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.

The Enigmatic World of Fungal Melanin: A Comprehensive Review

Synthetic dyes are generally not safe for human health or the environment, leading to the continuous search and growing demand for natural pigments that are considered safer, biodegrade more easily, and are environmentally beneficial. Among micro-organisms, fungi represent an emerging source of pigments due to their many benefits; therefore, they are readily viable on an industrial scale. Among all the bioactive pigments produced by fungi, melanin is an enigmatic, multifunctional pigment that has been studied for more than 150 years. This dark pigment, which is produced via the oxidative polymerization of phenolic compounds, has been investigated for its potential to protect life from all kingdoms, including fungi, from biotic and abiotic stresses. Over time, the research on fungal melanin has attracted a significant amount of scientific interest due to melanin's distinct biological activities and multifarious functionality, which is well-documented in the literature and could possibly be utilized. This review surveys the literature and summarizes the current discourse, presenting an up-to-date account of the research performed on fungal melanin that encompasses its types, the factors influencing its bioactivity, the optimization of fermentation conditions to enhance its sustainable production, its biosynthetic pathways, and its extraction, as well as biochemical characterization techniques and the potential uses of melanin in a wide range of applications in various industries. A massive scope of work remains to circumvent the obstacles to obtaining melanin from fungi and exploring its future prospects in a diverse range of applications.

Thymus richardii subsp. nitidus (Guss.) Jalas Essential Oil: An Ally against Oral Pathogens and Mouth Health

The genus Thymus L., belonging to the Lamiaceae family, contains about 220 species with a distribution that mainly extends in Europe, northwest Africa, Ethiopia, Asia, and southern Greenland. Due to their excellent biological properties, fresh and/or dried leaves and aerial parts of several Thymus ssp. have been utilized in the traditional medicine of many countries. To evaluate not only the chemical aspects but also the biological properties, the essential oils (EOs), obtained from the pre-flowering and flowering aerial parts of Thymus richardii subsp. nitidus (Guss.) Jalas, endemic to Marettimo Island (Sicily, Italy), were investigated. The chemical composition of the EOs, obtained by classical hydrodistillation and GC-MS and GC-FID analyses, showed the occurrence of similar amounts of monoterpene hydrocarbons, oxygenated monoterpenes, and sesquiterpene hydrocarbons. The main constituents of the pre-flowering oil were β-bisabolene (28.54%), p-cymene (24.45%), and thymol methyl ether (15.90%). The EO obtained from the flowering aerial parts showed as principal metabolites β-bisabolene (17.91%), thymol (16.26%), and limonene (15.59%). The EO of the flowering aerial parts, and its main pure constituents, β-bisabolene, thymol, limonene, p-cymene, and thymol methyl ether were investigated for their antimicrobial activity against oral pathogens and for their antibiofilm and antioxidant properties.

Melanin of fungi: from classification to application

Melanin is a secondary metabolite composed of complex heterogeneous polymers. Fungal melanin is considered to be a sustainable and biodegradable natural pigment and has a variety of functional properties and biological activities. On one hand, due to its own specific properties it can play the role of antioxidant, anti-radiation, adsorption, and photoprotection. On the other hand, it has good biological activities such as hepatoprotective effect, hypolipidemic effect and anti-cancer. Therefore, it is widely used in various fields of daily life, including dyeing, food, biomedical and commercial industry. It is conducive to environmental protection and human health. However, the insolubility of fungal melanin in water, acids and organic solvents has been an obstacle to its commercial applications. Thus, the chemical modification methods of fungal melanin are summarized to increase its solubility and expand the application fields. Although fungal melanin has been used in many industries, as the structure and function of fungal melanin and modified melanin are further studied, more functional properties and bioactivities are expected to be discovered for a wide range of applications in the future.

Shall We Tune? From Core-Shell to Cloud Type Nanostructures in Heparin/Silica Hybrids

Heparin plays multiple biological roles depending on the availability of active sites strongly influenced by the conformation and the structure of polysaccharide chains. Combining different components at the molecular scale offers an extraordinary chance to easily tune the structural organization of heparin required for exploring new potential applications. In fact, the combination of different material types leads to challenges that cannot be achieved by each single component. In this study, hybrid heparin/silica nanoparticles were synthesized, and the role of silica as a templating agent for heparin supramolecular organization was investigated. The effect of synthesis parameters on particles compositions was deeply investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). Transmission Electron Microscopy (TEM) reveals a different supramolecular organization of both components, leading to amazing organic-inorganic nanoparticles with different behavior in drug encapsulation and release. Furthermore, favorable biocompatibility for healthy human dermal fibroblasts (HDF) and tumor HS578T cells has been assessed, and a different biological behavior was observed, ascribed to different surface charge and morphology of synthesized nanoparticles.

