Biomedical Engineering Reference
In-Depth Information
the formation of a conical envelope that transforms into an inverted cone with
the apex at the edge of the rotating disc. The sharp edge of the rotating disc is
responsible for exerting a pulling force on the jet that leads to the assembly of
nanofi bers on the circumference of the disc in an aligned manner. Studies con-
ducted in the past few years also state the infl uence of fi ber alignment on ECM
production. In one such study, Lee et al. reported the infl uence of fi ber alignment
on ECM production by human ligament fi broblast. Their results demonstrated
that production of collagen on aligned fi bers was greater when compared to that
on non-aligned controls [92]. In another study, Xu et al. demonstrated the poten-
tial of biodegradable poly(L-lactic acid)/polycaprolactone (PLLA/PCL) scaffold
using aligned fi bers that matched the requirements of the middle layer in an
artery. They observed orientation of smooth muscle cells along the length of the
aligned fi bers with enhanced adhesion and proliferation thus indicating the
potential of the aligned nanofi ber-based scaffold for application in blood vessel
tissue engineering [93] .
Apart from alignment, fi ber diameter also plays a key role in gene expression.
Supramolecular property of the ECM is defi ned by the composition of protein
fi brils enmeshed within the hydrated network of glycosaminoglycans [94]. The
nano - dimensioned fi bers synthesized by electrospinning mimic this supramolecu-
lar property. However, smaller fi ber size (diameter) reduces the expression of
various genes involved in differentiation and migration due to less cellular attach-
ment points [95]. These problems can be overcome by combining the micro-
fi brous and nano-fi brous scaffolds in one system that would provide ECM like
structures to the cells and the ability for cell attachment and guidance [95,96].
Another limiting factor in tissue engineering applications could be the cell seeding
densities on electrospun nanofi bers. This can potentially be overcome by spinning
the matrix along with the cells to enable enhanced cellular densities, thereby
improving functional connections between the cells [97]. Thus, electrospun nano-
fi bers can serve as a potential scaffold in tissue engineering of ECM rich organs.
Variations in the process of electrospinning can be in terms of type of
spinneret or collector plate. Coaxial electrospinning involves the synthesis of
nanofi bers with core-shell type geometry. This has been mostly exploited for the
incorporation of water soluble growth factors that still remains a challenge in
conventional electrospinning. Jiang et al. exploited this technique for the incorpo-
ration of water soluble bioactive agents, bovine serum albumin (BSA) and lyso-
zyme within polyethylene glycol nanofi bers with a shell of polycaprolactone
(PCL) and demonstrated release of bioactive protein [98]. Researchers have also
explored the possibility of increased rate of nanofi ber production by employing
multiple spinnerets [99]. Variations in collector plate, for example, stationary col-
lector or rotating mandrel, determines fi ber alignment and has been discussed
earlier in this section.
Electrospinning is a relatively advantageous technique for scaffold produc-
tion in comparison to self assembly and phase separation, as it is a one step tech-
nique and involves a simple experimental set-up. Further, it can be modulated to
control the fi ber diameter, morphology and density that can meet specifi c tissue
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