Degree Name

Master of Philosophy


School of Mechanical, Materials and Mechatronic Engineering


Over the past decade, developments in the field of microfluidics have emerged several useful techniques for microparticle manipulation and cellular assays (e.g. mechanical, acoustic, hydrodynamic, magnetophoresis, and dielectrophoresis etc.). Among them, one is to use fluid inertia in “lab-on-a-chip” devices. Inertia-based methods are very popular due to the superior advantages, e.g., simplicity, passiveness, preciseness, continuity, and high-throughput. Two common channel structures: spiral and serpentine microchannels have been investigated intensively, and widely were reported. Recently, there are some reports to use obstacle structures patterned along one or two sides of the straight microchannel to focus and separate microparticles. However, after the microchannel and obstacles are designed and fabricated, its focusing pattern and performance on specific particles are settled. For new sets of microparticles, it has to design and fabricate new devices. In this work, I present a novel inertial platform for continuous, high-controllability, label-free particle and cell focusing and separation in the straight channel with symmetric semicircle obstacle arrays.

The main objective of this research is to carry out a high-controllability inertial focusing and separation in the identical straight channel containing semicircle obstacles array. Three basic focusing patterns were observed: (i) single focusing streak at the straight channel center; (ii) two focusing streaks at two sidewalls; (iii) The transition of focusing streaks between pattern i and pattern ii. Firstly we investigated the three different focusing patterns in the straight microchannels with circular obstacles array by the theory of the static superposition of inertial lift force and secondary flow drag force.

Besides, we implement a relative velocity gap between microspheres and fluid in a straight channel by exerting an electrophoresis (EP) force on the charged microparticles. Therefore, saffman lift force induced by relative velocity and fluid shear migrate particles towards or away from channel centerline along the lateral direction. The direction of saffman lift force depends on the vector product of relative velocity and shear rate. Two particles focusing streaks at two sidewalls can be altered by changing flow rate and magnitude of the voltage. This demonstrates the ii possibility to adjust particle inertial focusing pattern in the straight channel with obstacles array using Electrophoresis. Manipulation of lateral migration of focusing streaks increases controllability in an application such as blood cells filtration and separation cells by size.

In summary, we hope that our study can not only reveal the new possible explanation of inertial focusing in simple straight channels with symmetric semicircle obstacle arrays, but also provide high controllability and versatile particle filtration and manipulation platforms, for the practical application of biological sample treatment and clinical blood cells filtration.