Design of a mems device for studying cell migration and differentiation

Abstract

This work presents a novel device to study forces involved in cell migration using micro force-sensing arrays fabricated of a flexible and optical clear polymer called PDMS (polydimethylsiloxane). These arrays consisted of several micropillars with different arrangements and they were fabricated using soft lithography and replica moulding techniques. Three micropillar dimensions were proposed with a stiffness of 155 nN/µm, 56 nN/µm and 34 nN/µm respectively to detect forces within tens of nanonewton range using image analysis techniques. Device functionalization was performed with a protein called fibronectin which served as a model for the ECM (extracellular matrix). The novelty of this thesis relies on the adaptation of the functionalization techniques to coat the micropillars top only and not leave protein between pillars. Three different methods were compared including the traditional reverse microprinting technique, silane method and EDC/NHS (1-Ethyl-3- (3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide) activation. It was demonstrated that EDC/NHS coupling was the more reliable method to functionalize this type of devices. Force detection was done by recording videos of a cell migrating in the PDMS micropillars substrates. This cell migration caused deflections on the micropillars and these deflections were detected by a MATLAB code which calculated the corresponding exerting force with a resolution of 0.01 nN. The novelty of the image processing relies on a customised MATLAB code. This code detected the position of each pillar frame by frame; and then, exerted forces are calculated by using a mathematical equation which considers the micropillar stiffness and the relative displacement with respect to the previous frame. The efficiency of the devices was tested in epithelial cells and fibroblasts. It was demonstrated that devices were efficient to measure local forces of epithelial cell lines A549 and NCI-H226 and it was highlighted the key differences between their migration behaviour. Additionally, it was possible to study how cells sense the surrounding area with its lamellipodium as part of cell migration of A549 cells. Parallelly, devices were tested with human dermal fibroblasts where cell migration was minimal. This minimal migration led to the conclusion that this type of device was not suitable for cell migration studies due to the lack of data to carry a study and therefore, [iv] it is suggested to fabricate a device with a bigger stiffness to enhance cell migration in fibroblast cells. It was concluded that this device is ideal to study epithelial cell’s migration and therefore, processes where its migration are involved for instance metastasis. A better understanding of cell migration of cancerous cells could lead to the development of drugs to stop metastasis.