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. The antithrombotic effect of dextran is mediated through its binding of erythrocytes, platelets, and vascular endothelium, increasing their electronegativity and thus reducing erythrocyte aggregation and platelet adhesiveness. Dextrans also reduce factor VIII-Ag Von Willebrand factor, thereby decreasing platelet function. Clots formed after administration of dextrans are more easily lysed due to an altered thrombus structure (more evenly distributed platelets with coarser fibrin). By inhibiting α-2 antiplasmin, dextran serves as a plasminogen activator, so possesses thrombolytic features. Outside of these features, larger dextrans, which do not pass out of the vessels, are potent osmotic agents, thus have been used urgently to treat hypovolemia . The hemodilution caused by volume expansion with dextran use improves blood flow, thus further improving patency of microanastomoses and reducing thrombosis. Still, no difference has been detected in antithrombotic effectiveness in comparison of intra-arterial and intravenous administration of dextran. Dextrans are