Bioinspired antibacterial PVA/Melanin-TiO2 hybrid nanoparticles: the role of poly-vinyl-alcohol on their self-assembly and biocide activity

Hybrid Melanin-TiO₂ nanoparticles are promising bioinspired antibacterial agents for biomedical coatings and food-packaging fields. However, due to a very low colloidal stability, they showed a high tendency to self-aggregate and rapidly precipitate, making not easy their use in aqueous medium to produce homogeneous antimicrobial coatings or nanocomposites. A valid strategy to improve their dispersion is the combination with a hydrophilic water-soluble polymer such as poly-vinyl-alcohol (PVA), which is a good choice to improve the colloidal stability of nanoparticles and to modulate their agglomeration. In this work, we propose an in-situ synthetic approach based on the hydrothermal route, by which the hybrid Melanin-TiO₂ nanoparticles were prepared starting from the inorganic and organic precursors in the presence of PVA. Combined approach of TEM, XRD, TG/DSC, EPR and DLS techniques allows for assessing the PVA role in the formation of hybrids and on their morphological features as well as colloidal stability and aqueous dispersion. Antibacterial tests demonstrated the biocide activity of PVA/Melanin-TiO₂ nanoparticles against Escherichia coli bacterial cultures, which resulted partially influenced by the PVA content. This study provides key information on the mutual influence of organic/inorganic components on the functional properties of the final hybrid nanocomposites, contributing to define a much more far-reaching implementation in the synthesis of bioinspired polymer-based nanocomposites.

Silver (I) N-Heterocyclic Carbene Complexes: A Winning and Broad Spectrum of Antimicrobial Properties

The evolution of antibacterial resistance has arisen as the main downside in fighting bacterial infections pushing researchers to develop novel, more potent and multimodal alternative drugs.Silver and its complexes have long been used as antimicrobial agents in medicine due to the lack of silver resistance and the effectiveness at low concentration as well as to their low toxicities compared to the most commonly used antibiotics. N-Heterocyclic Carbenes (NHCs) have been extensively employed to coordinate transition metals mainly for catalytic chemistry. However, more recently, NHC ligands have been applied as carrier molecules for metals in anticancer applications. In the present study we selected from literature two NHC-carbene based on acridinescaffoldand detailed nonclassicalpyrazole derived mono NHC-Ag neutral and bis NHC-Ag cationic complexes. Their inhibitor effect on bacterial strains Gram-negative and positivewas evaluated. Imidazolium NHC silver complex containing the acridine chromophore showed effectiveness at extremely low MIC values. Although pyrazole NHC silver complexes are less active than the acridine NHC-silver, they represent the first example of this class of compounds with antimicrobial properties. Moreover all complexesare not toxic and they show not significant activity againstmammalian cells (Hek lines) after 4 and 24 h. Based on our experimental evidence, we are confident that this promising class of complexes could represent a valuable starting point for developing candidates for the treatment of bacterial infections, delivering great effectiveness and avoiding the development of resistance mechanisms.

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.

Hybrid humic acid/titanium dioxide nanomaterials as highly effective antimicrobial agents against gram(-) pathogens and antibiotic contaminants in wastewater

Humic acids (HAs) provide an important bio-source for redox-active materials. Their functional chemical groups are responsible for several properties, such as metal ion chelating activity, adsorption ability towards small molecules and antibacterial activity, through reactive oxygen species (ROS) generation. However, the poor selectivity and instability of HAs in solution hinder their application. A promising strategy for overcoming these disadvantages is conjugation with an inorganic phase, which leads to more stable hybrid nanomaterials with tuneable functionalities. In this study, we demonstrate that hybrid humic acid/titanium dioxide nanostructured materials that are prepared via a versatile in situ hydrothermal strategy display promising antibacterial activity against various pathogens and behave as selective sequestering agents of amoxicillin and tetracycline antibiotics from wastewater. A physicochemical investigation in which a combination of techniques were utilized, which included TEM, BET, ¹³C-CPMAS-NMR, EPR, DLS and SANS, shed light on the structure-property-function relationships of the nanohybrids. The proposed approach traces a technological path for the exploitation of organic biowaste in the design at the molecular scale of multifunctional nanomaterials, which is useful for addressing environmental and health problems that are related to water contamination by antibiotics and pathogens.

