Biomedical Engineering Reference
In-Depth Information
deposited on the metal collector
[57]
. Typical electrospinning processes create very long fibers having
diameters in the order of a few micrometers down to the tens of nanometers with large surface areas,
superior mechanical properties, and ease of fictionalization for various purposes. Biomedical field is
one of the important application areas among others like filtration, protective material, and nanofiber
reinforced composites because electrospinning can generate loosely connected 3D porous matrixes to
physically resemble the nanofibrous features of the natural extracellular matrix structure
[58-60]
.
While electrospinning has proven to be a relatively simple and versatile method for forming
fibrous mats, a number of parameters like molecular weight and architecture of polymer, polymer
solution properties (viscosity, conductivity, surface tension, etc.) and processing variables (electric
field, flow rate, capillary-collector distance, etc.), as well as environmental temperature and humid-
ity), all greatly influence the electrospinning process and the properties of the generated fibers
[61]
. In
addition to pure polymer or polymer mixtures, the electrospinning technique also has the capacity to
tailor the electrospun nanofibers network with a variety of types of additives. Ceramic nanoparticles
(HA and β-TCP) and carbon nanotubes (CNTs) were both encapsulated into polymer nanofibers by
being dispersed in polymer solution and electrospun
[62]
. Control of the process, fibers with various
surface morphology, cross-sectional shapes, beads, branches, and buckling coils or zigzags can also
be produced
[63]
.
Thus, by selecting a combination of proper components and by adjusting the component ratio, prop-
erties of electrospun fiber network can be tailored with desired new functions. The adjustment of several
electrospinning parameters allows for further control and refinement of fibrous matrix characteristics.
10.3.2
CNTs Incorporated into Nanofibers
CNTs are a macromolecular form of well-ordered, high aspect ratio allotropes of carbon. Both single-
walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) are constructed
of graphite sheet, possessing excellent thermal and chemical stability, high aspect ratio, high tensile
strengths, electrical and magnetic properties
[64]
. With these remarkable features, there has been
growing interest in using CNTs for biomedical applications
[65,66]
. CNT can be used as nanofillers
in polymeric materials to both dramatically improve mechanical properties and create highly aniso-
tropic nanocomposites
[67]
. The idea of dispersing or aligning CNTs in a nanofiber matrix to form
composite materials seems to be very promising from a mechanical and electrical perspective.
Sen et al.
[68]
electrospun CNT reinforced polystyrene and polyurethane nanofibers with
diameters in the range of 50-100 nm. The incorporation of ester functionalized SWCNTs into poly-
mer matrix increased the tensile strength more effectively than as-prepared SWCNTs being incorpo-
rated. And some literatures investigated the reinforcement of electrospun CNT-polyacrylonitrile(PAN)
composite nanofibers, the results demonstrated the composite nanofiber sheets possessed enhanced
electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and
dimensional stability
[69,70]
. Ji et al.
[71]
had obtained continuous macroscopic aligned PAN com-
posite nanofiber sheets embedded with PAN-grafted MWCNTs by electrospinning followed by hot-
stretching. The MWCNTs dispersed homogeneous and aligned highly along the fiber, which led to a
significant enhancement in the mechanical performance of the resulting composite nanofiber sheets.
CNTs can also be electrospun with biopolymers to form aligned matrices
[72]
. SWCNTs had
been embedded into electrospun poly(ethylene oxide) (PEO) by Salalha et al.
[73]
, the CNTs within
the nanofibers were in a straight and aligned form. Ko et al.
[74]
reported the preparation of CNT
