Bioactivities of Chitosan and Its Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 133

proceed for 8 h at room temperature. The reaction mixture was filtered to remove solvent. The
filtrate was dissolved in 100 mL of water and then 2.5 M HCl was added to adjust the pH to
7. After centrifugation and removal of the insoluble precipitate, 150 mL of anhydrous ethanol
was slowly added into the solution and the product was precipitated. The solid was filtered
and rinsed three times with anhydrous ethanol and vacuum dried at room temperature.
A simple and effective method for the coupling of OCMCS to the polyethylene terephtha-
late (PET) surface was developed through surface grafting PAA treated by plasma treatment.
In contrast to the PET surface, platelet adhesion and protein-adsorptive resistance of PET-
OCMCS were greatly improved. The blood compatibility of PET-OCMCS is believed to be
related to its zeta potential, the balance of hydrophilicity/hydrophobicity, and low adsorp-
tion of protein [120,121].
Vascular grafts made of expanded PTFE (ePTFE) are widely used in vascular recon-
structive surgery. Although successful as replacements for large-diameter blood vessels,
they are unsuitable for small-diameter ones because when the internal diameters of the
graft are less than 6 mm, they fail (without exception) due to blood clot formation. To
reduce platelet adhesion onto the ePTFE vascular graft, a novel method for binding the
chitosan-heparin (CS-Hp) complex to the surface of the vascular graft was developed. The
binding of chitosan was achieved by irradiating the azide-modified chitosan that was
coated on the ePTFE surface with ultraviolet light. By forming a complex with this coating
of chitosan, heparin was then bonded to the ePTFE surface. In vitro blood-compatibility
experiments showed that CS-Hp surface-modified ePTFE vascular grafts showed mark-
edly reduced platelet adhesion (Figure 3.9). The outstanding performance of these grafts
was further demonstrated by in vivo experiments, in which grafts were found to be still
unclogged two weeks postimplantation into dog veins ( Figures 3.10 and 3.11) [122].

3.2.4 Conclusions

Although chitosan does possess the necessary properties for biomedical product develop-
ment, for those applications that involve blood contact, chitosan promotes thrombosis and

(a) (b)

211200 20 KV X700 43 μm 211200 20 KV X1 . 00K 30 μm

Figure 3.9
SEM images of vascular grafts after being contacted with blood in vitro : (a) ePTFE (×700) and (b) ePTFE/CS/Hp
(×1000).