Biomedical Engineering Reference
In-Depth Information
and the blood-brain barrier for brain tumors.
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Currently, there is a huge demand for
controlled-release polymer systems, and the worldwide annual market exceeds
$60 billion. Electrospinning has developed into a versatile technique to fabricate
polymeric nanofiber matrices, and the ability to incorporate bioactive therapeutic
molecules without adversely affecting their structural integrity and biological
activity using the mild electrospinning process has generated significant interest
in polymeric nanofiber-based drug release patterns by changing the mode of
encapsulation as well as by varying the matrix polymer.
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2.2 FABRICATION OF NANOFIBROUS SCAFFOLDS
BY ELECTROSPINNING
Electrospinning generates a nonwoven mat of polymeric nanofibers from an electro-
statically driven jet of polymer solution. The basic elements of an electrospinning
system involve (1) a high-voltage supplier (2-40 kV), (2) a source electrode and
grounded collector electrode, and (3) a capillary tube with a needle of small diameter.
Electrospinning may be carried out with polymer solution as well as polymer melt for
fabrication of nanofibers. The morphology and fiber diameter of the electrospun
nanofibers can be controlled by varying the parameters, such as applied electric field
strength; spinneret diameter; distance between the spinneret and the collecting
substrate; temperature; feeding rate; humidity; air speed; and properties of the
solution or melt, including the type of polymer, and polymer molecular weight, such
as surface tension, conductivity, and viscosity, depending not only on the tempera-
ture but also on the concentration of the sample.
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The advantage of an electrospun
nanofibrous scaffold includes an extremely high (favorable) surface-to-volume ratio,
appropriate porosity, and malleability to conform to a wide variety of sizes, textures,
and shapes of superior architecture
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(Fig. 2.2).
In addition, scaffold composition and fabrication can be controlled to confirm
desired properties and biofunctionalities. The design and development of nano-
fibrous scaffolds for tissue engineering approaches involve the understanding of
biological processes that are mainly aimed at a conducive to ECM. Many studies
were also focused on the understanding and evaluations of several cell-scaffold
interactions.
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Interaction between the stem cells and nanofibers are crucial in a
cell-scaffold matrix while using them for different tissue engineering applications.
Because the nanofibrous scaffolds are highly porous and the pore size is smaller
than the normal cell size, scaffolds might inhibit cell migration. Despite this,
studies showed the capability of nanofibrous meshes to infiltrate cells. Cells
entering into the matrix through amoeboid movement to migrate through the
pores can push the surrounding fibers aside to expand the pore. Scaffolds
constructed from naturally occurring proteins, such as collagen, allows much
better infiltration of cells into the scaffold than the synthetic polymeric nanofibrous
scaffolds.
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The low-molecular-weight peptides (tripeptide and tetrapeptide)
found in ECM proteins, such as laminin, fibronectin, collagen, and vitronectin,
are found to modulate the cell behavior to a higher extent. Immobilizations of these
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