Design and Characterization of a Bilayer Patch Containing Curcumin for Improved Skin Permeation

Transdermal drug delivery systems (TDDS) have emerged as an effective alternative to conventional dosage forms due to their ability to provide controlled drug release, improved bioavailability, and enhanced patient compliance. The present study aimed to formulate and evaluate a bilayer hydrogel transdermal patch comprising an immediate-release layer containing menthol and camphor, and a sustained-release layer containing thymol and curcumin. The immediate-release layer was formulated using Hydroxypropyl Methylcellulose (HPMC), whereas the sustained-release layer was developed using Carbopol 940 as the polymeric matrix. Menthol and camphor acted as permeation enhancers and provided rapid analgesic activity, while thymol and curcumin offered prolonged anti-inflammatory and antioxidant effects. The prepared hydrogel patches were evaluated for physicochemical properties, surface pH, thickness, moisture content, moisture uptake, folding endurance, tensile strength, drug content uniformity, in-vitro drug release, and stability studies. The patches exhibited satisfactory physicochemical characteristics with uniform drug distribution and acceptable mechanical strength. In-vitro drug release studies demonstrated followed by sustained drug release up to 8–9 hours. Drug release kinetics were found to follow the Higuchi diffusion model. The developed bilayer hydrogel patch demonstrated significant potential as a patient friendly transdermal delivery system for the effective management of pain and inflammatory disorders. Keywords: Transdermal patch, Bilayer system, Menthol, Camphor, Thymol, Curcumin, Sustained release.