Surfaces modified with polyelectrolyte multilayers for bio-interface applications

Polyelectrolyte multilayers are made by the alternating adsorption of oppositely charged polyelectrolytes. Thin films with bioactive or biospecific properties may be designed and produced using an extraordinary range of multicomposites available from the individual charged components. The use of polyelectrolyte multilayers, PEMUs, in the biomedical field is attracting the attention of surface scientists due to the flexibility and ease with which PEMUs can be used to modify surfaces and change interfacial properties. The field of polyelectrolyte multilayers has grown rapidly for the last decade and is showing promising results for use in many other applications.; In this dissertation, protein adsorption modalities onto polyelectrolyte multilayer thin films will be presented. Several factors are found to control their disposal at multilayer surfaces such as surface charge, multilayer film thickness, surface hydrophobicity and buffer ionic strength. Models for protein adsorption on PEMUs are introduced and tested using surface sensitive techniques. Findings are extremely useful for the biotechnology field where protein adsorption control is a desirable need. pH-tunable PEMUs are also designed in this work to load/release proteins in a novel method that might have potential uses in separation and purification of acidic and basic proteins.; In another study, polyelectrolyte multilayer films are tested for their ability to support attachment of cultured smooth muscle cells. Effects of surface charge and hydrophobicity on cell adhesion, morphology, and motility are examined in this work. The hydrophobic nature and surface charge of different polyelectrolyte films affected cell attachment and spreading. Mimicking biological systems by designing films that have zwitterions, groups present on cell membranes, is presented and shows an outstanding performance potentially useful in directed cell growth and adhesion. PEMUs will have promising applications in new cell culture coatings where surface functionalization has never been easy.; The last part of this dissertation describes the ion rectification properties of PEMUs. Ion transport is studied using an electrochemical device designed to test the "salt gated" transistor principle, where under the influence of external solution ionic strength (salt concentration), sites for ion transport are reversibly created into the membrane. This system represents a new paradigm in the transduction of chemical potential into ion currents. Modifying electrodes by coating them with ultrathin polyelectrolyte multilayers has shown to have slight effect on the performance of these electrodes, which shows the significance of this surface modification method and its potential applications in biosensors and ion selective electrode modification.