The electrophoretic mobility of liposomes containing a negatively charged derivative of phosphatidylethanolamine with a large headgroup composed of the hydrophilic polymer polyethylene glycol (PEG-PE) was determined by Doppler electrophoretic light scattering. The results show that this method is improved by the use of measurements at multiple angles to eliminate artifacts and that very small mobilities can be measured. The electrophoretic mobility of liposomes with 5 to 10 mol% PEG-PE is approximately -0.5 mu ms-1/Vcm-1 regardless of PEG-PE content compared with approximately -2 mu ms-1/Vcm-1 for similar liposomes but containing 7.5% phosphatidylglycerol (PG) instead of PEG-PE. Measurements of surface potential by distribution of an anionic fluorescent probe show that the PEG-PE imparts a negative charge identical to that by PG, consistent with the expectation of similar locations of the ionized phosphate responsible for the charge. The reduced mobility imparted by the surface bound PEG is attributed to a mechanism similar to that described for colloidal steric stabilization: hydrodynamic drag moves the hydrodynamic plane of shear, or the hydrodynamic radius, away from the charge-bearing plane, that of the phosphate moities. An extended length of approximately 50 A for the 2,000 molecular weight PEG is estimated from the reduction in electrophoretic mobility.

There is growing concern in the medical community that silicones, ubiquitous in health care, may exhibit antigenic, immunogenic, and/or adjuvant activity. Sera from women with silicone breast prostheses were assayed by ELISA for humoral immunoreactivity to a variety of common interstitial and cellular components. In decreasing order of frequency, significant IgG avidities were found against silicone surfaces treated with fibronectin-laminin, phospholipids, no treatment, and fibrinogen when compared with sera obtained from healthy, age-matched, nonimplanted women and a population of nonimplanted women with previously diagnosed autoimmune diseases. Moreover, the sera from approximately 15% of the positive responders were found to react to matrix proteins independent of the siloxane polymer. The data show human antibody production to native macromolecules with antibody avidity being related to molecular conformation. Silicone may function as an adjuvant by inducing changes in the conformation of native molecules. 0 1993 John Wiley & Sons, Inc.

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