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Melanin Based Functional Materials

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Materials Science".

Deadline for manuscript submissions: closed (30 June 2017) | Viewed by 57076

Special Issue Editor


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Guest Editor
Department of Chemical Sciences, University of Naples Federico II, Via Cintia 4, I-80126 Naples, Italy
Interests: structure, synthesis, physicochemical properties, and reactivity of melanins; polydopamine and related bioinspired functional materials for underwater surface functionalization and hybrid nanostructures for bioelectronics and biomedical applications; design, antioxidant properties, and reactivity of bioactive phenolic and quinone compounds; free radical oxidations and nature-inspired redox-active systems for biomedical and technological applications; chemistry and physicochemical properties of natural or bioinspired heterocyclic compounds; bioorganic chemistry of organic sulphur and selenium compounds; model reactions and transformation pathways of polycyclic aromatic hydrocarbons and derivatives of astrochemical relevance
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Special Issue Information

Dear Colleagues,

“Melanins: from human pigments to innovative biomedical and technological solutions” or “Melanin-based technology: myth or reality?”; both of these sentences can be taken to summarize the aims and scope of this Special Issue: To bring to focus the latest advances in melanin research along with the manifold biomedical and technological opportunities offered by these biopolymers. Why this topic ? The melanins are an important class of biopolymers of diverse origin and chemical composition, which are found widespread in nature. In man, two main groups of melanins account for the variety of skin, hair and eye pigmentation: The black insoluble eumelanins, found in the dark phenotypes, and the reddish-brown, sulfur-containing pheomelanins typical of red-haired individuals. Both eumelanins and pheomelanins are produced within melanocytes by a complex biosynthetic pathway involving the tyrosinase-catalyzed oxidation of tyrosine. Other pigments commonly classified as melanins include cephalopod ink, the most accessible melanin source in Nature, and the black pigments found in higher plants, fungi and bacteria, which derive from non-nitrogenous phenolic precursors.

In nature, melanin pigments play a variety of roles, from photoprotection to photosensitization, antioxidant defense and metal/drug binding, which reflect a rather unique combination of chemical, optical, electrical and paramagnetic properties. Accordingly, over the past decade melanins have burst onto the scene of materials science as soft, biocompatible and bioavailable functional polymers for a broad range of applications, from human health to energy and sustainable technology.

The contributions collected in this Special Issue come from different laboratories and from both academic and industrial settings, and aim at providing a practical reference to both newcomers and practitioners of melanin research who are taking active part in the definitive maturation of melanin-based technology.

Main themes covered include biointerfaces, drug delivery, theranostics, democosmetics, nanotechnology, optoacoustics, organic-inorganic hybrids, bioelectronics, organic electronics, light harvesting, thin films and surface science. Although many excellent reviews are available in the literature, this Special Issue takes advantage of the open access format to offer a novel and stimulating perspective of the field. It is especially directed to raise the interests of researchers from industries and companies willing to invest on melanins for innovative and inspiring solutions.

Prof. Marco d’Ischia
Guest Editor

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Keywords

  • eumelanins
  • pheomelanins
  • polydopamine
  • biointerfaces
  • surface chemistry
  • nanotechnology
  • organic (bio)electronics
  • theranostics
  • drug delivery
  • sensing

Published Papers (8 papers)

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Editorial

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4 pages, 173 KiB  
Editorial
Melanin-Based Functional Materials
by Marco D’Ischia
Int. J. Mol. Sci. 2018, 19(1), 228; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms19010228 - 12 Jan 2018
Cited by 22 | Viewed by 4580
Abstract
Melanin biopolymers are currently the focus of growing interest for a broad range of applications at the cutting edge of biomedical research and technology. This Special Issue presents a collection of papers dealing with melanin-type materials, e.g., polydopamine, for classic and innovative applications, [...] Read more.
Melanin biopolymers are currently the focus of growing interest for a broad range of applications at the cutting edge of biomedical research and technology. This Special Issue presents a collection of papers dealing with melanin-type materials, e.g., polydopamine, for classic and innovative applications, offering a stimulating perspective of current trends in the field. Besides basic scientists, the Special Issue is directed to researchers from industries and companies that are willing to invest in melanin research for innovative and inspiring solutions. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)

