Jaime Lizardi-Mendoza

N-(furfural) chitosan hydrogels based on Diels-Alder cycloadditions and application as microspheres for controlled drug release.

In this study, chitosan was chemically modified by reductive amination in a two-step process. The synthesis 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 electron 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.

Effect of the molecular architecture on the thermosensitive properties of chitosan-g-poly(N-vinylcaprolactam).

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.

Acidic Proteases from Monterey Sardine (Sardinops sagax caerulea) Immobilized on Shrimp Waste Chitin and Chitosan Supports: Searching for a By-product Catalytic System

Solid wastes generated from the seafood industry represent an important environmental pollutant; therefore, utilization of those wastes for the development of processing biochemical tools could be an attractive and clean solution for the seafood industry. This study reports the immobilization of semi-purified acidic proteases from Monterey sardine stomachs onto chitin and chitosan materials extracted from shrimp head waste. Several supports (chitosan beads, chitosan flakes, and partially deacetylated flakes) were activated either with genipin or Na-tripolyphosphate and evaluated as a mean to immobilize acidic proteases. The protein load varied within the 67–91xa0% range on different supports. The immobilization systems based on chitosan beads achieved the highest protein loads but showed the lowest retained catalytic activities. The best catalytic behavior was obtained using partially deacetylated chitin flakes activated either with genipin or Na-tripolyphosphate. According to results, the immobilization matrix structure, as well as acetylation degree of chitin–chitosan used, has considerable influence on the catalytic behavior of immobilized proteases. Partially deacetylated chitin flakes represent a suitable option as support for enzyme immobilization because its preparation requires fewer steps than other supports. Two abundant seafood by-products were used to obtain a catalytic system with enough proteolytic activity to be considered for biotechnological applications in diverse fields.

Ultrastructural, Morphological, and Antifungal Properties of Micro and Nanoparticles of Chitosan Crosslinked with Sodium Tripolyphosphate

Recent studies have demonstrated the antibacterial effect of micro and nanoparticles of chitosan (CS) crosslinked with sodium tripolyphosphate (TPP), and incorporating metallic ions, bringing that the size, shape, and zeta potential are related to the antimicrobial potential. However, there are few studies on the antifungal activity and the effect of TPP on the antimicrobial potential. Micro and nanoparticles were prepared from CS by ionotropic gelation with TPP, and structurally characterized by transmission and scanning electron spectroscopy, and Fourier transformed infrared spectroscopy. Depending on the concentration of CS and TPP, spherical particles were obtained from 80xa0nm to 20xa0μm. Subsequently, particles were evaluated for their antifungal potential against Aspergillus parasiticus assessing radial growth, spore germination, and morphological changes. An increase in the antifungal potential compared with CS in solution was observed, inhibiting the development of the fungus causing clear morphological changes in both, hyphae and spores. Particle size and the availability of functional groups of CS/TPP (amino group and phosphate), suggest a possible synergistic effect between CS and TPP.

Preparation of chitosan nanoparticles by nanoprecipitation and their ability as a drug nanocarrier

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.

Furan–chitosan hydrogels based on click chemistry

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 10xa0%. 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 75xa0°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 10xa0Pa. These weak mechanical properties were interpreted as a consequence of the polymer degradation, which took place during the N-phthaloyl deprotection procedure.

Conformational study on the thermal transition of chitosan-g-poly(N-vinylcaprolactam) in aqueous solution

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.

Antifungal and antimycotoxigenic activity of essential oils from Eucalyptus globulus, Thymus capitatus and Schinus molle

Essential oils (EO) of eucalyptus (Eucalyptus globulus L.), thymus (Thymus capitatus L.) pirul (Schinus molle L.) were evaluated for their efficacy to control Aspergillus parasiticus and Fusarium moniliforme growth and their ability to produce mycotoxins. Data from kinetics radial growth was used to obtain the half maximal inhibitory concentration (IC50). The IC50 was used to evaluate spore germination kinetic and mycotoxin production. Also, spore viability was evaluated by the MTT assay. All EO had an effect on the radial growth of both species. After 96 h of incubation, thymus EO at concentrations of 1000 and 2500 µL L–1 totally inhibited the growth of F. moniliforme and A. parasiticus, respectively. Eucalyptus and thymus EO significantly reduced spore germination of A. parasiticus. Inhibition of spore germination of F. moniliforme was 84.6, 34.0, and 30.6% when exposed to eucalyptus, pirul, and thymus EO, respectively. Thymus and eucalyptus EO reduced aflatoxin (4%) and fumonisin (31%) production, respectively. Spore viability was affected when oils concentration increased, being the thymus EO the one that reduced proliferation of both fungi. Our findings suggest that EO affect F. moniliforme and A. parasiticus development and mycotoxin production.

Supercritical CO2 dried chitosan nanoparticles: production and characterization

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.

Optimal Immobilization of Acidic Proteases from Monterey Sardine (Sardinops sagax caeurelea) on Partially Deacetylated Chitin from Shrimp Head Waste

ABSTRACT Response surface methodology was employed to optimize the immobilization yield of acidic proteases from Monterey sardine (Sardinops sagax caeurelea) using partially deacetylated chitin as immobilization support. A rotatable central composite design was applied to evaluate the effects of immobilization conditions such as enzyme loading (X1), immobilization pH (X2), and tripolyphosphate concentration (X3) on the immobilization yield. The analysis of variance revealed that the established model was significant (p < 0.05), and the adjustment of the quadratic model with the experimental data was satisfactory. Under optimal conditions (X1 = 0.05 mg/mL, X2 = 3.16, and X3 = 0.75%), an immobilization yield of 79.1% was achieved; a value that was in accordance with the predicted one.