Biomedical Engineering Reference
In-Depth Information
groups can be suciently exposed to the outermost surface during the
contact with plasma proteins, and leads to the protein accumulation.
The adsorption state of fibrinogen was analyzed using QCM-D measure-
ment and the result is shown in Figure 12.6b. As mentioned above, a change
in the f value during the adsorption test indicates the mass change occurred
on the polymer surfaces. The amount of adsorbed proteins could be calcu-
lated by using the simplified Sauerbrey equation with overtone value 7 and
C
¼
17.7 ng cm
2
,
33
as follows:
d
n
3
r
4
n
g
|
3
Dm
¼
CDf/n
(12.3)
where m is adsorption mass, C is a proportional constant for the 5 MHz AT-
cut crystal used, and n is overtone value. As clearly shown, a significantly
large value of fibrinogen adsorption was observed during the contact with
fibrinogen only on the hydrophobic Au and mPRX surfaces. This result is
consistent with the result of micro-BCA
t
, which is a well-known protein
quantification kit. Although both Au and mPRX surfaces induce a large
amount of fibrinogen adsorption, the change in D values was quite different
between two surfaces. In the case of a bare Au surface, adsorbed fibrinogen
molecules showed very low value of DD/Df, which indicates that the state of
adsorbed fibrinogen molecules is very rigid due to strong interaction with
the Au surface. In contrast to this, adsorbed fibrinogen on the mPRX surface
showed a significantly higher value of DD/Df, which indicates that the energy
dissipation of adsorbed fibrinogen molecules are quite high. This phe-
nomenon could be observed only when adsorbed substances are weakly
interacted with materials surfaces.
34
The reason why this type of soft inter-
action occurred only on the mPRX surface is still unclear. However, taking
the dynamic nature of the mPRX surface into account, it is plausible that the
dynamic nature of the mPRX surface is responsible for the soft adsorption
behavior of a fibrinogen molecule. Generally, the strong hydrophobic
interaction of a protein molecule with the materials surfaces is known to
induce significant conformational changes of adsorbed proteins.
35
There-
fore, this weakly interacting protein layer on the dynamic PRX surface is
anticipated to reveal moderate conformational change comparing with a
rigid-uncoated surface. The conformational change of adsorbed fibrinogen
on the dynamic polymer surfaces was quantified using ELISA test. Two types
of primary antibodies which can specifically bind to a- and g-chains of ad-
sorbed fibrinogen were used to determine the degree of surface exposure of
each chain. In the case of non-coated (Cell Desk
t
, a commercial cell culture
dish) surface, the amount of binding antibody on both a- and g-chains was
higher than other hydrophilic polymer surfaces. This result indicates that
adsorbed fibrinogen on the Cell Desk
t
surface underwent significant con-
formational change. In contrast to this, other hydrophilic polymer surfaces
showed significantly low level of antibody binding in both a- and g-chains.
This is presumably due to the low level of adsorbed proteins as confirmed in
the micro-BCA
t
and QCM-D measurement. However, fibrinogen molecules
on the mPRX surface showed quite interesting tendency. In spite of the
.
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