Biomedical Engineering Reference
In-Depth Information
component due to carbon only bound to carbon and hydrogen at 284.8 eV. The data
treatment was performed with the Casa XPS software (Casa Software Ltd., UK). The peaks
were decomposed using a linear baseline, and a component shape defined by the product of
a Gauss and Lorentz function, in the 70:30 ratio, respectively. Molar concentration ratios
were calculated using peak areas normalized according to the acquisition parameters and
the relative sensitivity factors and transmission functions provided by the manufacturer.
2.5 Atomic force microscopy (AFM)
The surface topography was examined using a commercial AFM (NanoScope III MultiMode
AFM, Veeco Metrology LLC, Santa Barbara, CA) equipped with a 125 µm
¯
125 µm
¯
5 µm
scanner (J-scanner). A quartz fluid cell was used without the O-ring. Topographic images
were recorded in contact mode using oxide-sharpened microfabricated Si
3
N
4
cantilevers
(Microlevers, Veeco Metrology LLC, Santa Barbara, CA) with a spring constant of 0.01 N.m
-1
(manufacturer specified), with a minimal applied force (<500 pN) and at a scan rate of 5-6
Hz. The curvature radius of silicon nitride tips was about 20 nm. Images were obtained at
room temperature (21-24°C) in milliQ water. All images shown in this paper were flattened
data using a third order polynomial. The surface roughness (R
rms
) was computed over an
area of 1 µm
¯
1 µm using the Veeco software.
2.6 Water contact angle measurements
Water contact angles were measured at room temperature using the sessile drop method
and image analysis of the drop profile. The instrument, using a CCD camera and an image
analysis processor, was purchased from Electronisch Ontwerpbureau De Boer (The
Netherlands). The water (milliQ) droplet volume was 0.3 μL, and the contact angle was
measured 5 s after the drop was deposited on the sample. For each sample, the reported
value is the average of the results obtained on 5 droplets.
3. Results
AFM images obtained in water on SS samples after different treatments are presented in
Figure 1. The nat sample showed the presence of nanoparticles with different sizes (nat,
Figure 1, R
rms
= 3.2 nm), in agreement with previous results. The formation of nanoparticles,
presumably made of ferric hydroxide, resulted from oxidation occurring during the 48 h of
immersion subsequent to polishing (Landoulsi et al., 2008a). The surface of silanized SS
exhibited particles with a bigger size (sil, Figure 1) and the roughness decreased slightly (sil,
Figure 1, R
rms
= 2.4 nm). The treatment with Gox, with or without previous treatment with
BS, led to the formation of particles with a more uniform size and a higher density, in
comparison with nat sample, and no appreciable change of surface roughness (R
rms
= 1.7 nm
for sil+Gox and 2.5 nm for sil+BS+Gox, Figure 1).
XPS is a suitable method to obtain information regarding the different constituents at the
surface (substrate, silane, other organic compounds). The elemental composition of the
samples is given in Table 2. Representative C 1s and O 1s peaks recorded on SS surface prior
to and after silanization, and after further treatments are given in Figure 2. After BS and/or
Gox treatment of silanized SS, a relative increase of the component around 531.2 eV in the O
1s peak was observed (Figure 2). In the C 1s peak, an increase of the components at 286.3
and 288.7 eV was also clear, while the main component remained at 284.8 eV. The same
