Biomedical Engineering Reference
In-Depth Information
2.5
(a)
2.0
1.5
1.0
0.5
0.0
100
80
60
40
20
0
(b)
7.5
(c)
6.0
4.5
3.0
1.5
0.0
200
300 400 500
Annealing temperature ( ° C)
600
FIGURE 19.39 Band gap, resistivity, Hall mobility, and carrier concentration of a-C:H fi lms as functions of
annealing temperature. (From Yang, P. et al., Surf. Coating Tech ., 177-178, 747, 2004. With permission.)
Figure 19.40 exhibits the statistical results of the platelets adhered on the a-C:H fi lms of different
annealing temperatures from platelet rich plasma (PRP). In contrast with the results acquired from
the as-deposited fi lm, the numbering of adherent platelets on the annealed fi lms decreases, fl uctuates
slightly from 200°C to 500°C, and increases slightly at 600°C. The unactivated platelet percentages of
the annealed fi lms are close to that of the as-deposited one when the annealing temperature is lower
than 400 o C, and the percentages decrease when the annealing temperature is higher than 500°C. The
curve changes drastically at 400-500°C. It thus appears that annealing at a relatively low temperature
cannot cause retrogression of blood compatibility of our a-C:H fi lms, and the activation of platelets
adhered on the a-C:H fi lm surfaces is related to the change of the physical properties of the fi lms.
When blood comes in contact with an artifi cial surface, the fi rst event is protein adsorption.
If the adsorbed protein such as fi brinogen is denatured, the coagulation factors or platelets will be
activated, causing a series of cascade reaction of blood coagulation and then fi nally thrombosis. It
has been shown that denaturing of fi brinogen and coagulation factors FV, FVIII, FIX depends on
the transfer of its charges to the material, and this process is related to the electronic structure and
properties of the material [165,166]. Fibrinogen has an electronic structure similar to that of a semi-
conductor. When a material possesses a wider band gap than fi brinogen, there are less local states in
the band gap, lower carrier concentration and n-type structure, and consequently, fi brinogen dena-
turation is inhibited. Thus, it is reasonable that the as-deposited a-C:H fi lm with a larger band gap
and lower carrier concentration possesses lower surface activation of adherent platelets. It is prob-
ably the reason for the blood compatibility retrogression at a temperature higher than 400°C and the
signifi cant change in the electronic characteristics such as narrowing of the band gap (narrower than
 
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