been studied. The model sorbates (1-naphthol, 2-acetylnaphthalene and tannic acid) were selected according to the affinities towards each one of the two constituent polymers. Our studies reveal that these IPNs can be applied for the sorption of substances that can interact with the network by two mechanisms, i.e. inclusion within cyclodextrin cavities and/or via specific interactions with the functional groups present. Besides, due to the complementary character of their constituent polymers, these networks could also serve to retain two substances of different nature such as cetirizine and pseudoephedrine

Cyclodextrin-grafted TiO2 nanoparticles: synthesis, complexation capacity, and dispersion in polymeric matrices

The modification of the surface of titanium dioxide nanoparticles (TiO2 NPs) by the incorporation of cyclodextrins (CDs), cyclic oligosaccharides with a hydrophobic cavity, can largely improve the functionality of TiO2 by lodging molecules of interest in the CD to act directly on the surface of the nanoparticles or for further release. With this aim, we have synthesized beta CD-modified nanoparticles (beta CDTiO2 NPs) by a two-step reaction that involves the incorporation of a spacer and then the linking of the macrocycle, and characterized them by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The capacity of the functionalized structures to trap model compounds (Rhodamine and 1-naphthol) has been compared to that of bare TiO2 NPs by fluorescence and Ultraviolet-visible (UV-visible) spectroscopy. The presence of the CDs on the surface of the TiO2 avoids the photo-degradation of the guest, which is of interest in order to combine the photocatalytic activity of TiO2, one of its most interesting features for practical purposes, with the delivery of compounds susceptible of being photo-degraded. The beta CDTiO2 NPs have been dispersed in polymeric matrices of frequently used polymers, polyethylene (LDPE) and polyethylene oxide (PEO), by cryogenic high energy ball milling to produce nanocomposites in the form of films. The surface modification of the nanoparticles favors the homogenization of the filler in the matrix, while the nanoparticles, either in bare or functionalized form, do not seem to alter the crystallization properties of the polymer at least up to a 5% (w/w) load of filler

In-vitro release from reverse poloxamine/α-cyclodextrin matrices. Modelling and comparison of dissolution profiles

ABSTRACT: Gels obtained by complexation of octablock star PEO/PPO copolymers (Tetronic 90R4) with α-CD were evaluated as matrices for drug release. Both molecules are biocompatible so they can be potentially applied to drug delivery systems. Two different types of matrices of Tetronic 90R4 and α-CD were evaluated: gels and tablets. These gels are capable to gelifying in-situ and show sustained erosion kinetics in aqueous media. Tablets were prepared by freeze drying and comprising the gels. Using these two different matrices the release of two model molecules, L-Tryptophan (Trp), and a protein, bovine serum albumin (BSA), was evaluated. The release profiles of these molecules from gels and tablets prove that they are suitable for sustained delivery. Mathematical models were applied to the release curves from tablets in order to elucidate the drug delivery mechanism. Good correlations were found for the fittings of the release curves to different equations. The results point that the release of Trp from different tablets is always governed by Fickian diffusion while the release of BSA is governed by a combination of diffusion and tablet erosion