Production methods for heparosan, a precursor of heparin and heparan sulfate

► Heparosan chain length and the sugar unit backbone composition determine the biological activity of heparin and heparan sulfate. ► Different methods used to synthesize heparosan are reviewed. ► The use of biocatalysts in vitro is the most promising method to produce defined heparosan polymers. ► P. multocida heparosan synthase PmHS2 appears to be the most adequate biocatalyst. ► Advancements in the field of the synthesis of bioengineered heparin are also reported.