Critical Influences:Structural Lipid Matrix Influence of cholesterol -Condenses bilayer -Provides stabilizing effect -Proportion ·Fatty acids -Phase behavior .Liquid crystal vs.fluid ·Boundary effects Tendency to oxidize ·Chain reaction ·Head group Critical Influences:Surface Properties ·Naked lipid -Protein adsorption -Opsinization-rate of MPS uptake -Destabilization-drug leakage -Flocculation Surface charge -Sign -Charge density Surface coating -Carbohydrate -Polymer11