Biomedical Engineering Reference
In-Depth Information
Number of platelets
Percent of unactivated platelets
a-C:H-1
100
100
I
D
/
I
G
3.30
1.52
80
80
1.51
60
60
a-C:H4
40
40
20
20
0
0
a-C:H-1
a-C:H-2
a-C:H-4
FIGURE 2.11
Quantity of platelets adhered on surface of a-C:H films synthesized at different bias voltages (15 min incubation
in PRP). (Reprinted with permission from Yang et al.,
Biomaterials
, 24, 2821, 2003.)
higher bias voltage compared to those at lower bias voltage. The platelet attachment and
morphology studies suggest that the adhesion behavior is related to the surface energy of
the film. From Figure 2.12, the higher the bias voltage (lower the sp
3
/sp
2
ratio), the lower
the value of the polar component of the surface energy and, accordingly, the higher the
activation of adherent platelets.
Li and Gu [51] also found that the sp
3
fraction and surface energy of the film affects the
adhering platelets. They coated a-C:H on polymethylmethacrylate (PMMA) using IBAD
with different CH
n
+
beam bombarding energies. They investigated the effects of the bom-
barding energy on the chemical states and several sensitive cell attachments of the coatings
by means of extensive spectroscopic experiments and cultured cells in vitro. Compared
with the control sample (uncoated PMMA), a-C:H coatings show a lower platelet attach-
ment. The highest 800 eV CH
n
+
beam bombardment during the film synthesis resulted in a
more obvious decrease in the number of the platelets adhering to the surface of a-C:H coat-
ing. Analysis by XPS and Raman spectroscopy revealed an increase in sp
3
fraction within
the 800 eV coating. A simple contact angle measurement using water showed the film to be
more hydrophobic. In other words, the film had a lower surface energy that inhibited the
adhesion of platelets. However, one should note that the surface energy's relation with cell
adhesion is complex, and the study did not include comprehensive analysis of the films'
surface characteristics.
Logothetidis et al
.
[53] studied the hemocompatibility of unhydrogenated, hydrogenated
amorphous carbon and ta-C films based on the surface adsorption of the two proteins
human serum albumin (HSA) and fibrinogen (Fib); both are contained in human plasma.
The main characterization technique applied was Spectroscopic Ellipsometry (SE). From
the analysis of the SE data, using the appropriate modeling, the HSA/Fib surface concen-
tration ratio was derived. The higher the HSA/Fib ratio, the more hemocompatible the
coating. By using the SE technique, it is possible to determine the optical functions of thin
