Liposome-encapsulated hemoglobin using film hydration processing to form artificial red blood cells

Process parameters using a Microfluidizer M110 to produce liposome-encapsulated hemoglobin (LEH) were further studied to examine their effect on hemoglobin (Hb) encapsulation efficiency (yield), steady shear viscosity, mechanical stability, and oxygen delivery. Liposome formulation loading ratios of up to 300 mumol of lipid per ml of Hb solution were evaluated; a maximum yield was obtained at 300 mumol/ml. Liposomes containing encapsulated Hb concentrations as high as 15.5 g/100 ml were prepared. LEH particle size distribution, determined from negatively stained whole mount preparations using transmission electron microscopy, resulted in average vesicle sizes for optimal batches of about 155 nm. Steady shear viscosity of LEH (up to 40% by volume) in an isotonic-isooncotic solution of PBS containing either albumin or dextran were evaluated for shear rates to 2000 s-1. Values obtained were generally higher than those of whole blood at all shear rates tested. Little leakage of Hb from liposomes stored in isotonic PBS was observed as a function of storage time and shear rate. Administration of LEH supported life in rats whose hematocrit had been reduced via isovolemic exchange transfusion to levels well below 5%, which was incompatible with survival when exchange transfusion was performed with the isotonic-isooncotic PBS solution.