Melanin Particles Research Articles

Experimental and theoretical evidence for molecular forces driving surface segregation in photonic colloidal assemblies.

Surface segregation in binary colloidal mixtures offers a simple way to control both surface and bulk properties without affecting their bulk composition. Here, we combine experiments and coarse-grained molecular dynamics (CG-MD) simulations to delineate the effects of particle chemistry and size on surface segregation in photonic colloidal assemblies from binary mixtures of melanin and silica particles of size ratio (D large /D small) ranging from 1.0 to ~2.2. We find that melanin and/or smaller particles segregate at the surface of micrometer-sized colloidal assemblies (supraballs) prepared by an emulsion process. Conversely, no such surface segregation occurs in films prepared by evaporative assembly. CG-MD simulations explain the experimental observations by showing that particles with the larger contact angle (melanin) are enriched at the supraball surface regardless of the relative strength of particle-interface interactions, a result with implications for the broad understanding and design of colloidal particle assemblies.

Artificial melanin particles: new building blocks for biomimetic structural coloration

Melanin, a black component of human hair, plays an important role in bright structural colorations in nature. For example, the beautiful and highly visible colorations of peacock feathers are achieved by periodic structures formed by melanin granules that have light absorbing capabilities. In recent years, polydopamine, which is easily obtained by the self-oxidative polymerization of dopamine, has attracted attention as a mimic of natural melanin. This focus review provides an overview of our recent research on structural color materials created using polydopamine-based artificial melanin particles and research trends in this area. Melanin, a black component of human hair, plays an important role in bright structural colorations in nature. Polydopamine-based artificial melanin particles, inspired by natural melanin and its important role in structural coloration, were used to produce bright structural colors by controlling light reflection and absorption. A variety of structural coloration characteristics have become possible through our investigations of the assembly structure, composition, shape, and application of artificial melanin particles.

Melanins of Inonotus Obliquus: Bifidogenic and Antioxidant Properties.

Extracts and melanins from Inonotus obliquus are widely used in medicine due to their high antioxidant properties. This study is dedicated to define the influence of the physicochemical and antioxidant properties of Inonotus obliquus melanins and their bifidogenic effects on Bifidobacterium bifidum 1 and Bifidobacterium animalis subsp. lactis. For this purpose, melanins precipitated from Inonotus obliquus aqueous extracts, obtained by a few methods, and separated melanin fractions by organic solvents were used. For the melanin physicochemical properties analysis spectrophotometry, electron paramagnetic resonance (EPR) spectroscopy and dynamic light scattering methods were applied. Melanins and their fractions difference in particle size and charge, antioxidant properties, and redox potential were revealed. It was shown that the redox potential, the size of melanin particles and the z-potential had maximum influence on bifidobacteria growth. The greatest activating effect on bifidobacteria was established by using melanin isolated from aqueous microwave extracts in concentrations of 10−13, 10−10, 10−5 g/cm3. The use of this melanin with antioxidant activity 0.67 ± 0.06 mg/g (expressed as ascorbic acid equivalent), and with redox potential −5.51 ± 2.22 mV as a prebiotic allowed the growth of Bifidobacterium bifidum 1 s to increase by 1.4 times in comparison with ascorbic acid by 24 h of cultivation.

Synthesis and role of melanin for tolerating in vitro rumen digestion in Duddingtonia flagrans, a nematode-trapping fungus

ABSTRACTWe describe the synthesis and a function of melanin in Duddingtonia flagrans, a nematode-trapping fungus. We tested various culture media treated with L-DOPA, glucose and tricyclazole on fungal growth and melanin distribution using infrared spectroscopy (IS), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM). In vitro rumen digestion was used to test the environmental stress and then to evaluate the capacity of this fungus to trap nematode larvae. The growth and melanization of the fungus after 21 days of incubation at 30°C were best in Sabouraud dextrose medium. IS indicated the presence of melanin in D. flagrans, with similar bands for commercial melanin used as a control, and assigned the values obtained by EPR (g of 2.0051 ± 0.0001) to the production of melanin by the fungus. TEM indicated that melanin was produced in melanosomes but was not totally inhibited by tricyclazole. Within the limits of experimental error, the predatory activity of fungus treated with tricyclazole was drastically affected after 27 h of in vitro anaerobic stress with rumen inoculum. The deposition of melanin particles on the fungal cell wall contributed to the maintenance of D. flagrans predatory abilities after in vitro anaerobic ruminal stress.

