Microcapsules of alginate-chitosan - I - A quantitative study of
the interaction between alginate and chitosan
Biomaterials, 19 (20):
1815 -- 1825 (October 1998)Abstract
The binding of chitosan to alginate beads was studied quantitatively
by using radioactive labelled fractions of chitosan. The alginate-chitosan
capsules were made either by dropping a solution of sodium alginate
into a solution containing chitosan or by incubating calcium alginate
beads in a solution of chitosan. The first procedure yielded a binding
of 0.015 mu g chitosan per mm(2) of capsule surface, while the latter
procedure yielded over 2 mu g mm(-2). The maximum obtained weight
ratio of chitosan to alginate in a microcapsule after 24 h was 0.40.
The binding of chitosan was markedly increased by reducing the number
average molecular weight of chitosan below 20000 Da and by increasing
the porosity of the alginate gel. The porosity was increased by producing
homogeneous gels, and by adding calcium chloride to the chitosan
solution during the membrane forming stage. The effect of calcium
ions on the porosity of the gel was studied by experiments involving
release of blue dextran from calcium alginate beads. The binding
of chitosan was also found to increase with decreasing fraction of
N-acetylations, F-A on chitosan in the range of F-A = 0.3 to F-A
= 0, and with increasing pH in the range from pH 4 to 6. Capsules
with a diameter of 500 mu m had a higher weight ratio of chitosan
to alginate after 24 h of binding than-the capsules with the larger
diameter of 1500 mu m. (C) 1998 Published by Elsevier Science Ltd.
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