Biomedical Engineering Reference
In-Depth Information
TABLE 1.5
List of Naturally Occurring Polymers, Their Sources, and Applications [85]
Polymers
Source
Application
Collagen
Tendons and ligament
Multiapplications, including bone
tissue engineering
Collagen-Glycosaminoglycan (GAG)
(alginate) copolymers
Artifi cial skin grafts for skin
replacement
Albumin
In blood
Transporting protein used as coating
to form a thromboresistant surface
Hyaluronic acid
In the ECM of all higher animals
An important starting material for
preparation of new biocompatible
and biodegradable polymers that
have applications in drug delivery,
tissue engineering, and
viscosupplementation
Fibrinogen-Fibrin
Purifi ed from plasma in blood
Multiapplications, including bone
tissue engineering
Chitosan
Shells of shrimps and crabs
Multiapplications, including bone
tissue engineering
proteins. Natural polymers must be modifi ed and sterilized before clinical use. All methods of
stabilization and sterilization can moderately or severely alter the rate of
in vivo
degradation and
change the mechanical and physical properties of the native polymers. Each method has certain
advantages and disadvantages, and thus should be selectively utilized for scaffolds of specifi cally
sited bone tissue engineering [86].
1.3.4.2 Chitosan
The use of chitosan for bone tissue engineering has been widely investigated [84,87]. This is in
part due to the apparent osteoconductive properties of chitosan. Mesenchymal stem cells cultured
in the presence of chitosan have demonstrated an increased differentiation to osteoblasts compared
with cells cultured in the absence of chitosan [88]. It is also speculated that chitosan may enhance
osteoconduction
in vivo
by entrapping growth factors at the wound site [89].
1.3.5 S
YNTHETIC
P
OLYMERS
Although naturally occurring polymers possess the above-mentioned advantages, their poor
mechanical properties and variable physical properties with different sources of protein matrices
have hampered their progress in broad applications in tissue engineering. Concerns have also
been expressed regarding immunogenic problems associated with the introduction of foreign
collagen [37].
Following the developmental efforts regarding the use of naturally occurring polymers as scaf-
folds, much attention has been paid to synthetic polymers. Synthetic polymers have high potential in
tissue engineering not only because of their excellent processing characteristics, which can ensure
their off-the-shelf availability, but also because of their advantage of being biocompatible and bio-
degradable [37,90]. Synthetic polymers have predictable and reproducible mechanical and physical
properties (e.g., tensile strength, elastic modulus, and degradation rate) and can be manufactured
with great precision. Although they are unfamiliar to cells and many have some shortcomings,
such as eliciting persistent infl ammatory reactions, being eroded, not being compliant or able to