Homogeneous melanin/silica core-shell particles incorporated in poly (methyl methacrylate) for enhanced UV protection, thermal stability, and mechanical properties

Natural melanin is abundant in wide ranges of sources, especially in dark colored animal fibers. Despite the unique features and functionalities, its extensive analyses and applications have greatly been hindered due to its serious self-aggregation. To tackle this issue, this study uses the Stöber method to encapsulate the melanin particles extracted from colored alpaca fibers with a thin layer of silica. It was observed that the melanin/silica core-shell particles (MSCPs) with 20 h encapsulation time provided excellent dispersity and optical performance. Different concentrations of MSCPs were then doped in poly (methyl methacrylate) (PMMA) through an in-situ polymerization process to obtain MSCP/PMMA bulk materials. The produced composite materials showed homogeneous appearance, controllable UV absorbance and visible light transmittance. The thermal stability, durability under UV, and mechanical properties of the fabricated composites were examined and the role of melanin on the obtained results was elucidated. It was observed that the PMMA samples with MSCPs showed excellent durability under UV even after 100 h irradiation. Testing the thermal stability and mechanical properties (hardness and elastic modulus) of MSCP/PMMA samples confirmed the positive effect of MSCPs presence in PMMA. These results demonstrated the applicability of natural melanin-based materials and composites in UV-protection related fields.

Ellipsoidal Artificial Melanin Particles as Building Blocks for Biomimetic Structural Coloration.

Inspired by the structural coloration of anisotropic materials in nature, we demonstrate the preparation of structural color materials by the assembly of anisotropic particles. Spherical artificial melanin particles consisting of a polystyrene core and polydopamine shell were stretched asymmetrically to form uniform-sized ellipsoidal particles with different aspect ratios. The aspect ratio and assembly method of the ellipsoidal particles influence the structural coloration, indicating that the particle shape is one of the important parameters for controlling the structural coloration. The discovery of a method to control the structural color using ellipsoidal particles is useful in basic research on structural colors in nature and provides flexibility in material design and extends the application range of structural color materials.

The distribution of melanocytes and the degradation of melanosomes in fetal hair follicles

There have been many studies about the formation, storage, transport and degradation of melanosomes in epidermal melanocytes but studies of melanocytes and melanosomes in fetal hair follicles (HFs) have been limited and ambiguous. The goal of this study was to investigate the distribution of melanocytes and the degradation of melanosomes in fetal HFs. After obtaining approval and informed consent for the study, a scalp specimen from a 5 month gestational age fetus was obtained and was divided into two parts. One part was subjected to immunohistochemical staining with the melanocyte-specific marker HMB-45 and was then observed by light microscopy to detect the distribution of melanocytes in HFs. The other part underwent conventional processing for transmission electron microcopy (TEM). Subsequently, the morphology of melanosomes in HF melanocytes and their degradation in cortical keratinocytes were observed. Immunohistochemically, scattered round melanocytes lacking dendrites were mainly observed along the outer root sheath of the lower part of the HF. A few fusiform or tri-dendritic melanocytes were located at the bottom of the hair bulbs. Significantly melanized melanocytes with multiple dendrites were concentrated in the pigmented area in the center of the hair bulbs, only above the dermal papilla. Analysis by TEM revealed melanocytes containing melanosomes at all stages of development. Autophagosomes containing stage mature IV melanosomes were observed in some melanocytes. Many phagolysosomes containing numerous melanosomes were observed in the cortical keratinocytes. Some phagolysosomes were concentrically surrounded by 3–5 layers of endoplasmic reticulum. Melanosomes that had been degraded or were being degraded in phagolysosomes in keratinocytes had lost their integrity and had become an ill-defined melanosomal dust that were arranged irregularly. Partial melanin particles were released into the cytosol. Melanocytes in different regions of fetal HFs had different morphologies and were at various stages of differentiation. Fetal HF melanocytes contained not only melanosomes at different developmental stages, but autophagosomes were seen occasionally. Melanosomes were degraded into irregular pigment particles in the phagolysosomes of cortical keratinocytes. These results provide important clues to elucidate the mechanism of melanosome biodegradation.

