Dextran at a Glance: Structure, Function & Biocompatibility

What is Dextran?

 Dextran is a complex, branched polysaccharide composed primarily of D-glucose units linked by α-1,6 glycosidic bonds, with occasional α-1,3 branches. It is produced via the fermentation of sucrose-containing media by bacteria such as Leuconostoc mesenteroides B512F and Streptococcus mutans.

Dextran's molecular weight ranges from a few thousand to several million Daltons which influences its physical and chemical properties.

 Dextran is highly soluble in water, forming viscous solutions, and is known for its ability to retain moisture and stabilize proteins. These properties make it a versatile compound with numerous applications across various fields, including medicine, biotechnology, and industry.

Dextran Characteristics

Dextran fractions are primarily characterised by their average molecular weights and molecular weight distribution. These fractions range from Dextran 1 (1,000 Da) to Dextran 2000 (2,000,000 Da). The designation (e.g., Dextran 10) refers to the weight-average molecular weight divided by 1,000. Dextran fractions behave as flexible, extended polymers and exist in solution as expandable coils.

Dextran's molecular weight distribution is typically determined using size-exclusion chromatography, providing insight into product consistency and behaviour in solution.

Beneficial Properties of Dextran

Dextran's versatility is attributed to a range of favourable properties:

• Neutral and water-soluble

• Easily filtered

• Biocompatible

• Biodegradable

• Stable (3–5 years in dry form)

• Forms clear, stable solutions in water and many solvents

These characteristics make dextran ideal for use in diverse fields, particularly in pharmaceutical and medical formulations.

Dextran Structure

Dextran is an α-1,6-glycosidic linked D-glucan, with side chains α-1,3 linked to the backbone. The degree of branching in native dextran is generally around 5%, but this decreases as molecular weight decreases. Most branches are only 1–2 glucose units long.

Here is an illustration of a fragment of the dextran structure:

Physical Properties

Dextran fractions have a wide range of molecular sizes and display predictable physical behaviours. In solution, they exhibit stable viscosity and favourable osmotic properties, forming expandable coils that are suitable for various biological applications.

Molecular size

The designation 5, 10, etc. represents the weight-average molecular weight divided by 1,000 Daltons. Thus Dextran 10 corresponds to a weight-average molecular weight of 10,000 Daltons.

The molecular dimensions of some dextran fractions are shown below.

Solubility

Dextran is highly soluble in water and various electrolyte solutions, with minimal pH dependency. Concentrated solutions (>50% w/v) can be prepared. It is also soluble in some organic solvents like DMSO, DMF, NMP, pyridine, ethylene glycol, and glycerol, but insoluble in monohydric alcohols and many ketones.

Note: Low MW dextran fractions (5 and 10) may form turbid solutions over time. Boiling the solution after preparation can delay this effect.

Filtration

Dextran solutions are easily filterable. However, for concentrated solutions, filtration may require larger filters and higher pressure. Raising the temperature can improve filtration efficiency.

Stability

Dextran fractions are stable for over five years when stored in airtight containers at room temperature. They are hygroscopic and can absorb moisture if not properly sealed.

Dextran solutions are stable when sterilised via autoclaving and can be stored for extended periods at consistent temperatures. While pH 6–7 is ideal, stability is maintained between pH 4 and 10. Irradiation should be avoided, as it may degrade dextran.

Safety and Biocompatibility

Dextran has been used in human products for decades across IV, IM, oral, and topical applications. It holds a well-established safety profile and is classified as GRAS (Generally Recognised As Safe) by the US FDA.

Most safety studies focus on Dextran 40 and Dextran 70. Clinical use and long-standing biocompatibility make it a preferred choice in medicine. Dextran also demonstrates excellent tolerance in oral use and is included in products like Spasfon and Opalmon.

Biodegradability

Dextran is a naturally derived, biodegradable polysaccharide. In the body, smaller dextran molecules are eliminated renally, while larger molecules are broken down by dextranase in the liver or reticuloendothelial system into water and carbon dioxide. This dual elimination pathway is especially beneficial for patients with renal insufficiency.

Studies have shown that dextran accumulates primarily in the liver, where dextranase activity is highest. It is eventually excreted either through the kidneys or via respiration.