Biomedical Engineering Reference
In-Depth Information
Another synthetic scaffold, produced from PLGA, with or without incor-
poration of nHA and BMP-2, was implanted in the long tibia bone of nude
mice. Both scaffolds were biocompatible, and the best bone healing was
observed for the scaffolds with added nHA and BMP-2.
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PCL fibrous scaffolds were also tested
in vivo
. Before implantation into the
omenta of rats, the scaffolds were seeded with MSCs. Histological examina-
tion after 4 weeks showed collagen type I formation throughout the scaffold
and mineralization of the scaffold. This indicated that the scaffold was bio-
compatible, and that the preseeded cells provided the scaffold osteoinduc-
tivity, since ectopic mineralization of the scaffold was observed.
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F i n a l ly,
electrospun scaffolds of PCL, with or without the incorporation of the bone
formation-stimulating drug simvastatin, were implanted in 8 mm critical-
sized cranial defects in rats. Histological examination after 1, 3, or 6 months
showed biocompatibility and osteoconductivity of all scaffolds, with a sig-
nificant increase in bone formation for the drug-containing scaffold.
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The
in vitro
as well as the
in vivo
studies often show increased cytocompat-
ibility or biocompatibility of electrospun nanofibrous scaffolds in compari-
son with the bulk polymer. Therefore, these nanomaterials are considered
very promising in future bone tissue engineering applications.
4.4.3 Carbon Nanotubes-Cell Interaction
Nanomaterials produced from natural or synthetic polymers are often
degradable materials that are broken down and systemically removed
from the body.
131,132
Nanoceramic materials are remodeled and also gener-
ally regarded as nonhazardous since they are naturally occurring materials
in the body. CNTs, however, might pose a problem for future applications.
Therefore, many recent research studies focus on the interaction between
cells and CNTs in
in vitro
and
in vivo
situations. In light of this emphasis in
the literature, the current review will mainly describe CNTs with regard to
risks involved (not necessarily only on bone cells or tissue since incorpora-
tion of CNTs into bone implants and tissue-engineered constructs may also
introduce the possibility of exposure to other tissues).
CNTs are nondegradable and foreign to the body; however, the vast appli-
cations of this material make it still very popular. Various toxicity issues
proved to be related to the properties of this material, such as structure,
length, surface area, degree of aggregation, extent of oxidation, surface topol-
ogy, and bound functional groups. It can be argued that these are the same
physical and chemical properties that make the use of CNTs so interesting.
Besides the physico-chemical properties, also the concentration or dose to
which cells and tissues are exposed to this material were found to be of great
importance concerning safety risks.
78,83
Safety aspects start with the production process of the material, which may
already be hazardous, since CNT containing aggregates might become airborne
during production and remain airborne for long periods, causing health risks to
