Bioactivities of Chitosan and Its Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 130

or near the surface and/or on the protein-based coagulation cascade, whereas these are
harmful for maintaining a well-balanced function even the life during the treatment of
patients. For example, thrombogenicity of artificial organs, such as artificial heart valves
(AHVs), is a serious problem. Many of the deaths in animals given AHVs were caused not
by the malfunction of the artificial organ but by blood clot formation. Hence patients with
mechanical heart values must undergo lifelong anticoagulation therapy. Even so, the inci-
dence of thrombogenic complications and bleeding complications has been 1.5-3% per
year in the USA, and 58% of implanted mechanical heart valves have failed within the
past 12 years in China [112]. Improving the hemocompatibility of this kind of device has
become a very important task for biomedical material scientists [112].
Chitosan exhibits properties that make it a desirable candidate for biocompatible and
blood-compatible biomaterials [113-115]. N -acyl chitosans have already been reported as
blood-compatible materials [84].

3.2.3.1 Platelet Adhesion

Samples were rinsed with PBS and contacted at 37°C during 1 h with freshly prepared
platelet-rich plasma (PRP) of human blood. Samples were rinsed with PBS and then
treated with 2.5% glutaraldehyde for 30 min at room temperature. The samples were
washed with PBS again and subsequently dehydrated by systemic immersion in a series
of ethanol-water solutions (50%, 60%, 70%, 80%, 90%, 95%, and 100% v/v) for 30 min each
and allowed to evaporate at room temperature. Blood platelet adhesion in vitro was
observed through SEM. The platelet-attached surfaces were coated with gold prior to
being observed by SEM.

3.2.3.2 Protein Adsorption

Bovine fibrinogen (BFG, Sigma, F-8630) was obtained as lyophilized powder. The buffer
solution used in the protein adsorption experiments was PBS, pH 7.4. Quantification of
adsorbed protein on the polymer surfaces was performed using 125 I-labeled protein.
125 I-labeled protein was added to unlabeled protein solution in order to obtain a final activity
of about 10 7 cpm/mg. The samples were immersed in 1 mL of buffer solution at 37°C, and
then 1 mL of fibrinogen solution (0.2 mg/mL) was added and mixed. Adsorption tests were
carried out at 37°C during 1 h. After protein adsorption, samples were rinsed three times
with 2 mL of buffer solution. Gamma activities were counted with the samples placed in
radio-immunoassay tubes by a Gamma Counter. Four replicates were used. The counts from
each sample were averaged and the surface concentration was calculated by the equation

⋅

Counts (cpm) C ( µ g/mL )

2 = solution

BFGg/cm ( µ )

⋅

2

A ( cpm/mL ) S samples cm ( )

solution

where the count measures the radioactivity, S samples measures the surface area of the
samples, and C solution and A solution are the concentration and specific activity of the protein
solution, respectively.

3.2.3.3 Blood-Compatible Chitosan Derivatives

O -Butyrylchitosan (OBCS) was prepared as follows [116,117]. Chitosan (2.1 g) was added
to methanesulfonic acid (11 mL) and the mixture was stirred at 0°C for 15 min until a