**4. Conclusions**

Rutin nanocrystals were successfully prepared by the anti-solvent nanoprecipitation– ultrasonication method using various stabilizers such as non-ionic surfactants and non-ionic polymers. The type of stabilizer had a great influence on the nanocrystal properties. Thus, HP-β-CD gave the most favorable nanocrystal properties in terms of small particle size, high drug entrapment efficiency, high zeta potential, good colloidal stability, and the highest drug photostability. In addition, HP-β-CD-stabilized nanocrystals had around a 202- and 6.7-fold enhancement in drug aqueous saturation solubility and dissolution rate, respectively. HP-β-CD also affected the drug release rate and permeability through skin. Thus, HP-β-CD-stabilized rutin nanocrystals dispersed in HPMC hydrogel had around a 2.5-fold higher skin permeability than the free drug hydrogel. This better permeability resulted in an enhanced in vivo anti-inflammatory effect compared to the free drug hydrogel and commercial diclofenac sodium gel. Collectively, these results show the importance of the careful selection of nanocrystal stabilizers to optimize drugs' physicochemical properties and maximize their in vivo efficacy.

**Author Contributions:** Conceptualization, A.S.H. and G.M.S.; methodology, A.S.H.; software, A.S.H. and G.M.S.; data curation, A.S.H. and G.M.S.; formal analysis, A.S.H. and G.M.S.; writing—original draft, A.S.H. and G.M.S.; writing—review and editing, A.S.H. and G.M.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study protocol was approved by The Research Ethics Committee, Faculty of Pharmacy, South Valley University, Egypt (approval number P.S.V.U 125/22).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
