2. Alginate
Alginate is a well known polysaccharide (Fig. 1A) widely
used due to its gelling properties in aqueous solutions related
to the interactions between the carboxylic acid moieties and
bivalent counter ions, such as calcium, lead, and copper; it is
also possible to obtain an alginic acid gel by lowering the
environmental pH value. Alginate can be extracted from
marine brown algae or it can be produced by bacteria. It exhibits a backbone of (1→4) linked β-D-mannuronic acid
(M) and α-L-guluronic acid (G) residues of widely varying
composition and sequence. This polymer can be regarded as a
true block copolymer composed of homopolymeric regions of
M and G, called M- and G-blocks, respectively, interspersed
with regions of alternating structure. The physico-chemical