Biomedical Engineering Reference
In-Depth Information
has also been developed as a suitable scaffold for engineering adi-
pose tissue constructs.
47
Use of a Pluronic gel as a suitable scaf-
fold for adult-derived or somatic lung progenitor cells constructs
resulted in the development of tissue with less inflammatory reac-
tion compared to polyglycolicacid (PGA).
48
7.3.2
PEG-Other Degradable Polyesters as
in situ
-Forming
Hydrogel Scaffolds
Block copolymers contain both PEG as hydrophilic and polyester
as hydrophobic segments investigated as a candidate for
in situ
-
forminghydrogelscaffoldsinordertoendowgoodmechanicalprop-
erties, biodegradability, long residence times, and no toxicity.
In 1997, Kim
et al
. reported the injectable gel system
using biodegradable triblock copolymers, composed of poly(
D
,
L
-
lactide-co-glycolide) (PLGA) and PEG.
49
After that,
in situ
-forming
hydrogel scaffolds using various block copolymers composed of
PEG and polyester blocks have been investigated extensively
as well. The reported polyester blocks are poly(
ε
-caprolactone)
ε
δ
poly(
-valerolactone) (PVL),
poly(trimethylene carbonate) (PTMC), poly(
-caprolactone-
co
-
D
,
L
-lactic acid) poly(
ε
-carprolactone-
co
-
trimethylene carbonate) (PCL-
co
-PTMC), poly(
ε
-carprolactone-
co
-
1,4-dioxan-2-one) (PCL-
co
-PDO), poly(propylene fumarate) (PPF),
poly-[(
R
)-3-hydroxybutyrate] (PHB), etc.
50
-
55
Theaqueoussolutionsofmostblockcopolymersformasolution
at ambient temperatures, due to the attribution to the dominance
of hydrophilic association between the hydrophilic PEG segments
and the surrounding water molecules. With an increase in temper-
ature, however, the hydrophobic association between the polyester
blocks causes the dehydration of hydrophobic segments and leads
to the formation of hydrophobic interactions between hydrophobic
domainstates,whicheventuallyresultsinagelatbodytemperature
(Fig. 7.5).
Thesol-geltransitiontemperaturewasinfluencedbythecopoly-
mercompositionandspecificallybythelengthofPEGandpolyester
blocks. The gel formation occurring at body temperature makes
this system an ideal candidate for
in situ
-forming hydrogel scaf-
folds for tissue engineering. We and some groups developed
in
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