Formulation Optimization of an Indomethacin-Containing Photocrosslinked Polyacrylic Acid Hydrogel as an Anti-inflammatory Patch

Photocrosslinked polyacrylic acid hydrogel, made from polyacrylic acid (PAA) modified with 2-hydroxyethyl methacrylate (HEMA), is a promising candidate adhesive for dermatological patches. In this study, we investigated the further availability of hydrogel as an adhesive for dermatological patches using a hydrogel containing indomethacin (IDM) as a model anti-inflammatory patch. From an orthogonal experimental study, we clarified the relationships between formulation factors and characteristics of model formulation. Formulations with a lower degree of swelling were prepared by increasing the degree of HEMA modification and the addition of Tween 80. Apparent permeation rate was increased by addition of L-menthol and Tween 80. A tendency for higher HEMA modification to be accompanied by the prolongation of the lag time of IDM was observed. To obtain an applicable anti-inflammatory patch, we conducted a formulation optimization study using a novel optimization method, a response-surface method incorporating multivariate spline interpolation (RSM-S). Consequently, a highly functional anti-inflammatory patch in terms of its adhesive properties and bioavailability was successfully obtained. Since a wide range of functions can be fully controlled by manipulating the formulation factors, photocrosslinked polyacrylic acid hydrogel is an attractive candidate adhesive for dermatological patches.