Melanin and Melanin-Like Hybrid Materials in Regenerative Medicine

Recent Development and Applications of Polydopamine in Tissue Repair and Regeneration Biomaterials

The various tissue damages are a severe problem to human health. The limited human tissue regenerate ability requires suitable biomaterials to help damage tissue repair and regeneration. Therefore, many researchers devoted themselves to exploring biomaterials suitable for tissue repair and regeneration. Polydopamine (PDA) as a natural and multifunctional material which is inspired by mussel has been widely applied in different biomaterials. The excellent properties of PDA, such as strong adhesion, photothermal and high drug-loaded capacity, seem to be born for tissue repair and regeneration. Furthermore, PDA combined with different materials can exert unexpected effects. Thus, to inspire researchers, this review summarizes the recent and representative development of PDA biomaterials in tissue repair and regeneration. This article focuses on why apply PDA in these biomaterials and what PDA can do in different tissue injuries.

Hybrid Nanoparticle-Assisted Chemo-Photothermal Therapy and Photoacoustic Imaging in a Three-Dimensional Breast Cancer Cell Model

Bioinspired nanoparticles have recently been gaining attention as promising multifunctional nanoplatforms for therapeutic applications in cancer, including breast cancer. Here, the efficiency of the chemo-photothermal and photoacoustic properties of hybrid albumin-modified nanoparticles (HSA-NPs) loaded with doxorubicin was evaluated in a three-dimensional breast cancer cell model. The HSA-NPs showed a higher uptake and deeper penetration into breast cancer spheroids than healthy breast cell 3D cultures. Confocal microscopy revealed that, in tumour spheroids incubated with doxorubicin-loaded NPs for 16 h, doxorubicin was mainly localised in the cytoplasm, while a strong signal was detectable at the nuclear level after 24 h, suggesting a time-dependent uptake. To evaluate the cytotoxicity of doxorubicin-loaded NPs, tumour spheroids were treated for up to 96 h with increasing concentrations of NPs, showing marked toxicity only at the highest concentration of doxorubicin. When doxorubicin administration was combined with laser photothermal irradiation, enhanced cytotoxicity was observed at lower concentrations and incubation times. Finally, the photoacoustic properties of doxorubicin-loaded NPs were evaluated in tumour spheroids, showing a detectable signal increasing with NP concentration. Overall, our data show that the combined effect of chemo-photothermal therapy results in a shorter exposure time to doxorubicin and a lower drug dose. Furthermore, owing to the photoacoustic properties of the NPs, this nanoplatform may represent a good candidate for theranostic applications.

Melanin/melanin-like nanoparticles: As a naturally active platform for imaging-guided disease therapy

The development of biocompatible and efficient nanoplatforms that combine diagnostic and therapeutic functions is of great importance for precise disease treatment. Melanin, an endogenous biopolymer present in living organisms, has attracted increasing attention as a versatile bioinspired functional platform owing to its unique physicochemical properties (e.g., high biocompatibility, strong chelation of metal ions, broadband light absorption, high drug binding properties) and inherent antioxidant, photoprotective, anti-inflammatory, and anti-tumor effects. In this review, the fundamental physicochemical properties and preparation methods of natural melanin and melanin-like nanoparticles were outlined. A systematical description of the recent progress of melanin and melanin-like nanoparticles in single, dual-, and tri-multimodal imaging-guided the visual administration and treatment of osteoarthritis, acute liver injury, acute kidney injury, acute lung injury, brain injury, periodontitis, iron overload, etc. Was then given. Finally, it concluded with a reasoned discussion of current challenges toward clinical translation and future striving directions. Therefore, this comprehensive review provides insight into the current status of melanin and melanin-like nanoparticles research and is expected to optimize the design of novel melanin-based therapeutic platforms and further clinical translation.

Localized and regulated peptide pigment formation inside liquid droplets through confined enzymatic oxidation

Melanin pigments are found in most life forms, where they are responsible for coloration and ultraviolet (UV) light protection. Natural melanin is a poorly soluble and complex biosynthesis product produced through confined and templated enzymatic oxidation of tyrosine. It has been challenging to create water-soluble synthetic mimics. This study demonstrates the enzymatic synthesis of oxidized phenols confined inside liquid droplets. We use an amphiphilic, bifunctional peptide, DYFR9, that combines a tyrosine tripeptide previously shown to undergo enzymatic oxidation to form peptide pigments with broad absorbance, and polyarginine to facilitate complex coacervation in the presence of ATP. When ATP, DYFR9 are mixed and exposed to tyrosinase, pigmented liquid droplets result, while no appreciable oxidation is observed in the bulk.

