Kinetics of silver nanoparticle release from chitosan spheres
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Kinetics of silver nanoparticle release from chitosan spheres Luci Cristina de Oliveira Vercik, Andres Vercik , Eliana Cristina da Silva Rigo University of Sao Paulo, Av. Duque de Caxias Norte 225, 13635-000, Pirassununga - SP, Brazil. ABSTRACT The kinetics of silver nanoparticles release from chitosan spheres is addressed experimentally and theoretically in this work. From the experimental viewpoint, the study of silver nanoparticles release is performed by measuring the time-dependent UV-Vis spectra of solutions where spheres were dispersed. The UV-VIS spectra intensity reflects the concentration of nanoparticles in the solution. Despite simple expressions for drug release are found in the literature, as those that relate the amount of drug release with the square root of time, a proper modeling might require the inclusion of several phenomena such as the presence of stagnant layers, swelling or erosion of the matrix, accumulation of particles in the medium, amongst others. The experiments show that chitosan/silver nanoparticles complexes are actually released, indicating that both swelling and erosion of the matrix takes place during the release process. The simplest model for drug release, i.e., the Higuchi’s model, fits the observed results surprisingly well, which is a relevant result due to the lack of mathematical modeling for the release of nanoparticles. INTRODUCTION Drug delivery from matrix systems with different geometrical shapes has received much attention because of their capacity of carrying a specific dose of drug. Spherical structures, such as particles, capsules, lipid vesicles and dendrimers, are commonly used in biomedical, pharmaceutical or food industries for delivering of drugs, nutrients or other substances into a target environment [1–3]. The detailed knowledge of the releasing mechanism is relevant for proper design of the drug carrier systems not only for improving the efficiency of the delivering process, when a benefic effect is aimed, but also to prevent unwanted damages, such as excess of drug or even toxicity [4, 5]. A variety of materials, such as wax, lipid, natural and synthetic polymers have been used as carrier material in the preparation of matrix-type drug delivery systems. Biodegradable polymers have been extensively used for drug delivery systems and chitosan (CS) is of major importance [6–9]. Beyond drugs, the use of nanoparticles has also been proposed for the treatment of different diseases and, particularly, silver nanoparticles (AgNPs) have attracted attention due to their well-known antimicrobial effect [10–13]. In contrast to the large number of works found in literature dealing with the drug release modeling, fewer papers address the release of silver nanoparticles in aqueous media [4, 14], whereas there is a lack of mathematical modeling of nanoparticles release to the best of our knowledge. Modeling the release kinetics of drugs could be a difficult task, depending on the involved phenomena taken into account in simulations. Boundary layer effects, variable bounda
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