Photoprotective properties of alpaca fiber melanin reinforced by rutile TiO2 nanoparticles: A study on wool fabric

Melanin/titanium dioxide (TiO2) composite systems are introduced as efficient UV absorbers. Natural melanin particles were extracted from the pigmented alpaca fibers and the spindle-like rutile TiO2 nanoparticles were synthesized through a two-step sol-gel method at room temperature. The composites of melanin/TiO2 were prepared via electrostatic attraction force. In order to understand the UV absorption features of melanin and melanin/TiO2 composite systems, the prepared particles were applied to the surface of wool fabrics. Then, the UV protection and photostability of functionalized fabrics were assessed based on photoinduced chemiluminescence (PICL) emission, UV reflectance spectra, photoyellowing and ultraviolet protection factor (UPF). It was observed that the photostability of treated fabrics enhanced significantly, implying the generation of less free polymeric radicals in the substrate under UV irradiation. Among different synthesized composites, the proportion of melanin/TiO2 1/4 was the most efficient ratio inducing 80% reduction in the PICL emission peak intensity compared with untreated wool samples. The presence of melanin particles significantly enhanced the UPF values of fabrics where 30% increment was observed for wool samples after treating with melanin/TiO2 1/4 compared with pure TiO2. Having some advantages such as nontoxicity, eco-friendly and feasible synthesis approach, the prepared bio-organic/inorganic composite structures can be of some potential applications in photoprotecting and free radical quenching purposes.

Melanin Precursor Influence on Structural Colors from Artificial Melanin Particles: PolyDOPA, Polydopamine, and Polynorepinephrine

Polydopamine (PDA) is of interest as a mimetic material of melanin to produce structural color materials. Herein, to investigate the influence of the material composition of the artificial melanin particles on structural color, we demonstrated the preparation of core-shell particles by polymerization of norepinephrine or 3,4-dihydroxyphenylalanine, which are melanin precursors similar to dopamine, in the presence of polystyrene particles. It was revealed that the arrays of the prepared particles produce high-visibility structural color because of absorption of scattering light. Although poly(3,4-dihydroxyphenylalanine) showed the same tendency as PDA which was previous studied, polynorepinephrine can easily produce a smooth and thick shell layer compared with that of PDA, and pellets consisting of the particles showed angle-dependent structural color. Therefore, the artificial melanin particles that produce angle-dependent structural color became stable than ever before. These results indicated that material compositions of artificial melanin particles have influence on structural color, and an important finding for application as a coloring material was obtained.

Reverse Engineering To Characterize Redox Properties: Revealing Melanin’s Redox Activity through Mediated Electrochemical Probing

Melanins are ubiquitous in nature, yet their functions remain poorly understood, because their structures and properties elude characterization by conventional methods. Since many of the proposed functions of melanins (e.g., antioxidant, pro-oxidant, and radical scavenging) involve an exchange of electrons, we developed an electrochemical reverse engineering methodology to probe the redox properties of melanin. This mediated electrochemical probing (MEP) method (i) characterizes insoluble melanin particles that are localized adjacent to an electrode within a permeable hydrogel film, (ii) employs diffusible mediators to shuttle electrons between the electrode and melanin sample, and (iii) imposes complex sequences of input voltages and analyzes output response characteristics (e.g., currents) to reveal redox properties. Here, we illustrate the versatility of MEP and review results demonstrating that melanins have reversible redox activities, can exchange electrons with various reductants and oxidants, and ...

Biological responses to environmental contamination. How can metal pollution impact signal honesty in avian species?

