On the locomotion of planktonic micro-organisms in a microfluidic environment

Intervenante : Chen-li SUN professeure au Department of Mechanical Engineering, National Taiwan University

Planktonic micro-organisms play an important role in marine ecology, fishery, and the ocean carbon cycle. As the foundation of the oceanic food chain, phytoplankton and zooplankton form a complex food web, and their trophic interaction is vital to the prosperity of other marine life.
In this talk, I will demonstrate how microfluidic devices can be employed to gain a better understanding of marine ecosystem in a single-cell level.
Focusing on studying the locomotion of plankton K. veneficum (CCMP426), we design amicrocavity device to investigate the effects of different microflow conditions: stationary f/2-Si medium, steady flow, and oscillatory flow. After measuring the local flow field, we are able to determine the absolute and relative velocities of individual plankton cells, from which their rheotaxis can be derived. The probability density function, the expected value and the standard deviation are calculated in order to statistically represent the locomotion of the planktonic community. The experimental results show that when the plankton reside in stationary and homogeneous nutrient medium, the swimming velocity and the acceleration are 52.7±43.5 μ m s -1 and 878±820 μ m s -2 , respectively. In addition, K. veneficum is capable of maneuvering in a flow speed up to 150 μ m s -1 . Once the current is too strong, their locomotion is dominated by the flow.
Under the condition of oscillatory flow, K. veneficum exhibits positive rheotaxis. In the strong flow field region, planktonic cells can not directly cross the streamlines. Rather, they tend to cut through streamlines with small angle in order to reach the weak flow field region. The outcome of this study helps us clarify the interaction between the behavior of plankton and the microfluidic environment.
Chen-li Sun is Professor of Mechanical Engineering at National Taiwan University (NTU). She teaches in the areas of thermodynamics, heat transfer, energy engineering, two-phase flow, and thermal management for electronic devices. She is Visiting Professor at l’École normale supérieure de Rennes (Summer 2017) and l’Université Paris-Sud (Winter 2016). Prior to joining NTU, she was on the faculty of National Taiwan University of Science and Technology from 2003 to 2011. Prof. Sun received her B.S. degree from National Central University, Taiwan in 1994, M.S. from Stanford University in 1996, and Ph.D. from the University of California at Berkeley in 2002, all in Mechanical Engineering. In 2002-03, she was a postdoctoral researcher for Prof. Al P. Pisano in the Berkeley Sensor and Actuator Center (BSAC). Prof. Sun is the 2012 recipient of the Ta-You Wu Memorial Award, which recognizes young Taiwanese PIs dedicated to long-term outstanding research work. She is also the 2014 recipient of the Distinguished Young Scholar Award from the Society of Theoretical and Applied Mechanics. Dr. Sun’s research interest focuses on near-interface microscale transport phenomena and phase-change heat transfer in energy systems. Specifically, she is interested in exploring innovative measurement techniques for studying microscale transport in microfluidics.