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Wound dressings based on natural materials, such as fish skin, represent an important strategy for the treatment of burns. Despite their utility, contamination of these natural materials with bacteria (planktonic and biofilm forms) introduces significant risks to patients under treatment. This disadvantage can be overcome by modifying the material’s surface to prevent bacterial deposition through chemical or physical interactions. In this work, functional graphenic materials (FGM) with tunable surface charges were incorporated into tilapia (Oreochromis niloticus) fish skin as a part of a strategy to control the biofilm adhesion on surfaces. The antibiofilm activity was evaluated against S. aureus and K. pneumoniae due to the biofilm-forming properties of these bacterial strains. FGM-modified tilapia skin samples possess a strong capacity to reduce biofilm formation on the tilapia fish skin with a higher antibiofilm activity against Gram-positive bacteria, compared to Gram-negative bacteria. Negatively charged FGMs were more effective than positively charged FGMs in preventing biofilm formation on the impregnated tilapia skin xenografts: negatively charged Claisen graphene achieved an 88.8% reduction in biofilm formation on the tilapia skin. Overall, this study demonstrates the utility of FGM-impregnated tilapia skins as a treatment for burn wounds due to their ability to modulate bacterial adhesion. 

The balance of bacterial populations in the human body is critical for human health. Researchers have aimed to control bacterial populations using antibiotic substrates. However, antibiotic materials that non-selectively kill bacteria can compromise health by eliminating beneficial bacteria, which leaves the body vulnerable to colonization by harmful pathogens. Due to their chemical tunablity and unique surface properties, graphene oxide (GO)-based materials – termed “functional graphenic materials” (FGMs) – have been previously designed to be antibacterial but have the capacity to actively adhere and instruct probiotics to maintain human health. Numerous studies have demonstrated that negatively and positively charged surfaces influence bacterial adhesion through electrostatic interactions with the negatively charged bacterial surface. We found that tuning the surface charge of FGMs provides an avenue to control bacterial attachment without compromising vitality. Using E. coli as a model organism for Gram-negative bacteria, we demonstrate that negatively charged Claisen graphene (CG), a reduced and carboxylated FGM, is bacterio-repellent through electrostatic repulsion with the bacterial surface. Though positively charged poly- l -lysine (PLL) is antibacterial when free in solution by inserting into the bacterial cell wall, here, we found that covalent conjugation of PLL to CG (giving PLL n -G) masks the antimicrobial activity of PLL by restricting polypeptide mobility. This allows the immobilized positive charge of the PLL n -Gs to be leveraged for E. coli adhesion through electrostatic attraction. We identified the magnitude of positive charge of the PLL n -G conjugates, which is modulated by the length of the PLL peptide, as an important parameter to tune the balance between the opposing forces of bacterial adhesion and proliferation. We also tested adhesion of Gram-positive B. subtilis to these FGMs and found that the effect of FGM charge is less pronounced. B. subtilis adheres nondiscriminatory to all FGMs, regardless of charge, but adhesion is scarce and localized. Overall, this work demonstrates that FGMs can be tuned to selectively control bacterial response, paving the way for future development of FGM-based biomaterials as bacterio-instructive scaffolds through careful design of FGM surface chemistry. 

Graphene is a valuable material in biomedical implant applications due to its mechanical integrity, long-range order, and conductivity; but graphene must be chemically modified to increase biocompatibility and maximize functionality in the body. Here, we developed a foundational synthetic method for covalently functionalizing a reduced GO with bioactive molecules, focusing on synthetic peptides that have shown osteogenic or neurogenic capability as a prototypical example. X-ray photoelectron spectroscopy provides evidence that the peptide is covalently linked to the graphenic backbone. These peptide–graphene (Pep–G) conjugate materials can be processed into mechanically robust, three-dimensional constructs. Differences in their electrostatic charges allow the Pep–G conjugates to form self-assembled, layer-by-layer coatings. Further, the Pep–G conjugates are cytocompatible and electrically conductive, leading us to investigate their potential as regenerative scaffolds, as conductive surfaces can stimulate bone and nerve regeneration. Notably, PC12 cells grown on an electrically stimulated Pep–G scaffold demonstrated enhanced adhesion and neurite outgrowth compared to the control. The functionalization strategy developed here can be used to conjugate a wide variety of bioactive molecules to graphene oxide to create cell-instructive surfaces for biomedical scaffold materials.