Melanin is a biological pigment formed by indoles and phenolic compounds. It is widely found in living organisms and has a variety of unique properties. Due to its diverse characteristics and good biocompatibility, melanin has become the focus in the fields of biomedicine, agriculture, the food industry, etc. However, due to the wide range of melanin sources, complex polymerization properties, and low solubility of specific solvents, the specific macromolecular structure and polymerization mechanism of melanin remain unclear, which significantly limits the further study and application of melanin. Its synthesis and degradation pathways are also controversial. In addition, new properties and applications of melanin are constantly being discovered. In this review, we focus on the recent advances in the research of melanin in all aspects. Firstly, the classification, source, and degradation of melanin are summarized. Secondly, a detailed description of the structure, characterization, and properties of melanin is followed. The novel biological activity of melanin and its application is described at the end.

Multifunctional drug delivery carriers have emerged as a promising cancer drug delivery strategy. Here, we developed a vitamin E succinate-chitosan-histidine (VCH) multi-program responsive drug carrier. The structure was characterized by FT-IR and ¹H NMR spectrum, and the DLS and SEM results showed typical nanostructures. The drug loading content was 21.0 % and the corresponding encapsulation efficiency was 66.6 %. The UV-vis and fluorescence spectra demonstrated the existence of the π-π stacking interaction between DOX and VCH. Drug release experiments implied good pH sensitivity and sustained-release effect. The DOX/VCH nanoparticles could be efficiently taken up by HepG2 cancer cells and the tumor inhibition rate was up to 56.27 %. The DOX/VCH reduced the tumor volume and weight efficiently with a TIR of 45.81 %. The histological analysis results showed that DOX/VCH could effectively inhibit tumor growth and proliferation, and there was no damage to normal organs. VCH nanocarriers could combine the advantages of VES, histidine and chitosan to achieve pH sensitivity and P-gp inhibition, and effectively improve the drug solubility, targeting and lysosomal escape. Through the program response of different micro-environment, the newly developed polymeric micelles could successfully be utilized as a multi-program responsive nanocarrier system for the treatment of cancers.