[99]. Nano-HA has been used as a biomaterial for bone repair because it provides
bioactive properties and increases adhesion between the natural tissue and composite biomaterial. The nano-HA improves osteoblast adhesion to the biomaterial
surface, providing a bioactive bonding interface. The composite material displayed
typical viscoelastic properties, with the elastic properties being contributed by the
crystalline regions of the PVA and the nano-HA particles, and the viscous characteristics coming from the amorphous PVA regions and incorporated free water. The
addition of nano-HA changed the tensile properties of the material by increasing the
strength with an increase in HA weight percent, until 4.5 wt%, at which point the
strength begins to decrease with an increase in HA content. These trends were
accounted for by the increase in interfacial bonding strength between nano-HA
particles and polymer matrix, until a certain point at which agglomeration of nanoHA particles reduces the composite strength. The tensile modulus was shown to
increase initially with an increase in nano-HA content and then decrease and
stabilize due to improved rigidity and decreased degree of crystallinity occurring
simultaneously as nano-HA content increased. The effect of elongation and freeze–
thaw cycle times on the tensile modulus was studied and it was found that the
tensile modulus increased linearly as elongation ratio increased and also increased
as FTC time increased. The relationship of tensile modulus and elongation is
similar in the composite material and in natural articular cartilage because good
deformation ability occurs under low stress conditions. The biomaterial can better
withstand high stress conditions due to its higher tensile modulus. These properties
are beneficial for a material that must withstand both low and high stress activities,
uniformly distribute stress across the tissue, and resist large compressive forces to
prevent tissue damage [99].
Another composite material, PVA-BC (described in Sect. 4.1), was studied by
Millon et al. as a potential material for cartilage tissue replacement. Bacterial
cellulose added to PVA to form a nanocomposite cryogel showed improved
strain-rate dependence and good viscoelastic properties for mimicking natural
cartilage tissue [45].
Research efforts so far indicate that PVA-C and its composites are promising
artificial cartilage replacement materials. Future research efforts should focus on
increasing the strength and stiffness of PVA-C. This could be achieved by betterdesigned nanocomposites. Another challenge is the incorporation of strain-rate
dependence properties into the PVA-C material, which are essential for it to
withstand high rates of stress changes and function like natural cartilage tissue.
5.1.4 Cardiovascular Devices
Due to the necessity of maintaining blood flow in the cardiovascular system, a
positive pressure is always maintained within the system. As a result, tissues
making up the system are always under pulsatile tensile stress. In considering the
use of PVA-C in cardiovascular applications, its response to pulsatile tensile stress
must be taken into consideration. Mechanical property parameters of relevance
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
309
bioactive properties and increases adhesion between the natural tissue and composite biomaterial. The nano-HA improves osteoblast adhesion to the biomaterial
surface, providing a bioactive bonding interface. The composite material displayed
typical viscoelastic properties, with the elastic properties being contributed by the
crystalline regions of the PVA and the nano-HA particles, and the viscous characteristics coming from the amorphous PVA regions and incorporated free water. The
addition of nano-HA changed the tensile properties of the material by increasing the
strength with an increase in HA weight percent, until 4.5 wt%, at which point the
strength begins to decrease with an increase in HA content. These trends were
accounted for by the increase in interfacial bonding strength between nano-HA
particles and polymer matrix, until a certain point at which agglomeration of nanoHA particles reduces the composite strength. The tensile modulus was shown to
increase initially with an increase in nano-HA content and then decrease and
stabilize due to improved rigidity and decreased degree of crystallinity occurring
simultaneously as nano-HA content increased. The effect of elongation and freeze–
thaw cycle times on the tensile modulus was studied and it was found that the
tensile modulus increased linearly as elongation ratio increased and also increased
as FTC time increased. The relationship of tensile modulus and elongation is
similar in the composite material and in natural articular cartilage because good
deformation ability occurs under low stress conditions. The biomaterial can better
withstand high stress conditions due to its higher tensile modulus. These properties
are beneficial for a material that must withstand both low and high stress activities,
uniformly distribute stress across the tissue, and resist large compressive forces to
prevent tissue damage [99].
Another composite material, PVA-BC (described in Sect. 4.1), was studied by
Millon et al. as a potential material for cartilage tissue replacement. Bacterial
cellulose added to PVA to form a nanocomposite cryogel showed improved
strain-rate dependence and good viscoelastic properties for mimicking natural
cartilage tissue [45].
Research efforts so far indicate that PVA-C and its composites are promising
artificial cartilage replacement materials. Future research efforts should focus on
increasing the strength and stiffness of PVA-C. This could be achieved by betterdesigned nanocomposites. Another challenge is the incorporation of strain-rate
dependence properties into the PVA-C material, which are essential for it to
withstand high rates of stress changes and function like natural cartilage tissue.
5.1.4 Cardiovascular Devices
Due to the necessity of maintaining blood flow in the cardiovascular system, a
positive pressure is always maintained within the system. As a result, tissues
making up the system are always under pulsatile tensile stress. In considering the
use of PVA-C in cardiovascular applications, its response to pulsatile tensile stress
must be taken into consideration. Mechanical property parameters of relevance
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
309