The work showed that this composite material is able to achieve similar mechanical
properties as the natural cornea and better than pure PVA-C. The composite
containing 12 wt% BC had a tensile strength of 3.9 MPa, which is very close to
the human cornea tensile strength of about 3.8 MPa [74–76]. Furthermore, the water
content of the PVA-BC composites decreases as BC concentration increases.
However, composite water content was close to that of the human cornea (78 %
[77]) at 67–73 %. Of utmost importance for this application is light transmittance of
the material. PVA-BC composite was found to have a high visible light transmittance. Some of the tested compositions actually had a higher transmittance of
visible light than pure PVA, due to the nano-effect of the BC nanofibrils. In
addition, PVA-BC has good UV absorbance, which is important in preventing
damage to internal eye tissue. Overall, this composite material is promising for
use as an artificial cornea material [78].
4.2 Chitosan-PVA Composites
Another material that has been added to PVA to produce a composite cryogel is
chitosan. Chitosan is obtained from chitin by alkaline deacetylation. It is a cationic
polysaccharide, and has been proposed as a good material for addition to the PVA
matrix for cryogel composite production in order to enhance protein absorption
[79]. Due to the hydrophilicity of PVA, cell adhesion proteins are not able to
absorb, preventing cell adhesion [79]. Because of this, work to create a more
favorable environment for cell growth while still maintaining the beneficial
mechanical properties of the PVA cryogel structure is important for certain
applications.
PVA cryogels used for vascular tissue engineering scaffolds were modified to
improve cell attachment [80]. In this work, chitosan was added to PVA because of
its ability to improve vascular smooth muscle and endothelial cell attachment. The
blend was subjected to FTCs, immersed in a KOH/Na 2 SO 4 coagulation bath, and
the surface modified with collagen type I. The structures were then seeded with
bovine aortic vascular smooth muscle and endothelial cells. The presence of
chitosan resulted in cell attachment to the surface in patches, which suggests that
the regions of high cell density are chitosan-rich and that the other areas are
chitosan-poor. Cell attachment and proliferation were shown to increase with an
increase in FTCs. Since the coagulation bath treatment essentially eliminates the
mechanical difference between samples of different numbers of FTCs, the surface
topography is suspected to be responsible for this difference [80].
In another study that focused on the mechanical and morphological properties of
PVA-chitosan cryogels, water-soluble chitosan with a deacetylation degree of 85 %
(WSC), and water-insoluble chitosan (WIC) were added to PVA separately to
produce two different chitosan-PVA cryogel materials, as well as a control plain
PVA cryogel. After freeze–thaw cycling, the samples were submerged in a coagulation bath to crosslink the chitosan, because it would not be crosslinked by
304
W. Wan et al.
properties as the natural cornea and better than pure PVA-C. The composite
containing 12 wt% BC had a tensile strength of 3.9 MPa, which is very close to
the human cornea tensile strength of about 3.8 MPa [74–76]. Furthermore, the water
content of the PVA-BC composites decreases as BC concentration increases.
However, composite water content was close to that of the human cornea (78 %
[77]) at 67–73 %. Of utmost importance for this application is light transmittance of
the material. PVA-BC composite was found to have a high visible light transmittance. Some of the tested compositions actually had a higher transmittance of
visible light than pure PVA, due to the nano-effect of the BC nanofibrils. In
addition, PVA-BC has good UV absorbance, which is important in preventing
damage to internal eye tissue. Overall, this composite material is promising for
use as an artificial cornea material [78].
4.2 Chitosan-PVA Composites
Another material that has been added to PVA to produce a composite cryogel is
chitosan. Chitosan is obtained from chitin by alkaline deacetylation. It is a cationic
polysaccharide, and has been proposed as a good material for addition to the PVA
matrix for cryogel composite production in order to enhance protein absorption
[79]. Due to the hydrophilicity of PVA, cell adhesion proteins are not able to
absorb, preventing cell adhesion [79]. Because of this, work to create a more
favorable environment for cell growth while still maintaining the beneficial
mechanical properties of the PVA cryogel structure is important for certain
applications.
PVA cryogels used for vascular tissue engineering scaffolds were modified to
improve cell attachment [80]. In this work, chitosan was added to PVA because of
its ability to improve vascular smooth muscle and endothelial cell attachment. The
blend was subjected to FTCs, immersed in a KOH/Na 2 SO 4 coagulation bath, and
the surface modified with collagen type I. The structures were then seeded with
bovine aortic vascular smooth muscle and endothelial cells. The presence of
chitosan resulted in cell attachment to the surface in patches, which suggests that
the regions of high cell density are chitosan-rich and that the other areas are
chitosan-poor. Cell attachment and proliferation were shown to increase with an
increase in FTCs. Since the coagulation bath treatment essentially eliminates the
mechanical difference between samples of different numbers of FTCs, the surface
topography is suspected to be responsible for this difference [80].
In another study that focused on the mechanical and morphological properties of
PVA-chitosan cryogels, water-soluble chitosan with a deacetylation degree of 85 %
(WSC), and water-insoluble chitosan (WIC) were added to PVA separately to
produce two different chitosan-PVA cryogel materials, as well as a control plain
PVA cryogel. After freeze–thaw cycling, the samples were submerged in a coagulation bath to crosslink the chitosan, because it would not be crosslinked by
304
W. Wan et al.