Abstract

Digital Microfluidics with Liquid Marbles: Fundamentals and Applications

Nam Trung Nguyen, Professor & Director, Queensland Micro- and Nanotechnology Centre, Griffith University

We report the use of liquid marbles, liquid droplets coated with hydrophobic microparticles, floating on another liquid surface as a digital microfluidics platform especially suitable for culturing three-dimensional cell spheroids. We first reports fundamental insights on the floating mechanisms of liquid marbles by analysingthe shape of the liquid marble and the angles at the three-phase contact line. We next developed actuation mechanisms for floating liquid marbles.The first mechanism is magnetic actuation of floating liquid marbles filled with magnetic particles. We varied the magnetic flux density, flux density gradient, concentration of magnetic particles and speed of the marble to elucidate the relationship between the acting forces. We subsequently determined the suitable operating conditions for the actuation and derived the scaling laws for the actuation parameters. The second mechanism is based on Marangoni solutocapillary effect using liquid marble containing a volatile substance such as ethanol. We derived the scaling laws relating the dynamic parameters of the motion to the physical properties of the system such as the effective surface tension of the marble, the viscosity and the density of the supporting liquid, the coefficient of diffusion of the ethanol vapour, the geometrical parameters of the marble, the speed, the trajectory and the lifetime of the autonomous motion. Finally, we show the proof of concept for the use of floating liquid marbles for culturing three-dimensional cell spheroids. Floating liquid marbles allow the cells to freely associate and interact to produce OEC spheroids with uniform shapes and sizes. Co-culture of different cell types into a three-dimensional spheroid was also demonstrated.