Dextran, polymer degradation

Other important examples are blood and blood products, which are collected and processed in sterile containers, and plasma substitutes, for example dextrans and degraded gelatin. Dextrans, glucose polymers consisting essentially of (1 - 6) a-links, are produced as a result of the biochemical activities of certain bacteria of the genus Leuconostoc, e.g. L. mesenteroides (see Chapter 25). 

K. Kauffman, C. Do, S. Sharma, M. Gallovic, E. Bachelder, K. Ainslie, Synthesis and characterization of acetalated dextran polymer and microparticles with ethanol as a degradation product, Appl. Mater. Interface 4 (2012) 4149-4155. 

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

The main product of anaerobic degradation of sugars by these organisms is lactic acid. Other products of bacterial carbohydrate metabolism include extracellular dextrans (see p. 40)—insoluble polymers of glucose that help bacteria to protect themselves from their environment. Bacteria and dextrans are components of dental plaque, which forms on inadequately cleaned teeth. When Ca salts and other minerals are deposited in plaque as well, tartar is formed. 

Beside chemical modification and degradation of the polymer backbone, NMR spectroscopy is a capable method for structure determination of dextran [29-32], Moreover, from the experiences of the authors in the field of structure characterisation of polysaccharides and their derivatives, NMR spectroscopy is one of the most important methods for obtaining detailed... 

One argument for the selection of dextran as a drug carrier has often been its susceptibility to degradation. However chemical modification of the polymer may impair the biodegradability. Therefore we have studied the biodegradation of dextran and a number of dextran derivatives by dextranase. For this study model derivatives were prepared using the activation procedures discussed before. 

The dextran derivatives were incubated with dextranase (from Sigma Chem Comp., Grade I product) in a citrate buffer pH=6 at 37°C. The degradation of the polymer was monitored by means of gel permeation chromatography on an analytical Sephadex G-25 column. For comparison degradation of unmodified dextran was carried out as well. In order to differentiate hydrolytic from dextranase-induced processes the degradation was also investigated in absence of enzymes. 

These degradation studies of dextran derivatives, mutually differing in the nature and the degree of modification, clearly demonstrate that the biodegradability of dextran is significantly reduced upon chemical modification of the polymer backbone. This phenomenon should be beared in mind when using dextran as a carrier molecule for the preparation of macromolecular drug derivatives. 

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