Structural and Functional Tailoring of Melanin-Like Polydopamine Radical Scavengers

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 Apr 2020Structural and Functional Tailoring of Melanin-Like Polydopamine Radical Scavengers Peng Yang†, Zhipeng Gu†, Fang Zhu and Yiwen Li Peng Yang† College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China) , Zhipeng Gu† College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China) , Fang Zhu College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China) and Yiwen Li *Corresponding author: E-mail Address: [email protected] College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065 (China) https://doi.org/10.31635/ccschem.020.201900077 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail 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 π-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. Download figure Download PowerPoint Introduction Melanin refers to a family of biopigments distributed mostly in animals, in particular, on the human body, and also, from some plant sources. The pigment possesses many intriguing physicochemical and biological functions, including photoprotection, photothermal conversion, energy dissipation, metal ion-chelation capacity, and free-radical scavenging properties.1–6 Despite its ubiquitous existence in nature, it remains part of a class of enigmatic materials. Unlike other types of biomacromolecules such as proteins or nucleic acids, the sophisticated biosynthetic pathways toward natural melanin formation, particularly, the mechanisms that govern the polymerization and the self-assembly of the disordered oligomers, have not been fully understood yet.7–13 Notably, such a poor understanding substantially limits the rational strategies for controlling and fine-tuning of the electronic, optical, and free-radical properties of melanin-inspired synthetic biopolymers. Therefore, the current resurgence of interest in this area is to explore melanin in both natural and synthetic systems to elucidate their structure-function relationships, mimic, and improve the emergent functionalities. One of the essential features of body melanin or its synthetic analogues [i.e., polydopamine (PDA) nanospheres] is the balance between its generation and the presence of reactive oxygen species (ROS), which, otherwise might lead to oxidative stress and consequently, serious disease states in the human body.14–21 Recently, a couple of studies have illustrated that melanin-like PDA nanomaterials could be employed as a class of intelligent free-radical scavengers for the treatment of a series of diseases, including reactive oxygen and nitrogen species-induced ischemic stroke, acute inflammation-induced injury, oxidative stress-induced periodontal diseases, and osteoarthritis.22–25 Thus, further tailoring and improvement of the free-radical scavenging activities of melanin and its polymeric derivatives seem nontrivial to promote their ultimate technological utilization. d'Ischia's group26 pioneered the elucidation of structure–property relationship of 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-based and 5,6-dihydroxyindole (DHI)-based melanins. They observed the former compound could exhibit a superior free-radical scavenging property since the extra carboxylate group was able to twist the inter-ring oligomeric angles and induced the formation of nonplanar microstructures with weak aggregating interactions, consequently accounting for greater accessibility of free radicals in DHICA-based melanin, compared with the DHI-based melanin-containing compact π-stacked microstructures. Although this model wa