Project funded by Marie Curie Actions IEF. Project 235673 "Study of magnetic responsive biopolymer based materials"

Biopolymer: Sodium alginate

The polymer matrix used is a polysaccharide extracted from marine brown algae, the Alginic acid (Alginate). It is a linear copolymer containing β-1,4-D-mannuronate (M) and α-1,4-L-guluronate (G) units in various proportions and sequences depending on the season, age and the part of the plant used for extraction (Figure 1).


Figure 1. Diagram of sodium alginate

With one carboxylate group in each M or G unit, alginate is a highly negatively charged polyelectrolyte at neutral or basic pH.

Alginate belongs to a group of biopolymers used in food and pharmaceutical industries and has also recognized potential in the removal of toxic heavy metals from industrial wastes by bisorption.

Gel formation can be achieved by specific and strong interactions between G units and divalents ions such as Ca2+ which induce inter-chain association and formation of gel junctions.

Preparation of alginate gel

Alginate sodium aqueous solution can form a gel by elelctrostatic interactions between divalent ions such as Ca2+ and carboxylate groups (COO-) of polymer chains. There are several methods for gelation of alginate solution by adding calcium ions. We used the internal gelling method using EGTA-Ca as Ca source: EGTA-Ca is added and then calcium ions are released by slow acidification of the solution with addition of Glucono delta-Lactone (GDL). This way, the release of calcium is controlled and the obtained gel is homogeneous.


The ferrofluid used consists of maghemite (γ-Fe2O3) nanoparticles dispersed in aqueous media. They are synthsized by a co-prectipitation method.

At pH 7 (pH of alginate solutions) maghemite nanoparticles are not stable in aqueous solution. In order to obtain stable ferrofluids, citrate ions are adsorbed on the surface of the particles, by dispersion of sodium citrate in the solution (Figure 2).


Figure 2. Maghemite nanoparticles functionalized by citrated ions

Alginate and ferrofluid solutions

The protocol of preparation of alginate and ferrofluid solutions was optimized and homogeneous solutions with different concentrations of alginate and volume fractions of ferrofluid were preparerd.
A volume of ferrofluid was added to an alginate solution and the mixture was stirred by means of a mechanical stirrer. The speed of stirring, the time and the temperature were carefully controlled.


To prepare the ferrogel the internal gelling method was also used and the ferrofluid was added before starting the gelation process (release of calcium ions).