Biomedical Engineering Reference
In-Depth Information
12.2 Hydrated Viscoelastic Factor of Polymeric
Biomaterials
Being different from metallic or ceramic materials, polymeric materials re-
veal dynamic conformations in aqueous medium including biological en-
vironments. Hydrated polymer materials, especially in the case of outermost
surface layer, generally show a swelled state in aqueous medium. This causes
the increase of intermolecular distance between the polymer chains, thus it
induces the dynamic dimensional change resulting in highly viscoelastic
properties.
18
The effect of these dynamic changes of polymer surface influ-
ences the protein/cell responses and it has been suggested as one of the
important factors in designing biomaterials.
19,20
However, a systematic
study to understand the effect of surface dynamics on the protein/cell re-
sponses has not yet conducted because of its diculties in measuring dy-
namic properties of the outermost surfaces of polymer materials, and in
modeling the polymer materials.
Recently, a quartz crystal microbalance-dissipation (QCM-D) technique
has been shown to allow measuring changes in hydrated viscoelastic prop-
erty at the molecular level.
21
The quartz crystal between a pair of electrodes
in the sensor chip is oscillated as showing acoustic resonance frequency (f
A
)
when the AC voltage is given to the electrodes. When the substance is ad-
sorbed on the sensor surface, a change in the frequency will be observed in
proportion to the amount of adsorption. When the AC voltage is removed,
the oscillation of the quartz crystal is exponentially decayed and provides the
dissipation factor of oscillating energy (D). When a highly viscous substance
is adsorbed on the surface, the energy dissipation of the sensor surface will
be rapidly increased (high DD) due to the energy transfer to the substance
(Figure 12.2a). Namely, a change in the f (Df) is generally related with the
mass changes on the outermost surfaces denoting the release or adsorption
of substance, whereas a change in the D (DD) represents the change in vis-
coelastic properties of the surfaces. Therefore, the hydrated viscoelastic
factor (Mf) on the outermost cast polymer surfaces on the sensor surface
could be obtained in the normalized value using eqn (12.1).
d
n
3
r
4
n
g
|
3
.
TIP: It is recommended to cast around 10-20 mg of polymers on sensor sur-
face, because the DD value will be saturated and show no significant change
along different polymer surfaces. A polymer solution prepared by a vaporish
solvent should be carefully cast to prevent segregation of solutes on the center
of the sensor surface.
Mf
ΒΌ
D
polymer
;
wet
D
gold
;
wet
f
gold
;
dry
f
polymer
;
dry
(12
:
1)
where Df indicates the amount of coated polymer on the electrodes, whereas
DD indicates the total amount of changes in dissipation energy on the
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