Biomedical Engineering Reference
In-Depth Information
3.5.2
Bony defect replacement therapy
As dental implant treatment of replacing missing teeth becomes highly predictable, supplemental
bone augmentation therapy using synthetic and cadaveric bone biomaterials also attains increased
popularity. Insufficient volume or bony defects of alveolar bone can be caused by the periodontal
disease, tooth loss, and/or trauma. Wide range of biomaterials from bone fillers to tissue engineered
composite materials, such as calcium sulfate, calcium phosphate, HA, polymers, and CNTs have
been explored as candidates to achieve predictable bony defect replacement. It was reported that
nanoscale HA was formed on the surface of MWNT when immersed in calcium phosphate solution
of 37
C for 2 weeks, indicating CNTs potential use for bone
tissue engineering.
Guided bone regeneration is a dental surgical procedure that utilizes barrier membrane to guide
the new bone formation at sites having insufficient volumes of bone while inhibiting the epithelial
cell growth into the bony defect sites. Researchers have developed a biomembrane by electron-
spinning a suspension of poly (
L
-lactic acid) (PLLA), MWNT and HA to promote guided bone
regeneration. Authors found that the membrane was able to promote desirable periodontal ligament
cell (PDLC) adhesion and proliferation by 30% while inhibiting less desirable epithelial cell
proliferation (
Figure 3.4
)
[240]
. Furthermore, a new chitosan
MWNT composite has been devel-
oped which can promote osteoblast proliferation and apatite crystal formation on the surface of
MWNT while discouraging adhesion of fibroblast
[241]
. However, whether and how these engi-
neered membranes used for guided bone regeneration can be removed or will be resorbed
completely in a pattern similar to that of currently available Teflon-based and collagen-based
membranes are the questions that need to be answered before they are introduced to the clinic.
The key factors for the successful bony defect replacement therapy are whether sufficient blood
supply can be maintained to the grafted sites and whether the grafted materials can be immobilized
and protected to achieve a desired dimension after healing. A small bony defect which is well
surrounded by the adjacent native bone can be replaced predictably using patient's own bone or
cadaveric/animal particulated bone graft materials. However, larger bony defects which do not
have surrounding native bone supports face challenges of achieving immobilization of the grafted
materials as well as sufficient blood supply. Engineered bone scaffolds which mimic the anatomy
of bone structure and can provide structures for new bone formation have been studied widely.
Highly porous interconnected scaffolds were fabricated using thermal-cross-linking particulate-
leaching technique for bone defect replacement therapy
[242]
. The porogen content was found to
dictate the porosity of scaffold and the higher porosity improved the interconnectivity of the pores.
However, compressive mechanical properties declined as porosity increased. Authors found that
nanocomposites with ultrashort SWNT showed higher compressive strength compared to poly(pro-
pylene fumarate) scaffold, indicating that highly porous polymer scaffold which mimicks natural
trabecular bone structure can be strengthened by the incorporation of CNT. Composite scaffolds of
electrospun poly(lactic-co-glycolic acid) nanofibers onto the knitted scaffold made from MWNT
yarn
[243]
resulted in uniform cell distribution and spanning of cells on the knotted scaffold sur-
face. This indicates the potential of knitted composite to be used as a scaffold for bone
replacement.
Mineral formation on CNT
PCL composite fabricated using LbL self-assembly technique by
human fetal osteoblast was better than mineral formation on the titanium surface (
Figure 3.5
)
[219]
.
Increasing the number of layers of SWNT on PCL polymer increased the mechanical properties.
