Biomedical Engineering Reference
In-Depth Information
Table 6.1
Typical values for the time constants related to protein adsorption
Process
Time constant
Adsorption
<0.5 s
Desorption
>15 min
Lateral diffusion
<0.5 s
Spreading
~3-4 min
at one constant rate and readily desorbs at another due to the reversible
nature of the adsorption process. At the same time, the adsorbed protein is
capable of undergoing rapid structural rearrangement, and after a certain
residence time, the adsorbed protein remains in a particular denatured state.
After a prolonged period of residence time, the adsorbed protein proceeds
to a further denatured state and is in a signifi cantly different conformation
than that of the initially adsorbed ones. Typical values for the time constants
involved in protein adsorption process are listed in Table 6.1.
6.6
The Vroman effect
The Vroman effect involves the displacement of adsorbed coagulant pro-
teins on a surface.
29,30
Studies not only show the initial observation occurring
on many synthetic materials,
31,32
but also identify three major properties that
describe the occurrence of maximum adsorption of fi brinogen from blood
plasma on a surface: a relatively sharp peak shortly after the commence-
ment of adsorption; a maximum at an intermediate dilution of plasma; and
in a ring structure measured at some distance from the center.
33
These time-,
concentration- and space-dependent observations now constitute the broad
defi nition of the Vroman effect, in which individual proteins in a mixture
compete for a fi nite number of surface adsorption sites.
34
Other factors have
also been identifi ed that infl uence fi brinogen adsorption to many artifi cial
surfaces, namely, surface properties, buffer composition, temperature and
residence time.
10,32,34-38
The molecular mechanisms responsible for the dis-
placement of fi brinogen are not fully understood.
6.7 Structure and functions of fibrinogen
The structure and the corresponding physiological functions of human
fi brinogen are briefl y described in the following.
6.7.1 Structure
Fibrinogen is a dimeric molecule consisting of two sets of three polypeptide
chains, namely Aα, Bβ and γ.
4,39
Functional domains for disulfi de crosslinks,
