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Chitosan (CS) nanosystems have potential applications for the control of microorganisms in the medical, environmental, and agrifood fields. In vivo and in vitro assays of CS nanosystems have experienced increased activity due to improved physicochemical properties, biological activity, and reactivity. Hence, it is important to determine whether their application involves toxicological risks. The aim of this study was to evaluate the mutagenic, cytotoxic, phytotoxic, and in vivo antifungal activity of chitosan-pyrrole-2-carboxylic acid nanobiocomposites (CS-PCA). The CS-PCA nanoparticles were synthesized by means of the nanoprecipitation technique with a size and ζ-potential of 502 ± 72 nm and + 54.7 ± 15.0 mV, respectively. According to the Ames test, no evidence of mutagenic activity was observed in Salmonella typhimurium strains. The cytotoxic assay showed that the incorporation of PCA into the CS matrix increased the toxic effect on ARPE-19 cells. However, fluorescence microscopy of ARPE-19 cells did not reveal morphostructural changes allusive to cell injury. CS-PCA exhibited strong phytotoxicity on lettuce seeds and the complete inhibition of seed development. The antifungal assay demonstrated that the CS-PCA delayed Aspergillus niger infection in tomato fruit until day 3; however, its use for the pre-treatment of seeds might exert adverse effects on plant development.

El quitosano es un polisacárido natural que ha sido utilizado frecuentemente en el desarrollo de distintos materiales, debido a sus excepcionales propiedades fisicoquímicas y biológicas. Las nanopartículas de quitosano son generalmente producidas por estrategias denominadas de construcción (del inglés “bottom up”), donde el ensamblado polimérico es promovido por distintas interacciones moleculares. Sin embargo, un grupo de estrategias llamadas de deconstrucción (del inglés “top-down”) basadas en la fragmentación de estructuras macroscópicas, han generado un gran interés recientemente como alternativa para la obtención de nanomateriales. El presente trabajo hace una revisión bibliográfica de los resultados obtenidos por distintas investigaciones sobre la producción de sistemas de nanopartículas basadas en quitosano durante las últimas décadas. Las evidencias demostraron que las nanopartículas de quitosano juegan un papel preponderante en la investigación de los nanomateriales poliméricos con aplicaciones biomédicas y farmacéuticas, debido a la gran diversidad de métodos de obtención existentes que determinan las propiedades de los materiales, tales como tamaño de partícula, capacidad de incorporación y liberación de compuestos bioactivos, carga superficial, mucoadhesividad, entre otras.

This work aimed to design a synthetic route under mild conditions allowing the main chitosan chain to be grafted with β-cyclodextrin (β-CD) and poly(N-isopropyl acrylamide) (PNIPAm), at C2 and C6 positions, respectively. For this reason, the regioselectivity of proposed reactions is an important factor to be considered. β-CD is an oligosaccharide with a cyclic structure capable of forming inclusion complexes with hydrophobic molecules. Grafting β-CD onto the chitosan backbone by reductive N-alkylation at C2 position was carried out. With this purpose, the previous preparation of β-CD monoaldehyde was required. PNIPAm is a thermosensitive polymer with a transition temperature near 33 °C. To regioselectively anchor poly(N-isopropyl acrylamide) chains onto chitosan at C6 position, it was required to attach at the C6 position of chitosan an alkyl group for the subsequent grafting of PNIPAm-N3 by means of copper-catalyzed azide-alkyne cycloaddition click reaction. To guarantee the regioselectivity of the functionalization of chitosan with a C6 terminal alkyne, its oxyalkylation with glycidyl propargyl ether in a solvent composed of LiOH/KOH/urea was used. The structure of all derivatives was confirmed by FT-IR and 1H-NMR spectroscopy.

The materials produced by the supercritical CO drying have outstanding properties that allow the incorporation of molecules in their porous structure. In this context, dried chitosan nanoparticles including β-lactoglobulin were obtained. First, the nanoparticles in water suspension were produced by ionotropic gelation incorporating the protein with high loading efficiency. Later, solvent exchange and CO supercritical drying procedures were performed. The physicochemical characteristics and structural properties were determined, demonstrating a stable porous structure in the dried materials and corroborating the presence of the protein after the drying. The CO supercritical dried chitosan nanoparticles can be effectively resuspended in acidic aqueous medium remaining in the nanoscale with minimum effect on the loading parameters. The release of the β-lactoglobulin was highly influenced by the pH, reaching around 40% under acidic conditions in ten hours. The obtained results demonstrate the possibility to apply these chitosan materials as a controlled release material., The authors want to acknowledge the financial support of CONACYT through the Project CB-2011-01-169626 and the fellowship DC2013-256 for FJCL. Similarly, it is highly appreciated the valuable input of the Biomaterials Research Group of the ICTP and the technical staff of the Biopolymers Research Group of CIAD.

