Biomedical Engineering Reference
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three different endothermal peaks: the first one related to temperature of thermal de-
naturation (T
d
) of collagen and the other two were connected with a complex phenom-
enon of collagen modified by HA compared to unmodified collagen is significantly
shifted to the region of thermal modification, finally leading to the destruction of ma-
terials. However, the maximum of the peak for collagen modified by HA compared to
unmodified is significantly shifted to the region of higher temperatures (from 69.5 to
85°C).
It is known that intra- and inter-molecular hydrogen bonds as well as hydrogen
bound water are responsible for the stability of the triple helix conformation of col-
lagen macromolecules. The mechanism of the EDC/NHS reactions with collagen/CS
was presented previously in Figure 8 (Pieper et al., 1999).
Figure 8.
Scheme of cross-linking reactions of collagen by EDC and NHS.
These findings suggest that similar reactions may occur between collagen and HA,
because the chemical structure of HA is similar to other GAGs except that HA is un-
sulfated disaccharide. Hence, the most important reactions occurring in the collagen-
HA system with the mixture of EDC and NHS can be schematically presented as in
Figure 9.
O
O
O
O
+
+
HA
C
O
N
H
2
N
HA
C
H
H
N
O
O
coll
(NHS)
coll
Figure 9.
Scheme of covalent attachment of HA to collagen using EDC and NHS.
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