# Stabilization of Argan Oil Nanoemulsions Using Chitosan Extracted from Pink Shrimp Shells
## 3 Results and Discussion
### Nanoemulsion
#### 3.2.1 Effect of Chitosan on Formulation Thermodynamic and Storage Stability
In topical delivery, the enhanced viscosity can improve the formulation adhesion and retention on the skin, leading to the more controlled release of encapsulated drugs or active ingredients while simultaneously improving the overall stability of the nanoemulsion system [26]. Droplet size analysis revealed that the formulations had nano-sized droplets with a low polydispersity index, indicating a narrow size distribution (Figure 5). Increasing chitosan concentration resulted in slightly larger droplet sizes, likely due to the formation of a chitosan coating around the droplets, as reported in a previous study [16]. This protective layer contributed to steric stabilization while preserving the nanometric size and narrow size distribution of the emulsions. Figure 4: Effect of chitosan concentration on formulation pH and viscosity. Unoated nanoemulsions displayed a negative zeta potential due to the adsorption of hydroxyl ions (OH\(-\)) from the water onto the droplets (Figure 6) [27]. Introducing chitosan shifted the zeta potential from negative to positive, which is attributed to the protonated amino groups on chitosan adsorbing onto the droplets. As the chitosan concentration increased, the zeta potential rose, indicating stronger electrostatic repulsion between the droplets, which improved stability over time. The high zeta potential values (positive or negative) indicate highly stable colloidal systems, typically within the range of \(-30\) mV and \(+30\) mV. However, values exceeding this range suggest even greater stability. The specific range can vary depending on the composition and intended use of the nanoemulsion. Positively charged nanoemulsions can also enhance interaction with negatively charged cell membranes, potentially enhancing drug delivery efficiency [28]. Chitosan coating of nanoemulsions can significantly enhance the stability and bioavailability of encapsulated compounds through multiple synergistic mechanisms. The cationic amino groups in chitosan interact electrostatically with negatively charged emulsion droplets, reinforcing structural integrity and preventing destabilization. Additionally, hydrogen bonding between chitosan's hydroxyl and amino groups and emulsifiers, water molecules, or bioactive compounds, along with hydrophobic interactions with lipid components, further strengthens the coating and improves compound retention. The increased viscosity imparted by chitosan creates a thicker interfacial layer around the droplets, providing steric hindrance that limits droplet mobility and aggregation [16]. Moreover, the chitosan coating acts as a protective barrier against oxidative degradation, preserving the structural integrity and functional efficacy of bioactive compounds. Previous research has shown that modifying chitosan through alkaline treatment improves its antioxidant activity and antimicrobial properties by increasing its positive surface charge and reducing crystallinity, thereby enhancing its interaction with biological systems [29]. Beyond stability, chitosan enhances bioavailability by promoting mucoadhesion and facilitating transport across biological membranes. Its cationic nature enables strong interactions with negatively charged cell surfaces, improving cellular uptake and absorption of encapsulated compounds [28]. Figure 5: Effect of chitosan concentration on formulation average droplet size, PDI, and zeta potential. Chitosanan-decorated nanoemulsions, with their tailored physicochemical properties, show promise for topical and transdermal drug delivery. Their enhanced stability, positive surface charge, and controlled viscosity improve skin permeation and retention, making them suitable for applications requiring sustained or localized drug release [25]. The physicochemical properties of nanoemulsions, particularly droplet size and interfacial characteristics, are significantly influenced by polymer coatings like chitosan. These modifications enhance stability and bioavailability, ensuring that the formulations remain robust and effective for diverse applications [16].