Herein are reported the production and characteristics of chitosan nanoparticles that go through supercritical CO2 drying. First, chitosan nanoparticles in aqueous colloidal suspension were produced by ionic crosslinking with sodium tripolyphosphate. The produced nanoparticles have a surface charge (ζ-potential) of +27 mV and an average diameter of approximately 100 nm, measured by dynamic light scattering and field emission-scanning electron microscopy observations. The liquid phase of the nanoparticle suspension was replaced successively with ethanol and supercritical CO2 to produce dried chitosan nanoparticles finally. The main characteristics of the obtained nanoparticles were determined by diverse analytical techniques. Infrared spectroscopy, solid-state 13C nuclear magnetic resonance and X-ray diffraction studies were performed to explore possible physicochemical changes induced by the drying procedure. Also, the thermal stability of the dry chitosan nanoparticles was determined by thermogravimetric assay and dynamic scanning calorimetry. Structural properties were analyzed and compared with lyophilized nanoparticles finding that the supercritically dried chitosan nanoparticles have a surface area an order of magnitude higher. Microscopy images showed that the supercritically dried chitosan nanoparticles have a porous conglomerated structure, suggesting that there is particle aggregation through the drying process. Notwithstanding, the dry chitosan nanoparticles resuspended in the dilute acid medium readily; microscopy observations showed that the size of the resuspended particles remains in the nanoscale range. The proposed procedure is able to furnish dried chitosan nanoparticles with structural characteristics and functional properties that are appealing for their use in diverse applications.

Chitosan nanoparticles (CS) and chitosan/pepper tree (Schinus molle) essential oil (CS-EO) bionanocomposites were synthesized by nanoprecipitation method and the in vitro antifungal activity against Aspergillus parasiticus spores was evaluated. The shape and size were evaluated by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The surface charge was determined by assessing the zeta potential and the inclusion of essential oil in bionanocomposites using Fourier transform infrared spectroscopy (FT-IR). The effect on cell viability of the fungus was evaluated using the XTT technique and morphometric analysis by image processing. SEM and DLS analysis indicated that spherical particles with larger diameters for CS-EO biocomposites were observed. Zeta potential values were higher (+11.1 ± 1.60 mV) for CS nanoparticles. Results suggest a chemical interaction between chitosan and pepper tree essential oil. The highest concentration of CS-EO complex caused a larger (40–50%) decrease in A. parasiticus viability. The inclusion of pepper tree oil in CS nanoparticles is a feasible alternative to obtain antifungal biocomposites, where the activity that each compound presents individually is strengthened.

Polysaccharide-based nanoparticles represent a very promising drug delivery platform, particularly for the transmucosal delivery of bioactive macromolecules. Thus, the aim of this paper is to revisit the nanoprecipitation processes for preparing chitosan nanoparticles and to evaluate the influence of the process parameters on their characteristics. Chitosan was dissolved in water as N-(methylsulfonic acid) chitosan or directly in aqueous acetic acid. Methanol was used as the nonsolvent diffusing phase. Nanoparticles became smaller as the polymer concentration decreased or the nonsolvent to solvent volume ratio increased. Particles prepared in acidic media are slightly larger than those precipitated from N-(methylsulfonic acid) chitosan. Replacement of methanol by water in the suspension medium resulted in a notorious increase in their size. On the other hand, very little additions of Tween-80 to the nonsolvent phase render smaller nanoparticles, with a similar mean-size values. Nanoparticles precipitated in methanol have roughly the same dimensions, regardless of the ionic strength of the chitosan solution. These chitosan nanoparticles have good association and loading efficiency values of a model substance showing their ability as a nanocarrier for drug delivery systems.

Conformational changes of the thermal transitions of chitosan-graft-poly(N-vinylcaprolactam) copolymers in aqueous solution were studied by varying of the length of the grafted poly(N-vinylcaprolactam) (PVCL) chains, as well as the ionic strength and the pH of the solution. The conformational properties of the copolymer were monitored by means of dynamic light scattering and ζ-potential measurements. A series of copolymers with defined molecular architecture were synthesized. Obtained results point out that hydrophobic hydration plays a crucial role on the solubility of this copolymer at neutral and slightly alkaline solutions. The evolution of the size of macromolecular aggregates indicates that, in the coil state, there is a monomodal distribution, passing through a bimodal distribution in the pre-transition region, just before the phase separation. The role of the charge of the copolymers on the cooperative transition is also analyzed. The phase transition of these amphiphilic copolymers shows a strong dependence on the ionic strength of the solution.

