Mimicking Melanosomes: Polydopamine Nanoparticles as Artificial Microparasols.

A primary role of melanin in skin is the prevention of UV-induced nuclear DNA damage to human skin cells, where it serves to screen out harmful UV radiation. Melanin is delivered to keratinocytes in the skin after being excreted as melanosomes from melanocytes. Defects in melanin production in humans can cause diseases, many of which currently lack effective treatments due to their genetic origins (e.g., skin cancer, vitiligo, and albinism). The widespread prevalence of melanin-related diseases and an increasing interest in the performance of various polymeric materials related to melanin necessitates novel synthetic routes for preparing melanin-like materials. In this work, we prepared melanin-like nanoparticles (MelNPs) via spontaneous oxidation of dopamine, as biocompatible, synthetic analogues of naturally occurring melanosomes, and investigated their uptake, transport, distribution, and UV-protective capabilities in human keratinocytes. Critically, we demonstrate that MelNPs are endocytosed, undergo perinuclear aggregation, and form a supranuclear cap, or so-called microparasol in human epidermal keratinocytes (HEKa), mimicking the behavior of natural melananosomes in terms of cellular distribution and the fact that they serve to protect the cells from UV damage.