Biomedical Engineering Reference
In-Depth Information
forming proteoglycans, and have an important role in binding of growth
factors, maintaining the sol-gel property and water holding capacity of ECM
[136] .
13.4.1.2.1 HYALURONIC ACID ( HA ). Hyaluronic acid is a non - sulphated
GAG, made up of repeating disaccharide units
β
- 1, 4 - D - glucuronic acid and
β
-1, 3-N-acetyl-D-glucosamine. It is the simplest form of all the GAGs present in
the ECM [137,138] and is unique in that it does not exist in bound form
with protein, that is, as a component of proteoglycans. An important property of
hyaluronan is its capacity to bind large amounts of water (1000-times its own
weight). This property makes them excellent lubricators and shock absorbers
[136]. Electrospinning of hyaluronic acid can be challenging because of high vis-
cosity and surface tension of HA in solution even at low concentrations. To over-
come the high viscosity of HA that is obtained even at low concentrations, a low
molecular weight thiolated form of hyaluronic acid that is a 3,3
- dithiobis - (pro-
panoic dihydrazide)-modifi ed derivative (HA-DTPH) has been reported [139].
In a recent study, Ji et al. reported the electrospinning of a blend of HA-DTPH
and poly (ethylene oxide) (PEO), wherein PEO was added to further reduce the
viscosity of HA and hence allow for HA fi ber (diameters ranging from 50 to
300 nm) formation using electrospinning. The HA-DTPH/PEO nanofi brous scaf-
folds were further treated with water to remove PEO from the scaffolds to
achieve pure HA-DTPH scaffolds. Disulfi de linkages were introduced during
electrospinning of HA-DTPH/PEO solution. The electrospun nanofi bers of HA-
DTPH/PEO had poor mechanical properties and they were water soluble. Ji et al.
further cross-linked the scaffold with poly (ethylene glycol)-diacrylate (PEGDA)
as cross-linking agent. Cross-linking improved the mechanical strength of the
scaffold [139] .
Um et al. fabricated HA nanofi bers using a new set up called electro-
blowing, wherein the HA solution was heated to reduce its surface tension and
viscosity and electrospun using air blowing. The air blowing enhanced the rate
of solvent evaporation and HA nanofi bers in the range of 49-74 nm were obtained
[140]. To overcome the problems associated with the high viscosity of HA,
blends of HA and gelatin solution in DMF as the solvent have also been reported.
This study demonstrated that blending of HA with gelatin and use of DMF as
a solven reduced the viscosity of HA, thereby making it easy to electrospin
[141]. The ability to electrospun HA via blending with other polymer or electro-
blowing has improved the possibility of synthesizing HA nanofi bers, and as a
consequence, its potential for being used as a scaffold in tissue engineering
applications.
′
13.4.1.2.2 ALGINATE. Alginate is a linear polysaccharide obtained from
marine brown algae or seaweeds. It is composed of (1-4) linked
β
- D - mannuronic
acid (M units) and
-L-guluronic acid (G units) monomers along the polymer
backbone [142]. The alginate molecule is a block copolymer with repeated M and
G blocks or with regions of MG blocks and is naturally available as a sodium or
α
Search WWH ::
Custom Search