Characterisation of EFV12 a bio-active small peptide produced by the human intestinal isolate Lactobacillus gasseri SF1109

EFV12 is a small bioactive peptide produced by Lactobacillus gasseri SF1109, a human intestinal isolate with probiotic features. In this study, EFV12 antimicrobial and anti-inflammatory properties are characterised. In particular, we propose a possible mechanism of action for EFV12 involving bacterial membranes targeting. Moreover, we show that this small peptide is able to bind lipopolysaccharides (LPS) and to counteract its inflammatory insult preventing LPS action on Toll-like receptor 4, thus interfering with extracellular signal-regulated kinase, p38 and Jun N-terminal kinase, mitogen-activated protein kinases signalling pathways. Altogether these observations suggest that the bioactive peptide EFV12 is a good candidate to promote L. gasseri induced gut homeostasis and counteracting intestinal pathogens.

Shedding Light on the Free Radical Nature of Sulfonated Melanins

Melanin, an important class of natural pigment found in the human body, has stood out as a promising bioelectronic material due to its rather unique collection of electrical properties and biocompatibility. Among the available melanin derivatives, the sulfonated form has proven to not only be able to produce homogeneous device quality thin films with excellent adhesion, even on hydrophobic surfaces, but also to act as an ion to electron transducing element. It has recently been shown that the transport physics (and dominant carrier generation) may be related to a semiquinone free radical species in these materials. Hence, a better understanding of the paramagnetic properties of sulfonated derivatives could shed light on their charge transport behavior and thus enable improvement in regard to use in bioelectronics. Motivated by this question, in this work, different sulfonated melanin derivatives were investigated by hydration-controlled, continuous-wave X-band electron paramagnetic resonance spectroscopy and electronic structure calculations. Our results show that sulfonated melanin behaves similarly to non-functionalized melanin, but demonstrates a less pronounced response to humidity vis-à-vis standard melanin. We thus speculate on the structural and charge transport behavior in light of these differences with a view to further engineering structure-property relationships.

Melanin and Melanin-Like Hybrid Materials in Regenerative Medicine

Melanins are a group of dark insoluble pigments found widespread in nature. In mammals, the brown-black eumelanins and the reddish-yellow pheomelanins are the main determinants of skin, hair, and eye pigmentation and play a significant role in photoprotection as well as in many biological functions ensuring homeostasis. Due to their broad-spectrum light absorption, radical scavenging, electric conductivity, and paramagnetic behavior, eumelanins are widely studied in the biomedical field. The continuing advancements in the development of biomimetic design strategies offer novel opportunities toward specifically engineered multifunctional biomaterials for regenerative medicine. Melanin and melanin-like coatings have been shown to increase cell attachment and proliferation on different substrates and to promote and ameliorate skin, bone, and nerve defect healing in several in vivo models. Herein, the state of the art and future perspectives of melanins as promising bioinspired platforms for natural regeneration processes are highlighted and discussed.

Tuning Functional Behavior of Humic Acids through Interactions with Stöber Silica Nanoparticles

Humic acids (HA) exhibit fascinating multifunctional features, yet degradation phenomena as well as poor stability in aqueous environments strongly limit their use. Inorganic nanoparticles are emerging as a powerful interface for the development of robust HA bio-hybrid materials with enhanced chemical stability and tunable properties. Hybrid organic-inorganic SiO2/HA nanostructures were synthesized via an in-situ sol-gel route, exploiting both physical entrapment and chemical coupling. The latter was achieved through amide bond formation between carboxyl groups of HA and the amino group of 3-aminopropyltriethoxysilane (APTS), as confirmed by Fourier-Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy. Monodisperse hybrid nanoparticles about 90 nm in diameter were obtained in both cases, yet Electron Paramagnetic Resonance (EPR) spectroscopy highlighted the different supramolecular organization of HA. The altered HA conformation was reflected in different antioxidant properties of the conjugated nanoparticles that, however, resulted in being higher than for pure HA. Our findings proved the key role of both components in defining the morphology of the final system, as well as the efficacy of the ceramic component in templating the HA supramolecular organization and consequently tuning their functional features, thus defining a green strategy for bio-waste valorization.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.