Microalgae Cell Separation and Concentration in a Microfluidic Channel Under Dielectrophoresis (DEP) Effect
Microalgae biomass is an essential part of the global ecosystem. Not only is it responsible for 50% of the global oxygen but also proved to be useful in the development of organic polymers, antioxidants, pharmaceuticals, and feedstocks for aquatic animals. It is considered as an important source of lipids in the production of efficient renewable bio-fuels. Still, lipid production from microalgae has not been economically viable which require effective and low-cost cell separation downstream processes where microalgae cells are concentrated and differentiated based on their lipid content.
Incidentally, dielectrophoresis (DEP) has evolved as an interesting technology allowing the vital, flawless, and label-free cell sorting inside the miniaturized systems (in µm range). DEP-based separation avoids the cell-cell-interaction and exploits the polarizability of the cells (dissolved inside a liquid medium) in inhomogeneous electrical fields. By applying an alternating voltage (through metal electrodes) across a microfluidic channel, the microalgae cells are separated. However, the DEP force strongly depends on the range of frequency (f) and voltage amplitude (V) during the operation, the morphology of the cells, and electrical properties of the cells and the medium. These parameters also decide if the DEP force is positive or negative i.e. cells move in the direction of the electric field or deviates from the field. Hence, a FEM simulation is essential in the study of the physical, chemical, and electrical properties of both microalgae cells and the microfluidic system with respect to each other.
Chlamydomonas reinhardtii is a prominent microalgae species (found in both sea and salty water) in the production of biopharmaceuticals and bio-fuels due to its high lipid content. In this paper, C. reinhardtii is the test cell to investigate and simulate its separation and concentration based on different lipid contents by the method of dielectrophoresis. The first objective of this paper is to determine the correct AC-DEP voltage amplitude, frequency, and microfluidic flow rate using the Electric Currents, Laminar Flow, and Particle Tracing for Fluid Flow interfaces in COMSOL Multiphysics® 5.4. The second objective is to find the temperature distribution in the entire microfluidic set up through additional use of Heat transfer in fluids interface. The velocity of the fluid, temperature distribution, electrical field gradient, real-time cell flow and separation in the microfluidic channel is obtained through various COMSOL Multiphysics® studies like Stationary, Frequency-Stationary, frequency Domain, and Time Dependent respectively.
After design and simulation of various configuration/geometry of electrodes, 56 pairs of gold electrodes with 20 µm wide skew-symmetric structure were successfully simulated as top and bottom electrodes that impart AC-DEP voltage on a 5000 (L) x 300 (W) x 50 (H) µm3 microchannel. Subsequently, 2.80 µL/min of flow velocity for the aqueous solution (with microalgae cells) is achieved in effective isolation of the cells at 12 Vpp and 1.894 MHz. The microchannel is created as a physical gap between two PDMS sheets. The entire setup is covered with Silica glass. The maximum temperature around the top bottom electrode microfluidic setup is found as 314 K (at 293 K ambient Temperature).
