Abstract
This review presents and critically evaluates recent advances in non-conventional gelation method of native alginate. A special focus is given to the following three methods: cryotropic gelation, non-solvent induced phase separation and carbon dioxide induced gelation. A few other gelation approaches are also briefly reviewed. Results are discussed in the context of subsequent freeze and supercritical drying. The methods are selected so as to provide the readers with a range of novel tools and tactics of pore engineering for alginate and other anionic polysaccharides.
Highlights
IntroductionAlginates is is aa family family of of linear linear copolymers copolymers with with homopolymeric homopolymeric blocks blocks of of (1,4)-linked (1,4)-linked Alginates β-D D-mannuronate -mannuronate (M) L-guluronate M andG residuals are β(M) and and its its C-5C-5epimer epimerα-αL -guluronate(G) (G)residues. residues.TheThe
Systematic studies on cryogelation of polymers such as polyvinyl alcohol (PVA) and crosslinked polyacrylamide began in the 1970s
The results clearly indicated that thermally reversible gelation of sodium alginate occurred at 15–16 ◦ C (1.5 wt %, Mw = 291 kDa, M content 39 ± 4%); the resulting gels were very weak
Summary
Alginates is is aa family family of of linear linear copolymers copolymers with with homopolymeric homopolymeric blocks blocks of of (1,4)-linked (1,4)-linked. It is well known that monovalent salts of alginates undergo are linked together in different sequences. There are two conventional ways to gel alginates [4]: by lowering pH below the pKa values (3.4 and 3.6 for M and G units) and by introducing cations, i.e., through ionotropic gelation. In the internal setting method, the gelation is mediated by a change in pH, which, in its turn, releases crosslinking cations from insolubility of a chelated form. The focus of the review is on non-conventional gelation methods for native alginate. They are merely presented by a few examples in the literature, but, in our eyes, offer flexible and auspicious approaches for the engineering of porous alginate-based materials. The alginate characteristics such as molecular weight and the G/M composition are given (in the form identical to the original publication)
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