Silica-Eumelanin Hybrid Nanoparticles Engineered by Covalent Conjugate Polymerization

Organo-inorganic hybrids, made by coupling inorganic nanostructures to organic molecules, provide the opportunity to invent a huge set of new multifunctional materials with a large spectrum of known and as yet unknown properties. Eumelanins, hydrophobic natural pigments, are emerging as a powerful organic component for developing biologically active materials because of their numerous biological functions, such as photo-protection, photosensitization, free radical quenching, metal ion chelation and even intrinsic antimicrobial behavior. Silica is one of the few inorganic material recognized as ‘safe' by the US FDA. In addition, the endogenous nature of silica and its functional versatility make it one of the most intensively investigated among inorganic materials in the field of biotechnology, health and medicine both for imaging and delivery. Furthermore, it is biocompatible and easy to functionalize to guarantee active targeting, as well as long circulation times. Following a bioinspired approach, herein we propose a novel synthesis strategy to the design eumelanin-silica hybrid nanoparticles integrating the potent antioxidant properties of DHICA eumelanin into a stable, bioactive and biocompatible silica matrix. These systems prove that eumelanin’s biofunctional and physico-chemical properties can be markedly enhanced, if its formation occurs through templated polymerization in the presence of a ceramic phase. Particularly, this approach presents manifold potentialities that can ultimately lead to cutting-edge functional hybrid materials featuring relevant antioxidant and cytoprotective nanoparticles endowed with high stability, biocompatibility and specific cell localization to lysosomes.