Journal
CARBOHYDRATE POLYMERS
Volume 77, Issue 4, Pages 725-735Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.carbpol.2009.02.018
Keywords
Mannuronan; Alginate epimerases; Hydrogels; Periodate oxidation; Acid hydrolysis; NMR and small-strain oscillatory measurement
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Funding
- Research Council of Norway [145945/120]
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The study of alginate hydrogels is of increasing interest,given their potential applications as biomaterials for tissue engineering and for encapsulating drugs and living cells. In this study, we present a new strategy for tailoring alginates on the basis of homopolymeric mannuronan, where the chain stiffness and the content of G-residues could be varied independently. Partial periodate oxidation (0-8%) followed by borohydride reduction, introducing flexible linkages through C2-C3 cleavage and ring opening, was combined with in vitro epimerization, introducing either alternating (MG) sequences (in the case of enzyme AlgE4) or G-blocks (in the case of enzyme AlgE6). Both enzymes are recombinantly expressed from Azotobacter vinelandii. Two strategies were followed: (a) oxidation/reduction followed by epimerization(b) epimerization to 90% G followed by oxidation/reduction. The resulting alginates were characterised by NMR spectroscopy and size-exclusion chromatography (SEC) with multi angular laser light scattering (MALLS) and viscosity detectors. Gels were prepared Using the 'internal setting' method with either 10 mM or 20 mM Ca(2+) present, and studied by small-strain oscillatory measurements. It was found that periodate oxidation, in the range P(0) = 0.02-0.06, had a pronounced influence on the gelling properties. The decrease in dynamic storage modulus (G') could mainly be attributed to increased local flexibility and not only a decrease in G-block lengths as a consequence of oxidation. The new alginate gels are easily degradable in a mild acidic environment and the degradation is easier to control than gels made of unoxidized alginate. (C) 2009 Elsevier Ltd. All rights reserved.
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