Biomedical Engineering Reference
In-Depth Information
In brief, medical grade PLLA was dissolved in chloroform and mixed with 100-355 µm sodium
chloride (NaCl) crystals and naphthalene with irregular shape and size around 5 µm to form a
composite that was placed into a mold of 9 mm diameter. Following chloroform evaporation and
polymer solidifi cation, salt was leached from the polymer composite by placing scaffolds in double
distilled water for 2-3 days, with gentle agitation, and then dried at room temperature. After NaCl
salt was leached out by water, naphthalene was removed by tetrahydrofuran (THF), and this step
was followed by the removal of THF by ethanol. Finally, the scaffolds were rinsed with distilled
water and dried. Two different naphthalene/polymer ratios, 10% and 20%, were used to optimize
the structural changes in the pore morphology.
3.5.1.2
Controlled Morphology and Degradation Rate
in Fibrous Chitosan Scaffolds Produced by Wet Spinning
Fibers are very attractive structures for the production of scaffolds because they provide a large sur-
face area as well as a considerably large porosity and interconnectivity, which can be optimized for
specifi c applications. Our objective for choosing fi brous scaffolds was twofold: adjusting both the
porosity and the degradation rate. In this study, based on a previously described wet-spinning tech-
nique,
75
a new method for tailoring the morphology of chitosan fi ber-mesh scaffolds was developed.
The starting material was chitosan powder with a deacetylation of 89% and a molecular weight of
366 kDa, purifi ed by reprecipitation. To produce fi brous scaffolds, a 2% chitosan solution in 2%
acetic acid was wet spun into a sodium hydroxide/sodium sulfate solution which, was acting as the
precipitation agent. The diameter of the fi ber and the porosity of the scaffolds were controlled by
using different needles and changing the total volume of the chitosan solution used for spinning,
147
as described in Figure 3.4. Four types of cylindrical shape scaffolds (
φ
5 mm
4 mm) with fi ber
diameter of 65 and 105 µm and two different porosities ranging between 70% and 90% were pro-
duced. Two distinct degradation profi les were obtained from the four types of structures, which
indicated the potential of this technique on adjusting several properties of these type of scaffolds.
×
3.5.1.3
Creation of Dual Pore Modes in Chitosan Scaffolds
Engineering specifi c organized tissue or organ demands equally specifi c scaffold architecture, which
can guide cell and matrix growth in harmony with natural tissue organization. Chitosan scaffolds
with dual pore modes have been fabricated aiming to generate engineered tendon. The dual pore
mode chitosan scaffolds possess micropores and microchannels, which were fabricated based on a
modifi cation of a method described elsewhere.
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A 2% chitosan solution was prepared by dissolving
95% deacetylated chitosan fl akes in 1% v/v glacial acetic acid. The resulting solution was cast in a
cylindrical plastic mold containing a needle array. Stainless steel needles of 250 μm diameter were
used to produce 3
C and subsequently
freeze-dried. The remaining acetic acid in the resulting scaffolds with microchannels was removed
in a gradient of ethanol (i.e., 100%, 70%, and 50%) since the use of sodium hydroxide to neutralize
acetic acid leads to the change of crystallinity, which results in deformation and shrinkage of the
scaffolds.
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Finally, the scaffolds were stored in phosphate-buffered saline (PBS).
×
2 or 3
×
4 arrays. Constructs were frozen overnight at
−
20
°
3.5.2 M
ONITORING
THE
S
CAFFOLDS
' A
RCHITECTURE
Development of nondestructive and online imaging technique to monitor the scaffolds' architecture
provides dual benefi t for TE. The monitoring enables controlling the fabrication process and adjust-
ing processing parameter in a rapid mode. More importantly, the imaging system can investigate the
degradation and tissue turnover processes within the scaffolds. µ-CT and OCT have been applied
to assess the scaffolds described in section 3.5.1.1-3.5.1.3. The experimental work described in this
section (3.5.2) sets a good example of how the new imaging modalities can be benefi cial for TE.
