Biomedical Engineering Reference
In-Depth Information
adhesion force of adsorbed fi brinogen on highly wettable surfaces is lower
than on poorly wettable surfaces, although in both cases the adhesion force
is measured to be at the order of nanoNewtons range. Meanwhile, a sin-
gle energy barrier for the adhesion of fi brinogen molecules on the former
is observed whereas multiple ones are observed on the latter. A possible
explanation is that the unfolding and hence the conformational changes of
fi brinogen on poorly wettable surfaces elicits an increases in the number of
contact points, which makes it diffi cult to remove the fi brinogen molecules
off the surface. Similar reasoning can be used to explain the observation that
increasing the contact time between fi brinogen and the surface increases
the diffi culty of pulling adsorbed fi brinogen molecules off the surface. The
adhesion force would reach a maximum beyond a certain long contact time,
regardless of the wettability of the underlying surfaces.
6.12.6 Ligand-receptor interactions
The interactions between fi brinogen and its receptor/antibody are probed
by determining the debonding force. Using an AFM tip modifi ed with
monoclonal antibodies that recognize part of the dodecapeptide region of
Aα chain, its debonding force with fi brinogen adsorbed on hydrophilic mica
has the highest frequency at about 100 pN. The antigen-antibody interac-
tion reaches its peak about 45 minutes after fi brinogen adsorption, which
correlates well with the time for the recognition by platelet.
191
This value
of the debonding force is comparable to that determined in a different
setup (93 pN) in which the AFM tip modifi ed with an RGD-containing pep-
tide is brought close to interact with platelets adhered on a hydrophobic
surface.
192
The conformational states of adsorbed fi brinogen are probed indirectly
via the exposure of different epitopes by binding the RIBSs of fi brinogen
with gold-labeled mAb, which were then imaged by AFM.
193
This not only
provides direct visualization of the exposed epitope but also confi rms the
idea that fi brinogen undergoes structural changes upon adsorption on a
hydrophobic surface. In a separate study, fi brinogen binding to GPIIb-IIIa
reconstituted in planar phospholipids was examined
in situ
. The binding of
fi brinogen is found to be specifi c because the binding site of the integrin
receptor can be blocked with soluble RGD peptide analog. Furthermore,
the domain of fi brinogen that is responsible for integrin recognition appears
to go through the D domain.
191
Such a concept for the recognition of sur-
face-adsorbed fi brinogen at the molecular level is further demonstrated by
surface patterned, two-component protein fi lm. The specifi c recognition of
fi brinogen, in the presence of albumin, is made possible by antibody conju-
gated to nanogold particles. The presence of antibody-conjugated nanogold
