Interaction between liposomes and neutral polymers; effect of stabilizing on drug release.

Interactions of neutral polymers (PVA and PVP) with liposomal membranes wer e investigated, and based on the adsorption isotherms we have found out tha t PVA adsorbs in higher rate than PVP due to the stronger H-bridge bonds. T he polymer-membrane interactions were detected by several measuring techniq ues and among them the dynamic laser light scattering convinced us that in case of stabilizing liposomes with PVA the average diameter of liposomes is larger, thus the layer adsorbed is thicker than when they are interacted w ith PVP. Titration microcalorimetric measurements were only made on the sys tems containing PVA proving the existence of exothermic interactions at the beginning of the adsorption process. XRD studies on films made of liposome s and swollen by exposure to water vapour proved the structure-modifying ef fect of the polymer present in the membrane. PVA allows smaller expansion t o the membrane bilayer than PVP via swelling with water vapour. From remote loading experiments we have concluded that our test compound, acridine ora nge (marked as NA in the text) can be entrapped in liposomes most effective ly in media buffered with Tris-HCl. The optimal NA/PL ratio was found to be 0.1. Drug release experiments also confirmed the stabilizing effect of the polymer.