442 Prakt. Met. Sonderband 38 (2006) 
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Photon Energy 
Figure 3: Dielectric function before and after immersion in HAS 
Figure 3 gives the measured real and imaginary parts of the dielectric function prior tO (E4.p, E2- 
b) and after (£1.a, E2.a) immersion of the film in the HSA and Fib protein solutions. The 
difference between the two spectra contains information about the amount and the density of 
the proteins that are adsorbed on the surface. A two-layer model, as shown in Fig. 4, was 
used to simulate the films. The dielectric functions established by Logothetidis were used as 
references for both types of proteins.'® Film thickness was, therefore, the only variable that 
needed to be determined from the simulation. Based on the results of the simulation, the 
relative surface concentration I" (ug/cm?) of the HSA and Fib were derived using Cuypers 
one-component model: 
Nam —1 
P=0.14 Nam) Stk 
A (N fim +2) 
Where, d is the protein film thickness (nm), M the molar mass (g/mol), A the molar refractivity 
(1/mol.ml), and Nf the protein film refractive index. The results of the evaluation of the 
haemocompatibility of the films deposited using different experimental conditions are given in 
Table 1. The HSA/Fib ratios for our samples and for the carbon-based samples reported by 
Logothetidis'® were compared: 
» HSA/Fib = 0.9-1.3 for ZrN-Ag 
HSA/Fib = 0.1-0.3 for amorphous tetrahedral C 
HSA/Fib = 0.2-0.6 for amorphous C 
+ HSA/Fib = 0.5-1.0 for hydrogenated amorphous C