Research

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2868 KiB  
Article
Replacing Nitrogen by Sulfur: From Structurally Disordered Eumelanins to Regioregular Thiomelanin Polymers
by Mariagrazia Iacomino, Juan Mancebo-Aracil, Mireia Guardingo, Raquel Martín, Gerardino D’Errico, Marco Perfetti, Paola Manini, Orlando Crescenzi, Félix Busqué, Alessandra Napolitano, Marco D’Ischia, Josep Sedó and Daniel Ruiz-Molina
Int. J. Mol. Sci. 2017, 18(10), 2169; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18102169 - 17 Oct 2017
Cited by 13 | Viewed by 5413
Abstract
The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT [...] Read more.
The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level. Quite unexpectedly, nuclear magnetic resonance (NMR) analysis of the early oligomer fractions indicated linear, 4-, and 7-linked structures in marked contrast with DHI, which gives highly complex mixtures of partially degraded oligomers. Density functional theory (DFT) calculations supported the tendency of DHBT to couple via the 4- and 7-positions. These results uncover the role of nitrogen as a major determinant of the structural diversity generated by the polymerization of DHI, and point to replacement by sulfur as a viable entry to regioregular eumelanin-type materials for potential applications for surface functionalization by dip coating. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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4374 KiB  
Article
Deciphering Molecular Mechanisms of Interface Buildup and Stability in Porous Si/Eumelanin Hybrids
by Elisa Pinna, Claudio Melis, Aleandro Antidormi, Roberto Cardia, Elisa Sechi, Giancarlo Cappellini, Marco D’Ischia, Luciano Colombo and Guido Mula
Int. J. Mol. Sci. 2017, 18(7), 1567; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18071567 - 19 Jul 2017
Cited by 15 | Viewed by 5136
Abstract
Porous Si/eumelanin hybrids are a novel class of organic–inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation [...] Read more.
Porous Si/eumelanin hybrids are a novel class of organic–inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation of the eumelanin–silicon interface. Herein we report an integrated experimental and computational study aimed at probing interface stability via surface modification and eumelanin manipulation, and at modeling the organic–inorganic interface via formation of a 5,6-dihydroxyindole (DHI) tetramer and its adhesion to silicon. The results indicated that mild silicon oxidation increases photocurrent stability via enhancement of the DHI–surface interaction, and that higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of growing eumelanin. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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4582 KiB  
Article
Calcium-Mediated Control of Polydopamine Film Oxidation and Iron Chelation
by Luke Klosterman and Christopher J. Bettinger
Int. J. Mol. Sci. 2017, 18(1), 14; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18010014 - 22 Dec 2016
Cited by 28 | Viewed by 8082
Abstract
The facile preparation of conformal polydopamine (PDA) films on broad classes of materials has prompted extensive research into a wide variety of potential applications for PDA. The constituent molecular species in PDA exhibit diverse chemical moieties, and therefore highly variable properties of PDA-based [...] Read more.
The facile preparation of conformal polydopamine (PDA) films on broad classes of materials has prompted extensive research into a wide variety of potential applications for PDA. The constituent molecular species in PDA exhibit diverse chemical moieties, and therefore highly variable properties of PDA-based devices may evolve with post-processing conditions. Here we report the use of redox-inactive cations for oxidative post-processing of deposited PDA films. PDA films incubated in alkaline CaCl2 solutions exhibit accelerated oxidative evolution in a dose-dependent manner. PDA films incubated in CaCl2 solutions exhibit 53% of the oxidative charge transfer compared to pristine PDA films. Carboxylic acid groups generated from the oxidation process lower the isoelectric point of PDA films from pH = 4.0 ± 0.2 to pH = 3.1 ± 0.3. PDA films exposed to CaCl2 solutions during post-processing also enhance Fe2+/Fe3+ chelation compared to pristine PDA films. These data illustrate that the molecular heterogeneity and non-equilibrium character of as-deposited PDA films afford control over the final composition by choosing post-processing conditions, but also demands forethought into how the performance of PDA-incorporated devices may change over time in salt solutions. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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3343 KiB  
Article
Green Synthesis of Silver Nanoparticles Stabilized with Mussel-Inspired Protein and Colorimetric Sensing of Lead(II) and Copper(II) Ions
by Ja Young Cheon and Won Ho Park
Int. J. Mol. Sci. 2016, 17(12), 2006; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms17122006 - 30 Nov 2016
Cited by 63 | Viewed by 9440
Abstract
This articles reports a simple and green method for preparing uniform silver nanoparticles (AgNPs), for which self-polymerized 3,4-dihydroxy-l-phenylalanine (polyDOPA) is used as the reducing and stabilizing agent in aqueous media. The AgNPs functionalized by polyDOPA were analyzed by UV–Vis spectroscopy, high-resolution [...] Read more.
This articles reports a simple and green method for preparing uniform silver nanoparticles (AgNPs), for which self-polymerized 3,4-dihydroxy-l-phenylalanine (polyDOPA) is used as the reducing and stabilizing agent in aqueous media. The AgNPs functionalized by polyDOPA were analyzed by UV–Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), Raman spectrophotometry, and X-ray diffraction (XRD) techniques. The results revealed that the polyDOPA-AgNPs with diameters of 25 nm were well dispersed due to the polyDOPA. It was noted that the polyDOPA-AgNPs showed selectivity for Pb2+ and Cu2+ detection with the detection limits for the two ions as low as 9.4 × 10−5 and 8.1 × 10−5 μM, respectively. Therefore, the polyDOPA-AgNPs can be applied to both Pb2+ and Cu2+ detection in real water samples. The proposed method will be useful for colorimetric detection of heavy metal ions in aqueous media. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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Review

