Biomedical Engineering Reference
In-Depth Information
tion in hydrophilic conditions. Thus, hybrid materials that combine the properties
of both natural and synthetic polymers are a potential alternative. The properties
possessed by such hybrid polymers include improved mechanical properties, high
processability, negligible batch-to-batch variability and also the specifi c recogni-
tion ability to elicit a favorable cell response. Blending of polymers is also per-
formed to improve the electrospinnability of some polymers and hence their
potential use in tissue engineering. Blends can be composed of two or more
natural polymers, or two or more synthetic polymers, or a combination of natural
and synthetic polymers.
Blends of natural polymers that are ECM mimics have found great potential
in tissue engineering. Nevertheless, electrospinning of natural polymers can be
challenging. For example, silk fi broin is a collagen mimic but is mostly composed
of hydrophobic residues. Thus, blending of silk fi broin with a hydrophilic polymer
would render its electrospinning relatively easy. Making use of this concept, Park
et al. demonstrated the synthesis of electrospun nanofi bers using silk and chitin
blends. The presence of chitin increased the conductivity of the solution that led
to the production of nanofi brous matrices with reduced diameters (340nm-
920 nm as compared to 1260 nm for pure silk fi bers) [172] .
Blends between synthetic polymers combine the properties of the individual
polymers. Zong et al. evaluated the ability of biodegradable blends of PLGA and
PEG-PLA [(poly(ethylene glycol)-poly(lactic acid)] in preventing postsurgical
adhesions in a rat model [173]. PLGA/PEG-PLA electrospun membranes main-
tained a good 3D stability as compared to shrink-prone hydrophobic PLGA
membranes when implanted in rats. Mo et al. exploited the properties of PLLA
and PCL and demonstrated the potential of electrospun PLLA/PCL blends in
tissue engineering applications. They varied the ratio of both the polymers,
thereby modulating the degradation rate and, as a consequence, permeation rates
of steroids [174].
Some of the natural polymers, such as gelatin, when dissolved in water cannot
be processed by electrospinning because a colloidal solution is formed that in
turn cannot be quickly volatilized during the process. Potential solutions either
involve the use of volatile solvent systems or blending with synthetic polymers.
Various volatile solvents have been studied for electrospinning of gelatin (see
section on natural polymers) [124]. Using the second strategy of blending, Li et al.
electrospun silk by blending it with polyethylene oxide (PEO), thereby generat-
ing a viscosity and surface tension suitable for electrospinning [102]. Further, Li
et al. electrospun PLGA, gelatin and elastin together to form a nanofi brous matrix
that maintained the properties of the individual polymers. PLGA was the syn-
thetic manipulative component while gelatin and elastin were the natural compo-
nents serving for the mechanical properties of the ECM as well as cell migration
and cell attachment [175].
There are other synthetic polymers that have been electrospun into nanofi -
bers and applied in the area of tissue engineering. However, describing all poly-
mers is beyond the scope of this chapter and hence they have been enumerated in
Table 13.2 .
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