Research progress on the molecular structure, biosynthetic mechanism, and multidisciplinary applications of natural melanin

Melanin is an important biological resource with significant scientific and practical value. Consequently, its structure, sources, extraction and purification methods, functional properties, and applications have garnered widespread attention from researchers. Melanin is categorized into several types based on its synthesis pathways and intermediate metabolic products, including eumelanin, phaeomelanin, pyomelanin, and 1,8-dihydroxynaphthalene (DHN) melanin. Its biological sources mainly include bacteria, fungi, animals, and plants. Depending on the source, various extraction methods are employed, such as alkaline solutions, acidic solutions, alcohol solutions, and mixed solvents, with multi-factor experiments conducted for each method to determine optimized parameter combinations. Furthermore, purification methods such as alkaline precipitation, hydrochloric acid hydrolysis, and chromatography are utilized. Due to its characteristics, including radiation resistance, antioxidant properties, photothermal stability, metal chelation, amorphous semiconductivity, and enhanced pathogenic toxicity, melanin has found widespread applications in agriculture, materials science, industry, and medicine. This paper particularly highlights its applications in novel materials and pharmaceuticals. Through a systematic summary and review of key stages from melanin production to application, this study aims to deepen the understanding of natural melanin production and application, providing theoretical foundations and technical references to enhance the use of melanin in various fields.