# Synthesis of Star Nanoparticles and Their Applications for Bioactive Compound Encapsulation
## 2 SNP Preparation Method
### Nanoprecipitation  
Nanoprecipitation process involves the successive addition of a dilute solution of polymer to a solvent which leads to the polymer precipitation on the nanoscale. This method is essentially based on the deposition or displacement of the polymer in the interface followed by the displacement of the solvent from the lipophilic solution [13]. A schematic representation of this nanoprecipitation method is shown in Figure 2.  
One of the most common solvents used by many authors is acetone which leads to the precipitation of the starch in the form of nanoparticles when it is added dropwise from an aqueous phase where it was previously dissolved. [PERSON] et al. prepared SNPs using acetylated corn starch and optimized the reaction of native starch using acetic anhydride and acetic acid with low and high degrees of substitution (DS). A size range of 221-324 nm  
Figure 1: Top-down and bottom-up processes for the synthesis of the SNPs. Figure 2: Synthesis of SNPs through nanoprecipitation method and TEM micrographs of corn SNPs (**a**) [14] and (**b**) [15]. Reprinted from [14] with permission from Elsevier. Copyright (2015). was obtained by studying different DS levels and water/acetone ratios [16]. In 2018, [PERSON] et al. used native and acetylated starch obtained from green bananas for the synthesis of SNPs by a nonoprecipitation method where they also used acetone as the solvent. Both systems presented similar results, obtaining a size of 135 nm when the native starch was used and 190 nm when the acetylated starch was used. In turn, to understand the size difference of the SNPs, they studied the size of the starch granules. A slight aggregation in the acetylated banana starch granules was observed which was due to the increase in the intermolecular hydrogen bonds starch granules and water which could explain the difference size observed in the nanoparticles with both starches [17]. Similar studies were carried out by [PERSON] et al. who also used native and acetylated banana starches for the synthesis of the SNPs. As in the previous case, larger particle sizes (198 nm) were obtained when acetylated starch was used, while using native starch, sizes of 141 nm were obtained [18]. Another common solvent used in nanoprecipitation method is absolute ethanol. In some cases, it is added dropwise to a deionized water solution containing the dissolved starch or vice versa. In recent studies, [PERSON] et al. synthesized NPs from corn starch and amylose by this method. They observed that most of the corn SNPs were spheres with some aggregates obtaining particles from dozens of nanometers up to 500 nm. On the other hand, the amylose NPs presented irregular shapes which were smaller than the previous ones. The diffraction patterns in both NPs presented two peaks, the smaller one had practically the same position for both, however, the position of main peak turned out to be slightly different suggesting higher sizes for the corn SNPs compared to the amylose NPs. Nevertheless, both NPs presented a V-type crystalline structure. Finally, the average size of the starch particles obtained was 350 nm while that for the amylose particles was 250 nm [19]. [PERSON] et al. reported a method that combined nano-precipitation methods with acid hydrolysis resulting in SNPs with different crystallinity. The acid hydrolysis method produced SNPs with high relative crystallinity, whereas the ethanol preparation method resulted in SNPs with low crystallinity. In order to vary the hydrophilicity of the starch SNPs were also modified by using different cationic, anionic, and nonionic surfactants. The morphology observed before the modification was flaky for SNPs obtained by the hydrolysis and spherical for the nanoprecipitation ones. Significant changes were not observed after the modification with cationic and anionic surfactants for both methods. However, when nonionic surfactant was used, a significant change was observed appearing as different adsorption mechanisms on the SNPs surface in both cases.