Formation and stability of multiple-layered liposomes by layer-by-layer electrostatic deposition of biopolymers

The sequential deposition of biopolymers onto the surface of liposomes; lamellar bilayer vesicles composed of polar lipids; was investigated. Submicron-sized liposomes were prepared from lecithin with a high speed blender and an ultrasonic homogenizer. Positively (chitosan), and negatively (high methoxyl pectin and lambda-carrageenan) charged biopolymers were alternatingly added to liposomes to build up to 6 sequentially-stacked interfacial layers on top of the phospholipid membranes. After formulation, particle size and zeta-potential of liposomes were determined using dynamic light scattering. The primary liposomes had diameters of approximately 80 nm. Particle size increased linearly with each successive deposition up to four layers but increased to several micrometers when a fifth and sixth layer was deposited indicating that aggregation may have occurred. Addition of lambda-carrageenan as an anionic biopolymer led to less aggregation than when high methoxyl pectin was used. Results were attributed to (i) unbound polymers in the aqueous phase forming coacervates that may lead to depletion flocculation and (ii) unoccupied binding sites and uneven charge distributions causing bridging flocculation. Our results show the limitations of the layer-by-layer deposition approach, which is important for food manufacturers wishing to form very thick polymer layers to stabilize dispersions such as emulsions or liposomes. (C) 2012 Elsevier Ltd. All rights reserved.