Microfluidic assembly of lipid nano-vesicles (liposomes and niosomes): investigation on membrane fluidity and stability by surface modifications

Abstract

Lipid nano-vesicles (liposomes and niosomes) have been extensively used to increase bioavailability of nutraceuticals or pharmaceuticals. In this study, novel microfluidic assembly method was used for the lipid nano-vesicle production, because of its easy control of size distribution and food-grade solvent usage. For building block lipids of liposomes and niosomes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and sorbitan mono-palmitate, Span 40 (SMP) were selected, respectively. Cholesterol was incorporated into the lipid bilayer to control mechanical firmness and membrane permeability. As a result, liposomes with 20%(mol) cholesterol and niosomes with 50%(mol) cholesterol showed monodisperse 100 nm size distribution from dynamic light scattering (DLS) analysis. Meanwhile, zeta potentials of the liposomes were near -5 mV, whereas those of the niosomes were below -30 mV. Therefore, the liposomes were fabricated with various ionic surfactants to enhance their colloidal stability. Accordingly, liposomes incorporated with 20%(mol) palmitic acid (PAL), 4%(mol) dicetyl phosphate (DCP), and 4%(mol) hexadecylamine (HDA) showed the greatest stability in their DLS, transmission electron microscopy (TEM), and zeta potential results. In addition, food-grade biodegradable polymers (chitosan and pectin) were coated onto the lipid nano-vesicles to endow additional physicochemical stability. Anionic pectin was coated onto cationic HDA liposomes, and 0.003%(w/v) pectin coating showed the best colloidal stability with -21.5 mV zeta potential. Meanwhile, cationic chitosan was coated onto anionic niosomes, DCP, and PAL liposomes, and those with 0.020%(w/v), 0.030%(w/v), and 0.080%(w/v) chitosan were shown to overpass the minimum zeta potential criterion (20.0 mV), respectively. Branched chain amino acids (BCAAs) were selected as model food materials for encapsulation efficiency measurement. For BCAA purification, gel permeation chromatography was conducted, and 3.0-5.5 mL fraction volume was collected. Finally, the encapsulation efficiencies of niosomes, DCP, and PAL liposomes were 42.2%, 31.2%, and 26.4%, respectively. On the basis of these results, in-depth researches on in vitro digestion model of BCAA encapsulated lipid nano-vesicles could be conducted in the near future.