Flexible and Stretchable Microfluidics

Abstract

Microfluidics is the science and technology of manipulating and analysing small amounts of liquid. Microfluidics has several advantages including small sample volume, small footprint, being cheap, portable, and precise. Microfluidics has applications in a wide range of areas such as in chemistry, electronics, and most importantly in biological sciences. Microfluidic functions are greatly influenced by the geometry and dimensions of the microchannels. The main challenge facing microfluidics is that once the conventional rigid microfluidic device is fabricated, its dimensions cannot be changed or modified. To overcome this problem, we proposed the concept of flexible and stretchable microfluidics. Stretchable microfluidics allows flexible devices to change their dimensions and thus enabling new functionalities. This thesis aims to (i) understand the fundamentals of flexible microfluidics, (ii) design and fabricate a new generation of stretchable microfluidic devices with tuneable dimensions, and (iii) apply stretchable microfluidics to three main handling tasks of separation mixing and trapping. Our main goal is to evaluate how the dimensions of different types of microfluidic devices alter under elongation and how these dimensional changes influence its functions. In this thesis, following a comprehensive introduction in chapter 1, a thorough literature review over flexible microfluidics is provided in chapter 2. The review covers three main areas of flexible microfluidics including materials, effect of flexibility on microfluidic functions, and the current applications and future perspectives of flexible microfluidics. Chapter 3 and 4 investigate the effect of stretchability on inertial microfluidics. Inertial microfluidics is a promising approach for particle separation. The current obstacle of inertial microfluidics in biological applications is the broad size distribution of biological microparticles. Rigid microfluidic devices work well for a narrow range of particle sizes. For focusing and separating a new set of particles, troublesome and time-consuming design, fabrication, testing, and optimization procedures are needed. Thus, a stretchable a microfluidic device with tuneable dimensions was fabricated and studied in chapter 3. By changing the channel dimensions under elongation, the device could be adapted to different particle sizes and flow rate ratios. Stretching the device significantly improved the focusing and separation efficiency of the specific particle sizes. In chapter 4, we focused on the application of stretchable inertial microfluidics for cancer detection. The performance of the stretchable device was verified by isolating cancer cells from WBCs and from whole blood with high recovery rates and purities. Chapter 5 studies the effect of stretchability on micromixing. A micromixer is an indispensable component in miniaturised platforms for chemical, biochemical, and biomedical applications. Mixing in microscale is challenging due to the laminar flow associated with low Reynolds numbers. This chapter reports a stretchable micromixer with dynamically tuneable channel dimensions. Periodic elongation of the stretchable micromixer results in mixing disturbance in intermediate Reynolds numbers. Periodically stretching the device changes the channel geometry and dimensions leading to dynamically evolving secondary and main flows. We evaluated the performance of this stretchable micromixer both experimentally and numerically. Chapter 6 reports a stretchable microtrapper. Microfluidic technologies have been widely used for single-cell trapping. However, there are no robust methods for the facile release of the captured cells for subsequent studies. Therefore, we developed a stretchable microfluidic cell trapper for easy on-demand release of cells in a deterministic manner. By tunning the horizontal elongation of the device, the gap at the bottom of the traps widened and provided ample space for releasing particle/cell with sizes of interest. The proposed stretchable micro trapper demonstrated a deterministic recovery of the captured cells by adjusting the elongation length of the device. Flexible and stretchable microfluidic devices with tuneable dimensions were introduced and studied extensively in this thesis. We showed that by applying stretchability to microfluidic functions including inertial microfluidics, micromixing, and single cell studies, several drawbacks associated with fixed dimensions were addressed and recovered. We believe that flexible and stretchable microfluidics is a new research direction of microfluidics.