A series of thermoresponsive copolymers based on chitosan- g -poly( N -vinylcaprolactam) were synthesized by amidation reaction using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride as coupling reagent. The effect of molecular architecture on the thermoresponsive properties of the graft copolymers solutions was studied by varying the chain length of the grafted poly( N -vinylcaprolactam), PVCL, (in the range from 4 to 26 kDa) and the spacing between grafted chains onto the chitosan backbone. The most interesting characteristic of these copolymers is their solubility in water at temperatures below their lower critical solution temperature (LCST). These solutions presented a LCST between 36 and 44 °C, which decreases with the spacing and length of grafted PVCL chains onto the chitosan backbone, in contrast with the limited decrease of the LCST of PVCL above a critical M ¯ n value around 18 kDa. This behavior offers tangible possibilities for the preparation and application of sensitive bioactive formulations and “smart” drug delivery systems.

A wide variety of chitosan (CS) biomaterials have been loaded with different antimicrobial agents to improve the activity of CS against phytopathogenic fungi. Recently, the antimicrobial activity of 1H-pyrrole-2-carboxylic acid (PCA) has been reported as a secondary metabolite of Streptomyces griseus, which was identified as the main bioactive compound in the biological control. However, it is sensitive to light and its activity against filamentous fungi has not yet been reported. The aim of the present research work was to evaluate the biological activity of CS-PCA biocomposites for the control of Aspergillus niger. CS-PCA biocomposites were obtained through nanoprecipitation. In vitro antifungal activity was determined by viability assay, spore germination, morphometric analysis of spores and hyphae, and the analysis of cellular components by fluorescence microscopy. CS-PCA showed an average size and Z potential of 502 ± 72 nm and + 54.7 ± 15 mV, respectively. Micrographs demonstrated well-distributed biocomposites with an apparently spherical shape. A new signal at 1473 cm−1 in the FT-IR spectrum of the CS-PCA biocomposite was observed, confirming the presence of PCA in the composition of the CS-PCA nanosystem. CS-PCA biocomposites reduced the spores’ viability by up to 58%. Effects on fungi morphometry, observed as an increase in the spores’ average diameter, swelling, distortion, and an increase in the branching of hyphae, were observed. Fluorescence analysis showed oxidative stress and membrane and cell wall damage, mainly at early growth stages. The inhibitory effect against CS-resistant fungi, such as A. niger, opens a door for the control of CS-sensitive fungi.

The transport of hydrophobic drugs in the human body exhibits complications due to the low solubility of these compounds. With the purpose of enhancing the bioavailability and biodistribution of such drugs, recent studies have reported the use of amphiphilic molecules, such as phospholipids, for the synthesis of nanoparticles or nanocapsules. Given that phospholipids can self-assemble in liposomes or micellar structures, they are ideal candidates to function as vehicles of hydrophobic molecules. In this work, we report mesoscopic simulations of nanoliposomes, constituted by lecithin and coated with a shell of chitosan. The stability of such structures and the efficiency of the encapsulation of capsaicin, as well as the internal and superficial distribution of capsaicin and chitosan inside the nanoliposome, were analyzed. The characterization of the system was carried out through density maps and the potentials of mean force for the lecithin-capsaicin, lecithin-chitosan, and capsaicin-chitosan interactions. The results of these simulations show that chitosan is deposited on the surface of the nanoliposome, as has been reported in some experimental works. It was also observed that a nanoliposome of approximately 18 nm in diameter is stable during the simulation. The deposition behavior was found to be influenced by a pattern of N-acetylation of chitosan.

The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim to prepare new materials with specialized characteristics. In the present article, we summarize the latest methods for the modification and derivatization of chitin and chitosan, trying to introduce specific functional groups under experimental conditions, which allow a control over the macromolecular architecture. This is motivated because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins and reactions in ionic liquids are discussed.

The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized characteristics. In the present review, we summarize the latest methods for the modification and derivatization of chitin and chitosan under experimental conditions, which allow a control over the macromolecular architecture. This is because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as the click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins, and reactions in ionic liquids are discussed.

The materials produced by the supercritical CO

a b s t r a c t In this study, chitosan was chemically modified by reductive amination in a two-step process. The syn- thesis of N-(furfural) chitosan (FC) was confirmed by FT-IR and 1 H NMR analysis, and the degrees of substitution were estimated as 8.3 and 23.8%. The cross-linkable system of bismaleimide (BM) and FC shows that FC shared properties of furan-maleimide chemistry. This system produced non-reversible hydrogel networks by Diels-Alder cycloadditions at 85 ◦C. The system composed of BM and FC (23.8% substitution) generated stronger hydrogel networks than those of FC with an 8.3% degree of substitution. Moreover, the FC-BM system was able to produce hydrogel microspheres. Environmental scanning elec- tron microscopy revealed the surface of the microspheres to be non-porous with small protuberances. In water, the microspheres swelled, increasing their volume by 30%. Finally, microspheres loaded with methylene blue were able to release the dye gradually, obeying second-order kinetics for times less than 600 min. This behavior suggests that diffusion is governed by the relaxation of polymer chains in the swelled state, thus facilitating drug release outside the microspheres.

