Researchers at the Catholic University of the Sacred Heart (UCSC) and the National Research Council (ISC-CNR) in Italy have used graphene oxide to develop an antimicrobial ‘cloak’ which could play a key role in protecting from the build-up of dangerous microbial biofilms.
The team found that an agar hydrogel that contains graphene-oxide and laser printed to mimic the shell surface of the Cancer pagurus crab, acts to lower growth of gram-positive and gram-negative bacteria, and fungal cells. The Cancer pagurus crab evolved an interesting defense against microbial infection - a shell where the outer surface, or the carapace, is shaped in a way which makes it much harder for microbes to grow.
The researchers then set out to test the efficiency of the hydrogel, and see how it affected the growth of three different organisms Staphylococcus aureus, Escherichia coli (gram-positive and gram-negative bacteria, respectively), and the fungus Candida albicans. To check this, they grew the organisms on four types of surface: plain agar, agar shaped to mimic the crab’s carapace, agar with embedded graphene oxide and the agar hydrogel itself.
They found that both the agar shaped to resemble the carapace and the agar containing graphene oxide reduced the growth of all organisms by about 10% as compared to the plain agar. But when the agar was both shaped to mimic the carapace and contained graphene oxide, this reduction of growth was much more prominent. The growth of S. aureus was reduced by as much as 53%, E. coli by 40% and C. albicans by 30%.
The colonies of the organisms that were able to grow were also significantly smaller on the agar hydrogel, with S. aureus colonies reduced by 70%, E. coli by 65% and C. albicans’ colonies decreased by 45%.
The researchers also tested the degree of damage caused to the organisms by measuring the amount of nucleic acids released. They found that both bacteria showed a much higher amount of nucleic acid leakage when grown on the agar hydrogel, suggesting that the graphene oxide residues are able to efficiently slice open the bacterial cells. However, C. albicans didn’t show any significant amount of nucleic acid release - perhaps due to the thicker nature of its cell wall, which is able to protect it from the worst of the compound’s cutting action.
Biofilms are layers of microorganisms growing on a surface, that can pose a massive risk to people's health, especially when located on medical devices like scalpels and catheters. Antimicrobial substances are used to remove this layer of growth but for these to be effective over long periods of time they need to be continuously re-applied, which can have a cumulative toxic effect on cells. To overcome this, a design is required for a substance that is cheap, can be applied over large and uneven surfaces and is less toxic than these existing biofilm deterrents.
Graphene oxide's antimicrobial properties make it an attractive material for such applications. GO's main method of killing microbes is by slicing through their membrane, causing their cellular contents to leak out and leading to cell death. It also has several advantages, such as low cost and easy large-scale production, and is environmentally friendly.
In November 2016, Biolin Scientific commercialized a graphene oxide sensor developed by ICN2, and in May 2016 A study coordinated by Italian institutions showed that graphene oxide can 'buffer' synapses, could be used to treat epilepsy.
