バイオテクノロジーとバイオマテリアル

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Biomaterials 2020: Actinobacterial Reduction of Nano Graphene Oxide for Biomedical Applications

Kavitha and R. Balagurunathan

Graphene oxide (GO) reduction, in particularly, the simple, cost effective and environmental benign microbial method attracts high over the other methods. Extracellular mediated actinobacterial reduction of nano graphene oxide is focused for the high purity and productivity of the product without any toxicity. In addition, Indian plant Cynodon dactylon also have an excellent ability to reduce the GO. Reduction of the nano-graphene oxide (nGO) to graphene nanoparticles (nRGO) was identified by visual colour change from brown to black. Further, the reduction of nGO into nRGO was confirmed through XRD pattern. Fig. 1 shows the disappearance of the peak at 2θ = 10° in the GO and formation of new broad peak at 2θ = 26° (JCPDS no. 411487) supports that the GO is completely reduced into graphene. The average Crystallite size of rGO is 8-10nm (Scherrer’s equation).  Further the bioactivity of biological reduced nano graphene give the superior results compare than the chemically synthesized particles. Appropriate degradation as well as HAp layer formation supports the biological synthesis and suggests for the fruitful outcome for therapeutical applications. Microorganism has ability to produce secondary metabolites, which have found application in  combating a variety of human infections. Among the microorganisms, marine bacteria particularly actinomycetes produce unique and novel secondary metabolites and it is useful for different biological activities, such as antifungal, antibacterial, antitumor, anticancer, anti-parasitic and immunosuppressive activities. Soil dwelling, actionbacteria are more potent source of novel enzymes and secondary metabolites, including many antibiotics and bioactive compounds than the other microorganism. Nearly 80% of naturally occurring antibiotics have been isolated from different actinomycetes especially from Streptomycetes. Streptomycetes yielded many therapeutic agents such as streptomycin, erythromycin, tetracycline, amphotericin, chloramphenicol, daptomycin fosfomycin, lincomycin, neomycin, puromycin, anticancer drugs exemplified by adriamycin and the immunosuppressant tacrolimus. There are more bioactive

compounds such as avermectin (Streptomyces avermitilis), bleomycin (Streptomyces verticillus) and daunomycin (Streptomyces peuceticus) as antitumor compounds, Tacrolimus, is an binding protein formerly known as FK506 or fujimycin (Streptomyces tsukubaensis) as an immunosuppressant, and validamycin (Stereptomyces hygroscopicus var. limoneus) as a treatment of rice sheath blight disease. Methicillin- resistant Staphylococcus aureus (MRSA) is a pathogen responsible for a wide range of infections such as boils, pneumonia, osteomyelitis, endocarditis, bacteremia, etc. and has developed resistance to the majority of conventional antibiotics. Similarly, Enterococcus infections are caused mostly by vancomycin resistant Enterococcus faecalis and E.coli (VRE). Clinical pathogens such as Staphylococcus aureus, Pseudomonas, and Enterobacteriaceae, Candida albicans, C. glabrata and Cryptococcus neoformans plays vital role in many degenerative diseases. Similarly, Candida species such as C. albicans, C. glabrata and Cryptococcus neoformans cause arthritis, infections in immune suppressed individuals and infections with bone rupture and cause degenerative diseases. Pathogens often transform their genomic alignment against existing antibiotics and loss their sensitivity and became a drug resistant pathogens. The number of drug resistant pathogens are increasing day by day and become serious public health problems. In addition, recent years new therapeutic agents have entered in the clinical area, unfortunately with some side effects. Compare than the graphene oxide, reduced graphene oxide facilitates incredible properties such as high surface area, bacterial inhibition, enhanced mechanical property, bioactive nature. Especially, nano-graphene possess unique reinforcing behaviour with a large surface area plays a key role in osteoinduction and osteoconduction which promotes cell adherence. Hence, grapheme is used for orthopaedic and bone regeneration application vitally. In addition, the cancer cell targeting and diagnosis through graphene attract us more towards the biomedical application. The most commonly used chemical reducing agents for graphene oxide are anhydroushydrazine, hydrazine monohydrate, sodium borohydride, and hydroquinone. These reducingagents are highly toxic and harmful. Moreover, hydrazine-reduced graphene tends to agglomerate irreversibly and converts into graphite. Metal/hydrochloric acid reduction is another alternative; however, an impurity formed from the residual metal hinders further applications. Therefore, search towards the environmental friendly, green production of graphene is increased. Especially, microbial mediated syntheses are focused for owing to its simplicity, nill-toxicity, stability,viability, and scalability.