Biomedical Engineering Reference
In-Depth Information
the dynamic imaging rate and the reduction in non-specifi c adhesion during
the tip approach to the surface.
154-156
Combinable and complementary techniques
The scope of the information obtained from AFM can be enhanced by com-
bining or complementing AFM with other techniques. In early studies, a
number of techniques are used to obtain independent measurement so as
to complement AFM results, including electron microscopy,
157-159
spectros-
copy,
160,161
confocal microscopy,
162
fl uorescence microscsopy
163
and electro-
physiology.
164,165
Subsequently, researchers started to integrate different
techniques with AFM for simultaneous measurements. An example is the
combination of scanning near-fi eld optical and atomic force microscopy,
166
which provides better spatial resolution than conventional confocal micros-
copy. Reichert and co-workers built a combined total internal refl ection
fl uorescence (TIRF) and AFM so that information regarding cell-surface
contact could be captured by TIRF whereas the corresponding microme-
chanical changes and force transmission on the cell membrane are obtained
by AFM.
167,168
Moreover, a custom-made scanning force microscopy inte-
grated with a refl ection interference contrast microscopy (RICM)
169,170
is
used to monitor the interference of non-specifi c protein-probe interactions
during ligand-receptor binding force measurement.
171,172
6.12 Interfacial properties of fibrinogen studied
by AFM
Owing to fi brinogen's role in hemostasis and thrombosis, its adsorption on
a surface is frequently used to determine the biocompatibility of a piece
of testing material.
173-175
Here, we highlight some of the recent AFM stud-
ies that reveal the interfacial properties of fi brinogen as they relate to the
development of biomaterials.
6.12.1 Adsorption profi le and interfacial relaxation
By fi tting the data into the Langmuir model, the adsorption profi les of the
whole molecule on hydrophobic graphite and hydrophilic mica are deter-
mined to be 2.2 × 10
−4
mL/µg/s and 2.7 × 10
−4
mL/µg/s, respectively. The
adsorption on hydrophobic graphite is reversible with a desorption rate
of 8.3 × 10
−5
s
−1
whereas there is virtually no desorption on the hydro-
philic mica.
176
The desorption rate is comparable to that determined using
a different surface analytical technique.
94
The adsorption on electropol-
ished 316L stainless steel also appears to be irreversible with a rate of
