Structural and Functional Tailoring of Melanin-Like Polydopamine Radical Scavengers

Melanin is a ubiquitous but poorly understood polymeric, dark brown to black pigment biomaterial found both in nature and by organic synthesis. Its structural heterogeneity and disordered covalent/noncovalent interactions make it a grand challenge to tune and improve the physical and biological properties of both melanin sources. Herein, we report a facile one-pot fabrication approach for synthetic melanins with controlled size and composition via copolymerization of dopamine and basic amino acid such as arginine in an aqueous solution. The resulting arginine-doped polydopamine melanin-like nanoparticles possess less ordered nonplanar microstructures within the particles, whereas the conventional polydopamine-based melanins contain a variety of compact p-stacked microstructures. The assembly of these distinct polymeric microstructures could lead the preceding ones for greater accessibility to free radicals, with resultant stronger free-radical scavenging effect, and thus, exhibit superior antioxidant performance toward cellular oxidative stress. This work has inspired us to continue to fabricate new synthetic melanin pigments with tunable and improved functions by rational structural tailoring.