chitosan and plga microspheres as drug delivery ... - UniCA Eprints

6. RFP Loaded PLGA Microspheres Prepared by Solvent Evaporation MethodPLGA microparticles size is normally affected by the presence of an emulsifier. In this casePVA was used to prevent aggregation of the emulsion droplets and polymer sticking duringstirring. 4% of PVA was able to stabilize particles also during their storage. This is confirmedby the polydispersity index tha was very low because aggregation did not occur and particlesmantained a narrow distribution, as confirmed also by SEM study.When working with microparticulate systems, it is often helpful to visualize particle shapesand surface characteristics in order to correlate other properties such as surface area and sizedistribution. RFP-loaded PLGA microspheres prepared using the solvent evaporation methodwere spherical in shape with a very smooth surface, as shown in Figures 6.1a and 1b. Theloading of the antimicrobial agent did not cause any significant change in morphology.SEM micrographs confirmed the narrow distribution of particles size found by PCSmeasurement, for each batch. As can be seen, no difference in particle morphology was foundas a consequence of the preparation method.abFigure 6.1: SEM Micrographs of PLGA Microspheres Obtained by Adding the Drug inthe Aqueosus Phase (a) or in the Organic Phase (b).6.2.3. Surface ChargeMicroparticle formulations were characterized also in term of zeta potential because, as wellknown, it can influence particle stability as well as particle mucoadhesion. In theory, morepronounced zeta potential values, being positive or negative, tend to stabilize particlesuspension. The electrostatic repulsion between particles with the same electric chargeprevents the aggregation of the spheres. The PLGA particles made by the solvent evaporationmethod were negatively chargedas can be seen in table 6.2 and, hence, were poorlymucoadhesive. At a neutral pH value the mucus layer is an anionic polyelectrolyte.Mucoadhesion is promoted by a positive zeta potential value and, thus, the presence of the92