Chemical, physical and biological properties of alginates and their biomedical implications

doi:10.1016/j.foodhyd.2009.10.007

Food Hydrocolloids

Volume 25, Issue 2, March 2011, Pages 251-256

https://doi.org/10.1016/j.foodhyd.2009.10.007 Get rights and content

Abstract

Alginates are binary, linear copolymers of (1 → 4) linked ß-d-mannuronic acid (M) and α-l-guluronic acid (G) residues of widely different composition and sequence. The monomers do not occur randomly but rather in a block-like fashion, where the G-blocks are responsible for the specific ion binding and hence also the gelling properties of alginates. Alginates have for decades been used as medical devices in various products, and research has been conducted on alginate gel beads as entrapment devices for the transplantation of e.g. insulin producing cells. Until recently, no pharmaceutical activity of the alginate molecule itself had been claimed. The fact that alginates high in mannuronate residues are able to induce cytokine production and may stimulate Toll-like receptors has changed this picture. Furthermore, it has quite recently also been shown that oligoguluronates are able to transiently modify mucin network structures to such an extent that it opens up possibilities for the treatment of pathological respiratory diseases as well as a general increased drug bioavailability due to increased mucosal uptake. This review presents a summary of the physicochemical properties of alginates and their entry into biotechnology and biomedicine.

Graphical abstract

Introduction

Alginates occur both as structural components in marine brown algae (Phaeophyceae) as well as capsular polysaccharides in some bacteria (Draget, Moe, Skjåk-Bræk, & Smidsrød, 2006). Commercial alginates are at present still exclusively extracted from algal sources although production by microbial fermentation is technically feasible. Industrial applications of alginates, based on their gelling, viscosifying and stabilizing properties, account for the quantitatively most important uses of alginates. In comparison, emerging and knowledge demanding speciality applications within biotechnology and medicine are based on biological effects of the alginate molecule, of alginate molecular building blocks, or alginate's unique, gentle and almost temperature independent sol/gel transition in the presence of multivalent cations (e.g. Ca²⁺), which makes alginate highly suitable as an immobilization matrix for biocatalysts such as living cells. Advanced research within these areas is promoting a further detailed understanding of structure–function relationships of the alginate molecule.

Section snippets

Physicochemical properties

Alginates constitute a family of linear binary copolymers, consisting of (1 → 4) linked β-d-mannuronic acid (M) and α-l-guluronic acid (G) residues (see Fig. 1a and b). Chemical composition and sequence may vary widely between algae species and even between different parts of the algae and the time of year when it is harvested. Alginate with a very high content of guluronic acid, which is of importance for the mechanical properties of the alginate gel, can be prepared from special algal tissues

Alginate gels and their properties

A direct mixing of alginate and multivalent cations rarely produces homogeneous gels due to the very rapid and irreversible binding of such ions. A controlled introduction of cross-linking ions is possible by the two fundamental methods for preparing an alginate gel: the diffusion method and the internal setting method (Smidsrød & Draget, 1996). The diffusion setting technique, which is the only method to be described in this paper, is characterized by allowing a cross-linking ion (e.g. Ca²⁺)

Traditional biomedical alginate applications

Alginates have for many years been used as devices in various human health applications, such as excipients in drug delivery (DDS), wound dressings, as dental impression materials and in some formulations preventing gastric reflux. One advantage of using alginates in oral tablet formulation is their property of preserving a solid-like attribute (gel) also at gastric (acid) conditions due to the formation of an alginic acid gel. This property allows for the protection of delicate compounds

Potential biomedical and pharmaceutical alginate applications

Over the last couple of decades, new knowledge about the impact of chemical composition and sequential arrangement of alginate on biological systems points towards more advanced biomedical devices as well as pharmaceutical properties of alginate in its own right.

Conclusions

Although alginates have been exploited for several decades as devices in a multitude of pharmaceutical and biomedical applications, there has this far not been any pharmaceutical claims on the alginate molecule itself. We may now be in the midst of an inflection point where this may change in the near future.

Acknowledgements

The authors would like to thank Prof. Em. Olav Smidsrød for valuable discussions, and the Norwegian Research Council and Helse Midt-Norge for financial support.

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Chemical, physical and biological properties of alginates and their biomedical implications

Abstract

Graphical abstract

Introduction

Section snippets

Physicochemical properties

Alginate gels and their properties

Traditional biomedical alginate applications

Potential biomedical and pharmaceutical alginate applications

Conclusions

Acknowledgements

Carbohydrate Polymers

FEBS Letters

Trends in Biotechnology

Carbohydrate Polymers

Trends in Biotechnology

The Lancet

Carbohydrate Polymers

Biomaterials

The tumor necrosis factor-inducing potency of lipopolysaccharide and uronic acid polymers is increased when they are covalently linked to particles

Clinical Diagnostic Laboratory Immunology

A comparison of the efficacy of the alginate preparation, Gaviscon Advance, with placebo treatment of gastro-oesophageal reflux disease

Current Medical Research and Opinion

Alginates

Modification of gelling kinetics and elastic properties by nano structuring of alginate gels exploiting the properties of polyguluronate

A family of modular type mannuronan C-5-epimerase genes controls alginate structure in Azotobacter vinelandii

Molecular Microbiology

Mechanisms of host immune response to alginate microcapsules

Application of alginate gels in biotechnology and biomedicine

Carbohydrates in Europe

Studies on the sequence of uronic acid residues in alginic acid

Acta Chemica Scandinavica