Abstract:
Adipic dihydrazide-modified heparin was prepared and
subsequently immobilized on surface-activated silica wafers. X-ray
photoelectron spectroscopy (XPS) was used to quantify the elemental
composition of the silica surface at each stage of activation and results
showed that successful immobilization had taken place. Contact angle
measurements were made to verify the high hydrophilicity of the
heparinized and unheparinized silica surfaces. In situ ellipsometry was
used to study protein concentration effects on adsorption kinetics exhibited
by human plasma fibrinogen on unheparinized and heparinized silica. The
adsorbed amount of fibrinogen increased with concentration, on each type
of surface. At all concentrations, fibrinogen adsorbed in diminished
amounts and at a slower rate on heparinized as compared to unheparinized
silica. Buffer elution experiments showed that fibrinogen was less tightly
bound on heparinized silica. To examine the history dependence of
adsorption, fibrinogen was added for a second time, after rinsing. The
difference in adsorption rates between the first and second adsorption cycle
evaluated at identical mass density, indicated that post-adsorptive
molecular rearrangements had taken place. These rearrangements
presumably involved aggregation of adsorbed fibrinogen, in this way
increasing unoccupied area at the interface. Fibrinogen was postulated to
be more mobile on heparinized silica.
