Biomedical Engineering Reference
In-Depth Information
fibers with ethylene diamine improved the adhesion and migration of adult rat
brain derived NSCs into the scaffold [93]. Fiber diameter is a significant factor
in controlling the differentiation of NSCs. Reduction in diameter led to increased
cell proliferation, spreading, and differentiation. A lower degree of cell aggregation
was also reported for scaffolds made of nanofibers with smaller diameters [94].
Electrical stimulation has been recognized as another contributing factor for
neurite sprouting. To this end, we fabricated a scaffold of conductive core-sheath
nanofibers through a combination of electrospinning and aqueous polymerization.
Specifically, electrospun nanofibers of PCL or PLLA were employed as templates to
generate uniformsheaths of conductive polypyrrole (PPy) via
in situ
polymerization.
Figure 9.5e shows a Transmission electron microscope (TEM) image of hollow PPy
tubes obtained by dissolving the core polymer. Electrical stimulation, when applied
through the scaffolds of conductive core-sheath nanofibers, was found to further
increase the maximum length of neurites for aligned samples by 47% relative to
the controls with no electrical stimulation [92]. Figure 9.5f shows the synergetic
effect of electrical stimulation and topographic guiding in promoting the uniaxial
extension of neurites from DRG over long distances.
Although many efforts have been devoted to the field of nerve repair, challenges
still exist. For example, the development of double-layered NGCs (with random
nanofibers as the outer layer and the aligned nanofibers as the inner layer) has
achieved some promising results [95], but the central cavity in the NGCs fails to
provide contact guidance for neuronal outgrowth and thus will probably lead to
a mismatch between proximal and distal ends. An NGC that provides 3D contact
guidance throughout the whole conduit has yet to be developed.
9.5.2
Dura Mater Repair
The dura mater is the outermost layer of the three meninges that surround the
brain and the spinal cord. Its major function is to help retain the cerebrospinal
fluid (CSF). Traumatic injury or surgical operation often leaves a defect in the dura
mater, which needs to be covered by a dural substitute to prevent CSF leakage
and promote the regeneration of dura tissue [96]. Materials that have been used
as dural substitutes include native autografts, xenografts, and synthetic polymers.
Whereas native autografts such as fascia lata work well as dural substitutes due to
their low immunogenicity, their availability and the morbidity associated with the
explanted sites severely limits their use [97]. Various xenologous collagen grafts,
including bovine and ovine pericardium, have been developed as alternatives, but
with limited success due to the risk of disease transmission and immunogenicity
from animal-derived materials [98]. Other concerns such as low-tensile strength
and rapid bioresorption also plague the use of xenologous collagen grafts. Scaffolds
based on synthetic, biodegradable polymers have gained popularity in recent years
because of their low cost, zero risk of disease transmission, and good mechanical
properties. In particular, the high rate of cell infiltration and the ability to provide
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