Antibacterial evaluation of CNF/PVAm multilayer modified cellulose fiber and cellulose model surface

摘要

Earlier studies have shown that 3-layer-modified cellulose fibers with poly(acrylic acid) (PAA) as the middle layer between two cationic polyelectrolyte polyvinylamine (PVAm) layers have strong antibacterial efficacy in terms of both bacteria adsorption and bacterial growth inhibition. In the present work, the fossil-based PAA middle layer was replaced by sustainable wood-based cellulose nano-fibrils (CNF), i. e., the fibers were modified by a 3-layer PVAm/CNF/PVAm system. Interestingly, the antibacterial efficacy of this system was greater than that of the previous PVAm/PAA/PVAm system. A higher salt concentration and lower assembly pH in the multilayer buildup resulted in better bacterial reduction. As the surface of a cellulose fiber is heterogeneous, making it difficult to characterize and visualize at high resolution, more homogeneous cellulose model surfaces were prepared by spin coating the dissolved cellulose fiber onto a silica surface to model the fiber surface. With increasing ionic strength, more aggregated and heterogeneous structures can be observed on the PVAm/CNF/PVAm modified model surfaces. The adsorbed bacteria distributed on the structured surfaces were clearly seen under fluorescence microscopy. Adsorbed amounts of bacteria on either aggregate or flat regions were quantified by scanning electron microscopy (SEM). More adsorbed bacteria were clearly seen on aggregates than on the flat regions at the surfaces. Degrees of bacteria deformation and cell damage were also seen under SEM. The surface roughness of the modified model surfaces was examined by atomic force microscopy (AFM), and a positive correlation was found between the surface roughness and the bacterial adhesion. Thus, an additional factor that controls adhesion, in addition to the surface charge, which is probably the most dominant factor affecting the bacteria adhesion, is the surface structures, such as roughness.