Biomedical Engineering Reference
In-Depth Information
CH
3
O
O
HO
CH
2
CH
2
O
CH
2
CHO
CH
2
CH
2
O
H
RCH
2
CH
2
O
CCH
2
O
CCHO
CH
3
H
m
y
x
x
n
PEO-PPO-PEO
PLGA-PEG-PLGA
O
O
O
RCH
2
CH
2
O
C
O
H
RCH
2
CH
2
O
C(CH
2
)
6
O
CCHO
CH
3
H
m
n
m
n
P
P
Hydrophilic
CH
2
CH
C
n
O
CH
3
O
HN
NHCH(R)CHCOOR'
m
a
c
N
R
'
R''
N
P
N
P
n
R', R'' = H, H Poly(acrylamide)
R'. R" = H, CH(CH
3
)
2
Poly(
N
-isopropylacrylamide)
R', R'' = H, CH
2
CH
2
CH
3
Poly(
N-n
-propylacrylamide)
R', R'' = CH
3
, CH
3
Poly(
N,N'
-dimethylacrylamide)
R', R'' = CH
2
CH
3
, CH
2
CH
3
Poly(
N, N'
-diethylacrylamide)
NHR''
NHCH(R)CHCOOR'
b
a
Biodegradable
Hydrophobic
Figure 7.4.
Typical polymer structure of
in situ
-forming hydrogels via
hydrophobic interactions.
Synthetic polymers used for tissue engineering must possess
specific bulk and surface properties, easy handling at room temper-
ature, amenability to sterilization, and structural integrity during
in
vivo
application.Forsuccessfulapplicationintheregenerativemedi-
cine, further important polymer properties are adjustable degrada-
tion, which should correspond with the production rate of a new
extracellular matrix by the incorporated cells to maintain a balance
of assembly of new tissue and degradation of the scaffold mater-
ial. Another crucial prerequisite for the practical
in vivo
application
of scaffolds is an understanding of the potential for a host tissue
response after implantation.
Poly(ethylene glycol) (PEG) is a nontoxic and biocompatible
materialthatiswidelyusedinbiomedicalapplications.
34
Thismakes
for a longer-acting medicinal effect and reduces toxicity, and it
allows longer dosing intervals. on the basis of this reason, PEG
may provide a useful starting point to make
in situ
-forming hydro-
gels. In addition, the PEG-polyester copolymers have a relatively
easier-to-design molecular criterion for achieving optimal tissue
engineering. Thus, these
in situ
-forming hydrogels from synthetic
polymers, especially PEG- polypropylene glycol (PPG) and PEG-
polyester blockcopolymers, willbe highlighted inthe nextsection.
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