Interaction of bacteria with flat and nanostructured plasma polymers

Biofilm formation causes severe and costly problems in maritime, food and biomedical applications. Therefore, the ability to minimise bacterial attachment and growth will have significant impact on a wide number of industries. Surface microtopography and chemistry are known to affect bacterial attachment. However, the role of surface nanotopography and chemical cues is unclear. In this thesis, colloidal lithography and plasma polymerisation were combined to fabricate a platform that would enable the roles of surface chemistry and nanotopography to be isolated. Modification of the colloidal assembly process enabled large (400 x 400 μm2) surface arrays to be formed. SEM was used to characterise the morphology and the area covered with colloidal arrays. The atomically composition and physico-chemical stability of the thin films were characterised by XPS, QCM-D, contact angle, and AFM. The attachment of E. coli onto carboxyl (ppAAc) and hydrocarbon (ppOct) rich plasma polymer films on either flat or colloidal array surfaces revealed that chemistry plays a critical role in bacterial attachment; while the effect of surface nanotopography is more difficult to define. Analysis of nanostructured ppOct surfaces suggested a more homogeneous colonisation of the surface in comparison to the flat ppOct. In addition, results indicated that when given a choice on hydrophilic ppAAc, cells appeared to prefer the nanostructured rather than the flat regions. The influence of surface chemistry on bacterial attachment was also examined by fabricating a plasma polymer from the essential oil, eucalyptol (ppCO). The antimicrobial activity of the oil was investigated against E. coli and S. aureus. The results illustrated that the oil was more effective against E. coli than S. aureus when tested in solution. When the oil was formed into a plasma polymer film, attachment decreased by 63 % with S. aureus and 98 % with E. coli compared with the glass control. The short-term behaviour of ppCO was similar to negative control (ppOct). However, long-term experiments using E. coli revealed that after five days ppCO showed isolated cells attached while ppOct reported approximately 3 % of the surface covered with biofilm. The significant reduction in the number of E. coli attached to ppCO open a wide range of applications in industries where E. coli biofilm formation in the initial days of exposure causes significant environmental and financial cost.