Stability of liposome encapsulated hemoglobin dispersions

The demand for artificial blood substitutes in cases of elective surgeries, trauma, and civilian mass catastrophes increases every day [1-4]. However, few studies have been done to characterize the mechanical stability of blood substitutes, especially liposome encapsulated hemoglobin (LEHb) dispersions. In this work, the stability of LEHb dispersions was investigated by fitting Jung et al.'s liposome size distribution model [5] to experimentally measured LEHb size distributions [6] (produced via extrusion) using asymmetric flow field-flow fractionation coupled with multi-angle static light scattering. The effective bending constant (K_B) and radius of curvature (R₀) of each liposome dispersion were regressed from the size distribution fits. The model was found to be in agreement with the size distributions of LEHbs extruded through 400, 200 and 100 nm pore diameter membranes, but not in agreement with LEHbs extruded through 80 and 50 nm pore diameter membranes. Although the magnitude of K_B fluctuated, we deduced a general trend for K _B to decrease with decreasing pore diameter, and increasing initial Hb concentration. LEHbs extruded through 400 nm pore diameter membranes were stabilized by the spontaneous curvature effect, while those extruded through 80 and 50 nm pore diameter membranes were mostly stabilized by thermal undulations, regardless of the initial Hb concentration. For LEHb dispersions extruded through 200 and 100 nm pore diameter membranes, there was a transition of stabilization mechanism from spontaneous curvature to thermal undulations with increasing initial Hb concentration. Taken together, these results suggest that moderate Hb encapsulation might actually impart better mechanical stability to LEHb dispersions extruded through 200 and 100 nm pore diameter membranes.