The modification of polymers by click chemistry has increased abruptly over the past years. In this study, furan groups were attached onto chitosan chain via reaction of 6-azido-6-deoxy chitosan and furfuryl propargyl ether. With this purpose, 6-azido-6-deoxy chitosan was synthesized by bromination and the subsequent nucleophilic substitution with sodium azide on the C6 hydroxyl groups of a previously amino-protected N-phthaloyl chitosan. Then, 6-azido-6-deoxy chitosan was reacted with furfuryl propargyl ether by the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction, resulting in an o-substituted furan–chitosan derivative with a degree of substitution of 10 %. The structure of all derivatives was analyzed and confirmed by means of infrared and nuclear magnetic resonance spectroscopies. Clicked chitosan with furan side groups was cross-linked with a bismaleimide to produce a polymer network via Diels–Alder reaction at 75 °C. The system presented a sol–gel transition with some syneresis. The gelation process was monitored by the evolution of the viscoelastic properties of the reaction mixture. The generated chitosan–furan–maleimide polymer network exhibited the typical pattern of a soft polymer hydrogel, in which both moduli were almost frequency independent with values lower than 10 Pa. These weak mechanical properties were interpreted as a consequence of the polymer degradation, which took place during the N-phthaloyl deprotection procedure.

The aim of the present study was to investigate the mechanical and thermal properties of mixed chitosan–acemannan (CS–AC) mixed gels and the antibacterial activity of dilute mixed solutions of both polysaccharides. Physical hydrogels of chitosan comprising varying amounts of non-gelling acemannan were prepared by controlled neutralization of chitosan using ammonia. As the overall acemannan concentration in the mixed hydrogel increased while fixing that of CS, the mechanical strength decreased. These results indicate that AC perturbs the formation of elastic junctions and overall connectivity as it occurs in the isolated CS network. Heterotypic associations between CS and AC leading to the formation of more compact microdomains may be at play in reducing the density of the gel network consolidated by CS, possibly due to shorter gel junctions. Micro-DSC studies at pH 12.0 seem consistent with the suggestion that molecular heterotypic associations between CS and AC may be at play in determining the overall physical properties of the mixed gel systems. In dilute solution, CS showed antimicrobial activity against Staphylococcus aureus but not against Escherichia coli; AC did not exert antimicrobial activity against any of the two bacterial species. In blended solutions of both polysaccharides, as the amount of AC increased, the antimicrobial activity of the system against S. aureus ceased. In conclusion, this study demonstrates that it is feasible to incorporate acemannan in chitosan–acemannan gels and that although the mechanical strength decreases due to the presence of AC, the gel network persists even at high amount of AC. This study anticipates that the CS–AC mixed gels may offer promise for the future development of biomaterials such as scaffolds to be used in wound therapy.

The procedures to obtain two types of acemannan (AC) physical gels and their respective aerogels are reported. The gelation was induced by the diffusion of an alkali or a non-solvent, then supercritical CO2 drying technology was used to remove the solvent out and generate the AC aerogels. Fourier-transform infrared spectroscopic analysis indicated that alkali diffusion produced extensive AC deacetylation. Conversely, the non-solvent treatment did not affect the chemical structure of AC. Both types of gels showed syneresis and the drying process induced further volume reduction. Both aerogels were mesoporous nanostructured materials with pore sizes up to 6.4 nm and specific surface areas over 370 m2/g. The AC physical gels and aerogels enable numerous possibilities of applications, joining the unique features of these materials with the functional and bioactive properties of the AC.

Non-stoichiometric polyelectrolyte complex membranes between chitosan-g- N -isopropylacrylamide (PNIPAm) and pectin were prepared and subjected to a thermal treatment by which ionic bonds were converted into amide bonds. Membranes are hydrophilic, with opaque appearance, but vitreous when dry. Swollen membranes undergo a sharp shrinking process with an inflexion point at 33.1 °C. Below LCST, NIPAm chains are hydrated and completely stretched. As temperature increases above LCST, NIPAm chains contract and water is expelled from the polymer matrix, giving rise to the phase transition that is associated to an endothermic peak and is fully thermoreversible. These membranes are not only sensitive to temperature, but also to the pH of the medium whose variation has no influence on LCST. Nevertheless, transition enthalpy decreases when pH increases within studied interval, showing the same trend as equilibrium swelling.

