Asymmetric copolymer vesicles to serve as a hemoglobin vector for ischemia therapy†
Self-aggregated vesicles have been considered to be promising candidates for hemoglobin-based oxygen carriers. Here, amphiphilic hetero-triblock copolymers are designed and synthesized with the capacity to self-assemble into polymer vesicles (polymersomes). Conceivably, vesicles are formed with asymmetric membranes, which achieve enhanced encapsulation efficiency of hemoglobin (Hb) beyond the diblock counterpart. Furthermore, hemoglobin-loaded vesicles (HbV) are fabricated with high Hb content and submicron particle sizes. The gas-binding capability, oxygen affinity and methemoglobin (metHb) level of the HbV dispersions are all comparable to the natural erythrocytes. In vitro HbV stability studies further reveal that the encapsulation of Hb within vesicles can greatly avoid the existence of free Hb and shows no interference with cells, especially for blood components. To evaluate the efficacy on ischemia reperfusion, HbV suspended in a plasma expander is transfused as a resuscitation fluid into an acute anemia rat model. Results demonstrate that the combined infusion of the plasma expander with HbV effectively ameliorates the lethal shock symptom and reduces short-term mortality. Concurrently, rats transfused with HbV are void of the acute tubular necrosis caused by the filtration of dissociated Hb dimers from glomeruli. We envision that the oxygen carriers derived from polymer self-assembly technology will become an alternative strategy for future development of blood substitutes.