Ellipsoidal Artificial Melanin Particles as Building Blocks for Biomimetic Structural Coloration

Kohri, Michinari; Tamai, Yuki; Kawamura, Ayaka; Jido, Keita; Yamamoto, Mikiya; Taniguchi, Tadatsugu; Kishikawa, Keiki; Fujii, Syuji; Teramoto, Naozumi; Ishii, Haruyuki; Nagao, Daisuke

doi:10.1021/acs.langmuir.9b00400

Cited by 32 publications

(37 citation statements)

References 43 publications

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“…stretched polystyrene particles to ellipsoids and then coated a melanin layer to get ellipsoidal core‐shell melanin particles. [ 111 ] They demonstrated that an increase in the aspect ratio of the ellipsoidal particles caused a blue shift in the reflected light.…”

Section: Bioinspired Optics‐related Applicationsmentioning

confidence: 99%

Bioinspired Melanin‐Based Optically Active Materials

Xiao

Shawkey

Dhinojwala

2020

Advanced Optical Materials

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the properties and functions of melanin, the synthesis of melanin-like nanoparticles, and its versatile applications in catalysis, energy, and biomedical fields. Over the last 5 years, more than 1000 papers on melanin have been published annually, based on data from the Web of Science. Quite a few of these papers have reviewed melanin's chemical structure, physiochemical properties, and biomedical applications. [4-6] However, a critical review focusing on optical functions of melanin is still lacking, despite tremendous emerging work on melaninbased photonic materials. The purpose of this review is to summarize current advances in bioinspired melanin-based optically active materials. Specifically, we will cover inherent optical properties of melanin, and then summarize melanin's optical functions in nature and its optics-related applications. 2. Melanin Structure and Optical Properties Melanin has complex chemical structures that is not yet fully understood, however, it does not hinder the exploration of their optical properties. In this section, we will first discuss classifications of melanin and then summarize unique optical properties of melanin, which will be important for both understanding its biological function in nature and synthetic applications. 2.1. Classification and Structure Conventionally, all black pigments are called melanin. Recently, d'Ischia et al. suggested that any phenolic polymers that have broadband light absorption, antioxidant, and intrinsic free radical character should be characterized as melanin. [5] Exact chemical structures of melanin remain elusive, mainly due to their insolubility in solvents, close binding with other cellular tissues, and an amorphous structure. Here, we do not elaborate on the complexities of melanin's chemical structures, [7] but rather focus on its classification. Melanin can be categorized as either natural or synthetic depending on whether it was synthesized in vivo or in vitro. Both have similar macroscopic properties, but their structures are likely quite different. Natural melanin, including eumelanin, pheomelanin, and neuromelanin, is produced from a series of enzymatic reactions starting from L-tyrosine in biological systems (Figure 1). [1] In cells (commonly melanocytes), the tyrosinase oxidizes L-tyrosine to dopaquinone (DQ). If cysteine concentration in Melanin is a widespread multifunctional biological pigment that has emerged as a promising platform for applications in coating, catalysis, energy, drug delivery, and medical therapy. Melanin is also a compelling material for photonic applications because of its favorable material characteristics, including broadband absorption, high refractive index, tunable fluorescence, and UV blocking capabilities. However, there is not yet a critical review focusing on optical functions of melanin. This review summarizes current advances in bioinspired melanin-based optically active materials, covering melanin's inherent optical properties and functions both in nature and in optics-related applications. It is ...

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Section: Bioinspired Optics‐related Applicationsmentioning

confidence: 99%

Bioinspired Melanin‐Based Optically Active Materials

Xiao

Shawkey

Dhinojwala

2020

Advanced Optical Materials

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“…As mentioned above, in the structural color of peacock feathers, rod-shaped melanin granules are used as a building block [37][38][39]. Mimicking the shape of the building block, our group reported the structural coloration from ellipsoidal artificial melanin particles [89]. Ellipsoidal artificial melanin particles were obtained by stretching a polyvinyl alcohol (PVA) film containing PS@PDA particles at a temperature above the glass transition temperature of the core PS particles, cooling the sample, and then melting the PVA.…”

Section: Effect Of Particle Shape On Colormentioning

confidence: 99%

Progress in polydopamine-based melanin mimetic materials for structural color generation

Kohri

2020

Science and Technology of Advanced Materials

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Structural color is a color derived from optical interaction between light and a microstructure and is often seen in nature. Natural melanin plays an important role in bright structural coloration. For example, the vivid colors of peacock feathers are due to structural colors. The periodic arrangement of melanin granules inside the feathers leads to light interference, and the black granules absorb scattered light well, resulting in bright structural color. In recent years, polydopamine (PDA) has attracted attention as a melanin mimetic material. This review article summarizes recent research on structural coloration using PDAbased artificial melanin materials. It also outlines possible applications using bright structural colors realized by artificial melanin materials and future perspectives.

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“…Some researchers tried to enhance the contrast of structural colours by adding black-coloured materials. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] For instance, adding a small amount of carbon black powder to a colloidal crystal of polystyrene nanoparticles reduced the incoherent scattering considerably. [16][17][18][19][20][21][22] A black coating on the nanoparticles could also increase the saturation of structural colours.…”

Section: Introductionmentioning

confidence: 99%

“…[16][17][18][19][20][21][22] A black coating on the nanoparticles could also increase the saturation of structural colours. [23][24][25][26][27][28] As a result, effective improvements have been made in various structural colours (from blue to red) based on the size, refractive index, and packing structure of nanoparticles. However, in both strategies mentioned above, the introduction of black-coloured materials was also detrimental to the iridescent colour effect by disturbing the particle arrangement in the colloidal crystal.…”

Section: Introductionmentioning

confidence: 99%