Topical application of synthetic melanin promotes tissue repair

In acute skin injury, healing is impaired by the excessive release of reactive oxygen species (ROS). Melanin, an efficient scavenger of radical species in the skin, performs a key role in ROS scavenging in response to UV radiation and is upregulated in response to toxic insult. In a chemical injury model in mice, we demonstrate that the topical application of synthetic melanin particles (SMPs) significantly decreases edema, reduces eschar detachment time, and increases the rate of wound area reduction compared to vehicle controls. Furthermore, these results were replicated in a UV-injury model. Immune array analysis shows downregulated gene expression in apoptotic and inflammatory signaling pathways consistent with histological reduction in apoptosis. Mechanistically, synthetic melanin intervention increases superoxide dismutase (SOD) activity, decreases Mmp9 expression, and suppresses ERK1/2 phosphorylation. Furthermore, we observed that the application of SMPs caused increased populations of anti-inflammatory immune cells to accumulate in the skin, mirroring their decrease from splenic populations. To enhance antioxidant capacity, an engineered biomimetic High Surface Area SMP was deployed, exhibiting increased wound healing efficiency. Finally, in human skin explants, SMP intervention significantly decreased the damage caused by chemical injury. Therefore, SMPs are promising and effective candidates as topical therapies for accelerated wound healing, including via pathways validated in human skin.

Enhanced Photoacoustic Response by Synergistic Ag-Melanin Interplay at the Core of Ternary Biocompatible Hybrid Silica-Based Nanoparticles

Photoacoustics (PA) is gaining increasing credit among biomolecular imaging methodologies by virtue of its poor invasiveness, deep penetration, high spatial resolution, and excellent endogenous contrast, without the use of any ionizing radiation. Recently, we disclosed the excellent PA response of a self-structured biocompatible nanoprobe, consisting of ternary hybrid nanoparticles with a silver core and a melanin component embedded into a silica matrix. Although preliminary evidence suggested a crucial role of the Ag sonophore and the melanin-containing nanoenvironment, whether and in what manner the PA response is controlled and affected by the self-structured hybrid nanosystems remained unclear. Because of their potential as multifunctional platforms for biomedical applications, a detailed investigation of the metal-polymer-matrix interplay underlying the PA response was undertaken to understand the physical and chemical factors determining the enhanced response and to optimize the architecture, composition, and performance of the nanoparticles for efficient imaging applications. Herein, we provide the evidence for a strong synergistic interaction between eumelanin and Ag which suggests an important role in the in situ-generated metal-organic interface. In particular, we show that a strict ratio between melanin and silver precursors and an accurate choice of metal nanoparticle dimension and the kind of metal are essential for achieving strong enhancements of the PA response. Systematic variation of the metal/melanin component is thus shown to offer the means of tuning the stability and intensity of the photoacoustic response for various biomedical and theranostic applications.

Towards nanostructured red-ox active bio-interfaces: Bioinspired antibacterial hybrid melanin-CeO2 nanoparticles for radical homeostasis

Redox-active nano-biointerfaces are gaining weight in the field of regenerative medicine since they can act as enzymes in regulating physiological processes and enabling cell homeostasis, as well as the defense against pathogen aggression. In particular, cerium oxide nanoparticles (CeO2 NPs) stand as intriguing enzyme-mimicking nanoplatforms, owing to the reversible Ce+3/Ce+4 surface oxidation state. Moreover, surface functionalization leads to higher catalytic activity and selectivity, as well as more tunable enzyme-mimicking performances. Conjugation with melanin is an adequate strategy to boost and enrich CeO2 NPs biological features, because of melanin redox properties accounting for intrinsic antioxidant, antimicrobial and anti-inflammatory power. Herein, hybrid Melanin/CeO2 nanostructures were designed by simply coating the metal-oxide nanoparticles with melanin chains, obtained in-situ through ligand-to-metal charge transfer mechanism, according to a bioinspired approach. Obtained hybrid nanostructures underwent detailed physico-chemical characterization. Morphological and textural features were investigated through TEM, XRD and N2 physisorption. The nature of nanoparticle-melanin interaction was analyzed through FTIR, UV-vis and EPR spectroscopy. Melanin-coated hybrid nanostructures exhibited a relevant antioxidant activity, confirmed by a powerful quenching effect for DPPH radical, reaching 81 % inhibition at 33 μg/mL. A promising anti-inflammatory efficacy of the melanin-coated hybrid nanostructures was validated through a significant inhibition of BSA denaturation after 3 h. Meanwhile, the enzyme-mimicking activity was corroborated by a prolonged peroxidase activity after 8 h at 100 μg/mL and a relevant catalase-like action, by halving the H2O2 level in 30 min at 50 μg/mL. Antimicrobial assays attested that conjugation with melanin dramatically boosted CeO2 biocide activity against both Gram (-) and Gram (+) strains. Cytocompatibility tests demonstrated that the melanin coating not only enhanced the CeO2 nanostructures biomimicry, resulting in improved cell viability for human dermal fibroblast cells (HDFs), but mostly they proved that Melanin-CeO2 NPs were able to control the oxidative stress, modulating the production of nitrite and reactive oxygen species (ROS) levels in HDFs, under physiological conditions. Such remarkable outcomes make hybrid melanin-CeO2 nanozymes, promising redox-active interfaces for regenerative medicine.

