Biomedical Engineering Reference
In-Depth Information
TABLE 14.1. Properties of the p AA m - MG s Prepared at Different Temperatures
Temperature,
° C
Gel fraction
yield, %
Compressive
strength, kPa
Watch fl ow at a pressure of
1 m, watch column, cm/h
− 12
79 ± 4
28.3
310
− 20
83 ± 3
29.2
215
− 30
68 ± 4
21.0
30
Reproduced from [Plieva et al., 2006a] with permission.
14.3.2.2 Concentration and Composition of Gel Precursors in the
Initial Reaction Mixture. An increase in initial co-monomer concentration
(when other conditions were identical) gives rise to increase in both polymer con-
centration in pore walls and the overall strength of macroporous gel material, but
results in decrease in interconnectivity of macropores [Plieva et al., 2005]. The
latter is due to lower amount of solvent, which is frozen out from the more con-
centrated initial solution and, as a consequence, smaller total volume of ice crys-
tals forming the macropores. Pore size and thickness of pore walls in the MGs are
controlled in a wide range by simply changing the monomer/macromonomer con-
centration in the feed and type of the cross-linker used [Plieva et al., 2006a,b,c].
The control of pore size also allows for optimizing the availability of the ligands
coupled to polymer backbone for different biological targets. Depending on the
potential application, one could, with the same technique, produce materials
with large pores and porosity up to 90% (e.g., materials attractive as potential cell
scaffolds) [Kumar et al., 2006a,b; Nilsang et al., 2007] or materials with smaller
pores, thicker pore walls having suffi ciently large interface for interacting
with biomolecules and good mechanical properties (e.g., materials attractive
as potential chromatographic adsorbents) [Dainiak et al., 2004; Plieva et al.,
2004b, 2005 ].
Increasing the concentration of monomers from six to 15% during the prepa-
ration of pAAm-MGs resulted in decreasing the pore volume in the pAAm-MGs
from 93 to 80% [Plieva et al., 2005]. The same was observed for the preparation
of MGs from polymeric precursors as polyvinyl alcohol (PVA): the pore volume
decreased from 91 to 84% when increasing the initial concentration of PVA from
3.5 to 8% [Plieva et al., 2006b]. Typically, the thickness of pore walls was increased
and interconnectivity of pores was decreased at increasing the concentration of
monomer or polymer precursors in the initial reaction mixture [Plieva et al., 2005;
Plieva et al., 2006a,b]. The thickness of pore walls along with density of pore walls
determine the macroscopic mechanical properties of the pAAm-MGs, while the
pore size and pore wall density affect the accessibility of the ligands chemically
bound to the polymer backbone [Plieva et al., 2005]. Despite increased density of
MGs prepared from high monomer concentration, the MGs remained highly
elastic. The load-displacement curves obtained for pAAm-MGs prepared from
the feeds with 6, 10 and 15% monomer concentration, respectively, show typical
behavior of the highly elastic materials (Figure 14.5) with extensive fl exibility and
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