Melanin, the What, the Why and the How: An Introductory Review for Materials Scientists Interested in Flexible and Versatile Polymers

Abstract

Today, western society is facing challenges to create new medical technologies to service an aging population as well as the ever-increasing e-waste of electronic devices and sensors. A key solution to these challenges will be the use of biomaterials and biomimetic systems. One material that has been receiving serious attention for its biomedical and device applications is eumelanin. Eumelanin, or commonly known as melanin, is nature’s brown-black pigment and is a poly-indolequinone biopolymer, which possess unique physical and chemical properties for material applications. Presented here is a review, aimed at polymer and other materials scientists, to introduce eumelanin as a potential material for research. Covered here are the chemical and physical structures of melanin, an overview of its unique physical and chemical properties, as well as a wide array of applications, but with an emphasis on device and sensing applications. The review is then finished by introducing interested readers to novel synthetic protocols and post synthesis fabrication techniques to enable a starting point for polymer research in this intriguing and complex material.

Stress Dependent Biofilm Formation and Bioactive Melanin Pigment Production by a Thermophilic Bacillus Species from Chilean Hot Spring

“…The fluorescence of the brown pigment is demonstrated in Figure 5A and the spectra of B. haynesii CamB6 melanin have a Gaussian shape, showing a maximum absorption at 488.6 nm (Figure 5B). This behavior is similar to that previously reported from other melanin samples [45,46]. Some authors point out that such a profile can be due to the inherent structural heterogeneity, at the primary and secondary level, of melanin samples [46].…”

The Bright Side of the Tiger: Autofluorescence Patterns in Aedes albopictus (Diptera, Culicidae) Male and Female Mosquitoes

“…The presence of intermediate products of the melanin synthesis pathway has been already confirmed to contribute to the color of wing scales in butterflies [ 70 , 71 ], in addition to a recognized participation in the modulation of a wide range of physiological processes that are conserved across insects, including immunity, wound healing and protection from parasitoids and UV light [ 72 , 73 ]. Melanins are reddish or brown-black heterogeneous biopolymers, respectively termed pheomelanin or eumelanin, derived from the common precursor tyrosine [ 74 ]. Both eumelanin and pheomelanin strongly absorb visible light, with a continuous absorption curve decreasing exponentially from the shorter to the longer wavelengths in the visible spectral interval [ 75 , 76 , 77 ] and can exhibit distinct AF properties.…”

Water-Activated Semiquinone Formation and Carboxylic Acid Dissociation in Melanin Revealed by Infrared Spectroscopy

“…As shown in Table 2, the atomic composition (atomic concentration in at% and atomic ratio) of the sample can be seen. Melanin is an oligomeric mixture primarily composed of the DHI and DHICA moieties and their assorted oxidative states [11,72,73]. Consequently, it is expected that melanin samples will have an overall atomic ratio profile that falls in between those expected for DHI and DHICA (see Table 2, "Expected").…”