# Encapsulation of Rose Extract in Polyurethane Structures Modified for Enhanced Aqueous Solubility
## 4 Discussion
The skin frequently returns to its normal pH level when it comes into touch with substances that have a different pH because of its capacity to preserve its natural equilibrium. But for most parts of the body, the ideal pH range for skin is between 4.7 and 5.75. As a result, topical treatments usually function in the pH range of 4 to 7 [36]. A key characteristic of materials, the refractive index is important for the optical characterization and sensors used in drug carrier research. The obtained value (1.60) is similar to those reported by other research teams [37; 38]. One of the most important factors in optimizing the final structures is the amount of extract trapped in the PU carrier. A quantity of 35.3 \(\upmu\)g free extract (Wf) was found overall in the mixture used to wash sample PU_1. The extract's entrapment efficiency was determined to be 71.76% by using Equation (1). Significant variation can be seen in this parameter, which can vary from 32.40% for D-\(\alpha\)-tocopherol polyethylene glycol 1000 succinate-resveratrol-solid lipid nanoparticles [39] and 69.35% for emodin, a naturally occurring antidiabetic agent encapsulated in nano-transferases [40], to 89.00% for P. amarus nanoencapsulated ethanolic extract [41] and higher. Also, the entrapment efficacy is high, so another main parameter is probably more important in this field. A sustained release of the active agents from the carrier is crucial because it maintains a stable plasma extract concentration over time, which is essential for the treatment of many disorders [42]. Figure 4a depicts the extract release from the PU structures placed in a simulated plasma fluid. In order to determine which model performed best, drug release kinetics studies were conducted in relation to zero- and first-order, Higuchi, and Korsmeyer-Peppas models. As a result, the first-order model best expressed the in vitro release profile, as shown by the plot's regression value of 0.975, which is significantly higher than in the other cases. It can be assumed that the extract will be released locally on the gum without entering the systemic circulation because Figure 4b shows a faster degradation of PU structures in a simulated saliva fluid due to the presence of enzymes than the penetrability rate (Figure 5). The importance of permeability rate across membranes on medication absorption, bioavailability, and overall therapeutic efficacy makes it a crucial criterion for carriers. Improved absorption and controlled release can result from comprehending and improving this parameter. Researchers persist in investigating many approaches, such as innovative materials and nanotechnology, to create sophisticated delivery systems with optimal membrane penetration characteristics [43]. There were no discernible variations found in the samples' permeation profiles. Almost 75% of the PU structures passed through the membrane in the first 24 h, which is probably due to the fact that the samples consist of multi-population structures with different sizes. The samples' wide size dispersion and multimodal character (several populations of structures) were shown by the zetasizer measurements' findings (Table 2). For PU_0 and PU_1, the mean diameter ranged from 98 to 106 nm and from 149 to 203 nm, respectively; the polydispersity index verified this finding. Furthermore, each sample's \(\zeta\)-potential measurement, with values ranging from \(-\)21.1 to \(-\)23.4 mV, showed a medium stability of structures against aggregation. The examined samples had consistently dispersed agglomerated clusters, as seen by the SEM pictures. These findings show that there is less aggregation and a greater number of solitaries, non-spherical structures, in the case of sample PU_0, while the aggregation was greater in the case of the other sample.