Bioactive Materials for Bone Regeneration: Biomolecules and Delivery Systems

Novel tissue regeneration strategies are constantly being developed worldwide. Research on bone regeneration is noteworthy, as many promising new approaches have been documented with novel strategies currently under investigation. Innovative biomaterials that allow the coordinated and well-controlled repair of bone fractures and bone loss are being designed to reduce the need for autologous or allogeneic bone grafts eventually. The current engineering technologies permit the construction of synthetic, complex, biomimetic biomaterials with properties nearly as good as those of natural bone with good biocompatibility. To ensure that all these requirements meet, bioactive molecules are coupled to structural scaffolding constituents to form a final product with the desired physical, chemical, and biological properties. Bioactive molecules that have been used to promote bone regeneration include protein growth factors, peptides, amino acids, hormones, lipids, and flavonoids. Various strategies have been adapted to investigate the coupling of bioactive molecules with scaffolding materials to sustain activity and allow controlled release. The current manuscript is a thorough survey of the strategies that have been exploited for the delivery of biomolecules for bone regeneration purposes, from choosing the bioactive molecule to selecting the optimal strategy to synthesize the scaffold and assessing the advantages and disadvantages of various delivery strategies.

The Multifaceted Opportunities Provided by the Pheomelanin-Inspired 1,4-Benzothiazine Chromophore: A Still-Undervalued Issue

1,4-Benzothiazines are the main building blocks of the naturally occurring pheomelanin pigments, and their chromophoric properties have been strongly related to the well-known phototoxicity of these pigments, partly responsible for the high incidence of melanoma and other skin cancers in red-haired people. However, some peculiar features of the 1,4-benzothiazine chromophore could be functionally exploited in several sectors. Within this context, in this perspective, an overview of the very recently reported applications of the 1,4-benzothiazine chromophore in pH sensing, filter permeability control, smart packaging, electrochromic device fabrication, bioimaging, photocatalysis, and HPLC detection systems is provided, together with a brief presentation of recently developed synthetic approaches to the 1,4-benzothiazine scaffold, with the aim of emphasizing the still-undervalued multifunctional opportunities offered by this class of compounds.

Melanin biopolymers from microbial world with future perspectives-a review

Melanin is an amorphous polymer made of heterogeneous functional groups synthesized by diverse organisms including fungi, bacteria, animals, and plants. It was widely acknowledged for its biological processes and its key role in the protection of organisms from environmental stress. Recently, melanin clutches attention in the field of nanobiotechnology, drug delivery, organic semiconductors and bioelectronics, environmental bioremediation, photoprotection, etc., Furthermore, melanin from natural sources like microbial community shows antimicrobial, fighting cancer, radical scavenging, cosmeceuticals, and many therapeutic areas as well. Though the multipotentiality nature of melanin has been put forth, real-world applications still flag fall behind, which might be anticipated to the inadequate and high price essence of natural melanin. However, current bioprocess technologies have paved for the large-scale or industrial production of microbial melanin, which could help in the replacement of synthetic melanin. Thus, this review emphasizes the various sources for melanin, i.e., types-based on its pathways and its chemical structures, functional efficiency, physical properties, and conventional and modern methods of both extraction and characterization. Moreover, an outlook on how it works in the field of medicine, bioremediation, and other related areas provides perspectives on the complete exploitation of melanin in practical applications of medicine and the environment.

