Tacrolimus encapsulated mesoporous silica nanoparticles embedded hydrogel for the treatment of atopic dermatitis

Atopic dermatitis (AD) is a repetitive inflammatory skin disorder with limited treatment options. Innovative targeted therapies are gaining significant interest and momentum towards disease control including better ways to deliver drugs topically. Tacrolimus is one such compound which is used to manage moderate to severe AD without causing atrophy which is one of the common side effects of steroids. However, Tacrolimus suffers from poor solubility and retention in the skin when used alone in hydrogel. Therefore, we have prepared Tacrolimus loaded mesoporous silica nanoparticles (TMSNs) to overcome the issues related to its solubility and effective topical delivery. Mesoporous silica nanoparticles (MSNs) were synthesized using sol gel technique and surface functionalized using amino (-NH₂⁺) and phosphonate (-PO₃^-) groups. Tacrolimus was loaded into MSNs and the particles were characterized for particle size (TEM and DLS), zeta potential (DLS), solubility studies, FTIR, TGA, XRD, BET and cytotoxicity studies. Water solubility of Tacrolimus was increased by 7 folds with phosphonate functionalized MSNs compared to free Tacrolimus. Further the TMSNs were incorporated in to carbopol gel, and the gel formulation was evaluated for various gel characterization tests (pH, spreadability, viscosity), in vitro tests (drug release, permeability studies) and in vivo tests (skin irritation study and efficacy studies) using 1-Fluoro-2,4-dinitrobenzene (DNFB) induced dermatitis in Balb/c mice. Results of in vitro and in vivo study showed that TMSNs loaded gel showed significantly higher amount of Tacrolimus retained (ex vivo - rat skin) and much higher reduction in ear thickness and improved histology (in vivo - in mice). Our data collectively suggest that MSNs incorporated hydrogel as a promising new formulation strategy for topical delivery of poorly soluble drugs.