Polymer-Concentration–Dependent Diffusion and In-Vitro Biological Evaluation of a Rutin-Loaded Hydrogel for Periorbital Application

Dark circles or periorbital hyperpigmentation are a tricky issue caused by a combination of excess melanin, oxidative stress, and poor circulation. Rutin, a natural antioxidant and anti-inflammatory, is a perfect candidate to treat this, but it has two major flaws: it doesn't dissolve well in water and it struggles to penetrate the skin on its own. To solve this, we tested how changing the amount of Carbopol 940 (a thickening agent) in a hydrogel could affect delivery of Rutin. We created six different versions (F1–F6), varying the polymer from 0.5% to 1.0%. Various tests were performed, including using a Franz diffusion cell to mimic how the drug moves through a membrane and checking how well it blocks tyrosinase, the enzyme responsible for skin pigment. The results showed a clear thick-to-slow relationship: as we added more Carbopol, the gel became denser, which slowed down the Rutin's escape. Formulation F4 was the standout winner. It released about 80% of the Rutin steadily over 12 hours, following the Higuchi model (R2=0.991). This confirms that the drug isn't just dumping out all at once; it's diffusing through the gel in a controlled, predictable way. Crucially, Rutin preserved its efficacy within the gel, inhibiting tyrosinase activity by up to 78.2%. This proves that we can use polymer levels to fine-tune how long a treatment lasts without weakening its ability to brighten the skin. By adjusting the gel's density, we’ve created a steady, gentle delivery system that is perfect for the sensitive skin around the eyes.