Structural Regime Identification in Ionotropic Alginate Gels: Influence of the Cation Nature and Alginate Structure

Abstract

The morphologies of several ionotropic alginate hydrogels and aerogels were investigated by SAXS according to the nature of the divalent metal cation (Mn(2+), Co(2+), Zn(2+), Cu(2+)) and the guluronic fraction of the alginate. All alginate hydrogel and aerogel samples show isotropic small-angle X-ray scattering. Gelation results from cooperative associations of cations and chain segments and yields different nanostructures, that is, nanofibrillar morphology or multiple junction morphology, according to cation type and eventually mannuronic/guluronic ratio. Therefore, Mn and Cu gels present the same morphology whatever the guluronic ratio, whereas Co and Zn gels yield different nanostructures. In the size range investigated by SAXS (~10-200 Å), the structure of aerogels obtained by CO(2) supercritical drying is found to be inherited from the morphology of the parent hydrogel whatever the initial structural regime.

Hybrid polyion complex micelles from poly(vinylphosphonic acid)-based double hydrophilic block copolymers and divalent transition metal ions

“…6c). The peculiar complexing behavior of Cu 2þ ions has previously been observed in complexation with (macro)molecules (for example alginates) [61]. The very high stability of copper complexes is general and is due to the JahneTeller effect and the tetragonal distortion of the cation polyhedron.…”

Synthesis of “click” alginate hydrogel capsules and comparison of their stability, water swelling, and diffusion properties with that of Ca+2 crosslinked alginate capsules

“…The divalent Cu ions have strong affinity to both guluronic and mannuronic residues and have shown to induce alginate gelation with fibrillar morphology. 39,40 To remove Cu…”

A redox strategy to tailor the release properties of Fe(III)-alginate aerogels for oral drug delivery

“…5 and in S4 in the Supporting Information) a peak should be seen at h ≈ 1/R c in the case of structures containing randomly oriented rods (where R c is the mean gyration radius of the rods). This peak is absent in the Fe(III)-alginate aerogels indicating the so-called multiple junction structure (Agulhon, Robitzer, David, & Quignard, 2012). The formation of the multiple junction structure takes place when the cross-linking and gelation of alginate is carried out under acidic conditions.…”