Biomedical Engineering Reference
In-Depth Information
In general, the most interesting biological stimulus is
temperature.
2
,
3
Thus, both electrostatic and hydrophobic physical
interactions by change of temperature under physiological condi-
tionscanbeexploitedinthedesignof
in situ
-forminghydrogels.This
chapter provides an overview of creating
in situ
-forming hydrogels.
Particularinterestisgivento
in situ
-forminghydrogelscaffoldsthat
are applicable in scaffolds for regenerative medicine.
7.2
In situ
-Forming Hydrogels Formed
by Electrostatic Interactions
An electrostatic interaction can be induced by molecular inter-
actions between electric charges such as cationic and anionic
polyelectrolytes.
4
,
5
The magnitude of an electrostatic interaction
between two electric charges is directly proportional to the magni-
tude of each of the charges. Thus, the intrinsic strength of electric
chargeisaveryimportantpointtocreate
in situ
-forminghydrogels.
There are various anionic and cationic polymers with several prop-
erties. Recent studies have shown that a mixture of various anionic
and cationic polymers is capable of forming a gel
in situ
.
4
-
6
The for-
mationofagelatcertaintemperaturescanbeattributedtothedom-
inance of electrostatic association between electric charges such as
cationicand anionicgroup insidethe polymers.
Typicalanionicpolymersarealginate,sodiumcarboxymethylcel-
lulose (CMC), hydroxypropylmethylcellulose (HPMC), tripolyphos-
phate, etc., as natural materials and polyacrylic acid derivatives
as synthetic biomaterials.
6
And cationic polymers include poly-
ethyleneimine (PEI), chitosan, polylysine, etc. Among several
anionic and cationic polymers, introduction of
in situ
-forming
hydrogels based on chitosan, alginate, and CMC via electrostatic
interactionsandtheirpotentialin
in situ
-forminghydrogelscaffolds
are described later.
7.2.1 In situ
-Forming Chitosan Hydrogel Scaffolds
Chitosan, an amino-polysaccharide obtained by an alkaline deacety-
lated derivative of chitin, is a natural and abundant polymer.
7
Its
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