Adsorption kinetics of DPPG liposome layers: A quantitative analysis of surface roughness

Roughness of a positively chargedpoly(allylamine hydrochloride) (PAH) polyelectrolyte surface was shown to strongly influence the adsorption of 1.2-dipalmitoyl-sn-3-Glycero-[phosphorrac-(1-glycerol)] (DPPG) liposomes on it. Adsorption kinetics curves of DPPG liposomes onto alow roughness PAH layer reveal an adsorbed amount of 5 mg/m2, pointing to liposome rupture while, high roughness surface leads to adsorbed amounts of 51 mg/m2, signifying adsorpion of intact liposomes. Adsorption kinetic parameters calculated from adsorption kinetics curves, allow us conclude that the adsorption process is due to electrostatic interactions and also depends on processes such as diffusion and re-organization of lipids on surface. Analysis of the roughness kinetics enabled to calculate agrowth exponent of 0.19±0.07 and a roughness exponent around 0.84 revealing that DPPG-liposomes adsorbed onto rough surfaces follow the Villain self-affine model. By relating self-affine surfaces with hydrophobicity, the liposomes integrity was explained by the reduction of the number of water molecules on the PAH surface, contributing for counterions anchorage near PAH ionic groups, reducing the liposome/PAH layer electrostatic forces and, consequently, avoiding the liposome rupture. Roughness of a positively chargedpoly(allylamine hydrochloride) (PAH) polyelectrolyte surface was shown to strongly influence the adsorption of 1.2-dipalmitoyl-sn-3-Glycero-[phosphorrac-(1-glycerol)] (DPPG) liposomes on it. Adsorption kinetics curves of DPPG liposomes onto alow roughness PAH layer reveal an adsorbed amount of 5 mg/m2, pointing to liposome rupture while, high roughness surface leads to adsorbed amounts of 51 mg/m2, signifying adsorpion of intact liposomes. Adsorption kinetic parameters calculated from adsorption kinetics curves, allow us conclude that the adsorption process is due to electrostatic interactions and also depends on processes such as diffusion and re-organization of lipids on surface. Analysis of the roughness kinetics enabled to calculate agrowth exponent of 0.19±0.07 and a roughness exponent around 0.84 revealing that DPPG-liposomes adsorbed onto rough surfaces follow the Villain self-affine model. By relating self-affine surfaces with hydrophobicity, the liposomes integrity was explained by the reduction of the number of water molecules on the PAH surface, contributing for counterions anchorage near PAH ionic groups, reducing the liposome/PAH layer electrostatic forces and, consequently, avoiding the liposome rupture.