Interpenetrated polymer networks of chitosan (CHI), polyacrylic acid (PAA) and polyacrylamide (PAM) were prepared by free radical polymerization. These hydrogels were either washed with double distilled water (CHI/PAA/PAM) A or hydrolyzed with 1M sodium hydroxide (NaOH), (CHI/PAA/PAM) S. Both types of hydrogels were characterized by infrared spectroscopy, microstructural techniques and compressive mechanical testing. Finally, hydrogels were loaded with bovine serum albumin (BSA) and release followed at different pHs. Infrared spectra analysis showed correspondence between hydrogels and monomer feed compositions. Hydrolyzed hydrogels, had increased water content and pH swelling dependence. Compression modulus of swelled hydrolyzed hydrogels decreased with increasing equilibrium water content. Higher BSA loadings were achieved on hydrolyzed hydrogels due to their high water content and porosity. Protein release from hydrogels was low (≤ 20% after 10 hours) at pH 1.2, but sustained release was observed at pH 6.8 and 7.4. The integrity of the protein released at 6.8 and 7.4 by hydrolyzed hydrogels was unaffected. The hydrogles showed no cytotoxic effects on human skin dermal fibroblasts as determined by MTT assay except for two compositions of (CHI/PAA/PAM) A samples, which after seven days presented a viability lower than 80% respect to the control.

Chitosan-g-N-isopropylacrylamide (NIPAm) water-soluble copolymers were synthesized and characterized by FTIR and (1)H NMR spectroscopies combined with conductometric and potentiometric titrations. Their thermoresponsive, fully reversible, behavior in aqueous solutions was characterized by means of microcalorimetry and rheology. During heating of copolymer solutions there is a well-known endothermic effect, which coincides with a marked increase in G' and a moderate decrement in G'' due to the formation of a hydrophobic network at the expense of the net amount of sol fraction. It was also found that a straight dependence between the values of G' above the LCST and the enthalpies associated with the transition reflecting that the connectivity in the gel network is governed by the net number of formed enthalpic-hydrophobic driven-junctions. Both the LCST and the enthalpy change vary with the ionic strength of copolymer solutions, but no dependence was found with the neutralization of the polyelectrolyte chain.

On heating, alkali chitin solutions undergo phase separation describing a characteristic "U-shaped" cloud point curve with a lower critical solution temperature (LCST) centered at ∼30∼°C. The process is accompanied by gelation of the polymer-rich phase. A different strategy to induce alkali chitin phase separation/gelation is by applying vacuum to the solution at room temperature during aprox. 72∼h. Once washed to neutrality, chitin gels had a degree of acetylation of ∼30-40% (i.e. they were converted into chitosan). On cooling, these gels exhibit an exothermic peak in micro-DSC and a depression in G " and tan δ traces, evidencing a volume phase transition centered at ∼20∼°C. This transition is observed only within a narrow range of pH ∼7.3-7.6. Variation in the mechanical response as a result of cyclic stepwise changes in temperature between 50 and 0∼°C at pH values from 7.3-7.6, revealed that the G' modulus of the gels increases on heating and decreases on cooling, a behavior that persists over at least four cycles of temperature change. Only marginal changes in G' at pH 8.0 and not at all at pH 12.0 are observed. By contrast, the variation of G " persists throughout the range of pH. This behavior is rationalized in terms of the existence of a fine balance between hydrophobic and hydrophilic interactions at varying temperature and pH, thus effectively controlling swelling and shrinking states of the gel network. The degree of swelling at pH 7.6 reaches a minimum at ∼22-25∼°C. © Springer-Verlag 2007.

Membranes of the polyelectrolyte complex between chitosan and pectin were prepared by precipitating the complex from a mixture of both polysaccharides. It was shown that the swelling kinetics of these membranes follows a Fickean behavior. The membranes were heated at 120 °C in order to convert the –NH3+-OOC- salt bonds into amide bonds. The thermally treated membranes were stable in strongly acid and basic media. The extent of amide bond formation was followed by FTIR spectroscopy. It was found that as the reaction time increased, both the absorbance ratio A1744/A1082 and the maximum swelling of the membrane decreased. The surface morphology of the membranes did not vary appreciably with the thermal treatment.

Calcium alginate capsules containing shark liver oil were prepared by ionotropic gelation of alginate solutions. Since the capsules were permeable to the oil, they were coated with a membrane of chitosan-alginate polyelectrolyte complex to reduce permeability. Encapsulation efficiencies (expressed as the percentage of shark liver oil entrapped) greater than 87% (w/w) were obtained by using 6% (w/v) alginate solution. The oil content in the capsules was higher than 65% (w/w) when the oil was dispersed in the alginate solution at 10% (v/v) or more. However, at the level of 15 or 20% (v/v) the oil was exuded after 48 h. Capsules were degraded in vitro by enzymes, with lipase being more effective than pancreatine. No release of oil from the capsules up to 4 h at pH 1.2 was observed, but after 4 h the capsules became very fragile when they were immersed in buffer solution at pH 7.4.

Synthetic astaxanthin was microencapsulated in a chitosan matrix cross-linked with glutaraldehyde by using the method of multiple emulsion/solvent evaporation. A powdered product was obtained containing microcapsules with a diameter of 5–50 μm. The stability of the pigment in the microcapsules was studied under storage at 25, 35 and 45 °C for 8 weeks by measuring isomerization and loss of concentration of pigment. Pigments were extracted from the microcapsules with a mixture of dichloromethane/methanol (50:50) and the astaxanthin was analyzed by HPLC with a diode array detector (480 nm). Results showed that the microencapsulated pigment did not suffer isomerization nor chemical degradation under the investigated storage conditions.

