Biomedical Engineering Reference
In-Depth Information
bacteria is only 5 Ǻ [74]. For the same purpose Chen
et al.
, reported the
persistence length range from 8 to 12 Ǻ [66].
h is proves that the chitosan
with higher MW (shorter persistence length) can easily pass through the cell
wall of Gram-positive species, but it is blocked outside of the cell wall of the
Gram-negative species. Hence, the ef ect of MW of chitosan is signii cant on
the growth inhibition ability of Gram-positive species.
h e ef ect of MW and antibacterial activity is said to be dependent on
the concentration range used [75]. Dif erent MW chitosans (55 to 155 kDa)
with the same degree of deacetylation (80 % ± 0.29), were investigated for
antimicrobial activities against
E. coli
. All of the chitosan samples with
MW from 55-155 kDa had antimicrobial activities at the concentrations
higher than 200 ppm. h e antibacterial activity of chitosan had relation-
ship to the MW at the concentration range from 50-100 ppm. At a lower
concentration (<0.2 mg/mL), the polycationic chitosan does probably bind
to the negatively charged bacterial surface to cause agglutination, while
at higher concentrations, the larger number of positive charges may have
imparted a net positive charge to the bacterial surfaces to keep them in
suspension [58, 76].
6.4.2.2
Degree of Deacetylation (DDA)
h e antimicrobial activity of chitosan is directly proportional to the DDA
of chitosan [38, 60, 65, 77]. Higher DDA of chitosan brings more positive
charges and the positive charges will interact with the negatively charged
bacteria. So, a higher DDA of chitosan causes higher growth inhibition
activity. However, higher DDA also results in longer persistence length that
hinders chitosan penetrating through the cell wall
due to the more positive
charges and increased intermolecular electric repulsion [78].
In vitro
and
in silico
studies supplement the observations related to MW
and DDA with respect to the mechanism of surface interference [79]. h e
in vitro
studies of chitosan- lipopolysaccharide (LPS) interactions using
ligand-enzyme solid phase assay were carried out for high MW chitosans
(80 kD) of dif erent degree of acetylation, low MW chitosan (15 kD), acyl-
ated oligochitosan (5.5 kD) and chitooligosaccharides (biose, triose and
tetraose). h e LPS-binding activity of chitosans (80 kD) increased with
increase in degree of deacetylation. Activity of N-monoacylated chitooli-
gosaccharides was in the order- oligochitosan >tetra> tri> disaccharides.
In
silico
studies of the three-dimensional structures of complexes of LPS and
chitosans was performed by molecular modeling with MOE sot ware pack-
age (Molecular Operating Environment, http://www.chemcomp.com/) and
its docking module (FlexX). h e number of bonds stabilising the complexes
