Biomedical Engineering Reference
In-Depth Information
HO
H
x
O
PEG
O
O
H
3
C
O
O
Sn(Oct)
2
, 140°, 5 h
O
O
CH
3
O
O
glycolic acid
lactic acid
O
O
O
O
HO'
( ) ( )( )( ) ( )
H
O
O
O
CH
3
O
O
PLGA-PEG-PLGA
triethylamine
acryloyl chloride
80°, 3 h
O
O
O
( ) ( ) ( )( )( )
O
O
O
O
O
m
O
x
n
m
x
O
CH
3
O
CH
3
O
PLGA-PEG-PLGA diacrylate
Scheme 9.1
Synthetic methods of PLGA - PEG - PLGA diacrylate.
hydrogen-bonded network in which p(MAA-
co -
EA) contains H-bond donor groups,
PVP contains H-bond acceptors, and PEG contains both. The hydrogel fi lms are
malleable and retain their integrity upon hydration - a feature characteristic of
covalently crosslinked hydrogels. The polymer blend fi lms remained intact at
pH 5.6 but underwent dissolution at pH 7.4 due to loss of hydrogen bonding and
development of charge repulsion [26].
Hydrogen-bonding interaction can also be used to produce hydrogels by freeze-
thawing. A novel double-network elastic hydrogel fabricated with PVP and PEG
was prepared through a simple freezing and thawing method. PVA/PEG hydrogel
structure was formed by a PVA-rich fi rst network and a PEG-rich second compo-
nent, in which hydrogen bonding existed. The two polymers were dissolved in
ultrapure water and exposed to repeated cycles of freezing at
20 ° C for 8 h and
thawing at room temperature for 4 h. Figure 9.2 illustrates the structural formation
of elastic PVA/PEG double-network hydrogels. The condensed PVA-rich phase
forms microcrystals fi rst, which bridge with one another to form a rigid and inho-
mogenous net backbone to support the shape of the hydrogels, and the dilute
PEG-rich phase partially crystallizes among the cavities of voids of the backbone.
PEG clusters in the cavities of PVA networks absorb the crack energy and relax
−
