Study of the effect of mechanical stiffness substrata, assembled with polyelectrolyte multilayer thin films, on biofilm forming staphylococcus epidermidis' initial adhesion mechanism

Abstract

Polyelectrolyte multilayer thin films are polymer films assembled through a layer-by-layer sequential addition of oppositely charged polymers. The layer-by-layer film assembly technique allows for properties such as film thickness, chemical functionality, and elastic moduli to be easily altered by changing the pH in solution, or the number of bilayers added. This thesis examined the use of polyelectrolyte multilayer films, assembled with poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), to alter substrata mechanical stiffness, which was used to explore the response of biofilm forming staphylococci epidermidis. The formation of biofilms on medical device surfaces is currently responsible for a significant amount of infections acquired in hospitals. Currently mechanisms responsible for the initial adhesion of bacteria are not completely understood. Previous work completed in the Rubner and Van Vliet labs at MIT suggests a mechanoselective adhesion mechanism in prokaryotes. The existence of a positive correlation between mechanical stiffness and bacterial adhesion, independent of surface roughness or charge density, has already been shown in a non-biofilm forming strain of bacteria. This thesis focused on exploring the role mechanical stiffness substrata has on biofilm forming bacterial adhesion by conducting bacterial assay experiments on polyelectrolyte multilayer films. The results showed no positive correlation between mechanical stiffness and cell adhesion with biofilm forming staphylococcus epidermidis. Also, even under an applied shear force the amount of bacteria adhered on the surface was not affected. In all cases tested, the biofilm forming strain of bacteria was able to adhere and grow successfully.