Biomedical Engineering Reference
In-Depth Information
been explored as templates for bone and neural tissue engineering. In these circumstances, the
surrounding tissues come in contact with CNT-based composites. Unrestricted growth and prolifera-
tion of human osteoblast hFOB 1.19 cells were observed around CNT regions indicating biocompati-
bility
[226]
. Studies of bone cells interaction with polyurethane
CNT foams indicated no osteoblast
cytotoxicity or hindrance on osteoblast differentiation or mineralization
[227]
. SWNTs with negative
charge allow the nucleation and crystallization of hydroxyapatite (HA), a component of bone
[228,229]
. Polyurethane
CNT composites also displayed improved anticoagulant functions
[230]
.
Several studies have been conducted that evaluated CNTs as templates for neuronal growth
[173,174,231
233]
. Neurons were observed to grow on unmodified MWNT
[177]
, while more
branched neuritis were observed when grown on 4-hydroxynonenal-coated MWNT. Positively
charged MWNTs yielded more numerous growth cones, longer average neurite length, and elaborate
neurite branching than neutrally or negatively charged MWNTs. In a subsequent study
[232]
, posi-
tively charged poly(ethylenimine) (PEI)-grafted SWNT had reduced neuronal growth characteristic
than a pure PEI. CNT-based composites improve the neural signal transfer probably due to the high
electrical conductivity
[174]
.
3.5
CNT applications in dentistry
The use of CNT in the dentistry field has been explored modestly since its introduction in the early
1990s. The applications of CNT in the dental field can be categorized into three areas: (i) applica-
tion to dental restoration materials, (ii) application to bony defect replacement therapy, and (iii)
application to protein, gene, and drug delivery and cancer treatment.
3.5.1
Dental restorative materials
Dental composite resin is a tooth-colored restorative material used to replace a decayed portion of
tooth structure. Its esthetic appearance is the main advantage over the conventional dental amal-
gam. Typical composite resin is composed of a resin-based matrix, such as bisphenol A-glycidyl
methacrylate and inorganic filler like silica. The filler gives the composite improved mechanical
property, wear resistance, and translucency. Functionalized SWNT has been applied to the dental
composite to increase its tensile strength and Young's modulus to help improve the longevity of
composite restoration in oral cavity. Addition of functionalized SWNT increased its flexural
strength significantly by absorbing more stress
[234]
. However, further effort in development of
CNT-reinforced composite resin has been hampered because of its dark color primarily from CNT,
which is a major drawback for esthetic composite resin.
CNT has been applied to the interface of dentin and composite resin to compensate for micro-
leakage development in long-term use, which is a major cause of restoration failure. Once micro-
leakage develops between tooth and composite resin interface, it works as a nidus for bacterial
colonization; thus, secondary decay can develop. CNT has shown the potential to provide
protection against bacteria and initiates the nucleation of HA on its surface
[235]
. Studies have
reported that hydrophobic interaction between CNTs and exposed collagen fibers from dentin as a
mechanism for CNT's attachment to the dentin surface
[236]
and that the bond strength between
CNT-coated dentin and composite resin restoration material was not affected by the presence of the