Marcela Mihai

Complex Nanoparticles Based on Chitosan and Ionic/Nonionic Strong Polyanions: Formation, Stability, and Application

Interpolyelectrolyte complex (IPEC) nanoparticles formed between chitosan having different molar masses (470, 670, and 780 kDa) and two random copolymers of 2-(acrylamido)-2-methylpropanesulfonate (AMPS) with tert-butylacrylamide (TBA) [P(AMPS(54)-co-TBA(46)) and P(AMPS(37)-co-TBA(63))] were prepared by the dropwise addition of polyanion onto the chitosan solution. The effect of polyelectrolyte characteristics and the molar ratio between charges on the morphology of the complex nanoparticles and on their colloidal stability was deeply investigated by turbidimetric titration (optical density at 500 nm), dynamic light scattering, and atomic force microscopy. It was found that the lowest sizes of the IPEC nanoparticles were obtained, with both polyanions, when the chitosan having the lowest molar mass (470 kDa) was used as a major component. In this case, the particle sizes varied in a narrow range, even after the complex stoichiometry; i.e., when the polyanion was added in excess, the colloidal stability of these IPEC dispersions was very high. A mechanism of complex formation as a function of the ratio between charges was proposed. According to this mechanism, the nonstoichiometric complex nanoparticles formed at molar ratios between charges, n(-)/n+, lower than 0.2, i.e., far from the complex stoichiometry, would have a high density of positive charges in excess not only because of the chitosan in excess, which forms the shell, but also because of the mismatch of opposite charges, due to both the differences in the flexibility of complementary polyions and the presence of the hydrophobic comonomer, TBA, in the polyanion structure. Nonstoichiometric IPECs prepared at n(-)/n+ around 0.2 proved to be more efficient than chitosan in the destabilization of kaolin from a model suspension, with a lower optimum concentration flocculation and a much larger flocculation window being found compared with chitosan.

Calcium carbonate microparticle templates using a PHOS-b-PMAA double hydrophilic copolymer

The crystallization characteristics of calcium carbonate microparticles grown from supersaturated aqueous solutions in the presence of a double hydrophilic block copolymer poly(p-hydroxystyrene-b-methacrylic acid), PHOS-b-PMAA, have been investigated. The studies aim to highlight both the possibilities and the limitations of CaCO3/PHOS-b-PMAA microparticle formation under different relative inorganic/polymer ratio conditions, varying the initial solution supersaturation or the polymer concentration. Scanning electron microscopy and atomic force microscopy were used to provide high-resolution images of particles and thereby information on the particle morphology, while X-ray diffraction analysis was used to determine the polymorph type and crystallite characteristics. The presence of the polymer in the composite particles was shown by thermogravimetric, particle charge density and zeta potential analysis. The polymer-induced sensitivity of the new composites to environmental pH variations has been followed by streaming potential variation.

Autotemplate Microcapsules of CaCO3/Pectin and Nonstoichiometric Complexes as Sustained Tetracycline Hydrochloride Delivery Carriers

New types of composites were obtained by an autotemplate method for assembling hollow CaCO3 capsules by using pH-sensitive polymers. Five pectin samples, which differ in the methylation degree and/or amide content, and some nonstoichiometric polyelectrolyte complex dispersions, prepared with the pectin samples and poly(allylamine hydrochloride), were used to control the crystal growth. The morphology of the composites was investigated by scanning electron microscopy, and the polymorphs characteristics were investigated by FTIR spectroscopy. The presence of the polymer in the composite particles was evidenced by X-ray photoelectron spectroscopy, particle charge density, and zeta-potential. The new CaCO3/pectin hollow capsules were tested as a possible matrix for a tetracycline hydrochloride carrier. The kinetics of the drug release mechanism was followed using Higuchi and Korsmeyer-Peppas mathematical models.