Reynaldo Esquivel

Synthesis and Characterization of New Thiolated Chitosan Nanoparticles Obtained by Ionic Gelation Method

We derivatized low molecular weight chitosan (LMWC) with 3-mercaptopropanoic acid (3-MPA) by a coupling reaction. The chemical modification of LMWC was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance, 1HNMR. We researched the influence of 3-MPA on the nanoparticles formation by ionic gelation method using sodium tripolyphosphate (TPP) as cross-linker reagent. In order to optimize the nanoparticles formation, we studied the effect of the pH solution and molar ratio on nanoparticles stability. Analyses of particle size, morphology, and surface charge were determined by dynamic light scattering, Atomic Force Microscopy, and zeta potential, respectively. It was found that formation of semispherical and stable nanoparticles was improved due to the chemical modification of chitosan. Optimized semispherical nanoparticles of thiolated chitosan were synthesized with the parameters (pH 4.7, molar ratios 1 : 106). Additionally, we reported the thermodynamic profile of the nanoparticles formation determined by isothermal titration calorimetry (ITC). The aggregation process achieved to form nanoparticles of thiolated and nonmodified chitosan consisted of two stages, considering one binding site model. Gibbs free energy and binding constant () describe the aggregation process of thiolated chitosan/TPP, which is an initial reaction and followed by an endothermic stage. These results are promising for the possible application of these nanoparticles as nanocarriers and delivery systems.

Systematic evaluation of pH and thermoresponsive poly(n-isopropylacrylamide-chitosan-fluorescein) microgel

Abstract The interesting properties of stimuli-responsive polymers lead to a wide range of possibilities in design and engineering of functional material for the biomedical application. A systematic approach focused on the evaluation of the physical properties of multiresponse (pH and temperature) PNIPAM was reported in this work. The effect of three different molar ratios of poly(n-isopropylacrylamide): chitosan (1:49, 1:99 and 1:198) were evaluated and labeled correspondingly as PC1F, PC2F, and PC3F. An increase in the lower critical solution temperature (LCST) of sample PC1F (34°C) was observed by differential scanning calorimetry (DSC). The presence of low molecular weight chitosan (LMWC) full-interpenetrating polymer (Full-IPN) segments in poly(n-isopropylacrylamide) was confirmed by Fourier-transform infrared spectroscopy (FT-IR). The hydrogel’s water capture was analyzed by two models of swelling, the power law model and a model that considers the relaxation of polymeric chains of the hydrogel, finding good correlations with experimental data in both cases. Sample PC3F resulted with higher swellability, increasing the weight of the hydrogel around seven times. Hydrogel pH-sensibility was confirmed placing the samples at different pH environments, with an apparent increase in swellability for acidic conditions, confirming the highest swellability for sample PC3F, due to hydrogen bonds boosted by chitosan high molar ratio. Based on these results, the hydrogel obtained has potential as a thermo-pH triggered hydrogel in drug delivery applications.

Low intensity sonosynthesis of iron carbide@iron oxide core-shell nanoparticles

Here we demonstrate a simple method for the organic sonosynthesis of stable Iron Carbide@Iron Oxide core-shell nanoparticles (ICIONPs) stabilized by oleic acid surface modification. This robust synthesis route is based on the sonochemistry reaction of organometallic precursor like Fe(CO)5 in octanol using low intensity ultrasonic bath. As obtained, nanoparticles diameter sizes were measured around 6.38 nm ± 1.34 with a hydrodynamic diameter around 25 nm and an estimated polydispersity of 0.27. Core-Shell structure of nanoparticles was confirmed using HR-TEM and XPS characterization tools in which a core made up of iron carbide (Fe3C) and a shell of magnetite (γ-Fe2O3) was found. The overall nanoparticle presented ferromagnetic behavior at 4 K by SQUID. With these characteristics, the ICIONPs can be potentially used in various applications such as theranostic agent due to their properties obtained from the iron oxides and iron carbide phases.

Evaluation of a combined emulsion process to encapsulate methylene blue into PLGA nanoparticles

The delivery of photosensitizer compounds using biodegradable nanoparticles could improve dosage, controlled release and its bioavailability. In this study, methylene blue (MB) loaded PLGA nanoparticles (MB-PNP) are prepared by a new approach combining single and double emulsification techniques. Comparisons of MB-PNP obtained with the combined and the individual techniques are presented. Nanoparticles are characterized by dynamic light scattering, laser Doppler electrophoresis and scanning electron microscopy. Particles prepared by the combined technique presented hydrodynamic diameters of 186 nm. The sizes of MB-PNP obtained from the single emulsion technique are similar to the combined technique, while the diameter of particles prepared by double emulsion increased from 201 nm to 287 nm as the TDL increased. MB-PNP displayed an average zeta potential between −21 mV and −28 mV for all formulations. MB loading ranges between 0.3–1.4%, while the encapsulation efficiency ranges from 8–14%, both depending on the TDL and the preparation technique. In vitro release studies show a monophasic release profile that was analyzed by considering the mechanisms of initial burst, drug diffusion and a combination of them. Experimental results could be better described using a mathematical model of release that simultaneously combines the mechanisms of initial burst and drug diffusion. The approach presented to encapsulate MB and also to analyze the drug release could be extended to other drugs with partial solubility.

Poly(N-isopropylacrylamide)-coated gold nanorods mediated by thiolated chitosan layer: thermo-pH responsiveness and optical properties

Abstract A core-shell of colloidal metal-responsive polymer provides an innovative model in functional materials. These core-shell nanocomposites offer the possibility to control some properties, such as particle size, surface plasmon resonance and morphology. In this research, we demonstrate the successful synthesis and functionality of gold nanorods (GNR) coated with the polymers chitosan (Ch) and poly(N-isopropylacrylamide) (PNIPAM). The polymer coatings are performed using a two-step method. First, GNR were coated with a thiolated chitosan (GNR-Ch) by replacing hexadecyltrimethylammonium bromide with a chitosan thiomer. Structural modification of GNR-Ch was monitored by Fourier transform infrared spectroscopy. Then a second polymeric coating was done by in situ free radical polymerization of N-isopropylacrylamide (NIPAM) on GNR-Ch to obtain the nanocomposite GNR-Ch-PNIPAM. The nanocomposite average size was analyzed by dynamic light scattering. The evolution of ζ potentials during the coatings was measured using electrophoretic mobility. GNR-Ch-PNIPAM presented a collapsed structure when heated above the lower critical solution temperature. The particle size of GNR-Ch-PNIPAM was manipulated by changing the pH. Plasmonic properties were evaluated by UV-Vis spectroscopy. Results showed an important blue shift due to the PNIPAM coating thickness. Thermo- and pH-responsive properties of the nanocomposite GNR-Ch-PNIPAM could be used as a drug delivery system.