Eco-Friendly Active Film and Sealant for Underwater Drug Delivery to Diseased Corals

Symbiotic bacteria in corals play a role in regulating coral responses, modifying their distribution and community composition based on the corals’ conditions (e.g., oxidative stress). However, not all associated bacteria have beneficial effects on corals; some can induce harmful diseases, while others, such as opportunistic strains, can take advantage of favorable community dynamics to thrive and disrupt the holobiont equilibrium. Such diseases have become a threat to reefs, occurring more frequently and causing more destruction to these ecosystems. Only a few options to treat such infections have been proposed, involving the mechanical removal of the lesion or the administration of probiotics, phage therapy, or active molecules. However, these methods present drawbacks limiting their effectiveness, e.g. uncontrolled antibiotic administration may induce antibiotic-resistance to other bacteria in the surrounding environment, while probiotics and viruses can be difficult to administrate in nature and disadvantageous to scale at industrial level. Inspired by buccal delivery design systems to treat human infections in wet environments, we developed a new strategy to treat coral disease. We created an eco-friendly underwater drug delivery system to address coral bacterial infections. This system consists of an antibiotic-loaded hydrophilic film applied directly onto the infected coral tissue, alongside a hydrophobic bio-based sealant that covers the film. The sealant ensures adhesion and prevents drug leakage into the environment while the film continuously releases the drug at the infected site. The design was optimized to ensure monodirectional drug release to the infected coral tissue within one week of treatment, targeting the infected coral while preventing environmental release. This technology successfully inhibited the growth of Vibrio coralliilyticus (a common pathogen for corals, responsible for white syndromes and bacterial-induced bleaching) and halted the progression of tissue necrosis-like symptoms in in-vivo-tested corals. Moreover, 8 months from the application, coral base expansion was qualitatively observed.