thermal cycling, as well as to neutralize the low pH due to the presence of acetic
acid. It was found that, again, the number of FTCs has an impact on the mechanical
properties. Both WSC and WIC samples demonstrated similar elastic behavior, and
the PVA-chitosan samples provided a fairly good replication of the stress–strain
behavior of porcine aortic tissue. The macroporous structure was shown to change
with the addition of chitosan. For plain PVA, the structure changed visually as the
number of FTCs increased, but the change in pore size was not statistically
significant after one, two, and four FTCs. When either WSC or WIC was added,
the internal structure changed significantly as a function of the number of FTCs.
After the second FTC, the pore size increased, and it increased again after the fourth
FTC. This study was effective in showing that, although the addition of chitosan
may be beneficial for cell adhesion, we cannot ignore the effects that it has on the
PVA-C macrostructure and mechanical properties [81].
A system comprised of PVA and chitosan was produced for use as a drug
delivery vehicle for the antibiotic sparfloxacin, as well as for use in an antibacterial
wound healing device. The addition of chitosan for drug delivery systems can be
done to help sustain the release of water-soluble drugs or enhance the availability of
water-insoluble drugs. Chitosan also has an intrinsic antimicrobial activity. Different compositions of PVA and chitosan were made and processed through freeze–
thaw cycling. Results showed that swelling percentage and gel fraction percentage
increased with an increase in chitosan concentration and decreased with an increase
in PVA concentration and the number of FTCs. The amount of polymer degraded
over a fixed time increased with an increase in chitosan content or a decrease in
FTC number. Antimicrobial activity for a variety of Gram-positive and Gramnegative bacteria was tested and it was found that no antimicrobial activity was
present at low chitosan percentages but increased as chitosan content increased.
Sparfloxacin was added to the chitosan/PVA blend solution before freeze–thaw
cycling and its release was determined to be affected by the thickness of the
membrane, pH, and temperature of the medium. The total amount of drug released
was decreased with an increase in pH due to the presence of NH 2 within the
hydrogel structure that can be ionized at low pH to allow for release. The drug
release increased with an increase in thickness and media temperature. This system
shows how the addition of chitosan to the PVA cryogel can impart important
antimicrobial activity, as well as provide a temperature- and pH-responsive system
for drug release [82].
A comparison of composite materials using chitosan, gelatin, and starch added to
PVA was reported [79]. A sample for each different component added to PVA was
prepared and treated with freeze–thaw cycling and coagulation techniques for
application as artificial blood vessels. The resulting mechanical properties were
found to be controlled by the PVA rather than by the other components. Each PVA
composite sample was found to have similar stiffness behavior to arteries. Increasing the number of FTCs as well as coagulation bath treatment (7.5 % KOH and 1 M
Na 2 SO 4 ) increased the modulus of the hydrogels. Coagulation bath treatment was
also shown to increase the resistance of the hydrogel to degradation. Cell adhesion
and proliferation studies showed that the addition of a composite material was
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
305
acid. It was found that, again, the number of FTCs has an impact on the mechanical
properties. Both WSC and WIC samples demonstrated similar elastic behavior, and
the PVA-chitosan samples provided a fairly good replication of the stress–strain
behavior of porcine aortic tissue. The macroporous structure was shown to change
with the addition of chitosan. For plain PVA, the structure changed visually as the
number of FTCs increased, but the change in pore size was not statistically
significant after one, two, and four FTCs. When either WSC or WIC was added,
the internal structure changed significantly as a function of the number of FTCs.
After the second FTC, the pore size increased, and it increased again after the fourth
FTC. This study was effective in showing that, although the addition of chitosan
may be beneficial for cell adhesion, we cannot ignore the effects that it has on the
PVA-C macrostructure and mechanical properties [81].
A system comprised of PVA and chitosan was produced for use as a drug
delivery vehicle for the antibiotic sparfloxacin, as well as for use in an antibacterial
wound healing device. The addition of chitosan for drug delivery systems can be
done to help sustain the release of water-soluble drugs or enhance the availability of
water-insoluble drugs. Chitosan also has an intrinsic antimicrobial activity. Different compositions of PVA and chitosan were made and processed through freeze–
thaw cycling. Results showed that swelling percentage and gel fraction percentage
increased with an increase in chitosan concentration and decreased with an increase
in PVA concentration and the number of FTCs. The amount of polymer degraded
over a fixed time increased with an increase in chitosan content or a decrease in
FTC number. Antimicrobial activity for a variety of Gram-positive and Gramnegative bacteria was tested and it was found that no antimicrobial activity was
present at low chitosan percentages but increased as chitosan content increased.
Sparfloxacin was added to the chitosan/PVA blend solution before freeze–thaw
cycling and its release was determined to be affected by the thickness of the
membrane, pH, and temperature of the medium. The total amount of drug released
was decreased with an increase in pH due to the presence of NH 2 within the
hydrogel structure that can be ionized at low pH to allow for release. The drug
release increased with an increase in thickness and media temperature. This system
shows how the addition of chitosan to the PVA cryogel can impart important
antimicrobial activity, as well as provide a temperature- and pH-responsive system
for drug release [82].
A comparison of composite materials using chitosan, gelatin, and starch added to
PVA was reported [79]. A sample for each different component added to PVA was
prepared and treated with freeze–thaw cycling and coagulation techniques for
application as artificial blood vessels. The resulting mechanical properties were
found to be controlled by the PVA rather than by the other components. Each PVA
composite sample was found to have similar stiffness behavior to arteries. Increasing the number of FTCs as well as coagulation bath treatment (7.5 % KOH and 1 M
Na 2 SO 4 ) increased the modulus of the hydrogels. Coagulation bath treatment was
also shown to increase the resistance of the hydrogel to degradation. Cell adhesion
and proliferation studies showed that the addition of a composite material was
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
305