Gallic acid modified alginate self-adhesive hydrogel for strain responsive transdermal delivery

Transdermal drug delivery (TDD) has gained attention over the past decades as a pain-free drug administration path. Various drug release control mechanisms have also been developed for the advanced application of TDD. However, most controlled delivery systems depend on external stimuli such as temperature, pH and so on; making the design complicated and more expensive. In this study, we prepared mussel inspired self-adhesive hydrogel for monolith, drug in adhesive, strain-controlled transdermal delivery using a simple and effective method. The synthesis method involves modifying alginate with gallic acid followed by in-situ polymerization of polyacrylic acid. The resulting hydrogel (GA) is a heavily intertwined, interpenetrating supramolecular network mainly due to the numerous hydrogen bonds. It is extremely stretchable (800% strain) and adheres strongly on polymer, glass, and metal under both wet and dry conditions. Additionally, it has a layered and highly porous internal structure providing excellent elasticity and efficient drug delivery. Kinetic experiment results show that 77.47%, 82.09%, 87.64% and 42.54% of pre-loaded caffeine in GA is released within an hour under 100%, 50%, 25%, and 0% tensile strain, respectively. These results demonstrate that GA is a potential self-adhesive matrix for strain controlled TDD for caffeine possibly for other drugs as well.