Sedimentation field flow fractionation of fused unilamellar vesicles: comparison with electron microscopy and gel filtration.

Sedimentation field flow fractionation (SF3), a relatively new instrumentation methodology for separating particles according to size, has been used to monitor changes in vesicle size during the formation of fused unilamellar vesicles of dipalmitoylphosphatidylcholine. The fusion of 500-A small unilamellar vesicles to 700-A large unilamellar vesicles (LUVs) and the slower conversion to 950-A LUVs at 4 degrees C was readily monitored by SF3 over the time course of a month. Changes in the physical state of these vesicles as a result of structural reorganizations were characterized by high sensitivity differential scanning calorimetry. The advantages and limitations of SF3 are discussed and correlated with electron microscopy and gel filtration.