Background: The well-recognized but not fully explored antioxidant activity of marine-biota-derived, biologically active substances has led to interest in their study as substitutes of antibiotics, antiaging agents, anticancer and antiviral drugs, and others. The aim of this review is to present the current state of the art of marine-biota-derived antioxidants to give some ideas for potential industrial applications. Methods: This review is an update for the last 5 years on the marine sources of natural antioxidants, different classes antioxidant compounds, and current derivation biotechnologies. Results: New marine sources of antioxidants, including byproducts and wastes, are presented, along with new antioxidant substances and derivation approaches. Conclusions: The interest in high-value antioxidants from marine biota continues. Natural substances combining antioxidant and antimicrobial action are of particular interest because of the increasing microbial resistance to antibiotic treatments. New antioxidant substances are discovered, along with those extracted from marine biota collected in other locations. Byproducts and wastes provide a valuable source of antioxidant substances. The application of optimized non-conventional derivation approaches is expected to allow the intensification of the production and improvement in the quality of the derived substances. The ability to obtain safe, high-value products is of key importance for potential industrialization.
Microbial adhesion and biofilm formation is a common, nondesirable phenomenon at any living or nonliving material surface in contact with microbial species. Despite the enormous efforts made so far, the protection of material surfaces against microbial adhesion and biofilm formation remains a significant challenge. Deposition of antimicrobial coatings is one approach to mitigate the problem. Examples of such are those based on heparin, cationic polymers, antimicrobial peptides, drug-delivering systems, and other coatings, each one with its advantages and shortcomings. The increasing microbial resistance to the conventional antimicrobial treatments leads to an increasing necessity for new antimicrobial agents, among which is a variety of carbon nanomaterials. The current review paper presents the last 5 years’ progress in the development of graphene antimicrobial materials and graphene-based antimicrobial coatings that are among the most studied. Brief information about the significance of the biofouling, as well as the general mode of development and composition of microbial biofilms, are included. Preparation, antibacterial activity, and bactericidal mechanisms of new graphene materials, deposition techniques, characterization, and parameters influencing the biological activity of graphene-based coatings are focused upon. It is expected that this review will raise some ideas for perfecting the composition, structure, antimicrobial activity, and deposition techniques of graphene materials and coatings in order to provide better antimicrobial protection of medical devices.
In a previous paper (Shalaby A, Yaneva V, Staneva A, Aleksandrov L, Iordanova R, Dimitriev Y, Nanoscience & nanotechnology -nanostructured materials application and innovation transfer (14), ISSN 1313-8995, 2014) we studied reduced graphene oxide (RGO)/SiO 2 composite material by adding a small amount of RGO to silica in order to avoid the aggregation process and to solve the problems connected with the exfoliation and distribution of the sheets inside the composites. But from a practical point we needed to study the effect of high amounts of RGO on the composites at different temperatures. The purpose of this investigation is to study the effect of RGO on phase transformations of the composites heated at 200, 400 and 800 C. The sol-Gel method was used to obtain the RGO/SiO 2 composite by mixing high amounts of RGO with tetraethyl orthosilicate (TEOS). Data are presented for the transformation of the nanocomposites with increasing temperature in air atmosphere. RGO nanosheets were prepared by chemical exfoliation of purified natural graphite using the Hummers and Offeman method (Hummers WS, Offeman RE, J Am Chem Soc 80:1339, 1958) to obtain graphite oxide. Then the material was exfoliated to reduced graphene nanosheets by ultrasonication and reduction process using sodium borohydride (NaBH 4 ). Characterization of the material was performed by X-ray powder diffraction (XRD), A. Shalaby
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