Fully de-esterified Na-pectate with excellent gelling properties was isolated from linseed ( Linum usitatissimum ) using an alkaline extraction procedure aided with a sequestering agent. The gelling behavior of this material was studied as a function of amount of Ca 2+ added and temperature by dynamic oscillatory rheology. Calcium cross-linking adjusted at varying stoichiometric ratios, ( R =2[Ca 2+ ]/[COO − ]), resulted in unequivocal gel network formation with mechanical spectra characteristic of permanent gel structure. Crude shark liver oil (SLO) was encapsulated into a composite matrix comprising linseed Na-pectate, alginate and chitosan. To this end, SLO was loaded into a linseed pectin–alginate solution at 2% (w/v), and gel beads were formed by dropwise addition into a CaCl 2 bath and further coated by chitosan. Three different formulations were evaluated by varying the ratio of pectin to alginate (in % of the total equivalent concentration), while keeping constant the total polymer concentration at ∼4% (w/w). As the proportion of linseed pectin in the formulae increased, the gel beads lost mechanical strength, sphericity and swelled more rapidly in water by a transport mechanism controlled only by diffusion of the solvent. Loading efficiency was greater in the capsules in which pectin contributed to 28% of the negatively charged polymer species (P28), which retained 73% of SLO, while capsules of pure alginate (P0) and those with a higher amount of pectin (P71) retained 65 and 67% of SLO, respectively. The observed differences between the three types of capsules were a direct consequence of the strength of linseed pectin gels, weaker than those of alginate.

Chitosan is a weak cationic polysaccharide composed essentially of β(1 → 4) linked glucosamine units together with some N-acetylglucosamine units. It is obtained by extensive deacetylation of chitin, a polysaccharide common in nature. Chitosan is a biocompatible, biodegradable, and nontoxic natural polymer that exhibits excellent film-forming ability. As a result of its cationic character, chitosan is able to react with polyanions giving rise to polyelectrolyte complexes. Therefore, because of these interesting properties, it has become the subject of numerous scientific reports and patents on the preparation of microspheres and microcapsules. The techniques employed to microencapsulate with chitosan include, among others, ionotropic gelation, spray drying, emulsion phase separation, simple and complex coacervation, and polymerization of a vinyl monomer in the presence of chitosan. The aim of this work is to review some of the more common techniques used and to put forward the results obtained by our research group in preparing chitosan-based microcapsules: for taste masking and improving the stability of a nutritional oil, the sustained release of drugs, as well as the preparation of chitosan superparamagnetic microcapsules for the immobilization of enzymes. Scanning electron micrograph of some superparamagnetic chitosan particles and magnetic hysteresis loop of the microparticles.

The ability to form a gel through the physical or chemical crosslinking of chitosan has been well documented. In an attempt to mimic biological systems, thermal and pH-sensitive chitosan cylindrical hydrogels were produced by a combination of physical and chemical crosslinking processes. To this end, chitosan hydrogels prepared from alkali chitin were molded in cylinders and, once washed, were further crosslinked with glutaraldehyde at stoichiometric ratios, R (=[-CH=O]/[-NH 2 ]), of 1.61 and 3.22 × 10 -2 . Variation in swelling as a result of stepwise changes in temperature between 40 and 2 °C at pH values of 7.0, 7.6, and 8.0 revealed that the system responds in markedly different manners dependent upon the pH. At pH 7.0, cooling from 40 to 2 °C results in contraction of the gel network structure. While raising the temperature from 2 to 40 °C leads to a rapid swelling response (i.e., ca. a twofold increase in the amount of solvent uptake). Subsequent cooling to 2 °C is accompanied by a new contraction cycle. At pH ≥7.6 the temperature dependence of the swelling-contraction behavior is exactly the opposite of that observed at pH 7.0. Very similar trends were observed for the gels at both degrees of crosslinking. The swelling-shrinking behavior observed in gels of pH≥7.6, is similar in kind to that of uncrosslinked gels and is interpreted in terms of a lower critical solution temperature (LCST) volume phase transition, driven by hydrophobic association, presumably involving residual acetyl groups in the chitin. The results at pH 7.0 suggest that the slight ionization of the -NH + 3 groups leads to destruction of the hydrophobic hydratin thus effectively reversing the negative thermal shrinking.

The swelling of membranes of the polyelectrolyte complex (PEC) between chitosan and alginate shows a similar pattern to that of other PECs. However, if the swelled membranes are dried, a second swelling process is seen which exhibits Fickian behavior. The apparent activation energy was estimated to be 32.8 kJ . mol -1 . The release rate of model solutes was highly dependent on their molecular weight and the pH of the medium.

