Biomedical Engineering Reference
In-Depth Information
The
in situ
-forming chitosan gel scaffolds described in these works
offernumerousadvantagesasanoninvasivealternativeforregener-
ative medicine.
7.2.2 In situ
-Forming Alginate Hydrogel Scaffolds
Alginate, derived from seaweed, is an anionic linear polysaccha-
ride with mannuronic and glucoronic acid as repeating units.
21
Alginates are a well-known example of ionically cross-linkable
materials. Aqueous solutions of alginate form three-dimensional
hydrogels when mixed with divalent or polyvalent cations.
22
-
24
Alginate gels were extensively studied for tissue engineering appli-
cationsasacellencapsulationmaterialaswellasaninjectablethree-
dimensionalmatrix for
in vivo
cell delivery.
25
Several reports demonstrated alginate gels as carriers of vari-
ouscellsforcartilage,bone,andnerverepair.
26
-
28
Gelationtimeand
mechanical properties of
in situ
-forming alginate scaffolds have a
dependence on the polymer concentration and the type of cation.
Calcium cross-linking has been shown to yield gels with good
mechanical properties. The use of alginate as
in situ
-forming algi-
natehydrogelscaffoldsexhibitsenhancedimmunogenicityandpoor
bioresorbability, whichmay lead to adverse tissueinteractions.
7.3
In situ
-Forming Hydrogels Formed
by Hydrophobic Interactions
By far the most studied type of physical interactions useful for
in
situ
-forming hydrogels are hydrophobic interactions. Changes in
physical interactions caused by environmentally induced swelling
were first studied several decades ago.
29
,
30
Dusek
et al
.predicted
that changes in external stimuli might result in phase transitions
via hydrophobic interactions,
31
a theory since verified experimen-
tally by several researchers.
32
,
33
The main advantage of these types
of interactions is the ability to tailor their physical properties to
respond to a particular physiological stimulus. Various
in situ
-
forminghydrogelsfromtypicalbiodegradableorbioabsorbablesyn-
thetic polymers reported so far are shown in Fig. 7.4.
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