The aim of this study is preparation, characterization, and biological activity evaluation of 2 new collagen composites, collagen/ (Ag/ RGO) and collagen/ (Ag/RGO/SiO2) with expected antimicrobial activity. The loading of collagen matrix by self-prepared Ag/RGO and Ag/RGO/SiO2 was varied. The morphology of these antimicrobial agents, as well as of the corresponding collagen composites, was observed by SEM. Their biological activity was evaluated against 3 Gram-negative and 3 Gram-positive microbial strains, as well as against 3 type eukaryotic cells: osteoblast, fibroblast, and epithelial. Dependent on the concentration of Ag/RGO, well pronounced activity against Gram-negative bacterium (E. coli), fungus (C. Lusistaniae) and 2 Gram-positive bacteria (S. epidermidis and B. cereus) was found for collagen/ (Ag/RGO) composites at weight ratios of 2: 1, 2: 0.8, and 2: 0.6, at the last one accompanied by low cytotoxicity. Dependent on the concentration of Ag/RGO/SiO2 biological activity was found for the collagen/ (Ag/RGO/SiO2) composites also, better expressed than that of collagen/ (Ag/RGO) composites with the same level of antimicrobial agent loading. The experimental results demonstrated that the doping of RGO with Ag nanoparticles increases the antimicrobial activity of the collagen/ (Ag/RGO) composites. Improving its dispersion, the silane matrix in the Ag/RGO/SiO2 additionally increases the biological activity of the studied collagen/ (Ag/RGO/SiO2) composites and their well- pronounced, broad spectrum (against 3 Gram-negative, 2 Gram-positive bacteria and a fungus), antimicrobial activity is similar to that of the broad spectrum antibiotics. The novel collagen/ (Ag/RGO) and collagen/ (Ag/RGO/SiO2) composites are promising antimicrobial collagen biomaterials that widen the assortment of such for variety biomedical applications.

In this issue of JOVR, Derakhshan and coauthors1 describe the results of crosslinking for patients with early keratoconus. collagen crosslinking is a recently described technique of corneal tissue strengthening using riboflavin as a photosensitizer and ultraviolet A (UVA) radiation to promote the formation of intra- and interfibrillar covalent bonds by photosensitized oxidation.To date, it is the only published intervention that may retard the progression of keratoconus. collagen crosslinking has also been sequentially combined with other treatment modalities, namely intrastromal ring segments and photorefractive keratectomy, for treatment of keratoconus.Other possible indications include keratectasia following laser in situ keratomileusis (LASIK), infectious keratitis and bullous keratopathy.In vitro studies on human and porcine corneas have shown a significant increase in corneal rigidity after crosslinking as indicated by an increase in Young’s modulus.

With the idea of exploring the biological activity of some newly synthetized chemical compounds and their combinations for development of novel antimicrobial collagen biomaterials, a serial investigation was initiated, starting with the preparation and biological activity study of collagen/ ZnTiO3 nano- composites. This serial investigation continued with the preparation and biological activity study of new collagen-based composites in which self- prepared reduced graphene oxide (RGO) sheets were included as an antimicrobial agent. The new porous collagen/RGO composites demonstrated specific antimicrobial activity to different types microbial species; well pronounced activity against Gram- positive microorganisms (Listeria innocua and Bacillus cereus, both bacteria with typical chains forming, large size cells, and Candida lusitaniae, fungus with specific micelle organization) and lack of activity against Gram- negative bacteria (Pseudomonas putida, Salmonella enterica, Pseudomonas aeruginosa, and Escherichia coli; all bacteria with small size cells) combined with lack of cytotoxicity to eukaryotic cells. For the first time, well-pronounced antifungal activity of collagen/ RGO composites, depending on the RGO concentration was observed. Sterile zone of 17mmwas measured forC. lusitaniae on collagen/RGO composite, 2: 1 wt/wt. The possible mechanism of the biological activity of the new collagen/ RGO composites was correlated with their characteristics and the specific cell morphology and size of the test microorganisms. The results of this investigation demonstrated that with their specific and adjustable bioactivity, the new collagen/RGO composites are promising antimicrobial biomaterial for variety of biomedical applications, including tissue engineering.