Dextran is a complex branched glucan (polysaccharide derived from the condensation of glucose), originally derived from wine. IUPAC defines dextrans as "Branched poly-α-d-glucosides of microbial origin having glycosidic bonds predominantly C-1 → C-6". Dextran chains are of varying lengths (from 3 to 2000 kilodaltons). The polymer main chain consists of α-1,6 glycosidic linkages between glucose monomers, with branches from α-1,3 linkages. This characteristic branching distinguishes a dextran from a dextrin, which is a straight chain glucose polymer tethered by α-1,4 or α-1,6 linkages. Occurrence
Dextran was discovered by Louis Pasteur as a microbial product in wine, but mass production was only possible after the development by Allene Jeanes of a process using bacteria. Dental plaque is rich in dextrans. Dextran is a complicating contaminant in the refining of sugar because it elevates the viscosity of sucrose solutions and fouls plumbing.Dextran is now produced from sucrose by certain lactic acid bacteria of the family lactobacillus. Species include Leuconostoc mesenteroides and Streptococcus mutans. The structure of dextran produced depends not only on the family and species of the bacterium but on the strain. They are separated by fractional precipitation from protein-free extracts using ethanol. Some bacteria coproduce fructans, which can complicate isolation of the dextrans. Uses
Dextran 70 is on the WHO Model List of Essential Medicines, the most important medications needed in a health system.Medicinally it is used as an antithrombotic (antiplatelet), to reduce blood viscosity, and as a volume expander in hypovolaemia. Microsurgery
These agents are used commonly by microsurgeons to decrease vascular thrombosis.
and in certain intravenous fluids to solubilize other factors, such as iron (in a solution known as Iron Dextran). Intravenous solutions with dextran function both as volume expanders and means of parenteral nutrition. Such a solution provides an osmotically neutral fluid that once in the body is digested by cells into glucose and free water. It is occasionally used to replace lost blood in emergency situations, when replacement blood is not available, but must be used with caution as it does not provide necessary electrolytes and can cause hyponatremia or other electrolyte disturbances. Dextran also increases blood sugar levels. Dextran can be used in an ATPS for PEGylation

Laboratory uses
Dextran is used in the osmotic stress technique for applying osmotic pressure to biological molecules. It is also used in some size-exclusion chromatography matrices; an example is Sephadex. Dextran has also been used in bead form to aid in bioreactor applications. Dextran has been used as an immobilization agent in biosensors. Dextran preferentially binds to early endosomes; fluorescent-labelled dextran can be used to visualize these endosomes under a microscope. Dextran can be used as a stabilizing coating to protect metal nanoparticles from oxidation and improve biocompatibility. Dextran coupled with a fluorescent molecule such as fluorescein isothiocyanate can be used to create concentration gradients of diffusible molecules for imaging and allow subsequent characterization of gradient slope.