Biomedical Engineering Reference
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However, and importantly, the film stability can be tuned depending on the nature of
the film components and on the film's posttreatment. Regarding CHI/HA films, we found
that the stability depends on the molecular weight of the chitosan: whereas films built with
high-molecular-weight chitosan are stable in physiological medium (Richert et al. 2004c),
films built with chitosan oligosaccharides (
M
W
= 5000 g/mol) are exhibiting a change in
structure when introduced into the culture medium (Picart et al. 2005b). We evidenced that
this change in structure was mostly due to the presence of divalent ions (Ca
2+
, Mg
2+
in the
culture medium) and not to the change in pH. In fact, divalent ions are known to complex
chitosan (Rhazi et al. 2002) and also alginate (Amsden and Turner 1999). Interestingly, the
films can be degraded by enzymes present in body fluids such as hyaluronidase (Figure 8.8)
or lysozyme, a biodegradation that depends on the extent of film cross-linking (the more
cross-linked the films are, the more resistant they are).
14
(a)
12
10
8
6
4
2
0
0
200
400
600
800
1000 1200 1400
Time (min)
(b)
(c)
(d)
(e)
(f )
(g)
FIGURE 8.8
Degradation of a (CHI/HA)
24
-CHI
FITC
film after contact with hyaluronidase (type IV, 500U/mL) (same polyelec-
trolytes as in Figure 8.4): (a) followed by fluorimetry versus time for a native film (open symbols) and for a cross-
linked film (closed symbols). (b, c, e, f) observed by CLSM after 4 h of contact for native (b, e) and cross-linked
films (c, f) films. Cross-linking was achieved at 200 mM EDC concentration. Top views (56 × 56 μm
2
) of the films
(b, c) (scale bar, 10 μm) and vertical sections are shown (e, f). Control images of film before contact with enzyme
are also given (d and g). Vertical section scales are respectively 18.5 μm for image e and 19.5 μm for images f
and g (film thickness is about 6 μm, white line). (Reproduced with permission from Picart et al.,
Adv. Funct.
Mater.
, 15, 1771-1780, 2005b. Copyright Wiley-VCH Verlag GmbH & Co. KGaA 2005.)
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