Vasoconstriction and systemic hypertension are the main side effects associated with transfusion of current commercial polymerized hemoglobins (PolyHbs). It is hypothesized that the presence of free tetrameric hemoglobin (Hb) in the PolyHb solution is the root cause of these side effects. Therefore, increasing the size of PolyHbs and reducing the amount of free Hb in solution should dually reduce the extent of vasoconstriction and systemic hypertension. However, all current commercial PolyHb preparations have a small fraction of free fib in solution. Hence, there is an urgent need to develop novel chemical strategies to synthesize large PolyHb molecules with a higher degree of polymerization without free Hb in solution. In this study. a Hb-based oxygen carrier was synthesized by polymerizing human fib using a dimaleimide poly(ethylene glycol) derivative (1,11-bis(maleimido)triethylene glycol). The resultant PolyHb has a weight-averaged molecular weight of 1.49 +/- 0.62 MDa, O-2 affinity (P-50) of 2.75 +/- 0.55 mm Hg, and Hill coefficient (n) of 0.97 +/-0.07. Light scattering analysis of the PolyHb dispersion confirmed the absence of free Hb monomers, dimers, and tetramers in solution. This work is significant, as it should enable future engineering of nonvasoactive PolyHbs with potential applications in transfusion medicine. (C) 2010 American Institute of Chemical Engineers Biotechnol. Prog., 26: 1481-1485, 2010