Elaboration of poly(ethyleneimine) coated poly(,-lactic acid) particles. Effect of ionic strength on the surface properties and DNA binding capabilities

Poly(,-lactic acid) (PLA)-based particles, obtained by the emulsification–diffusion process, were surface-modified by electrostatic adsorption of poly(ethylenimine) (PEI). The amount of immobilized PEI and the conformation of the polycation at the interface were dependent on the ionic strength of the media. In the absence of salt, or at low ionic strength, the adsorbed amounts of PEI, the surface charge and the critical concentration for coagulation (CCC) of the modified particles were lower than when the adsorption was achieved at elevated ionic strength. Moreover, at low salt concentration, isotherms were of Langmuir type, suggesting the formation of monolayers. The differences in PEI surface conformation had consequences on the DNA binding capacity of the particles, on the plasmid DNA conformation at the interface and on the DNA release in various media. When PEI was adsorbed in a 50 mM phosphate buffer, the amount of bound plasmid and the strength of binding were higher than when PEI was adsorbed in water. From these differences in physico-chemical properties, one can expect differences in transfection or immunization performances of the vectors.