Astaxanthin (AX) is the major naturally occurring carotenoid pigment in marine crustaceans and the flesh of salmonids. These organisms are unable to synthesize AX de novo and when farmed commercially, require it in their feed. The high cost of synthetic AX has promoted research into new natural sources of the pigment, such as crustacean wastes. In this work, AX from demineralized crab (Callinectes sapidus) shell waste was extracted with a mixture of supercritical CO 2 and ethanol as a cosolvent, The effect of total solids load, pressure and temperature was assessed by response surface methodology (RSM). Extracted AX was determined by HPLC. The experimental data were fitted to a second order model whereby the conditions for maximum extraction yield were defined (≥ 34 MPa, 45C and solids load of 25 g). Pressure and solids load were the most important factors affecting AX extraction yields.

cited By 649; International audience; The use of infrared spectroscopy for characterization of the composition of chitin and chitosan covering the entire range of degree of acetylation (DA) and a wide variety of raw materials is examined further. The ratio of absorbance bands selected was calibrated using 1H liquid and 13C CP-MAS solid-state NMR as absolute techniques. IR spectra of the structural units of these polymers validated the choice of baselines and characteristic bands. The bands at 1650 and 1320 cm-1 were chosen to measure the DA. As internal reference, the intensities at 3450 and 1420 cm-1 were evaluated. The absorption band ratios involving the reference at 3450 cm-1 had poorer fit.. The absorption ratio A1320/A1420 shows superior agreement between the absolute and estimated DA-values (DA% = 31.92A1320/A1420 - 12.20; r = 0.990). © 2001 Elsevier Science Ltd.

Polyelectrolyte complexes (PECs) are formed through the electrostatic interactions between polymers carrying opposite charges. Here are presented results of basic studies on the PECs of chitosan with other polysaccharides such as sodium alginate, carboxymethyl cellulose, polygalacturonic acid and κ-carrageenan. An extensive study on chitosan/carboxymethyl cellulose membranes, regarding its swelling characteristics and water vapour sorption is offered. Also the interaction of chitosan with polyacrylic acid has been examined from the thermodynamic point of view.

The interpolyelectrolyte reaction between chitosan hydrochloride (CHI) and sodium polygalacturonate (NaPGA) has been investigated by conductimetric measurements. The composition of the reaction mixture, Z, was assessed by monitoring the conductivity when a CHI solution was added to a solution of NaPGA. It was determined to be unity at the equivalence point, indicating a 1:1 stoichiometry for the complex. The degree of complexation, θ, expressed as the fraction of groups reacted, was also obtained from the conductimetric measurements by means of a simple procedure. To this end the limiting ionic conductivities and transport coefficients of CHI and NaPGA were previously evaluated. It was found that θ varies with Z. It falls from unity to almost 0.8 as Z increases from 0.2 to 0.5 and then rises again up to 0.85 for Z=1.

Chitosan/polyacrylic acid I PN's were prepared by radical polymerization of acrylic acid, AA, activated at low temperature, in an aqueous/alcoholic chitosan dispersion. AA monomer to polymer conversion and membrane compositions were determined by elemental analysis and FTIR. Evidences of interpolyelectrolite complex formation were found from the FTIR spectra as well. The gravimetric measurements and the elemental analysis after some exhaustive PAA extraction support the existence of some PAA grafting on the reactive amine group of the chitosan. Swelling degree of the membranes is highly dependent on pH and composition, showing a higher swelling in membranes richer in AA and increased pH due to the breaking of interpolyelectrolite salt bonds.

Interpolymer complexing of poly(acrylic acid) (PAA) with poly(N-vinyl-2-pyrrolidone) (PVP) as well as with chitosans (CHI) of various chain lengths was studied at different temperatures by pH measurements. The degree of conversion (θ), the complex stability constant, K, and the thermodynamic parameters of these reactions were evaluated. Complexing proceeds cooperatively in both systems and values of θ near unity are obtained for the higher molecular weight samples. The variation of K with θ for the PAA-CHI system indicates that this complex comprises long sequences of bound pairs of monomer units.

Sorption of water vapour by chitosan/carboxymethyl cellulose polyelectrolyte complex membranes prepared at two different pHs was studied. A linear dependence of the water uptake (W) on time was observed for W values lower than 0.5 g of water per gram of membrane. For higher values of W diffusion becomes controlled by the relaxation of the chains, and second-order kinetics is observed. An equation that satisfactorily reproduces this behaviour is proposed. Desorption experiments were carried out at different temperatures and the W versus time curves obtained exhibited the same general pattern and were also adjusted by this equation. The approximate average diffusion coefficients were evaluated at each temperature and the apparent activation energy for the diffusion process is reported.