Green Routes for Bio-Fabrication in Biomedical and Pharmaceutical Applications

In the last decade, significant advances in nanotechnologies, rising from increasing knowledge and refining of technical practices in green chemistry and bioengineering, enabled the design of innovative devices suitable for different biomedical applications. In particular, novel bio-sustainable methodologies are developing to fabricate drug delivery systems able to sagely mix properties of materials (i.e., biocompatibility, biodegradability) and bioactive molecules (i.e., bioavailability, selectivity, chemical stability), as a function of the current demands for the health market. The present work aims to provide an overview of recent developments in the bio-fabrication methods for designing innovative green platforms, emphasizing the relevant impact on current and future biomedical and pharmaceutical applications.

Functionalization of and through Melanin: Strategies and Bio-Applications

A unique feature of nanoparticles for bio-application is the ease of achieving multi-functionality through covalent and non-covalent functionalization. In this way, multiple therapeutic actions, including chemical, photothermal and photodynamic activity, can be combined with different bio-imaging modalities, such as magnetic resonance, photoacoustic, and fluorescence imaging, in a theragnostic approach. In this context, melanin-related nanomaterials possess unique features since they are intrinsically biocompatible and, due to their optical and electronic properties, are themselves very efficient photothermal agents, efficient antioxidants, and photoacoustic contrast agents. Moreover, these materials present a unique versatility of functionalization, which makes them ideal for the design of multifunctional platforms for nanomedicine integrating new functions such as drug delivery and controlled release, gene therapy, or contrast ability in magnetic resonance and fluorescence imaging. In this review, the most relevant and recent examples of melanin-based multi-functionalized nanosystems are discussed, highlighting the different methods of functionalization and, in particular, distinguishing pre-functionalization and post-functionalization. In the meantime, the properties of melanin coatings employable for the functionalization of a variety of material substrates are also briefly introduced, especially in order to explain the origin of the versatility of melanin functionalization. In the final part, the most relevant critical issues related to melanin functionalization that may arise during the design of multifunctional melanin-like nanoplatforms for nanomedicine and bio-application are listed and discussed.

Recent Progress in Biomedical Sensors Based on Conducting Polymer Hydrogels

Biosensors are increasingly taking a more active role in health science. The current needs for the constant monitoring of biomedical signals, as well as the growing spending on public health, make it necessary to search for materials with a combination of properties such as biocompatibility, electroactivity, resorption, and high selectivity to certain bioanalytes. Conducting polymer hydrogels seem to be a very promising materials, since they present many of the necessary properties to be used as biosensors. Furthermore, their properties can be shaped and enhanced by designing conductive polymer hydrogel-based composites with more specific functionalities depending on the end application. This work will review the recent state of the art of different biological hydrogels for biosensor applications, discuss the properties of the different components alone and in combination, and reveal their high potential as candidate materials in the fabrication of all-organic diagnostic, wearable, and implantable sensor devices.

Recent Applications of Melanin-like Nanoparticles as Antioxidant Agents

Nanosized antioxidants are highly advantageous in terms of versatility and pharmacokinetics, with respect to conventional molecular ones. Melanin-like materials, artificial species inspired by natural melanin, combine recognized antioxidant (AOX) activity with a unique versatility of preparation and modification. Due to this versatility and documented biocompatibility, artificial melanin has been incorporated into a variety of nanoparticles (NP) in order to give new platforms for nanomedicine with enhanced AOX activity. In this review article, we first discuss the chemical mechanisms behind the AOX activity of materials in the context of the inhibition of the radical chain reaction responsible for the peroxidation of biomolecules. We also focus briefly on the AOX properties of melanin-like NP, considering the effect of parameters such as size, preparation methods and surface functionalization on them. Then, we consider the most recent and relevant applications of AOX melanin-like NPs that are able to counteract ferroptosis and be involved in the treatment of important diseases that affect, e.g., the cardiovascular and nervous systems, as well as the kidneys, liver and articulations. A specific section will be dedicated to cancer treatment, since the role of melanin in this context is still very debated. Finally, we propose future strategies in AOX development for a better chemical understanding of melanin-like materials. In particular, the composition and structure of these materials are still debated, and they present a high level of variability. Thus, a better understanding of the mechanism behind the interaction of melanin-like nanostructures with different radicals and highly reactive species would be highly advantageous for the design of more effective and specific AOX nano-agents.

