AVS 49th International Symposium
    Biomaterials Wednesday Sessions
       Session BI-WeA

Paper BI-WeA6
In-situ Measurements of Polyelectrolyte Multilayer Build-up using Ellipsometry and QCM-D : 9

Wednesday, November 6, 2002, 3:40 pm, Room C-201

Session: Polyelectrolyte Surfaces/Cell-Surface Interactions
Presenter: T.J. Thurell, YKI, Sweden
Authors: T.J. Thurell, YKI, Sweden
U. Elofsson, YKI, Sweden
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Polyelectrolyte multilayers are easily constructed by alternately exposing a charged surface to positively and negatively charged polymers. The aim of this study was to create a biocompatible surface for use in implant technology. The charged poly-amino-a cids PGA (Poly (L)Glutamic Acid) and PLL (Poly (L)Lysine) were coated on an initial layer of PEI (Polyethylimin) on both silica and titanium surfaces. Multilayer build-up was monitored in-situ using both ellipsometry and QCM-D. The polyelectrolytes adsor b ed firmly, with insignificant desorption upon rinsing, on both substrates used. In the ellipsometer up to 12 layer pairs were easily built while monitored in-situ. Comparing adsorbed amounts obtained from the ellipsometer, with those calculated from QC M-D measurements, one can see that these polymer-multilayer-films are highly hydrated (app. 70% water content). In the QCM-D measurements, an almost linear mass increase/layer are obtained from the second layer pair and up, whereas linear mass increase/l a y er is not achieved until the eighth layer pair in the ellipsometer. The observations indicate that the polymer film become denser with each added layer. This is also reflected in the increasing refractive index, which eventually level out at 1.457 af t er abo ut 10 layer pairs. The large fluctuations in refractive index and thickness found initially suggests that the polyelectrolytes in the two first layer pairs are unevenly adsorbed with gaps and holes where water may get trapped. One possible explanat io n for the variations in film density would be that the gaps and holes will eventually fill up resulting in constant film density and linear mass growth. This work is a part of the SIMI project (Surface Improvement of Metal Implants GRD1-2000-26823) funded by the European Commission.