Structure and Applications of Dextran

Dextran is a non-ionic branched polysaccharide, appearing as a white powder. Native dextran is prepared by fermentation of sugar, followed by subsequent harvest and purification. Native Dextran is then modified by hydrolysis and separation into the desired molecular weight. The molecular weight denotation of dextran is the molecular weight in Da divided by 1000. I.e. dextran 40 is dextran 40.000 Da (or 40 kDa). Typical denotations are: 1, 3, 5, 10, 40, 60, 70, 110, 150, 250, 500 and 750.

Structure
Dextran is a polysaccharide, and the main chain is formed by 1,6 glycosidic linkages. The side branches are primarily 1,3 linkages and the degree of branching is approximately 5%. The branches are mostly 1-2 glucose units long. The 1,6 glycosidic linkage is formed between a primary hydroxyl group and a secondary hydroxyl group. The much higher flexibility of the primary hydroxyl group is responsible for the high degree of flexibility of the dextran backbone as compared to e.g. cellulose. The flexibility of dextran is responsible for many of the highly desired properties of dextran.

Applications
Due to is biocompatibility, biodegradability and low toxicity, Dextran has a wide application area within life science and the medical industry. The most famous is the application of dextran is probably its roll as plasma volume expander. Since dextran is also easy to conjugate it is also commonly used for e.g. drug delivery and as a vaccine adjuvant.

Blood Volume Expander
Dextran is used as a plasma volume expander to treat decreased volume of circulating blood plasma, a condition referred to as hypovolemia. The dextran increases the blood volume, blood- and central venous pressure as well as the cardiac and urinary output. Dextran based plasma volume expanders have also been shown to reduce the blood viscosity and improve the peripheral blood flow.

Organ Preservation
Dextran is a common ingredient in preservation solution prior to organ transplantation. Dextran have been shown to reduce the graft failure in both human and animals. Corneas’ and lungs are well known examples of organs that are commonly prepared and/or stored with dextran.

Thrombosis prophylaxis
Dextran has been shown to inhibit clot formation and can thereby be used intravenously as a thrombosis prophylaxis. Thrombosis occurs when a clot forms inside a blood vessel and obstructs the blood flow through the circulation system.

Eye care
Due to its lubrication properties, dextran is commonly used in various eye drops and eye lubricants for ophthalmic applications. The lubricating properties of dextran can be used to treat dry and irritated eyes. It can also be used a s a tear replacement.

Cryopreservation
Cryopreservation is the process where biological materials, such as cells, tissue and organs are preserved at a very low temperature to preserve their viability. The preservation is typically performed at liquid nitrogen temperatures at −196 °C. Cryopreservation is often performed to preserve cells or organs prior transplantation, blood transfusion or in vitro fertilization. Dextran 7 can be used as a cryoprotectant, a substance used to protect the biological material from freezing damage.

Lyophilization
Lyophilization, more commonly known as freeze-drying, is a method for preserving of e.g. small molecules, proteins, and vaccines. The process involves freezing of the product, lowering the pressure, and thereafter placing it under vacuum. This allows the ice to change directly from solid to vapour, commonly referred to as sublimation. Dextran is used during lyophilization as a stabilizer of proteins and enzymes.

Drug delivery
Dextran can be used as a drug carrier to target the administ ration of the drug and to control its release. It can also reduce toxicity and side effects of the drug in the body. Another application area is chelation of metal ions. Dextran will form a stable and soluble compels with the metal ion, preventing the metals from reacting with other molecules.