Biomedical Engineering Reference
In-Depth Information
Fig. 17
Mechanical properties of alginate and chitosan hydrogel nerve conduits, assessed by the
shear-strain dependencies of the storage (
G
′
filled symbols
) and the loss moduli (
G
″
open sym-
bols
) as a function of the normal force during the measurement (
inverted filled triangle
3N,
filled
diamond
10N,
filled circle
30N). Reprinted from Gander et al. [
151
]. Copyright 2006 Wiley VCH
>7 h in buffer, the increased stiffness was reversed, showing the transient nature of
the hydrogel. The Young's modulus of the hydrogels is 110 kPa, which is consid-
erably lower than the modulus of whole nerves (500-70,000 kPa) [
153
,
154
]. This
should preclude possible mechanical irritation after implantation of the nerve con-
duits in the surrounding tissue as well as on the nerve.
In conclusion, Gander and coworkers showed the preparation and physico-
chemical characteristics of tubular hydrogels based on chitosan and alginate for
applications as neural conduits. This system shows mechanical characteristics that
are suitable for implantation without irritation of the nerve and the surrounding tis-
sue. Furthermore, the walls of the conduit can most likely be penetrated by growth
factors and nutrients, but they exclude cells, proteins, and immunoglubolins,
which can trigger immune reactions that hinder regeneration of the neural tissue.
Another widely used biopolymer is starch, a polysaccharide composed of
ʱ
-
d
-glucose units. Plants produce starch for energy storage; it is therefore one of
the most abundant biopolymers on Earth. Starch arose interest in the biomedi-
cal sector due to its biocompatibility, degradability, and availability [
155
,
156
].
However, unmodified starch is easily metabolized into saccharides under bio-
logical conditions, making chemical modifications necessary. A common way to
functionalize starch is to chemically crosslink it with epichlorohydrin, along with
further modification of the matrix by introduction of desired functionalities [
157
,
158
]. To avoid toxic crosslinking conditions, physical hydrogels based on starch
have been investigated.
Cukierman and coworkers presented a matrix for drug delivery based on poly-
cationic starch (MS) and
ʺ
-carageenan (KC), an anionic polysaccharide based on
sulfated
ʱ
-
d
-galactopyranose units [
159
]. Investigation of the binding of the poly-
mer chains of a granular mixture of freeze-dried KC and MS and a hydrogel pre-
pared by solutions of both by FT-IR showed slight shifts of the C-N and of the
sulfate bands, indicating formation of polyelectrolyte complexes in the hydrogel.
Search WWH ::
Custom Search