Glycerol-plasticized and tannic acid-modified ulvan films with enhanced mechanical and antioxidant properties

Excessive blooms of green macroalgae of the Ulva genus can lead to severe ecological and economic burdens. Therefore, strategies to circumvent these issues are required. As ulvan, the major sulfated polysaccharide extracted from Ulva, is biocompatible, biodegradable, and possesses sulfated functional groups and intrinsic film-forming capability, it is an attractive candidate for sustainable material development. In this study, ulvan was used to fabricate films and systematically evaluated for their mechanical performance and flexibility. Ulvan-based films were fabricated using glycerol as a plasticizer and tannic acid (TA) as a naturally derived functional modifier and bioactive component. The glycerol incorporation increased chain mobility and improved the polysaccharide matrix flexibility. TA introduced abundant phenolic hydroxyl groups capable of promoting hydrogen bonding within the polymer matrix, thereby contributing to enhanced intermolecular interactions. Spectroscopic and thermal analyses suggested enhanced intermolecular interactions and changes in thermal behavior as the TA content increased. Mechanical characterization revealed concentration-dependent changes in tensile strength and elongation behavior. TA incorporation increased the radical scavenging activity of the films in a concentration-dependent manner. MTT assays demonstrated the non-cytotoxicity of the developed films in human dermal fibroblasts and keratinocytes. Intracellular reactive oxygen species levels were further measured using DCFDA staining, which resulted in reduced intracellular oxidative stress levels. These findings demonstrate that tannic acid incorporation can be utilized to design eco-friendly polymer films with composition-dependent mechanical and biofunctional properties. The developed ulvan-based films may have potential applications in biomedical materials, including wound dressings, tissue interfaces, and protective bioactive coatings.