Biomedical Engineering Reference
In-Depth Information
(PLA), poly(ethylene terepthalate) (PET), poly(3-hydroxybutyrate) (P3HB), PCL, etc. have been
fabricated using the electrospinning technique and exploited for their potential in tissue engineer-
ing. Perhaps the most studied group of polymers is the biodegradable poly(α-hydroxy esters), which
are already used in the clinics. Polymers such as PLA or poly(glycolic acid) (PGA) have already
found multitude of applications in the biomedical fi eld, which was pioneered by the usage of resorb-
able sutures. Other polymers such as PCL, poly(anhydrides), poly(orthoesters), and other biodegrad-
able materials have also been electrospun and characterized.
Synthetic materials offer advantages over naturally derived materials since they have less batch-
to-batch variations, are more reliable source of raw materials, and can be designed to give a wider
range of properties, that is, by fi ne-tuning the homopolymer and their copolymers. Li et al. studied
the mechanical and degradation properties of six groups of electrospun poly(α-hydroxy esters) and
their copolymers, that is, PGA, PLGA5050, PLGA8515, PLLA, PDLLA, and PCL. It was revealed
that PGA and PLGA polymers were mechanically the stiffest but also more prone to hydrolytic
degradation in physiological conditions. PLLA and PCL on the other hand were the more compli-
ant and stable of the group [20]. These groups of electrospun polymers have also often reported
to exhibit good capability to support cellular attachment, proliferation, and differentiation. PCL
nanofi bers show promising potential to be used in cartilage tissue engineering as they were able
to sustain the phenotype of chondrocytes and cartilage-like matrix deposition [21]. Furthermore,
smooth muscle cells (SMC) and endothelial cells were successfully cultured
in vitro
on PLLA-CL
composite electrospun nanofi bers indicating potential applications of the polymer in the fi eld of
vascular tissue engineering [22].
Badami et al. [23] more specifi cally investigated the effect of fi ber diameter (0.14 and 2.1 µm)
of electrospun PLA and poly(ethylene glycol)poly(d,l-lactic acid) (PEG-PLA) block copolymer
randomly orientated membranes on the cellular behavior of osteoprogenitor cells (MC3T3-E1).
In vitro
cell studies in the presence of osteogenic factors after 14 days culture showed higher cell
densities on larger fi bers compared with smaller fi bers and the spin-coated controls; however, there
was no signifi cant difference in ALP activity. Cell morphology measured by the cell-projected area
was not infl uenced by fi ber diameter, but both were signifi cantly smaller than cells cultured on the
fl at spin-coated controls. However, the aspect ratio of the cells cultured on the 2.1 µm fi bers was
signifi cantly higher and attributed to increased contact guidance. Focal adhesion contacts occurred
predominantly as clusters along the polymer fi bers, and the actin stress fi bers extended perpendicu-
larly across the polymer fi bers and were parallel to each other.
Besides acting as cell delivery agents and tissue scaffolding, electrospun nanofi bers have
attracted attention as a vehicle of bioactive molecule delivery. Luong-Van et al. incorporated hepa-
rin into electrospun PCL nanofi ber mats and showed 50% release of the heparin during the fi rst
14 days. The heparin-containing PCL nanofi bers exhibited no proinfl ammatory response, uniform
distribution of heparin, and an antiproliferative effect toward SMCs [24]. Another study involved
the incorporation of plasmid DNA into electrospun PLGA with PLA-PEG block copolymer. Burst
release of DNA after 2 h was observed although release was continued until 20 days of the experi-
ments with up to 80% of the incorporated DNA released. The plasmid DNA was intact as assayed
by the expression of the β-Gal gene by MC3T3 cell line [25].
5.2.3.1 SolutionSpinning
Electrospinning of synthetic polymers from a solution is the conventional method of obtaining nano-
fi bers. Organic solvents such as chloroform, TFE, DMF, HFIP, and so on are commonly used to dis-
solve polymers into solutions of known concentrations and viscosity. Dielectric constant, volatility,
surface tension, and polymer solubility are aspects of solvents that need to be considered prior to
electrospinning. Furthermore, in tissue engineering and biomedical fi eld, toxicity of solvent becomes
an increasingly cr itical issue. Most of the solvents that can be used to dissolve synthetic polymer show
some degree of cytotoxicity. Thus it is imperative that solvent must be thoroughly removed from the
