Nonthermal plasma-based polymerization for antibacterial applications

Abstract

Bacterial contamination is a global issue and around 80% of pathogenic outbreaks are associated with biofilm formation following bacterial colonization on medical devices. This problem can be addressed using techniques governed by plasma physics. To curb bacterial contamination, creating an antibacterial coating is a putative way. Antibacterial coatings produced from natural compounds, like essential oils, have favourable results to inhibit biofilm formation. The interactions between bacterial surface proteins and natural monomers were also checked using computational biologydriven molecular docking studies. Initially, low-pressure pulse plasma was used to create a thin film through the polymerization of Carvone and Limonene. Physical changes were studied using water contact angle, Atomic Force Microscopy (AFM), Zeta potential analysis, and surface profiler while chemical changes were studied by Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) to understand the surface characteristics of the thin film and confirm the molecular structure of the monomers after polymerization. The results of these physio-chemical analyses show that the nano-thin films deposited on a glass substrate are optically transparent, homogenous, pinhole-free, stable, and smooth. The deposition rate of the optimized limonene thin film is 36.68 ± 0.42 nm/min, possessing a smooth surface with an average roughness of 0.23 ± 0.02 nm while the optimized carvone thin film deposition rate is 31.71 ± 0.20 nm/min with an average roughness of 0.062 ± 0.001 nm. After obtaining significant positive results with low-pressure pulse plasma polymerization, the study was expanded to include atmospheric pressure plasma polymerization for three monomers (Carvone, Limonene, and (3-Aminopropyl) triethoxysilane (APTES)). For this, we achieved a deposition rate of 30.72 nm/min and ~45 nm/min and average roughness of 0.08± 0.01 and 0.23 ±0.02 for carvone and limonene, respectively. XPS showed better retention of the monomer’s inherent bonds. Likewise, the deposited APTES layer had all the attributes to behave as a potent biosensor. Lastly, plasma-polymerized thin films of Carvone and Limonene exhibit bactericidal effects which were monitored by Field-Emission Scanning Electron Microscopy (FESEM), Fluorescence microscopy, and live-dead assay. Resultant FESEM images depict that the membranes of both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were ruptured and distorted upon attachment to the plasma polymerized thin film. The fluorescence effects from the biofilm assay and initial attachment assay were quantified. After 24 hours of incubation, the viability of E. coli and S. aureus in the plasma polymerized thin film of natural monomers was significantly reduced as compared to a clean glass slide. These results were further validated by Live-Dead Assay. The bacteriostatic activity estimated through limonene polymerized thin film using biofilm assay depicts a significant decrease of 94% and 93% in the case of E. coli and S. aureus respectively. In the case of carvone polymerized thin film the statistics change to 91.6% and 92.5% for the above-mentioned pathogens. The final product, a plasma polymerized thin film coating, using natural monomers is a remarkable biomedical innovation that promises to be fruitful in bacteriostatic and bactericidal surface development.