Bioactive Composite Methacrylated Gellan Gum for 3D-Printed Bone Tissue-Engineered Scaffolds

Gellan gum (GG) was chemically modified with methacrylic moieties to produce a photocrosslinkable biomaterial ink, hereinafter called methacrylated GG (GGMA), with improved physico-chemical properties, mechanical behavior and stability under physiological conditions. Afterwards, GGMA was functionalized by incorporating two different bioactive compounds, a naturally derived eumelanin extracted from the black soldier fly (BSF-Eumel), or hydroxyapatite nanoparticles (HAp), synthesized by the sol-gel method. Different ink formulations based on GGMA (2 and 4% (w/v)), BSF-Eumel, at a selected concentration (0.3125 mg/mL), or HAp (10 and 30% w_HAp/w_GGMA) were developed and processed by three-dimensional (3D) printing. All the functionalized GGMA-based ink formulations allowed obtaining 3D-printed GGMA-based scaffolds with a well-organized structure. For both bioactive signals, the scaffolds with the highest GGMA concentration (4% (w/v)) and the highest percentage of infill (45%) showed the best performances in terms of morphological and mechanical properties. Indeed, these scaffolds showed a good structural integrity over 28 days. Given the presence of negatively charged groups along the eumelanin backbone, scaffolds consisting of GGMA/BSF-Eumel demonstrated a higher stability. From a mechanical point of view, GGMA/BSF-Eumel scaffolds exhibited values of storage modulus similar to those of GGMA ones, while the inclusion of HAp at 30% (w_HAp/w_GGMA) led to a storage modulus of 32.5 kPa, 3.5-fold greater than neat GGMA. In vitro studies proved the capability of the bioactivated 3D-printed scaffolds to support 7F2 osteoblast cell growth and differentiation. BSF-Eumel and HAp triggered a different time-dependent physiological response in the osteoblasts. Specifically, while the ink with BSF-Eumel acted as a stimulus towards cell proliferation, reaching the highest value at 14 days, a higher expression of alkaline phosphatase activity was detected for scaffolds consisting of GGMA and HAp. The overall findings demonstrated the possible use of these biomaterial inks for 3D-printed bone tissue-engineered scaffolds.

Biodegradable and Electrically Conductive Melanin-Poly (3-Hydroxybutyrate) 3D Fibrous Scaffolds for Neural Tissue Engineering Applications

Due to the severity of peripheral nerve injuries (PNI) and spinal cord injuries (SCI), treatment options for patients are limited. In this context, biomaterials designed to promote regeneration and reinstate the lost function are being explored. Such biomaterials should be able to mimic the biological, chemical, and physical cues of the extracellular matrix for maximum effectiveness as therapeutic agents. Development of biomaterials with desirable physical, chemical, and electrical properties, however, has proven challenging. Here a novel biomaterial formulation achieved by blending the pigment melanin and the natural polymer Poly-3-hydroxybutyrate (PHB) is proposed. Physio-chemical measurements of electrospun fibers reveal a feature rich surface nano-topography, a semiconducting-nature, and brain-tissue-like poroviscoelastic properties. Resulting fibers improve cell adhesion and growth of mouse sensory and motor neurons, without any observable toxicity. Further, the presence of polar functional groups positively affect the kinetics of fibers degradation at a pH (≈7.4) comparable to that of body fluids. Thus, melanin-PHB blended scaffolds are found to be physio-chemically, electrically, and biologically compatible with neural tissues and could be used as a regenerative modality for neural tissue injuries. A biomaterial for scaffolds intended to promote regeneration of nerve tissue after injury is developed. This biomaterial, obtained by mixing the pigment melanin and the natural polymer PHB, is biodegradable, electrically conductive, and beneficial to the growth of motor and sensory neurons. Thus, it is believed that this biomaterial can be used in the context of healthcare applications.

