Design and fabrication of a piezoelectrically driven microfluidic cell sorter

Abstract

In this thesis, a new fabrication method for a polydimethylsiloxane (PDMS) microfluidic cell sorter chip using piezoelectric actuators is presented. Suggested device performance was simulated in COMSOL Multiphysics 5.4, and 2-dimensional (2D) hydrodynamic focusing was investigated. The deflection forces applied by the PZT (lead zirconate titanate) actuators on the main stream to sort the particles were defined in terms of incoming side flows. An optimum velocity for these deflective flows to change the trajectory of the particles moving with the main stream was established. As PZT actuators are used as the source of the deflection force, the relationship between deflective flow velocity and the displacement of the PZT discs was investigated. In the fabrication of the proposed device, a deep reactive ion etched silicon wafer was used for pattern transfer in the PDMS soft lithography process instead of commonly used SU-8 mould in the literature. Piezoelectric ceramic (PZT) discs are recessed into the PDMS layer and isolated from the actuation chambers by a thin PDMS membrane (0.36 mm thick); this facilitates assembly of a leak-free device. The actuation chambers, just under piezoelectric discs, have a low volume (9.42mm3 with 30μm height). With this approach, a small dead volume has been achieved, and the volume of sheath flow consumption is minimised. The design also facilitates insertion and removal of the PZT discs since they are not glued but recessed. In the proposed device, air-filled cavities were created near the fluid channels to minimise the acoustic interference by the PZT disc vibrations. Challenges of the suggested fabrication process, calibration of process recipes and experimental results of the fabricated device are presented. The efficiency of a coil type magnetic actuator, as an alternative to PZT actuators, is presented. Fabricated devices were tested with 10 μm polystyrene beads and 6 μm fluorescent beads with a 488 nmwavelength laser diode excitation. Simulation results were verified experimentally and 2D hydrodynamic focusing and deflection results are given. The performance of the membrane structure, which makes the device completely sealed and leak-free, allowing easy insertion and removal of the actuators, was critically assessed. Improvements for thev fabrication to make the device completely leak-free and integrated miniature detection system are presented as future work.