Biomedical Engineering Reference
In-Depth Information
reinforced spider silk fiber by electrospinning process. Initial tensile testing of the aligned silk com-
posites showed a tenfold increase in modulus, fivefold increase in strength, and threefold increase in
toughness with only 1 wt% of SWCNT in a silk matrix. Kang et al.
[75]
also prepared the MWCNTs-
incorporated silk fibroin nanofibers by electrospinning and identified that the MWCNTs were
well incorporated along the nanofibers and the tensile properties of the nanofibers being enhanced
by the incorporation of a small amount of MWCNTs.
CNT/polycaprolactone (PCL) nanofibers were fabricated by electrospinning PCL-grafted CNT
nanocomposite, and the grafts of PCL onto CNTs were conducted by in-situ polymerization
[76]
. The
nanocomposite CNT/PCL nanofibers showed a relatively broader diameter than the pure PCL nano-
fibers. The MWCNTs were embedded within the nanofibers and were well oriented along the axes of
the electrospun nanofibers, as confirmed by transmission electron microscopy.
All these data demonstrated that the electrospinning of CNT/biodegradable polymer composite
nanofiber network could potentially supply useful options for the fabrication of biomaterial scaffolds,
such as wound dressings and GTR membranes.
However, there are contradictory reports in regard to the biocompatible character of CNTs
[77,78]
.
On one hand, some studies reported that CNT are cytotoxic
[79-81]
, which decreased the viability of
certain cells significantly, such as A549, mesothelial cells, keratinocyte, glial, and HEK293 cell survival
[80,82-85]
. On the other hand, chemically functionalized CNTs have been used successfully as substrates
for neuronal
[86-89]
and mesenchymal stem cell growth
[90]
, especially for osteoblast cell
[91-93]
.
Overall, for biomedical applications, the toxicity and biocompatibility of CNT needs to be
thoroughly investigated. Detailed understanding of the balanced evaluation of risk/benefit ratios is
crucial and required before CNTs being incorporated into biomedical devices and applied
in vivo
.
10.3.3
Organic-Inorganic Composite Nanofibers
Naturally, bones are generally strengthened by the nucleation of HA into nano-sized gaps between colla-
gen molecules. In order to mimic chemical compositions and fibrous structure of natural bone extracellu-
lar matrix, the concept of combining a biodegradable polymer and calcium phosphates (HA and β-TCP),
most preferably in a nanoparticulate form, has already resulted in numerous investigations
[94-96]
. The
feasibility of incorporation of nanometer-sized particles into electrospun fibers has made it more attrac-
tive for the preparation of inorganic-organic composite nanofibers. Many researchers have investigated a
number of characteristics of electrospun polymer/HA or β-TCP composites nanofibers, using PLA, PCL,
PLGA, poly(3-hydroxybutyrateco-3-hydroxyvalerate), collagen, and gelatin
[52,97-105]
.
In the conventional method, inorganic powders were directly dispersed in polymeric solutions via
ultrasonic. The agglomeration between the nanoparticles tended to take place irreversibly due to their
high surface energy, thus it was a challenge to get a stable suspension. To produce electrospun com-
posite fibers with homogeneous structure, homogeneous dispersion of ceramic nanoparticles in poly-
mer solutions is crucial. Several methods had been proposed to effectively disperse HA or β-TCP
nanoparticles into electrospun polymeric fibers.
Kim et al.
[106]
dispersed HA powder in a surfactant hydroxysteric acid mediated chloroform
solution, followed by dissolving PLA into the solution. Continuous and uniform fibers were electros-
pun successfully with diameters of 1-2 μm, and featured a well-developed nanocomposite structure of
HA nanopowder-dispersed PLA. The amphiphilic surfactant existed between hydrophilic HA powder
and hydrophobic PLA to obtain a homogeneous mixture.