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4252 KiB  
Review
The Supramolecular Buildup of Eumelanin: Structures, Mechanisms, Controllability
by Anne Büngeler, Benjamin Hämisch and Oliver I. Strube
Int. J. Mol. Sci. 2017, 18(9), 1901; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18091901 - 06 Sep 2017
Cited by 37 | Viewed by 6226
Abstract
Research on the supramolecular buildup of eumelanin has gained high momentum in the last years. Several new aspects regarding the involved structures and mechanisms have been established, which has led to a better understanding of the entire process. This review intends to provide [...] Read more.
Research on the supramolecular buildup of eumelanin has gained high momentum in the last years. Several new aspects regarding the involved structures and mechanisms have been established, which has led to a better understanding of the entire process. This review intends to provide a clearly laid-out summary of previous and new findings regarding structures, mechanisms, and controllability. With respect to materials applications, the aspect of controllability is of supreme importance. A focus of this review is therefore set on a novel method with high potential for specific synthesis of various, isolated particle morphologies. Finally, open questions and possibilities for their elucidation are discussed. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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3716 KiB  
Review
Melanin-Based Contrast Agents for Biomedical Optoacoustic Imaging and Theranostic Applications
by Dario Livio Longo, Rachele Stefania, Silvio Aime and Alexander Oraevsky
Int. J. Mol. Sci. 2017, 18(8), 1719; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18081719 - 07 Aug 2017
Cited by 43 | Viewed by 5740
Abstract
Optoacoustic imaging emerged in early 1990s as a new biomedical imaging technology that generates images by illuminating tissues with short laser pulses and detecting resulting ultrasound waves. This technique takes advantage of the spectroscopic approach to molecular imaging, and delivers high-resolution images in [...] Read more.
Optoacoustic imaging emerged in early 1990s as a new biomedical imaging technology that generates images by illuminating tissues with short laser pulses and detecting resulting ultrasound waves. This technique takes advantage of the spectroscopic approach to molecular imaging, and delivers high-resolution images in the depth of tissue. Resolution of the optoacoustic imaging is scalable, so that biomedical systems from cellular organelles to large organs can be visualized and, more importantly, characterized based on their optical absorption coefficient, which is proportional to the concentration of absorbing chromophores. Optoacoustic imaging was shown to be useful in both preclinical research using small animal models and in clinical applications. Applications in the field of molecular imaging offer abundant opportunities for the development of highly specific and effective contrast agents for quantitative optoacoustic imaging. Recent efforts are being made in the direction of nontoxic biodegradable contrast agents (such as nanoparticles made of melanin) that are potentially applicable in clinical optoacoustic imaging. In order to increase the efficiency and specificity of contrast agents and probes, they need to be made smart and capable of controlled accumulation in the target cells. This review was written in recognition of the potential breakthroughs in medical optoacoustic imaging that can be enabled by efficient and nontoxic melanin-based optoacoustic contrast agents. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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1020 KiB  
Review
Melanin and Melanin-Related Polymers as Materials with Biomedical and Biotechnological Applications—Cuttlefish Ink and Mussel Foot Proteins as Inspired Biomolecules
by Francisco Solano
Int. J. Mol. Sci. 2017, 18(7), 1561; https://0-doi-org.brum.beds.ac.uk/10.3390/ijms18071561 - 18 Jul 2017
Cited by 125 | Viewed by 11202
Abstract
The huge development of bioengineering during the last years has boosted the search for new bioinspired materials, with tunable chemical, mechanical, and optoelectronic properties for the design of semiconductors, batteries, biosensors, imaging and therapy probes, adhesive hydrogels, tissue restoration, photoprotectors, etc. These new [...] Read more.
The huge development of bioengineering during the last years has boosted the search for new bioinspired materials, with tunable chemical, mechanical, and optoelectronic properties for the design of semiconductors, batteries, biosensors, imaging and therapy probes, adhesive hydrogels, tissue restoration, photoprotectors, etc. These new materials should complement or replace metallic or organic polymers that cause cytotoxicity and some adverse health effects. One of the most interesting biomaterials is melanin and synthetic melanin-related molecules. Melanin has a controversial molecular structure, dependent on the conditions of polymerization, and therefore tunable. It is found in animal hair and skin, although one of the common sources is cuttlefish (Sepia officinalis) ink. On the other hand, mussels synthesize adhesive proteins to anchor these marine animals to wet surfaces. Both melanin and mussel foot proteins contain a high number of catecholic residues, and their properties are related to these groups. Dopamine (DA) can easily polymerize to get polydopamine melanin (PDAM), that somehow shares properties with melanin and mussel proteins. Furthermore, PDAM can easily be conjugated with other components. This review accounts for the main aspects of melanin, as well as DA-based melanin-like materials, related to their biomedical and biotechnological applications. Full article
(This article belongs to the Special Issue Melanin Based Functional Materials)
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