Eumelanin from the Black Soldier Fly as Sustainable Biomaterial: Characterisation and Functional Benefits in Tissue-Engineered Composite Scaffolds

An optimized extraction protocol for eumelanins from black soldier flies (BSF-Eumel) allows an in-depth study of natural eumelanin pigments, which are a valuable tool for the design and fabrication of sustainable scaffolds. Here, water-soluble BSF-Eumel sub-micrometer colloidal particles were used as bioactive signals for developing a composite biomaterial ink for scaffold preparation. For this purpose, BSF-Eumel was characterized both chemically and morphologically; moreover, biological studies were carried out to investigate the dose-dependent cell viability and its influence on human mesenchymal stem cells (hMSCs), with the aim of validating suitable protocols and to find an optimal working concentration for eumelanin-based scaffold preparation. As proof of concept, 3D printed scaffolds based on methacrylated hyaluronic acid (MEHA) and BSF-Eumel were successfully produced. The scaffolds with and without BSF-Eumel were characterized in terms of their physico-chemical, mechanical and biological behaviours. The results showed that MEHA/BSF-Eumel scaffolds had similar storage modulus values to MEHA scaffolds. In terms of swelling ratio and stability, these scaffolds were able to retain their structure without significant changes over 21 days. Biological investigations demonstrated the ability of the bioactivated scaffolds to support the adhesion, proliferation and osteogenic differentiation of human mesenchymal stem cells.

Secrets of Flavonoid Synthesis in Mushroom Cells

Flavonoids are chemical compounds that occur widely across the plant kingdom. They are considered valuable food additives with pro-health properties, and their sources have also been identified in other kingdoms. Especially interesting is the ability of edible mushrooms to synthesize flavonoids. Mushrooms are usually defined as a group of fungal species capable of producing macroscopic fruiting bodies, and there are many articles considering the content of flavonoids in this group of fungi. Whereas the synthesis of flavonoids was revealed in mycelial cells, the ability of mushroom fruiting bodies to produce flavonoids does not seem to be clearly resolved. This article, as an overview of the latest key scientific findings on flavonoids in mushrooms, outlines and organizes the current state of knowledge on the ability of mushroom fruiting bodies to synthesize this important group of compounds for vital processes. Putting the puzzle of the current state of knowledge on flavonoid biosynthesis in mushroom cells together, we propose a universal scheme of studies to unambiguously decide whether the fruiting bodies of individual mushrooms are capable of synthesizing flavonoids.

Next-Generation Colloidal Materials for Ultrasound Imaging Applications

Ultrasound has important applications, predominantly in the field of diagnostic imaging. Presently, colloidal systems such as microbubbles, phase-change emulsion droplets and particle systems with acoustic properties and multiresponsiveness are being developed to address typical issues faced when using commercial ultrasound contrast agents, and to extend the utility of such systems to targeted drug delivery and multimodal imaging. Current technologies and increasing research data on the chemistry, physics and materials science of new colloidal systems are also leading to the development of more complex, novel and application-specific colloidal assemblies with ultrasound contrast enhancement and other properties, which could be beneficial for multiple biomedical applications, especially imaging-guided treatments. In this article, we review recent developments in new colloids with applications that use ultrasound contrast enhancement. This work also highlights the emergence of colloidal materials fabricated from or modified with biologically derived and bio-inspired materials, particularly in the form of biopolymers and biomembranes. Challenges, limitations, potential developments and future directions of these next-generation colloidal systems are also presented and discussed.

Spatiotemporal Control of Melanin Synthesis in Liquid Droplets

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration, and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Inspired by the pigment's biosynthesis, we developed a methodology to spatiotemporally regulate melanin formation in liquid droplets. The spatial control is achieved by sequestration of the reaction in dextran-rich droplets of a polyethylene glycol/dextran aqueous two-phase system, where the use of a photocleavable protected tyrosine provides a temporal control over its enzymatic oxidation-polymerization. We show that the liquid droplets allow for confined local reactivity as they serve as reaction centers for melanin synthesis and compartmentalize the melanin product. This methodology opens tremendous opportunities for applications in skincare and biomedicine.

Natural Melanin: Current Trends, and Future Approaches, with Especial Reference to Microbial Source

Melanin is a universal natural dark polymeric pigment, arising in microorganisms, animals, and plants. There is a couple of pieces of literature on melanin, each focusing on a different issue, the goal of the present review is to focus on microbial melanin. It has numerous benefits with very few drawbacks. The current situation and expected trends are discussed. Intriguing, numerous studies have provoked a serious necessity for a comprehensive assessment of microbial melanin pigments. So that, such review would help scholars from diverse backgrounds to realize the importance of melanin pigments isolated from microorganisms, with this aim in mind, information, and hypothesis from this review could be the paradigm for studies on melanin in the next era.

