Pulsed plasma polymerisation of carvone: characterisations and antibacterial properties

Abstract

The production of suitable coatings with excellent antibacterial performance has now become a viable technique for enhancing the functional qualities of various biomedical materials. Here, pulsed plasma polymerisation was used to produce an antibacterial coating from the carvone oil of the spearmint plant. The coating films have adjustable chemical and physical properties based on the deposition parameter – that is, duty cycle (DC). The static water contact angle (WCA) values of pulsed wave (PW) plasma-polymerised carvone (ppCar) increase with the increase in DC. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the molecular structure of carvone is less fragmented, retaining moieties associated with C–O and C=O when the DC is reduced. These C–O and C=O moieties likely reduced the measured static WCA. This surface chemical composition with predominantly C–O and C=O also showed a stronger bactericidal effect, based on the biofilm assay with bacteria (Escherichia coli and Staphylococcus aureus), compared with those coatings with C–C and C–H produced at a higher DC. As shown by the atomic force microscopy images, a lower DC resulted in smoother and more homogeneous coatings than those produced with a higher DC, while field emission scanning electron microscopy images show that when E. coli and S. aureus membranes were attached to PW ppCar, they ruptured and distorted with a pore created and that these distortions and ruptures increased as the DC was reduced.