integrity. Diseases of the IVD are among the causes of neck and back pain [84, 85]
that lead to work absenteeism [86], disability claims [87, 88], and a decrease in the
quality of life [89]. IVDs are cartilaginous, composed mainly of collagen and
proteoglycans, and have a high water content [84, 90, 91]. They also have low
cell numbers and little to no vascularity [84]. Therefore, IVDs have limited ability
to heal and regenerate to regain function. The main surgical treatment is to fuse
adjacent vertebrae together. However, this approach limits the movement of the
patient and effectively shifts the stress to the adjacent vertebrae, developing
problems down the road. In recent years, total disc replacement is gaining popularity. The FDA had approved several IVD prosthetic devices. These are mainly
made from metal and are typically designed for supporting the bodily load and
movements, but with questionable shock-absorbing capabilities. PVA-C prosthesis
for IVD total replacement has potential because of its shock absorption capability
and biocompatibility.
Wang and Campbell measured the characteristics of PVA-Cs made with varying
PVA solution concentrations (3–40 %) and FTCs (1–6) in an attempt to match the
mechanical behavior of IVDs based on the Young’s modulus, stress relaxation, and
creep characteristics under simulated physiological conditions. The authors were
only able to match the stress-relaxation and creep characteristic of the IVDs [54].
Instead of total disc replacement, another approach is the replacement or reinforcement of the nucleus pulposus (NP) at the center of the disc with a material that
can re-inflate the disc to restore disc height and function. Materials tested include
stainless steel ball bearings, polymethylmethacrylate, and silicon, all without much
success. More recently, NP implants have been made from cycle-6 cryogels fabricated from a mixture of PVA and polyvinyl pyrrolidone (PVP) with a ratio varying
from 1 to 5 % by weight. The implants have been tested and found to better match
the physical properties of the NP [92].
Future research efforts in IVD arthroplasty should focus on either partial or full
disc functional restoration. This may include NP implants and/or reinforcement or
total disc replacement. PVA-C, as a hydrogel, has many interesting properties, such
as its long-term biocompatibility and nontoxicity. It is also strongly hydrophilic and
viscoelastic with nonlinear stress–strain characteristics similar to the IVD. It has a
very low coefficient of friction and has good wear resistance [23]. However, its
strength is still too low to serve as a practical functional replacement of the annulus
fibrosus. PVA-BC may further increase the strength of the PVA-C to make it a
viable candidate material for IVD fabrication.
5.1.3 Cartilage
Damaged cartilage can occur from sports or accident-related injuries, as well being
a result of degenerative joint disease, which is very common. Total joint replacement is one of the main approaches for treating cartilage degeneration. There is
need for a synthetic biomaterial that can mimic the natural cartilage tissue for this
purpose. Commonly, ultrahigh molecular weight polyethylene (UHMWPE) is used
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
307
that lead to work absenteeism [86], disability claims [87, 88], and a decrease in the
quality of life [89]. IVDs are cartilaginous, composed mainly of collagen and
proteoglycans, and have a high water content [84, 90, 91]. They also have low
cell numbers and little to no vascularity [84]. Therefore, IVDs have limited ability
to heal and regenerate to regain function. The main surgical treatment is to fuse
adjacent vertebrae together. However, this approach limits the movement of the
patient and effectively shifts the stress to the adjacent vertebrae, developing
problems down the road. In recent years, total disc replacement is gaining popularity. The FDA had approved several IVD prosthetic devices. These are mainly
made from metal and are typically designed for supporting the bodily load and
movements, but with questionable shock-absorbing capabilities. PVA-C prosthesis
for IVD total replacement has potential because of its shock absorption capability
and biocompatibility.
Wang and Campbell measured the characteristics of PVA-Cs made with varying
PVA solution concentrations (3–40 %) and FTCs (1–6) in an attempt to match the
mechanical behavior of IVDs based on the Young’s modulus, stress relaxation, and
creep characteristics under simulated physiological conditions. The authors were
only able to match the stress-relaxation and creep characteristic of the IVDs [54].
Instead of total disc replacement, another approach is the replacement or reinforcement of the nucleus pulposus (NP) at the center of the disc with a material that
can re-inflate the disc to restore disc height and function. Materials tested include
stainless steel ball bearings, polymethylmethacrylate, and silicon, all without much
success. More recently, NP implants have been made from cycle-6 cryogels fabricated from a mixture of PVA and polyvinyl pyrrolidone (PVP) with a ratio varying
from 1 to 5 % by weight. The implants have been tested and found to better match
the physical properties of the NP [92].
Future research efforts in IVD arthroplasty should focus on either partial or full
disc functional restoration. This may include NP implants and/or reinforcement or
total disc replacement. PVA-C, as a hydrogel, has many interesting properties, such
as its long-term biocompatibility and nontoxicity. It is also strongly hydrophilic and
viscoelastic with nonlinear stress–strain characteristics similar to the IVD. It has a
very low coefficient of friction and has good wear resistance [23]. However, its
strength is still too low to serve as a practical functional replacement of the annulus
fibrosus. PVA-BC may further increase the strength of the PVA-C to make it a
viable candidate material for IVD fabrication.
5.1.3 Cartilage
Damaged cartilage can occur from sports or accident-related injuries, as well being
a result of degenerative joint disease, which is very common. Total joint replacement is one of the main approaches for treating cartilage degeneration. There is
need for a synthetic biomaterial that can mimic the natural cartilage tissue for this
purpose. Commonly, ultrahigh molecular weight polyethylene (UHMWPE) is used
Poly(Vinyl Alcohol) Cryogels for Biomedical Applications
307