An Adaptable Single-cell Trapping Device for a Wide Range of Cell Sizes

Abstract

In the last two decades many microfluidic devices have been developed in order to provide better and more reliable tools for biological assays and analysis. Microfluidic technology has proven its functionality and advantages over conventional cellomics methods such as flow cytometry (FC) and laser scanning cytometry (LSC) in particular for processes that require the analysis of single cells. Different microfluidic platforms capable of capturing, positioning, and sorting single cells have been developed; however, such devices are incapable of working with various sizes of cells. Therefore, once a device has been designed and fabricated it is not possible to modify its dimensions so a new device is required for each different cell size for analysis. In an effort to overcome the limitation of adaptability of microfluidic cell trapping devices, this thesis presents a new microfluidic single cell-trapping device capable of capturing cells of various diameters. This thesis conducts a review and analysis of several microfluidic cell trapping devices under the FCBPSS (function-context-behavior-principle-state-structure) framework to have a better understanding and classification of the most relevant microfluidic devices, followed by the design of a new device capable of trapping large batches of single cells and modifying its physical features in order to work with multiple sizes of cells. The design process of the new device is based on and guided by the Axiomatic Design Theory. From the thorough review of the literature, it was concluded that the most suitable structure to demonstrate the concept proposed on this thesis an array of single cell trappers, and the best tuning method would be a mechanical stretching to generate a uniform distributed strain on the device. After designing and modeling the new device, it was imperative for this research to fabricate a device which could be tested in accordance with the literature. The final device consists of two thin layers of polydimethylsiloxane (PDMS), one of which bears trapezoidal microstructures (traps) to physically capture cells. The size of the traps can be modified by stretching the device via a uniform distributed force, which is applied using a stretching apparatus. Finally, the performance of the new device was assessed by conducting two main experiments. The first experiment consisted of characterizing the mechanical behavior of the device when different strains were applied. It has been found that all the traps of the device have a uniform deformation when a strain is applied, and the minimum size increment permitted by the stretching apparatus is of 2μm.The second experiment was done in order to characterize the hydrodynamical and trapping behavior of the device. By using water-in-oil microspheres of various sizes the trapping of particles was demonstrated; it was determined that the device can capture particles between 20μm and 30μm. To demonstrate cell viability, the device was tested using melanoma cells. No visible damage onto the cells was observed after the experiments using the device; therefore, it is suitable for biological applications where various sizes of cells are required for analysis.