Biomedical Engineering Reference
In-Depth Information
ture. The excellent lubrication property of mammalian joints with minimal
coefficient of friction is mainly attributed to the presence of HA in the syn-
ovial fluid within the joints. HA is also found in the human eye (aqueous
humor) and the viscoelastic property of HA helps the proper functioning
of the eye [166]. The viscoleastic property of HA has been widely exploited
for ocular surgery and for alleviating osteoarthritis (OA) through its intra-
articular administration [167]. In a recent study, Langer and coworkers have
utilized this property of HA to create vocal cord replacements [168]. HA also
serves as a free radical scavenger and as an antioxidant [169]. Their ability as
a free radical scavenger has been hypothesized to enhance their role in treat-
ing symptoms of OA. HA is hydrophilic and its nonadhesive property make
it the primary component of Seprafilm, a postoperative adhesive used in sur-
gical applications. In addition to preventing protein adsorption, unmodified
HA also restricts cells adhesion because of their smooth surface and anionic
(hydrophilic) nature [170]. In order to increase cell adhesion, Ramamurthy
et al. have applied UV treatment to induce topographical changes to HA,
which subsequently enhances the attachment of neonatal rat smooth muscle
cells onto the HA materials [170].
HA is prevalent during wound healing and plays a significant role during
morphogenesis, embryonic development, and angiogenesis [171]. HA sup-
posedly promotes the early inflammation (a crucial criterion for the initial
wound healing) which then deteriorates slowly with time to allow matrix sta-
bilization [171]. Not surprisingly, HA has been identified to have a pivotal role
in tissue repair, and this property has been widely exploited for wound heal-
ing applications [171-173]. The potential of HA to be a unique biomaterial
is limited due to the fact that native hyaluronan can be rapidly metabolized
in vivo by free radicals and Hyaluronidase. Various methods such as cova-
lent crosslinking and chemical modifications, which exploit the carboxylic
and hydroxylic groups located on the HA backbone, have been adopted to in-
crease the longevity and mechanical properties of HA while still maintaining
its superior biological properties [166, 174-176]. For example, benzyl ester
of Hyaluronan (commercially known as HYAFF 11 by Fidia Advanced Bio-
polymers) has been extensively explored as a tissue-engineering scaffold. The
fact that nasoseptal de-differentiated chondrocytes seeded onto HYAFF re-
a favorable effect on chondrocyte phenotype [177].
HA is also known to interact with chondrocytes via the surface receptor
CD44, and this receptor-mediated signaling enables the chondrocytes to re-
tain their phenotype [178]. The presence of HA in the culture medium has
been used to enhance the proliferation of chondrocytes while keeping their
phenotype intact [179]. HA-based materials are therefore extensively used in
cartilage tissue engineering [180-183]. Hyalograft C is a tissue-engineered
cartilage graft where the chondrocytes are seeded within a Hyaff 11 scaffold
for cartilage regeneration [61]. Hyaff, has also been used as a scaffold for skin
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