Human hair is naturally
colored by melanin pigments, which afford
myriad colors from black, to brown, to red depending on the chemical
structures and specific blends. In recent decades, synthetic efforts
have centered on dopamine oxidation to polydopamine, an effective
eumelanin similar to the one found in humans. To date, only a few
attempts at polydopamine deposition on human hair have been reported,
and their translation to widespread usage and potential commercialization
is still hampered by the harsh conditions employed. We reasoned that
novel, mild, biocompatible approaches could be developed to establish
a metal-free route to tunable, nature-inspired, long-lasting coloration
of human hair. Herein, we describe synthetic and formulation routes
to achieving this goal and show efficacy on a variety of human hair
samples via multiple spectroscopic and imaging techniques. Owing to
the mild and inexpensive conditions employed, this novel approach
has the potential to replace classical harsh hair dyeing conditions
that have raised concerns for several decades due to their potential
toxicity.