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In-Depth Information
Fig. 11.4 (a) SEM images of the nanocomposites prepared in different weight ratios of the
montmorillonite (Mt) and urea (Ur); (b) scheme of the proposed path for urea intercalation in
extrusion process. Reprinted (adapted) with permission from Pereira et al. (
2012
), copyright 2014
American Chemical Society
et al.
2009
), pharmaceutical industry (Kondaveeti et al.
2013
), biomedical applica-
tions (Kaihara et al.
2008
; Wang et al.
2013
), tissue engineering and regeneration
(Zhang et al.
2011
), dressings (Sikareepaisan et al.
2011
), barrier materials to
regulate biological adhesions
(Roy et al.
2010
), and biosensors
(Khimji
et al.
2013
), among many others.
Beyond the physical and chemical character, hydrogels can be classified as
natural or synthetic. Natural hydrogels are composed of polymers from natural
origin, with or without chemical modification (hyaluronic acid, alginate, starch,
chitosan). Synthetic hydrogels are formed by polymerization of synthetic mono-
mers, such as acrylamide, methacrylic acid, etc. Hydrogels can also be obtained by
the combination of natural and synthetic polymers, such as polysaccharides, which
in many cases can improve the properties of the final material (Enas
2013
).
Hydrogels can be classified as homopolymers, copolymers, and interpenetrating
polymer chains, depending on the preparation method and ionic charge. Homopol-
ymer hydrogels are formed by a single type of hydrophilic monomer, which can
present cross-linking depending on the monomer nature and polymerization tech-
nique (Takashi et al.
2007
). Copolymer hydrogels are composed of two or more
different kinds of monomers having at least one hydrophilic component, arranged
in a random configuration (alternating or block), along the polymer chain network
(Yang et al.
2002
). Interpenetrated chain hydrogels or IPN (interpenetrating
