# Synthesis of Star Nanoparticles and Their Applications for Bioactive Compound Encapsulation
## 2 SNP Preparation Method
### Emulsion/Microemulsion  
This process consists of the formation of an emulsion through two phases, an aqueous solution containing the dissolved polymer and an organic solvent that is immiscible or partially immiscible in water. Subsequently, the two phases are emulsified with intense agitation which can be carried out by means of a mechanical homogenizer such as microfluidization or ultrasonic homogenization. The presence of a surfactant is required to stabilize the emulsion. The droplets formed due to the agitation act as nanoreactors that produce the controlled precipitation of the starch in the form of nanoparticles inside. A graphic representation of this method is depicted in Figure 3.  
Microemulsions can also be used to form SNPs, which typically lead to the formation of smaller and more uniform particles [26]. In this case, an intense agitation to form the microemulsions is not necessary since they form spontaneously with very little energy input. In 2017, [PERSON] and [PERSON] synthesized SNPs by a W/O microemulsion method where they dissolved corn starch in alkaline urea solution with different starch concentrations and further precipitated in ethanolic emulsion system using Tween 20 as surfactant  
Figure 3: Synthesis of SNPs through emulsion/microemulsion method and SEM micrographs of (**a**) corn SNPs [27] and (**b**) potato SNPs [28]. and sunflower oil by adding the starch solution dropwise into the microemulsion system. The SNPs produced this way were uniform in shape and size, due to homogeneous solution obtaining sizes of 40 nm. However, smaller sizes were obtained when the lowest starch concentrations were used [27]. [PERSON] et al. also carried out the formation of a W/O microemulsion to synthesize spherical SNPs. Maize starch was dissolved into an aqueous phase with sodium hydroxide and urea and then 1 mL of this solution was added into an organic phase under constant stirring. This organic phase was formed by oil (soybean and sunflower), a surfactant (Tween 20 and Span 60) with different concentrations, and absolute ethanol as a co-stabilizer. This method led to sizes from 35 nm to 147 nm with a higher particle formation capacity and without the presence of large agglomerates. The final SNPs size was not influenced by the type of oil used in the microemulsion formulation; however, smaller sizes were obtained by the use of very hydrophilic surfactants (Tween 20) [24]. [PERSON] et al. synthesized SNPs from hydrophobic starch derivative, propyl- potato starch through an emulsion-diffusion technique. This technique differs from the conventional microemulsion in the way that a W/O emulsion is formed within a partially water-soluble solvent and subsequently water is added to the system which causes the diffusion of the solvent towards the external phase, resulting in the formation of nanoparticles [29]. It has numerous advantages such as high performance and encapsulation efficiency, reproducibility, and scalability. The authors studied different nonionic surfactants and their effect on the SNPs size and homogeneity. Best results were obtained when polyvinyl alcohol (PVA) was used as a surfactant obtaining a low particle size and the most homogeneous formulation. Finally, the lowest particle size obtained was 245.5 nm, which was achieved with a drug: starch ratio of 1:5 [30]. [PERSON] et al. also used an emulsion-diffusion method to synthesize corn SNPs obtaining a particle size of 180 nm in the aqueous solution. Starch was dissolved in DMSO as the organic phase and a mixture of PVA and distilled water was used as the aqueous phase. The droplets obtained on the biphasic system were precipitated in the form of SNPs when DMSO was diffused by the addition of distilled water to the system [31]. Similarly, [PERSON] et al. synthesized SNPs with a W/O emulsion-diffusion method using two different propyl-starch derivatives with high degrees of substitution (1.05 and 1.45) and an unmodified starch polymer.