Biology Reference
In-Depth Information
can be incorporated into glycosaminoglycans and glycoproteins (
Pangburn,
Trescony, & Heller, 1982
). The length of the chains also affects the degra-
dation rate (
Huang, Khor, & Lim, 2004; Tomihata & Ikada, 1997; Zhang &
Neau, 2001
). Controlling degradation rate of chitin- and chitosan-based
biopolymers is essential in drug delivery and tissue regeneration applications.
The degradation rate also affects the biocompatibility as fast degradation rate
results in amino sugars accumulation that may lead to inflammatory
response. Chitosan samples with low DD may induce an inflammatory
response, whereas chitosan samples with high DD do not because of the
low degradation rate (
Hirano, Tsuchida, & Nagao, 1989; Kurita, Kaji,
Mori, & Nishiyama, 2000
;
Sashiwa, Saimoto, Shigemata, Ogawa, &
Tokura, 1991
).
The degradation rate of chitosan can be influenced by physical parame-
ters such as porosity, fiber diameter, blending with other polymers, or the
use of cross-linking agents. Chitosan scaffolds with high porosity degrade
faster than scaffolds with smaller pore diameter. Within the same range of
porosity, scaffolds with smaller pore diameter degrade faster (
Cunha-Reis
et al., 2007
).
Adjusting the pH of the solution of a nerve conduit has been reported to
influence degradation properties. In particular, increasing the layer numbers
and overcoming the acidity-caused autoacceleration of poly-
D
,
L
-lactic acid/
chondroitin sulfate/chitosan (PDLLA/CS/CHS) nerve conduit decrease its
biodegradability rate retaining its integrity up to 3 months (
Xu, Yan,
Wan, & Li, 2009
).
The degradation kinetics is inversely related to the crystallinity degree
which can be controlled by acting on the DD and on the distribution of ace-
tyl groups. The absence of acetyl groups or their homogeneous/random dis-
tribution results in low enzymatic degradation rates (
Aiba, 1992; Suh &
Matthew, 2000
). Chitosan nano-/microfiber meshes with a deacetylation
of 78% have a faster biodegradation rate than meshes with a deacetylation
of 93% and collapse over the time, causing occlusion of the tube made from
these meshes (
Wang, Itoh, Matsuda, Ichinose, et al., 2008
). Degradation of
chitosan films with very low (about 0.5%) or high (about 99.2%) acetylation
is minimal over 4-week period, whereas progressive mass loss to greater than
50% has been reported for chitosan film with 30-70% acetylation (
Freier,
Koh, et al., 2005
).
Blending of chitin with other biomaterials like gelatin results in a faster
degradation rate and significant loss of material compared with chitosan
alone (
Huang, Onyeri, et al., 2005
).