Preparation of Hybrid Sol-Gel Materials Based on Living Cells of Microorganisms and Their Application in Nanotechnology

Microorganism-cell-based biohybrid materials have attracted considerable attention over the last several decades. They are applied in a broad spectrum of areas, such as nanotechnologies, environmental biotechnology, biomedicine, synthetic chemistry, and bioelectronics. Sol-gel technology allows us to obtain a wide range of high-purity materials from nanopowders to thin-film coatings with high efficiency and low cost, which makes it one of the preferred techniques for creating organic-inorganic matrices for biocomponent immobilization. This review focuses on the synthesis and application of hybrid sol-gel materials obtained by encapsulation of microorganism cells in an inorganic matrix based on silicon, aluminum, and transition metals. The type of immobilized cells, precursors used, types of nanomaterials obtained, and their practical applications were analyzed in detail. In addition, techniques for increasing the microorganism effective time of functioning and the possibility of using sol-gel hybrid materials in catalysis are discussed.

MiR-19 3b regulated the formation of coat colors by targeting WNT10A and GNAI2 in Cashmere goats

MiRNAs as a series of small noncoding RNAs that play a crucial part in regulating coat color and hair follicle development. In the previous Solexa sequencing experiments, there were many miRNAs expressed differentially in alpacas with different coat color, including miR-193b.But the mechanism of miR-193b in mammalian pigmentation is still unknown. In this study, bioinformatics analysis showed that WNT10A and GNAI2 might be the target genes of miR-193b. qRT-PCR showed the expression of miR-193b in white Cashmere goats' skins was obviously lower than that in browns, and the expression of WNT10A and GNAI2 were similar with miR-193b. The protein levels of WNT10A and GNAI2 indicated the same findings. Furthermore, the expression of WNT10A and GNAI2 in keratinocytes were analyzed from mRNA and protein levels, the results manifested that the group of overexpression of miR-193b in HaCaT cells increased the expressions of target genes, and miR-193b inhibition group reduced expressions. Luciferase report assays confirmed that the targeting relationship between miR-193b and target genes (WNT10A and GNAI2), the results showed that miR-193b was positively correlated with target genes. These experimental data showed that miR-193b might participate in adjustment of coat color in skin tissue of Cashmere goat by targeting WNT10A and GNAI2.

Controlled Release of Doxorubicin for Targeted Chemo-Photothermal Therapy in Breast Cancer HS578T Cells Using Albumin Modified Hybrid Nanocarriers

Hybrid nanomaterials have attracted research interest owing to their intriguing properties, which may offer new diagnostic options with triggering features, able to realize a new kind of tunable nanotherapeutics. Hybrid silica/melanin nanoparticles (NPs) containing silver seeds (Me-laSil_Ag-HSA NPs) disclosed relevant photoacoustic contrast for molecular imaging. In this study we explored therapeutic function in the same nanoplatform. For this purpose, MelaSil_Ag-HSA were loaded with doxorubicin (DOX) (MelaSil_Ag-HSA@DOX) and tested to assess the efficiency of drug delivery combined with concurrent photothermal treatment. The excellent photothermal properties allowed enhanced cytotoxic activity at significantly lower doses than neat chemotherapeutic treatment. The results revealed that MelaSil_Ag-HSA@DOX is a promising platform for an integrated photothermal (PT) chemotherapy approach, reducing the efficacy concentration of the DOX and, thus, potentially limiting the several adverse side effects of the drug in in vivo treatments.

Natural Melanin/Alginate Hydrogels Achieve Cardiac Repair through ROS Scavenging and Macrophage Polarization

The efficacy of cardiac regenerative strategies for myocardial infarction (MI) treatment is greatly limited by the cardiac microenvironment. The combination of reactive oxygen species (ROS) scavenging to suppress the oxidative stress damage and macrophage polarization to regenerative M2 phenotype in the MI microenvironment can be desirable for MI treatment. Herein, melanin nanoparticles (MNPs)/alginate (Alg) hydrogels composed of two marine-derived natural biomaterials, MNPs obtained from cuttlefish ink and alginate extracted from ocean algae, are proposed. Taking advantage of the antioxidant property of MNPs and mechanical support from injectable alginate hydrogels, the MNPs/Alg hydrogel is explored for cardiac repair by regulating the MI microenvironment. The MNPs/Alg hydrogel is found to eliminate ROS against oxidative stress injury of cardiomyocytes. More interestingly, the macrophage polarization to regenerative M2 macrophages can be greatly promoted in the presence of MNPs/Alg hydrogel. An MI rat model is utilized to evaluate the feasibility of the as-prepared MNPs/Alg hydrogel for cardiac repair in vivo. The antioxidant, anti-inflammatory, and proangiogenesis effects of the hydrogel are investigated in detail. The present study opens up a new way to utilize natural biomaterials for MI treatment and allows to rerecognize the great value of natural biomaterials in cardiac repair.

