Biomedical Engineering Reference
In-Depth Information
15.3.3 A
LBUMIN
Albumins are water-soluble proteins that also exhibit a degree of solubility in concentrated salt
solutions. They are heat-sensitive and coagulate. Egg white contains albumin and the most com-
monly known albumin is serum albumin present in human blood. They are the most abundant blood
plasma protein, which act as transport proteins for several steroid hormones and fatty acids. Being
a naturally occurring protein in the human body, albumin has also been considered for biomedical
applications. Surfaces of polymers have been modifi ed by grafting albumin on their surfaces in
order to enhance blood compatibility. Functionalized albumin has been covalently linked to poly-
mers such as polyethylene, polycarbonates, and polypropylene, etc. The grafted albumin molecules
are retained on the surface, even on exposure to blood for extended periods; they function as good
oxygenators.
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Laser welding technologies have also been used to join, repair, and create hemostasis
on surfaces using human-serum-albumin based biodegradable biomaterials.
15.3.4 C
OLLAGEN
Collagen is another abundant protein, which is the main component of connective tissues in mam-
mals. It has a long fi brous structure and is found as “collagen fi brils,” which are tough bundles of
fi brillar proteins. They possess good tensile strength and are a component of cartilage, tendons,
ligaments, bone, and teeth. Collagen is also responsible for the elasticity and strength of the skin
and its degradation leads to wrinkles and facilitate aging. Collagen has an amino acid composition,
and interestingly, almost every third amino acid residue is a glycine unit and is known to contain
large fractions of proline. There are at least 28 types of known collagens [from Wikipedia, the free
encyclopedia]. Collagen Type I is the most abundant in human body, forms a structural component
of bone and teeth, and is present in scar tissue and in tendons. Collagen has been known for its use
as a “glue” since ancient times. More recently it has been widely used in soft tissue augmentation.
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Collagen has been used to develop biologic patches and for purposes of tendon augmentation and
is used in sports medicine,
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namely Zimmer Collagen Repair and TissueMend (TEI Biosciences,
Boston, MA, USA). Collagens on their own or in combination with silicones, glycosaminoglycans,
fi broblasts, growth factors, and other substances are employed in the management of burns and act
as artifi cial skin substitutes. Collagen-GAG scaffolds loaded with basic fi broblast growth factor
have been reported to signifi cantly enhance neovascularization and tissue remodeling in animal
models.
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Soft-tissue fi llers, most commonly injectable collagen or fat, can help fi ll in these lines
and creases, temporarily restoring a smoother, more youthful-looking appearance. When injected
beneath the skin, these fi llers plump up creased and sunken areas of the face. They can also add
fullness to the lips and cheeks. Injectable fi llers may be used alone or in conjunction with a resurfac-
ing procedure, such as a laser treatment, or a recontouring procedure, such as a facelift.
15.3.5 H
YALURONIC
A
CID
Hyaluron or hyaluronic acid (HA) is a non-sulfated glycosaminoglycan that is widely distributed
throughout connective, epithelial and neural tissues. Hyaluronan is a polymer consisting of disac-
charides with d-glucoronic acid and d-
N
-acetylglucosamine, linked via alternating beta-1,4 and
beta-1,3 glycosidic bonds. It is one of the main components of the extracellular matrix, contributes
signifi cantly to cell proliferation and migration, and may also be involved in the progression of
some malignant tumors. Polymers of hyaluronan can range in size from 10
2
to 10
4
kDa
in vivo
.
Hyaluronan is a major component of the synovial fl uid and is found to increase the viscosity of the
fl uid. It is also a main constituent of the articular cartilage, present as a coating on chondrocytes.
The high molecular mass HA, which plays an important role in many biological processes such
as tissue hydration, proteoglycan organization in the extracellular matrix, and tissue repair, has
found application in several clinical treatments and cosmetic use. Degradation of HA is enzyme
