Biomedical Engineering Reference
In-Depth Information
increased protein adsorption on MWCNTs and proposed it be the underlying mechanism for the
enhanced functions of C2C12 cells. Li et al.
[36]
also evaluated attachment, proliferation, osteogenic
gene expression, ALP/DNA, protein/DNA, and mineralization of human adipose-derived stem cells
cultured in vitro on MWCNT and graphite compacts with the same dimension. They placed the com-
pacts in culture medium with 50% fetal bovine serum (FBS) before cell culture. With the adsorption
of the protein in advance, the increments of the ALP/DNA and protein/DNA for the MWCNT com-
pacts were found to be significantly more than the increments of those for the graphite compacts.
It has been generally believed that matrixes interacted with proteins existing in culture medium
first and then attracted cells to attach and spread
[37]
, suggesting that the larger amount of protein
adsorbed on matrixes is crucial. Using this feature, CNTs/CNFs might stimulate inducible cells in
soft tissues to form bone by concentrating more proteins, including bone-inducing proteins. Some
reports showed that nano-roughness alone was sufficient to modulate cellular behavior and early stage
of stem cell lineage recruitment without the aid of an induction medium
[38]
. This phenomenon was
also found on CNT compacts. Tay et al.
[39]
cultured human MSCs on a thin mesh-like layer of
carboxylic-functionalized SWCNTs with a vertical height of less than 100 nm. It was observed that
the cells spread better on a SWCNT film as compared to cover slip, resulting in larger cell area and
having higher occurrence of filopodia (microspikes) at the cell boundaries. Cytoskeleton arrangement
was observed to be less orientated in the cells cultured on a SWCNT film as compared to control.
According to Khang et al.
[40]
, it should be the contribution of nanoscale surface roughness on the
adsorption of one key cell adhesive protein, fibronectin, that promoted cell differentiation. Khang
et al. prepared various surface energies by creating different nanosurface roughness features via
mixing MWCNTs and PCU. Specifically, independent contributions of surface chemistry (70%) and
surface nano-roughness (30%) were found to mediate fibronectin adsorption. The results clarified one
of the important reasons why MWCNTs/PCU composites enhance cellular functions and tissue
growth, which was their physical nano-roughness on promoting the adsorption of fibronectin, a pro-
tein well known to be critical for mediating the adhesion of anchorage-dependent cells.
All these studies indicate that the CNTs/CNFs and their composites can serve as osteogenic
scaffolds with good cytocompatibility properties, reinforced mechanical properties, and improved
electrical conductivity to effectively enhance bone tissue growth. In addition to those controversial
issues on cytotoxicity, however, another point needs to be stated, which is CNTs/CNFs are nonbio-
degradable. CNT/CNF scaffolds are quite unlike the conventional biodegradable polymeric scaf-
folds, which are able to disappear as the new bone grows. The nonbiodegradable CNTs/CNFs
would behave as inert matrixes, on which cells proliferate and deposit new live matrix, and finally
integrate into functional, normal bone. Therefore, more studies are needed to address how the body
will interact with nonbiodegradable CNTs/CNFs, more specifically the reaction of the immune
system, before we can fully take advantage of their promising applications in bone regeneration.
18.3
CNT/CNF applications in dentistry
One potential area in dentistry for carbon nanomaterial applications might be the carbon-fiber-
reinforced epoxy resin posts, for their close elastic modules to dentin, no erosion, less time-consuming,
and less expensive clinical procedures than conventional procedures for cast metal posts
[41]
. Another
application is carbon/graphite fiber-reinforced poly(methyl methacrylate) (PMMA) denture resin to