Fungal Melanins and Applications in Healthcare, Bioremediation and Industry

Melanin is a complex multifunctional pigment found in all kingdoms of life, including fungi. The complex chemical structure of fungal melanins, yet to be fully elucidated, lends them multiple unique functions ranging from radioprotection and antioxidant activity to heavy metal chelation and organic compound absorption. Given their many biological functions, fungal melanins present many possibilities as natural compounds that could be exploited for human use. This review summarizes the current discourse and attempts to apply fungal melanin to enhance human health, remove pollutants from ecosystems, and streamline industrial processes. While the potential applications of fungal melanins are often discussed in the scientific community, they are successfully executed less often. Some of the challenges in the applications of fungal melanin to technology include the knowledge gap about their detailed structure, difficulties in isolating melanotic fungi, challenges in extracting melanin from isolated species, and the pathogenicity concerns that accompany working with live melanotic fungi. With proper acknowledgment of these challenges, fungal melanin holds great potential for societal benefit in the coming years.

Fungal melanin as a biocompatible broad-spectrum sunscreen with high antioxidant activity

Melanin is considered a bio-inspired dermo-cosmetic component due to its high UV absorption and antioxidant activity. Among various melanin sources, fungal melanin is a promising candidate for sunscreen because of its sustainability and scalability; however, quantitative assessment of its function has not yet been sufficiently explored. In this study, melanin samples derived from Amorphotheca resinae were prepared, followed by the evaluation of their sunscreen performance, antioxidant activity, and cytotoxicity. Melanin-blended cream was prepared by blending a melanin suspension and a pure cream. The cream showed an in vitro sun protection factor value of 2.5 when the pigment content was 5%. The cream showed a critical wavelength of approximately 388 nm and a UVA/UVB ratio of more than 0.81, satisfying the broad-spectrum sunscreen requirement. Oxygen radical absorbance capacity assays indicated that fungal melanin had antioxidant activity similar to ascorbic acid but higher than reduced glutathione. Fungal melanin had no statistically significant cytotoxicity to human keratinocyte cell lines until 72 h of exposure, even at a concentration of 4 mg mL-1. Consequently, melanin pigment can be used as a biocompatible broad-spectrum sunscreen with high antioxidant activity and as a practical alternative in dermo-cosmetic formulations.

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

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.

Biomaterials Tailoring at the Nanoscale for Tissue Engineering and Advanced Therapies

The definition of the term "biomaterial" dates back to 1991, during the 2nd Consensus Conference on the Definitions in Biomaterials organized by the European Society of Biomaterials in Chester (UK) [...].

Multifunctional mats by antimicrobial nanoparticles decoration for bioinspired smart wound dressing solutions

Developing advanced materials for wound dressings is a very challenging, yet unaddressed task. These systems are supposed to act as temporary skin substitutes, performing multiple functions, including fluid absorption and antimicrobial action, supporting cell proliferation and migration in order to promote the skin regeneration process. Following a global bioinspired approach, in this study, we developed a multifunctional textile for wound dressing applications. Biodegradable polyhydroxybutyrate/poly-3-caprolactone (PHB/PCL) mats were fabricated by electrospinning to mimic the extracellular matrix (ECM), thus providing structural and biochemical support to tissue regeneration. Furthermore, inspired by nature's strategy which exploits melanin as an effective weapon against pathogens infection, PHB/PCL mats were modified with hybrid Melanin-TiO₂ nanostructures. These were combined to PHB/PCL mats following two different strategies: in-situ incorporation during electrospinning process, alternately ex-post coating by electrospraying onto obtained mats. All samples revealed huge water uptake and poor cytotoxicity towards HaCat eukaryotic cells. Melanin-TiO₂ coating conferred PHB/PCL mats significant antimicrobial activity towards both Gram(+) and Gram(-) strains, marked hydrophilic properties as well as bioactivity which is expected to promote materials-cells interaction. This study is going to provide a novel paradigm for the design of active wound dressings for regenerative medicine.