In Situ Synthesis of Keratin and Melanin Chromophoric Submicron Particles

[Image: see text] In humans, melanin plays an esthetic role, dictating hair and skin color and traits, while keratin is the protein that comprises most of the epidermis layer. Eumelanin and pheomelanin are types of melanin synthesized from the same building blocks via enzymatic oxidation. Pheomelanin has an additional building block, cysteine amino acid, which affects its final structure. Keratin contains high cysteine content, and by exploiting free thiols in hydrolyzed keratin, we demonstrate the formation of keratin–melanin (KerMel) chromophoric submicron particles. Cryo-TEM analyses found KerMel particle sizes to be 100–300 nm and arranged in the form of a central keratin particle with polymerized l-dopa chains. Attenuated total reflection (ATR)-FTIR, UV–vis, and fluorescence measurements identified new chemical bonds, indicating the formation of KerMel particles. Finally, KerMel replicated natural skin tones and proved cytocompatibility for human epidermal keratinocytes at concentrations below 0.1 mg/mL. Taken together, KerMel is a novel, tunable material that has the potential to integrate into the cosmetic industry.