Preparation of redispersible dry nanocapsules by means of spray-drying: development and characterisation

Nanoparticles suspensions very often present a physicochemical instability during their storage. In order to overcome this lack of stability and facilitate the handling of these colloidal systems, the water elimination from the aqueous dispersions to obtain a dry solid form appears as the most promising strategy. The present paper reports the use of the spray-drying technique for the nanocapsules (NC) suspensions conversion into redispersible dried solid particles in presence of different water-soluble excipients as drying auxiliaries. Following the combination of additives solutions with NC suspension, the final dispersion homogeneity was favoured, avoiding phase separations. According to the size measurement after a simple atomisation experiment, the NC, which have a thin and fragile shell structure can withstand the shear forces developed for the feed disintegration in droplets. During drying, certain additives molecules are able to act as NC protectors. The physicochemical characterization of the spray-dried powders included an investigation of their properties, such as residual moisture content, particulate density, morphology and redispersion in water. Using a NC concentration of 1% (w/v), the best result was obtained with the preparation containing 10% (w/v) of lactose which led to more desirable powder morphology and favouring NC suspension reconstitution with only approximately 2% of the size distribution in the micrometer range. The spray-drying technique is an attractive method to improve the NC conservation and facilitate future handling.