Biomedical Engineering Reference
In-Depth Information
Fig. 16
Structural characteristics, swelling degrees, and diffusive permeability of nerve conduits
composed of alginate and chitosan.
a
SEM micrograph of the porous structure of a freeze-dried
nerve conduit.
b
Diameter of the nerve conduit of two different batches of hydrogel of the same
composition (
circles
outer diameter;
triangles
inner diameter).
c
Permeation of fluorescein-
labeled dextrans through the wall of a swollen alginate-chitosan hydrogel nerve conduit, as
investigated by Gander and colleagues (
FD-4
4.4-kDa dextran;
FD-10
10-kDa dextran;
FD-20
20-kDa dextran). Reprinted from Gander et al. [
151
]. Copyright 2006 Wiley VCH
of the conduit within 7 h, as shown in Fig.
16
c. These experiments can serve as a
model for the permeation of nutrients or growth factors through the conduit, which
is dependent on their hydrodynamic radius. 20-kDa dextran exhibits a hydrody-
namic radius of 3.3 nm [
152
], which is similar to the radius of proteins. This simi-
larity indicates that the permeation of high molecular-weight proteins, cells, and
immunoglobulins through the conduit wall is likely to be hindered, which could
decrease the triggering of immune reactions during the regeneration. Growth fac-
tors and nutrients have a lower hydrodynamic radius and can permeate the wall of
the nerve conduits easier, increasing the chance of regeneration of the tissue.
To supplement these assessments of diffusive permeability, rheological meas-
urements were performed on hydrogel films under a normal force of 3, 10, and
30 N as a function of oscillatory shear strain. By inducing 3 and 10 N, no struc-
tural changes of the hydrogels could be observed. At 30 N, a high initial storage
modulus was detected, which relaxed throughout the measurement, as shown in
Fig.
17
. The measurements were repeated on the same gel, showing that the initial
storage modulus was lower than in the previous measurement. This observation
indicates structural changes induced by the normal force. After relaxation times of
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