| As alginate-based products become increasingly accepted, Are Kristiansen, Therese Andersen and Jan Egil Melvik at NovaMatrix speculate upon the likelihood that more and more will find their way onto the market
Alginates were first described by British chemist Stanford in 1881 (1), and are the most abundant polysaccharide in cell walls and intercellular space of brown algae (seaweed and kelp). Alginates are also produced by bacteria such as Azotobacter vinelandii and some Psedumonas species. They are a family of linear molecules composed of (1,4)-linked β-D-mannuronate (M) and α-L-guluronate (G), where the relative content of M and G is source-dependent. Alginates have been used for several decades in the food and pharmaceutical industries as emulsifying, thickening, film-forming and gelling agents, and they are also well-known in the biomedical and biotechnology arena. This article gives a brief review of the technology of cell immobilisation in alginates, and identifies and discusses new strategies and developments in the field. Furthermore, the aspects of standardisation and regulatory acceptance of alginates are discussed.
BASIC ALGINATE CHEMISTRY
The relative amount of M and G and their sequential arrangement along the polymer chain varies widely depending on the source. The monomer residues are distributed along the polymer chain in a block pattern, where homopolymeric blocks of G-residues, homopolymeric blocks of M-residues, and alternating sequences of M and G-units (MG-blocks) co-exist (see Figure 1). The content and distribution of the two monomers largely determines the physicochemical properties of alginates. Commercial alginates derived from seaweed and kelp typically have G-contents in the range of 30-70 per cent, and number-average Gblock lengths (excluding single Gs), NG>1 of 4-20. The latter parameter largely determines the ability of alginates to form strong gels through interaction with multivalent cations. pKa-values of M- and G-units are 3.38 and 3.65 respectively, therefore, alginates are polyanions at physiological conditions. The polymer chain length of commercially available alginates is in the range of 30-500kDa. The molecular weight strongly affects the viscosity of a solution containing alginate. |
