Biomedical Engineering Reference
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[Vlierberghe et al., 2007]. The absence of skin layer was shown also for agarose-
based cryogels [Plieva et al., 2007b].
Scanning electron microscopy (SEM) technique, which is suitable to charac-
terize the fi ne structures of porous materials only in the dried state, was shown to
be the method of choice for the analysis of the porous structure of MGs [Plieva et
al., 2006a,b]. The deformation of the porous structure of MGs due to the process-
ing of the samples for SEM analysis was not that signifi cant and fi ne porous struc-
ture was essentially preserved due to the mechanical stability of pore walls in
MGs. The pore walls in elastic and spongy pAAm-MGs are formed from highly
concentrated polymer network due to the pronounced concentration of the dis-
solved reagents. SEM images of dextran-MA-MGs showed the typical structure
of the MG, consisting of
m - in - size interconnected pores surrounded by dense
non - porous walls (Figure 14.13 b).
On the other hand, confocal microscopy (CM) allows for the analysis of the
shape and size of pores in the macroporous material and offers signifi cant advan-
tages over conventional microscopy in that it reduces “ out - of - focus - blur ” in
images [Hanthamrongwit et al., 1996]. Sample preparation for CM is simple and
less time consuming, simplifying the processes for fi xation, dehydration, embed-
ding, microtomy and staining required for optical microscopy. A CM image
obtained for pAAm-MGs (with covalently bound fl uoresceine - probe (fl uores-
ceinamine, isomer I)) is presented in Figure 14.13c.
Other useful technique for characterizations of such materials has been envi-
ronmental scanning electron microscopy (ESEM). The important advantage of
the ESEM technology is the possibility of monitoring changes in the structure of
the material whilst allowing the sample to dehydrate slowly [Rizzieri et al., 2003].
The ESEM images obtained for the PVA-MGs at high degrees of dehydration
were similar to the SEM images showing the macroporous structure with inter-
connected pores of hundreds micrometers in size and thin and dense pore walls
[Plieva et al., 2005] or microporous pore walls [Plieva et al., 2006b] (Figure
14.13 d).
The microcomputed tomography was used for the analysis of porous struc-
ture of the gelatin macroporous gel, prepared through combination of cryogenic
treatment of a chemically cross-linked gelatin gel, followed by removal of the ice
crystals formed through lyophilization (freeze-drying technique) [Vlierberghe
et al., 2007]. The 2D cross-sections of gelatin gel were used to segment the images
and determine their 3D porosity and pore size distribution using the software
(
μ
CTanalySIS) [Vlierberghe et al., 2007]. For determination of the pore size dis-
tribution, each pore was fi lled with the largest sphere possible (the so-called
“ maximum opening ” ). The total volume fi lled by this maximum sphere was deter-
mined during the analysis. Subsequently, the software fi lled the total volume of
each pore with a smaller sphere, while its total fi lling volume was determined.
This process continued until the total volume of each pore was comprised with
the smallest inscribed sphere, with a size of one voxel (Figure 14.14a). From this
analysis, data for all pores were acquired. The microcomputed tomography (
μ
-
CT) 3D images clearly showed that all pores in gelatin macroporous gels were
μ
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