Nobiletin is a polymethoxyflavonoid with a remarkable antiproliferative effect. In order to overcome its low aqueous solubility and chemical instability, the use of nanoparticles as carriers has been proposed. This study explores the possibility of binding nobiletin to chitosan nanoparticles, as well as to evaluate their antiproliferative activity. The association and loading efficiencies are 69.1% and 7.0%, respectively. The formation of an imine bond between chitosan amine groups and the carbonyl group of nobiletin, via Schiff-base, is proposed. Nobiletin-loaded chitosan nanoparticles exhibit considerable inhibition (IC50=8 μg/mL) of cancerous cells, revealing their great potential for applications in cancer chemotherapy.

The swelling of membranes of polyelectrolyte complexes formed from chitosan and carboxymethyl cellulose is reported. These membranes adsorb water until a maximum swelling is achieved after which they slowly shrink to an equilibrium value. The maximum swelling value and the time at which it is attained increases as the pH of formation of the complex increases from 4.0 to 5.8. Shrinkage observed at longer times is the result of the segmental mobility of the polyelectrolyte chains in the swollen state which allows the completion of the interpolyelectrolyte reaction. The water uptake up to maximum swelling obeys second order kinetics.

Chitosan was reacted consecutively with epichlorohydrin and thiourea. Subsequent hydrolysis of the isothiouronium salt yielded the mercaptan derivative of chitosan, which scavenges mercury ions from solution in the presence of a considerably high concentration of chloride ions. Sulfur contents varied with reacting conditions and reached values up to 7.3%. The derivative is insoluble due to partial crosslinking of chitosan during the reaction with epichlorohydrin. The resin exhibited a capacity of 8 mg of mercury per ml of resin basing on the breakthrough curve of the resin with a mercury chloride solution (8% chloride, 17 mg Hg 2+ /l)

The thermal degradation behaviour of chitosan and N -(2-hydroxy-3-mercaptopropyl)-chitosan (HMPC) has been studied by means of dynamic thermogravimetric analysis (TGA) in the range 30–600°C. Dynamic experiments showed that thermal decomposition of both products proceeds in four steps. The apparent activation energy values for each degradation step were obtained following the procedure of Broido. The first decomposition stage of both products was also studied by isothermal TGA and it was found that the apparent activation energy varies with degree of conversion, which is a manifestation of the complexity of this decomposition stage for both polysaccharides. In the pyrolysis-mass spectra of chitosan and HMPC the lower stability of the latter is apparent, since it exhibits peaks at m z 34, 47 and 76, not observed for chitosan, due to evolution of H 2 S and CH 3 S and C 2 H 4 OS fragments, respectively. The IR spectra of residual chitosan chars from isothermal pyrolysis gave an indication of degradation of the ring together with dehydration over the whole temperature interval studied. In the IR spectra of HMPC pyrolysis residues no appreciable degradation of the glycopyranosic ring was observed up to 200°C; at higher temperatures, the behaviour is similar to that of chitosan.

The aim of this work was to develop and characterize a new type of nanocapsules. To this end, a nanoemulsion bearing an oily core (Miglyol 812) was obtained by spontaneous emulsification and stabilized by dodecyl-trimethylammonium chloride (DTAC), a commercial cationic surfactant; this nanoemulsion was coated with proportionally very small amounts of κ-carrageenan (at molar charge ratios of Z ≤ 0.0045) that interact predominantly by an electrostatic mechanism with the positively charged sites at the polar heads of DTAC at the nanoemulsion's surface to harness nanocapsules of average size ~250-330 nm and zeta potential (ζ) ranging from ~+80 to +7 mV. The potential application of the new type of developed nanosystems as drug delivery vehicles has yet to be investigated and fully realized.

The adsorption of mercuric ions by chitosan was investigated. The study of the adsorption kinetics shows that the rate of adsorption of mercuric ions on chitosan can be interpreted in terms of intraparticle diffusion as the rate-limiting step. The experimental data of adsorption equilibrium from mercuric chloride solutions correlate well with the Langmuir isotherm equation, although at high-solute concentrations, a multilayer type of adsorption with the subsequent increase in the uptake is observed. Column experiment confirms the ability of chitosan for the removal of mercuric ions from solutions in the absence of a high concentration of chlorides.

Chitin is widely distributed in nature, constituting an important renewable resource. The main sources of chitin generally used are the crustacean wastes of the fishing industry. This chapter provides a brief account of the main processes employed in chitin isolation and the preparation of chitosan by extensive deacetylation of chitin. The common methods of characterization of chitin and chitosan, in terms of degree of acetylation and molecular weight, are discussed. Their crystalline structure and their solution properties, are also described. The capacity of chitin and chitosan of forming complexes with metal ions is shown, and mention is made to some of its diverse applications. The ability of chitosan to form polyelectrolyte complexes with polyanions, the cooperativity of this reaction and the properties of chitosan-based polyelectrolyte complex membranes, are also examined. The chapter ends with a review of the applications of chitin and chitosan in medicine, pharmacy, agriculture, the food industry, cosmetics, among others. © 2008 Elsevier Ltd. All rights reserved.