Biomedical Engineering Reference
In-Depth Information
is a component of the ECM, by exposure of free NH
2
adherence groups.
63
Incorporation of collagen itself and glycosaminoglycans (GAGs) has been
shown to improve cell growth on the scaffold.
64
GAGs are, like collagen,
ubiquitous components of the ECM that exert various biological effects.
Besides collagen, there is little focus in the literature on incorporation of other
proteins since denaturation of macromolecules occurs rapidly. Nevertheless,
two other proteins, bovine serum albumin and human β-nerve growth fac-
tor, have been successfully blended into poly(vinyl-alcohol) (PVA) and PCL
scaffolds, respectively.
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Another possibility to modify the fibrous matrices
is by the incorporation of bioactive agents, such as drugs and plasmid DNA.
Successful incorporation of the low molecular weight drugs ibuprofen, cefazo-
lin, rifampin, paclitaxel, itraconazole, mefoxin, and tetracycline hydrochloride
has already been reported. Usually, these drugs are released in a “burst release
mode,” meaning an instant release of the total amount of incorporated drugs.
Therefore, current research is focusing on controlling this release.
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Finally, blending different types of polymers or blending polymers with
substances such as nHA amorphous tricalcium phosphate (ATCP), bioactive
glass, calcium carbonate (CaCO
3
), or polysaccharides might be useful in pro-
ducing scaffolds with superior properties compared with the pure materials,
that is, by increased mechanical properties or biocompatibility.
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4.3 Carbon Nanotubes
With regard to nanomaterials in (bone) tissue engineering, a third material that
is attracting a lot of attention are CNTs. The unique physical-chemical proper-
ties of CNTs might enhance the mechanical, electrical, and thermal character-
istics of tissue engineering constructs extremely.
78,79
Subsequently, CNTs might
also be used as a carrier system for drug delivery, or as a cell tracking system
to expand our knowledge on cell behavior.
80-82
Already, many reports on the
effects of CNT incorporation into composite materials, regarding the mechani-
cal properties and biological behavior, can be found in the literature.
83,84
There are two groups of CNTs: single-walled CNTs (SWNTs) and multi-
walled CNTs (MWNTs) (Figures 4.6 and 4.7).
85
Sometimes, fullerenes are also
listed among the CNTs; however, their closed ball-shaped structure excludes
them from further discussion in this chapter. SWNTs are composed of only
one sheet of graphene, while MWNTs contain a multiple coaxial structure.
Different existing chiralities, that is, the armchair, the zigzag, and the chiral
chirality (Figure 4.8), of the graphene sheet in SWNTs determine the elec-
trical properties as a function of helicity and tube diameter.
86
Aside from
these basic structural features, defects present in the tube walls were found
to determine the Young's modulus of the CNTs, and they also provide the
possibility for covalent or noncovalent functionalization of the tubes.
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