Biomedical Engineering Reference
In-Depth Information
4
15-pAAm
2
10-pAAm
6-pAAm
0
0
0.4
0.8
Displacement, cm
Figure 14.5.
Load-displacement curves for pAAm MGs prepared from different concentra-
tion of monomers: 6% (6-pAAm), 10% (10-pAAm) and 15% (15-pAAm). Reproduced from
[Plieva et al., 2007a] with permission.
shape-recover property against compression. Due to the elasticity and sponge-
like morphology, most MGs can withstand large deformations and can be easily
compressed up to 80% without getting mechanically damaged, whereas tradi-
tional polyacrylamide gels are easily destroyed even when deformed less than
30% [Plieva et al., 2006a]. The high elasticity of the MGs was effi ciently exploited
for the detachment of affi nity-bound bioparticles through the mechanical defor-
mation of the MGs [Dainiak et al., 2006; Galaev et al., 2007]. After releasing
compression, the MGs immediately adopted initial shape. Due to the mechanical
stability, the MG monoliths can be compressed repeatedly with no distortion of
the porous structure. Increasing the concentration of monomers in the initial
reaction mixture resulted in increasing the mechanical strength of MGs
[Lozinsky, 2002; Plieva et al., 2006a; Srivastava et al., 2007].
Quite often the MGs prepared at subzero temperatures are more mechani-
cally stable compared to the conventional gels prepared at ambient temperature
from the same feedstock. The MGs prepared from 3wt% 2-hydroxyethylcellulose
(HEC) solution through irradiation with UV-vis light at
−
30 ° C had the storage
and loss moduli (G
) orders of magnitude higher than those for the gel
obtained from HEC solution irradiated at room temperature (Figure 14.6).
The reason is that due to the cryoconcentration of HEC chains in NFLMP,
the polymeric network of HEC MGs was formed from a solution with higher
HEC concentration. As was mentioned before, the cryoconcentration of the gel
precursors in NFLMP typically results in lowering the critical concentration of
gelation (CCG). The lowering of CCG for MGs compared to the conventional
gels prepared from the same feedstock is the common phenomenon in cryotropic
gelation [Lozinsky, 2002].
The MGs are hydrophilic materials with inert surface when no active
groups are presented on the cryogel surface. The pAAm-MGs were shown to
not contain any non-reacted monomer (AAm) as was confi rmed by gas liquid
′
and G
″
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