Biomedical Engineering Reference
In-Depth Information
chemical and biological characteristics of HA. Particular attention
is given to its useful chemical methods that are applicable in tissue
engineering asa scaffold andpharmaceuticals asa carrier.
9.2 Characteristics of Hyaluronic Acid
in Biomedical Engineering
HA, also called hyaluronate or hyaluronan depending on its polyan-
ion states, is a unique, non-sulfated glycosaminoglycan found in
the extracellular matrix, ocular vitreous, and joint fluid in all ani-
mals and a naturally derived polymer composed of disaccharide
repeat units of glucuronic acid and
N
-acetylglucosamine, linked by
1-3 bonds. It is obtained by either extraction from chicken roosts
or bacterial fermentation. The fermentation of HA is a unique and
highly controlled process. While most of the glycosaminoglycans
are synthesized in a cell's Golgi network, it is expressed at the
plasma membrane and immediately extruded out of a cell and into
the extracellular matrix during fermenting process. The molecu-
lar weight of native HA normally ranges over several million Dal-
tons depending on its fermenting methods. HA showed important
and specific biological roles in maintenance of stem cell's pluripo-
tency and differentiation, homeostasis, acceleration of wound heal-
ing, and anticancer, vascular disease, and antiarthritis therapy. Due
to its unique biological roles, it has been employed as a poly-
meric network for both hydrogel and solid scaffolds for its appli-
cations in various tissue regenerations and pharmaceuticals, even
though its biological mechanisms have not been completely eluci-
datedyet.ThreefunctionalgroupsinHA—carboxylicacid,hydroxyl,
and acetamide groups—have been employed as reaction sites for
chemicalmodifications(Fig.9.1).FabricationofHA-basedhydrogels
has been obtained mainly through the chemistry of those functional
groups.
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Biological characteristics of HA have been extensively studied,
such as its bindings to specific receptors, cluster determinant 44
(CD44), intracellular adhesion molecule 1 (ICAM-1), and the recep-
tor for hyaluronate-mediated motility (RHAMM) expressed by most
cells, including those implicated in the pathology of fibroblasts,
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