Authors: A. Jahn, J.E. Reiner, W.N. Vreeland, D.L. DeVoe, L.E. Locascio, M. Gaitan
Affilation: National Institute of Standards and Technology, United States
Pages: 684 - 687
Keywords: liposomes, microfluidics, encapsulation, self-assembly
A new method to tailor the size and size distribution of nanometer scale liposomes in a continuous-flow microfluidic design is presented. Encapsulation of a model drug into the liposomes is analyzed with Fluorescence Fluctuation Spectroscopy (FFS); and results show that this system allows for control of encapsulation efficiency as well as minimization of encapsulant consumption. A stream of lipids dissolved in isopropyl alcohol is hydrodynamically focused and sheathed between two oblique aqueous buffer streams in a microfluidic channel. In contrast to conventional mixing techniques where liposomes are formed in a bulk aqueous solution containing a homogenous concentration of the water-soluble encapsulant, this technique can confine the encapsulant to the immediate vicinity where lipids self-assemble into liposomes and concomitant encapsulation is expected to occur. The precise spatial localization of the encapsulant solely to the region of liposome formation allows for greatly reduced sample consumption without adversely affecting the liposome encapsulation efficiency. Using this technique, the liposome size is tunable over a mean diameter of 50 nm to 150 nm by adjusting the ratio of the alcohol-to-aqueous volumetric flow rate. The simplicity of this liposome formation and drug encapsulation strategy could allow for implementation in point-of-care drug encapsulation, eliminating shelf life limitations of the liposome preparation and reducing encapsulant consumption. The application of FFS for encapsulation efficiency measurements potentially allows integration in future lab-on-a-chip applications for online liposome characterization.