Biomedical Engineering Reference
In-Depth Information
controlled release and bioadhesive properties. Chitosan of ers reactive
functional groups, gel-forming properties, high adsorption capacity, bio-
degradability and can be prepared as tablets, capsules, gels, membrane
i lms, micro- & nanoparticles, sponges, etc [131]. h e lack of technology
transfer from academia to industry is an area that requires special focus in
order to expedite chitosan innovations through the value chain and into
the market.
5.7.4 AntimicrobialStudies
Numerous papers have been published reviewing the utility of chitosan
and its derivatives in the biomedical sector. h ese polymers have been
applied in a range of products. Chitosan itself possesses inherent antimi-
crobial properties where this property is dependent on the DDA, molecu-
lar weight, concentration, the species tested, length of the test period, etc.
A higher DDA results in a greater number of potentially cationic sites
available on the polymer backbone making chitosan more active against
bacteria at a lower pH.
h e mechanism of chitosans antimicrobial activity is yet to be proven.
Common theories postulate that the positively charged chitosan binds to
the negatively charged components present in the cell membrane of the
bacteria (phospholipids, proteins, amino acids)
via
an electrostatic attrac-
tion. Chitosan essentially af ects cell membrane permeability leading to the
loss of essential intracellular components of the bacterial cell (e.g. glucose
and lactate dehydrogenase) which in turn leads to cell death. In addition,
it was found that the cytoplasmic membrane of the bacterial cell detached
from the cell wall when exposed to chitosan. As a result of chitosan's metal
chelating ability, the polymer is able to bind to metal ions from the bacte-
rial intracellular l uid. Certain of these metals are essential for fungi and
bacterial growth. h is in turn leads to disruption of proper cell function
resulting in cell death [132, 133]. Chitosan also interacts with DNA in the
cell where it is thought that the polymer may inhibit synthesis of messen-
ger RNA and proteins [133].
Selected chitosan derivatives have been tabulated (Table 5.2) along with
organisms which they are active against.
Micro- and nanoparticles of chitosan have also been proven to have
antibacterial activity. To further improve this activity, certain metal ions
with known antibacterial action (e.g. Ag
+
, Zn
2+
, Mg
2+
, Cu
2+
) have been used
in conjunction with polymers. Nanoparticles loaded with these metal ions
showed higher activity against
E. coli
,
Salmonella choleraesuis
,
Salmonella
typhimurium
and
S. aureus
which suggests that the antibacterial activity is
