Figure 1: Development of Hemoglobin-based oxygen carriers as artificial blood. They are divided into four categories as: a) Recombinant hemoglobin: hemoglobin is genetically modified by Escherichia coli (size~5 nm) b) Polymerized hemoglobin: hemoglobin is cross-linked by a polymer (size~20 nm) c) ConjugatedI'm hemoglobin: hemoglobin is modified by a biocompatible polymer (size~40 nm) d) Liposomeencapsulated hemoglobin: hemoglobin enclosed into a lipid membrane (size~200 nm). Hemoglobin-based oxygen carriers are smaller than red blood cells; therefore, it will better supply oxygen in the site of injury.