Biomedical Engineering Reference
In-Depth Information
into the polymer, the presence and identity of the metal can be coni rmed
by the changes observed in the X-ray pattern. Disadvantages associated
with this technique are the high cost and samples need to be in the solid
state [24].
h is is by no means an exhaustive list of the techniques available to
characterize all properties of chitosan and its derivatives. Other common
techniques include: light scattering (dynamic and static), zeta potential
(measures charge which directly af ects antimicrobial activity of the poly-
mer), titrations (conductimetric, colloidal, isothermal titration calorim-
etry, turbidimetric, acid-base, potentiometric), High Performance Liquid
Chromatography, gas chromatography (can only be performed at er deg-
radation and derivitization of sample) - MALDI-TOF mass spectrometry,
gel-permeation chromatography, membrane osmometry, etc [20, 23, 25, 26].
h ese analysis techniques provide a clear understanding of the composition
and nature of the compound being studied allowing for the prediction of
various properties and applications of the samples analyzed.
5.3 ChitosanCo-polymers
A co-polymer is dei ned as a polymer chain consisting of more than one
type of polymer. h is combination leads to the synthesis of polymers with
a specii c set of desired properties. h ere are dif erent types of co-polymers
depending on the monomers present and the synthetic method used. A
random co-polymer is dei ned as a polymer with a relatively random dis-
tribution of the constituent monomers. Alternating co-polymers have
their polymers alternate regularly along the polymer chain. A block co-
polymer has long sequences of each polymer whereas a grat co-polymer
is a polymer that has a backbone consisting of one polymer and branches
of the other polymer [27].
In the case of chitosan, co-polymerization of ers the introduction of new
advantageous properties without the loss of the original properties of the poly-
mer as only a selected number of amino/hydroxyl groups are functionalized
(Table 5.1) [88]. h e common synthetic methods available for co-polymer-
ization include free radical polymerization used for grat co-polymers where
free radicals are generated on the polymer backbone; these radicals react
with vinyl or acrylic monomers. Chemical methods used to initiate this co-
polymerization include the use of ceric ions, Fenton's reagent, microwaves,
ammonium persulfate, gamma and UV radiation. Disadvantages associated
with free radical polymerization include the generation of homopolymers
and thereby undermining the stability of the polymer backbone [28, 29].
