Biomedical Engineering Reference
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modified with different useful molecules for promoting regeneration
in the injured CNS [12].
1.2 Structure and Properties of Hyaluronic Acid
Hydrogel
Hydrogels are crosslinked polymer networks with a high water
content and elasticity. They can provide a highly swollen three-
dimensional (3D) environment similar to that of native tissue. This
property enables encapsulation of cells and mediation of cellular
activities under physiological conditions, and thus promotes cell
migration, proliferation and specific differentiation [13-15]. The
properties of hydrogels make them ideal candidates for various
constructive tissue engineering applications. They can serve as
scaffolds for structural integrity repair, cells and drug delivery. Their
soft, porous and elastic physical characteristics are especially suitable
for neural tissue, therefore, hydrogels provide a unique tool in neural
injury repair, especially for brain and spinal cord regeneration [14].
1.2.1 Hyaluronic Acid is enriched in Extracellular Matrix
and Neural Stem Cell Niche
It is already known that the ECM actively participates in the development
and maturation of the nervous system and has a wide range of
regulatory functions in neural tissue, as mentioned by Zimmermann and
Dours-Zimmermann [7] and Franco and Müller [16]. The HA is an
essential component in the ECM, which has been reported by Rauch
[17]. It is a very large linear polymer built of repeating disaccharide units
consisting of glucuronic acid and
N
-acetylglucosamine, and is 2-25 µm
in length [18]. It acts as a scaffold for ECM and plays important roles in
a variety of biological processes, including the regulation of NSC during
neural development [17]. This is proved in the data from Lindwall and
co-workers [2], which have shown that HA is abundant in the ECM of
the developing rodent brain, and meanwhile, in the adult brain, it remains
at a high level in the subventricular zone (SVZ) and rostral migratory
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