Environmental pollution, for example with metals, can significantly affect the ecosystem balance leading to severe changes. Biologically active pigments are relevant for the appearance and condition of birds. Melanin and carotenoid particles are the most frequently deposited pigments in avian integument. They are responsible for the majority of colors of bird plumage. The phenotypic expression can be affected by metal contamination. It can be manifested as color bleaching or differences in the size of plumage badges. In this study, we performed a comprehensive review of related studies in order to estimate the underlying population effect of this potential dependency. The study is based on the review of the literature regarding several avian species. It was designed to identify an area where the effect of the exposure is still poorly known. The analysis was specifically conducted to investigate the correlation between trace element concentration and eumelanin deposition. Moreover, we searched for factors that could affect spectral properties of feathers with carotenoid‐based pigmentation. As a result, we found carotenoid‐based pigmentation to be of a good use in terms of visual condition assessment. Changes in melanin‐based pattern should be analyzed separately for eu‐ and pheomelanin as well as for a range of essential and toxic elements. Comprehensive studies on the subject are still scarce. Therefore, the issue requires further investigation.

Melanin particles isolated from the fungus Fonsecaea pedrosoi activates the human complement system.

BACKGROUNDMelanin production has been associated with virulence in various pathogenic fungi, including Fonsecaea pedrosoi, the major etiological agent for chromoblastomycosis, a subcutaneous fungal disease that occurs in South America.OBJECTIVEThe aim of this study was to evaluate the effects of acid-basic extracted F. pedrosoi melanin particles and fungal cell ghosts obtained by Novozym 234 treatment on their ability to activate the human complement system.METHODSThe ability of melanin particles and fungal cell ghosts to activate the human complement system was evaluated by complement consumption, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA).FINDINGSUnsensitised melanin particles and melanin ghosts presented complement consumption of 82.67 ± 2.08% and 96.04 ± 1.13%, respectively. Immunofluorescence assays revealed intense deposition of the C3 and C4 fragments on the surface of melanin particles and ghosts extracted from F. pedrosoi. Deposition of the C3, C4, and C5 fragments onto melanin samples and zymosan was confirmed by ELISA. Deposition of small amounts of C1q and C9 onto melanin samples and zymosan was detected by ELISA.CONCLUSION Fonsecaea pedrosoi melanin particles and fungal cell ghosts activated the complement system mainly through an alternative pathway.

Cell-wall dyes interfere with Cryptococcus neoformans melanin deposition.

Melanization is an intrinsic characteristic of many fungal species, but details of this process are poorly understood because melanins are notoriously difficult pigments to study. While studying the binding of cell-wall dyes, Eosin Y or Uvitex, to melanized and non-melanized Cryptococcus neoformans cells we noted that melanization leads to reduced fluorescence intensity, suggesting that melanin interfered with dye binding to the cell wall. The growth of C. neoformans in melanizing conditions with either of the cell-wall dyes resulted in an increase in supernatant-associated melanin, consistent with blockage of melanin attachment to the cell wall. This effect provided the opportunity to characterize melanin released into culture supernatants. Released melanin particles appeared mostly as networked structures having dimensions consistent with previously described extracellular vesicles. Hence, dye binding to the cell wall created conditions that resembled the 'leaky melanin' phenotype described for certain cell-wall mutants. In agreement with earlier studies on fungal melanins biosynthesis, our observations are supportive of a model whereby C. neoformans melanization proceeds by the attachment of melanin nanoparticles to the cell wall through chitin, chitosan, and various glucans.

Effects of Melanin on Optical Behavior of Polymer: From Natural Pigment to Materials Applications.

Melanin is a kind of ubiquitous natural pigment, which serves a variety of protective functions in many organisms. In the present study, natural melanin and synthetic melanin nanoparticles (NPs) were systematically investigated for its potential application in polymeric optical materials. A significant short-wavelength shielding and high visible light transparency polymer nanocomposite was easily obtained via tuning the melanin particle size. In particular, the nanocomposite film with melanin NPs (diameter ≈ 15 nm) loading even as low as 1 wt % blocks most ultraviolet light below 340 nm and still keeps high visible light transparency (83%) in the visible spectrum. More importantly, because of the excellent photoprotection and radical scavenging capabilities of melanin, the resulting polymer nanocomposite exhibits outstanding photostability. In effect, such fantastic melanin NPs is promising for applications in various optical materials.

