Optimization, physicochemical characterization, ex vivo and in vivo evaluation of astaxanthin ethyl cellulose nanosponge hydrogel to alleviate atopic dermatitis-like symptoms.

Astaxanthin (AST), a potent antioxidant with anti-inflammatory activity, is limited by poor solubility and stability. This study developed AST-loaded nanosponges (AST-NS) using a QbD-based Box-Behnken design and incorporated them into a carbopol hydrogel to improve topical delivery in atopic dermatitis (AD). Response surface curves indicated that increasing stirring speed significantly decreased particle size, while increasing PVA concentration decreased the PDI. Ethyl cellulose and PVA concentrations significantly increased %EE, whereas ethyl cellulose decreased and PVA increased ex vivo skin permeation. Optimized formulation prepared by emulsion solvent diffusion method, produced spherical NS with a mean diameter of 19.5 nm, a polydispersity index (PDI) of 0.317, zeta potential -26.7 mV, and entrapment efficiency of 89.88%. FE-SEM confirmed a spherical, porous morphology, BET analysis showed a mesoporous structure with a type IV isotherm, and BGH analysis showed a higher surface area of 27.009 m2/g for NS. Surface area increased as pore volume (0.02012 cc/g or cm3/g) and particle pore size increased for the NS. Amorphization behavior was observed with a shift in the AST melting peak toward the lower side in DSC studies, and reduced crystallinity in XRD. FTIR studies confirmed the entrapment of AST inside the NSs. Stability studies indicated better performance of AST-NS at room temperature, while aggregation was observed at lower temperatures. The AST-NS hydrogel demonstrated a suitable pH (5.89) and appreciable rheological properties for topical applications, with good spreadability (887.02 ± 2.62 N.mm) and extrusion (6.07 kg.s), acceptable gel strength (5002.33 ± 632.49 g), and adequate cohesiveness (5.410 ± 0.367 g) (supplementary table S2), which support retention at the application site. Ex vivo porcine skin studies showed significantly enhanced transdermal delivery and retention of AST from NS gel compared to free AST. In a DNCB-induced AD mouse model, treatment with AST-NS-hydrogel markedly improved skin lesions and inflammation, as evidenced by reductions in cytokine levels (IL-5, IL-4, IFN-γ), IgE, and leukocyte infiltration, and by restoration of normal skin histology. Therefore, AST-NS hydrogel offers effective and promising therapy in AD.