Stable plurilamellar vesicles

Stable plurilamellar vesicles comprising lipid vesicles comprising a plurality of lipid bilayers enclosing aqueous compartments containing at least one entrapped solute, the concentration of such solute in each aqueous compartment being substantially equal to the concentration of solute used to prepare the lipid vesicles, the lipid bilayers dividing each such aqueous compartment being substantially non-compressed, so that the lipid vesicles have a characteristic Long Spacing Signature, a Bragg Peak Signature and a Wide-angle X-ray Signature as determined by X-ray diffraction of the lipid vesicles suspended in an aqueous medium that is isosmotic to the aqueous medium used to prepare the lipid vesicles;

• and in which
• (a) the Long Spacing Signature of such stable plurilamellar vesicles composed of zwitterionic lipid bilayers suspended in an aqueous medium that is isosmotic to the aqueous medium used to prepare the stable plurilamellar vesicles appears substantially as depicted for stable plurilamellar vesicles in FIG. 4, in which the Long Spacing Signature is obtained by plotting the mean repeat spacing as determined by low angle X-ray diffraction which is a measure of the sum of the thicknesses of a bilayer and an interbilayer aqueous space versus temperature which is varied from 0.degree. C. to 40.degree. C.;
• and
• (b) the Bragg Peak Signature of such stable plurilamellar vesicles composed of zwitterionic lipid bilayers suspended in an aqueous medium that is isosmotic to the aqueous medium used to prepare the stable plurilamellar vesicles appears substantially as depicted in FIG. 5b or FIG. 5c, in which the width and asymmetry of the distribution of membrane repeat spacings as obtained by low angle X-ray diffraction at a temperature of 40.degree. C. are determined by the least square fit to the peak positions of the Bragg orders where the peak positions are taken as the centers of parabolas least-square fit to the peak profiles, and where the angle of diffraction, 2.theta., for a given order, n, follows from the Bragg relation:
• n.lambda.=2D sin .theta.
• where .lambda.=X-ray wavelength, and
• D=repeat spacing of the lattice;
• and
• (c) the Wide-angle X-ray Signature of such stable plurilamellar vesicles composed of zwitterionic lipid bilayers and suspended in an aqueous medium that is isosmotic to the aqueous medium used to prepare the stable plurilamellar vesicles appears substantially as depicted for stable plurilamellar vesicles in FIG. 6a or FIG. 6b, in which the Wide-angle Signature as determined at a temperature of 10.degree. C. by X-ray diffraction in the wide angle regime is obtained by plotting the X-ray intensity versus S.sup.-1 (.ANG.)
• .lambda./20 10.ANG.
• where=X-ray wavelength, and
• .theta.= the angle of diffraction.