Doxorubicin-Loaded Melanin Particles for Enhanced Chemotherapy in Drug-Resistant Anaplastic Thyroid Cancer Cells

Anaplastic thyroid cancer (ATC) is highly aggressive and tends to develop drug resistance to standard chemotherapies. To overcome the drug resistance of ATC, we synthesized dopamine-melanin nanoparticles (MNPs) loaded with doxorubicin (Dox) molecules. The Dox-loaded MNPs (Dox-MNPs) developed exhibited increased cellular uptake and enhanced therapeutic efficacy in drug-resistant ATC cell line HTh74R, compared with free Dox. The native MNPs were found to have excellent biocompatibility, which suggests that Dox-MNPs may have potential in the treatment of ATC.

Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging

AbstractPhotoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low‐cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross‐section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod‐shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased.

Ions doped melanin nanoparticle as a multiple imaging agent

BackgroundMultimodal nanomaterials are useful for providing enhanced diagnostic information simultaneously for a variety of in vivo imaging methods. According to our research findings, these multimodal nanomaterials offer promising applications for cancer therapy.ResultsMelanin nanoparticles can be used as a platform imaging material and they can be simply produced by complexation with various imaging active ions. They are capable of specifically targeting epidermal growth factor receptor (EGFR)-expressing cancer cells by being anchored with a specific antibody. Ion-doped melanin nanoparticles were found to have high bioavailability with long-term stability in solution, without any cytotoxicity in both in vitro and in vivo systems.ConclusionBy combining different imaging modalities with melanin particles, we can use the complexes to obtain faster diagnoses by computed tomography deep-body imaging and greater detailed pathological diagnostic information by magnetic resonance imaging. The ion-doped melanin nanoparticles also have applications for radio-diagnostic treatment and radio imaging-guided surgery, warranting further proof of concept experimental.

Stimuli-Responsive Structurally Colored Films from Bioinspired Synthetic Melanin Nanoparticles

Nature has evolved a fantastic gallery of structural colors, offering a source of inspiration for the development of artificial, multifunctional photonic devices. Inspired by the widespread use of melanin particles to produce structural colors in bird feathers, we recently demonstrated that synthetic melanin nanoparticles (SMNPs) offer the same rare, but critical combination of high refractive index and high absorption as natural melanin. Here, we show for the first time fast, significant, and reversible changes of structural coloration in self-assembled SMNP films in response to changes in humidity. This process is driven by the hygroscopic nature of the particles, leading to changes in the thickness of the SMNP layer that alter the interference color. This mechanistic explanation is supported by water absorption measurements, an optical model, and environmental scanning electron microscopy. Humidity-induced dynamic colors arising from SMNP films offer possible routes for synthetic melanin as an importan...

Melanin fate in the human epidermis: a reassessment of how best to detect and analyse histologically.

Melanin is the predominant pigment responsible for skin colour and is synthesized by the melanocyte in the basal layer of the epidermis and then transferred to surrounding keratinocytes. Despite its optical properties, melanin is barely detectable in unstained sections of human epidermis. However, identification and localization of melanin is of importance for the study of skin pigmentation in health and disease. Current methods for the histologic quantification of melanin are suboptimal and are associated with significant risk of misinterpretation. The aim of this study was to reassess the existing literature and to develop a more effective histological method of melanin quantification in human skin. Moreover, we confirm that Warthin-Starry (WS) stain provides a much more sensitive and more specific melanin detection method than the commonplace Fontana-Masson (FM) stain. For example, WS staining sensitivity allowed the visualization of melanin even in very pale Caucasian skin that was missed by FM or Von Kossa (VK) stains. From our reassessment of the histology-related literature, we conclude that so-called melanin dust is most likely an artifact of discoloration due to non-specific silver deposition in the stratum corneum. Unlike FM and VK, WS was not associated with this non-specific stratum corneum darkening, misinterpreted previously as 'degraded' melanin. Finally, WS melanin particle counts were largely similar to previously reported manual counts by transmission electron microscopy, in contrast to both FM and VK. Together these findings allow us to propose a new histology/Image J-informed method for the accurate and precise quantification of epidermal melanin in skin.

Melanin 'dust' or 'ghost'?

Melanin 'dust' or 'ghost'?