Capped flexosomes for prominent anti-inflammatory activity: development, optimization, and ex vivo and in vivo assessments.

This study aimed to formulate diacerein (DCN)-loaded flexosomes for enhanced efficacy against osteoarthritis. A 2³ D-optimal design was employed, investigating the impact of surfactant type (A), surfactant concentration (%w/v) (B), and oleylamine amount (mg) (C). Flexosomes were formulated using a rotary evaporator, and Design-Expert^® software was utilized to statistically analyze entrapment efficiency (EE%), zeta potential (ZP), poly-dispersity index (PDI), and particle size (PS) to determine the optimum formula. The selection criteria prioritized increased ZP (as absolute value) and EE%, coupled with decreased PDI and PS. Rigorous physicochemical, in vivo, and ex vivo tests were conducted to validate the safety, stability, and activity of the optimal formula. Physicochemical assessments encompassed pH measurement, transmission electron microscopy, differential scanning calorimetry, release profiles, storage effects, and Fourier transform infrared spectroscopy. In vivo tests included permeation studies, histopathology, anti-inflammatory activity, and skin irritancy, while ex vivo tests focused on permeation parameters and skin deposition. The optimum formula demonstrated high desirability (0.931), along with favorable EE% (90.93%), ZP (- 40.4 mV), particle size (188.55 nm), and sustained behavior. Notably, improved in vivo permeation (132 µm), skin deposition (193.43 µg/cm²), and antinociceptive activity (66%) compared to DCN suspension (48 µm, 66.31 µg/cm², and 26%, respectively) were observed. The optimal formula also exhibited excellent safety and storage characteristics. In conclusion, DCN-loaded flexosomes exhibit significant potential for effectively managing osteoarthritis.