Biomedical Engineering Reference
In-Depth Information
adsorption and specific protein interactions when they were compared with conventional materials
[11]
. Obviously, this would efficiently stimulate new bone growth, and this was thought to be the
underlying mechanism behind why carbon nanomaterials were excellent for bone regeneration
[11]
.
Moreover, the unique mechanical, physical, and chemical properties of CNTs/CNFs categorize
them as outstanding reinforcement additives in polymeric nanocomposites. With the extraordinary
stiffness and strength, CNTs/CNFs are deemed as ideal materials to provide structural reinforce-
ment for bone tissue scaffold, especially for those load-bearing defect reparations
[12]
. Thus,
CNTs/CNFs have been used in two main areas of bone tissue engineering: for structural and electri-
cal enhancement of polymer and ceramic composites, and for nanostructured coatings to improve
the bioactivity of titanium implant surfaces
[13]
.
However, pristine CNTs/CNFs tend to bundle up and are insoluble in most types of solvents,
making them difficult to be used in biological systems
[14]
. It was only after the development of
strategies to functionalize them with organic groups and render them soluble that had opened the
way to bio-applications of CNTs/CNFs. Moreover, there are conflicting data concerning the safety
and biocompatibility of CNTs/CNFs. Although in some cases, like gene delivery, CNTs/CNFs were
used without significant toxicity, other cytotoxic effects have been observed, including induction of
intracellular reactive oxygen species (ROS), DNA damage, and apoptosis (cell death)
[15]
. Usually,
the cytotoxicity of pristine CNTs/CNFs is due to the residual metal catalysts resulting from produc-
tion methods and also the insolubility of pristine CNTs
[16]
. Therefore, to integrate CNTs/CNFs
into biological systems, CNTs/CNFs need to be functionalized and purified by the removal of resid-
ual metal catalysts to improve their solubility and biocompatibility properties.
Having a high aspect ratio (i.e., the length to diameter ratio) and high surface area with many
dangling bonds on the side walls, CNTs/CNFs are capable of adsorbing or conjugating a wide vari-
ety of therapeutic molecules
[17,18]
. Thus, CNTs/CNFs can be surface engineered (i.e., functiona-
lized) and utilized as carriers of biomolecular motifs. In this chapter, attempts on CNTs/CNFs for
implant dentistry and bone regeneration application are reviewed.
18.2
Enhanced functions of osteoblasts on carbon nanomaterials
Efforts on bone regeneration by using cells/scaffold construction have been tried for decades, aim-
ing at replacing the use of autographs and allographs in bone transplantation
[19]
. Various materi-
als, including synthetic polymers, biopolymers, and ceramics, have been investigated as substrates
to grow bone-related cells (osteoblasts, bone-marrow-derived stromal cells (BMSCs), fibroblasts)
and induce bone formation both in vitro and in vivo.
When designing a material to be used as a bone scaffold, one criterion concerning the mechani-
cal properties of the materials is usually the first consideration because bone is a hard tissue provid-
ing mechanical support to the body and protecting internal organs. With the excellent mechanical
strength (Young's modulus, 0.2
63 GPa)
[20]
and diameters close to
the size of the triple helix of collagen fibrils (which are 1.5 nm in width and 300 nm in length and
have a periodicity of 67 nm)
[21]
, CNTs/CNFs are naturally ideal candidates as reinforcing agents
in bone scaffolds. Lahiri et al.
[22]
proposed the use of CNTs as reinforcements to increase the
mechanical properties of a polylactide-caprolactone copolymer (PLC) matrix. Addition of 2 wt %
1 TPa; tensile strength, 11
