Assembly and post-assembly manipulation of polyelectrolyte multilayers for control of bacterial attachment and viability

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 123-136).The overall goal of this thesis was to exploit the versatility of the polyelectrolyte multilayer (PEM) platform to consider bacteria-substrata interactions by varying multilayer assembly and post-assembly conditions. We developed multiple PEM systems to probe the ability of substrata to resist bacteria attachment or act as contact-killing antimicrobials. In the first study, by varying the pH of assembly, we developed PEMs of identical chemical composition (polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA)) with distinct mechanical moduli (1-100 MPa). Once characterized, these PEMs showed that, under certain conditions, bacterial attachment correlated with increasing modulus. Thus, substrata stiffness was found to be an additional parameter to consider when studying bacterial attachment. The next project focused on PEMs of PAH and poly(sodium-4-styrene sulfonate) (SPS) assembled at high pH that showed a reversible swelling transition upon immersion in a low pH solution. These acid-treated PEMs presented high positive charge density and mobility, and were capable of killing bacteria on contact. SPS/PAH PEMs were used as a model system to enumerate the design parameters that should be considered to create a cationic killing surface. A third PEM system was employed to further illustrate the effects of multilayer assembly and post-assembly conditions on bacteria. Cross-linked hydrogen-bonded PAA and poly(acrylamide) (PAAm) multilayers were modified post-assembly by the adsorption of PAH at various pH values. These multilayers underwent a variety of morphological transitions depending on the pH of PAH adsorption. At mid-range pH values, the film stiffened and promoted aqueous bacterial attachment.(cont.) At high pH values, PAH adsorbed onto the surface with many unbound uncharged amine groups. When the multilayer was exposed to physiological pH values for bacteria assays, the amine groups became protonated and participated in a cationic-killing effect. Finally, biofilm control was examined by investigating initial biofilm formation on films of various mechanical stiffness and surface charge. No differences were visible via optical microscopy. An alternative approach to biofilm control was considered whereby a dissociating multilayer region lifted-off a contaminated layer, exposing a clean, unfouled underlying surface.by Jenny A. Lichter.Ph.D