Reinforcement of alginate hydrogels with microbial melanin as multifunctional platforms for 3D human mesenchymal stem cell culture

The development of biomaterials that combine structural support with bioactive functionality is essential for advanced tissue engineering. In this study, microbial melanin produced by Streptomyces nashvillensis was incorporated into alginate hydrogels to create multifunctional scaffolds for three-dimensional (3D) culture of human mesenchymal stem cells (hMSCs). Melanin enhanced the physico-chemical properties of the hydrogels by preserving the fundamental chemical structure of alginate. Improvements were observed in viscoelastic behavior, electrical conductivity, and antioxidant activity, along with a reduction in enzymatic degradation. The structural characterization of the formulated hydrogels revealed a high compact and heterogeneous network, due to interactions between the microbial melanin and alginate. Melanin-containing hydrogels supported hMSC viability and proliferation, also promoting cell spreading and cytoskeletal organization, while intracellular reactive oxygen species (ROS) production was reduced and a modulation of the inflammatory gene expression, by up-regulation of IL-10 and downregulation of IL-1β gene expression in the melanin-containing hydrogels. These findings demonstrate that microbial melanin enhanced both the functional and biological performances of alginate suitable for 3D cell culture. Unlike previously reported systems mainly based on animal-derived or synthetic melanin, we propose biotechnologically produced extracellular microbial melanin as both a structural modulator and a bioactive component in a 3D hMSC culture platform.