AVS 53rd International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI-WeA

Paper BI-WeA6
Influence of pH and Ionic Strength on the Conformation of Grafted Pollallylamine

Wednesday, November 15, 2006, 3:40 pm, Room 2014

Session: Bio-Interfacial Modification and Bio-Immobilization II (Honoring Marcus Textor, ETH-Zürich for Substantial Contributions to the Field)
Presenter: L.G. Britcher, University of South Australia
Authors: L.G. Britcher, University of South Australia
L. Galea, University of South Australia
S. Griesser, University of South Australia
H.J. Griesser, University of South Australia
Correspondent: Click to Email
Polyallylamine (PAA) modified surface are useful for providing a hydrophillic underlayer for subsequent covalent binding of biologically active molecules via the amino groups. However, it is necessary to control the pH and ionic strength of the polyallylamine during the grafting in order to maintain a dense coating. In this study we investigated PAA grafting onto aldehyde plasma polymer (Ald pp) treated silicon wafers under different pH and ionic strength regimes. XPS analysis showed that the nitrogen atomic % on the PAA grafted samples was greatest at pH 9.3 which, is above the pKa of the PAA (pKa 8). Less nitrogen was observed when grafting was done at pH 6 or 7. This difference in grafting density can be explained by the percentage of ionisation of the PAA chains as a function of the pH. At pH 9.3 the ionisation degree is around 30%, so there is little repulsion between the chains, allowing them to form a mushroom conformation. While at pH 6 or 7 the ionisation degree is around 70%, so the PAA forms a flat conformation on the Ald pp due to repulsion between the chains. Changes in the ionic strength did show differences in the amount of nitrogen, but pH appeared to influence the grafting density. Analysis of the high resolution N 1s XPS multiplex showed the presence of primary and protonated amines from the grafted PAA. The ratio of the primary amines to protonated amines on the dried coatings was independent of the grafting pH or ionic strength. However, after a period of time in water, the degree of protonation decreased for all samples, confirming similar results obtained with PAA layers deposited using layer-by-layer techniques.