Design and Synthesis of Photoreactive Polymers for Biomedical Applications - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 257

11.2.2.2 Heparin
Heparin, a highly sulfated glycosaminoglycan, is widely used as an
injectable anticoagulant. It has the highest negative charge density of any
known biological molecule and has been used to form an inner antico-
agulant surface on various experimental and medical devices such as test
tubes and renal dialysis machines when coupled with azidoaniline [34-36].
The derivatized heparin was cast onto a fi lm from aqueous solution. After
drying, the fi lm was photoirradiated in the presence or absence of a photo-
mask. The subsequent micropatterning was confi rmed by staining with a
cationic dye. Mouse fi broblast STO and NIH3T3 cells were cultured on the
heparin-immobilized fi lm in the presence of bFGF; the growth of cells was
enhanced only on the heparin-immobilized regions. This result indicated
that micropattern-immobilized heparin activated bFGF for promoting cell
growth. In addition, the growth of cells was affected by the surface den-
sity of the immobilized heparin. This was regulated by differently sized
gaps between 2- m m-wide stripes of the substrate. Although a high-density
region with short gaps of immobilized heparin suppressed cell growth in
the absence of bFGF, it was enhanced in the presence of bFGF. The depen-
dence of cell growth on the density of immobilized heparin was visual-
ized using this gradient of micropattern immobilization.
11.2.2.3 Chitosan
Chitosan, a deacetylated form of chitin derived from crustacean exoskele-
tons, is the most abundant biomass on earth, after cellulose. Many studies
have revealed its unique biological properties, including wound healing,
stimulation of the secretion of fi broblast growth factor, and effects on the
restoration of bone tissues. It also displays antibacterial, hemostatic, fun-
gistatic, antitumor, and anticholesteremic activities. Because chitosan is
very similar to human tissues when combined with glucosamine, it has
been used widely for drug and gene delivery and tissue engineering.
Furthermore, the nontoxic nature and antibacterial activity of chitosan
make this compound an effective wound-healing agent. It has also been
examined for its pharmacological properties including use as an antico-
agulant, artifi cial skin, and medical material because of its cholesterol-
lowering effect and antitumor properties. Naturally occurring chitosan is
insoluble in water. We have demonstrated the applicability of photocur-
able chitosan derivatives for medical use [37, 38]. We utilized chitosan with
a degree of deacetylation of about 88% from crab shells and prepared low
molecular weight chitosan (LMW-CS) as follows. Chitosan was dissolved
in acetic acid solution with strong agitation. NaNO 2 dissolved in distilled
water was added dropwise to the chitosan solution in an ice bath. After
stirring for 2 h, the chitosan solution was neutralized with NH 4 OH. It is
known that nitrous acid decomposition of chitosan results in deamination