**3.1 Nanoprecipitation**

Nanoprecipitation, also named interfacial deposition method or solvent displacement, was the first method described [22], and it has been widely used in the last two decades, principally because it is fast, and it has extensive applicability, being able to be used with many types of materials, and allowing various drugs to be encapsulated. In addition, it is a low-cost and simple operation technique since it does not require any special equipment [5]. The preparation of nanocapsules using this method involves both an organic and an aqueous phase. Typically, the organic phase, which consists of oil, polymer, and the active compound dissolved in an organic solvent, is added slowly and with moderate stirring to the aqueous phase (in most cases water and a selected surfactant). Hence, the formation of nanocapsules results from a combination of the spontaneous emulsification of oily droplets and the simultaneous precipitation of polymer onto the water-oil interface during the diffusion of phases [23]. Finally, the colloidal aqueous suspension is obtained by eliminating the organic solvent via evaporation or through a drying process [6, 24]. The characteristics of nanocapsules formed by nanoprecipitation are mainly influenced by several process variables, such as nature, concentration, and compatibility of the components [21], volume ratio between organic and aqueous phase, and the selected method for the injection of the organic phase. In fact, there is some evidence that varying the organic phase injection rate, the aqueous phase agitation rate, and adding the organic phase through a thin needle, leads to a significant decrease in the average size of the nanocapsules, compared with the technique consisting in just pouring one phase over the other [25]. This is probably due to the increase of the contact surface between the phases [26].
