Single cell devices for migration and division studies

Microfluidic technologies and devices now provide powerful tools for many biological studies to gain knowledge and insight into cell behaviour because of their potential to control the local in vitro environment. This thesis aims to develop microfluidic devices for the single cell proliferation and migration studies that are fundamental in determining cell and tissue behaviour. There are two designs of microfluidic devices that have been used in this project. The first one is hydrodynamic single cell trap device having a bagatelle- like structure. The bagatelle-like devices were used to trap modified MCF7 cells expressing both mcherry-tubulin and GFP-actin and also to study the influences of the oestrogen hormone on MCF7 cells. It was found that the MCF7 cell proliferation could not be seen in the bagatelle-like devices either in the presence or absence of oestrogen. It was hypothesised that this might be due to cell stresses arising from being in a constrained area (trap) and subjected to strong fluid flow forces. The second, novel, device consists of three segregated layers and is termed a microhole device. It was specifically designed, fabricated, characterised and utilised in cancer cell proliferation and migration studies in this thesis. The microhole devices were designed to address the limitations of the bagatelle-like device. In each microhole device, the lower layer comprises of a network of submerged channels linked to an upper layer through cavity-like holes. The networks of submerged channels provide a route through which cells can migrate. The middle layer consists of an array of circular holes used to organise single cells into the cavities beneath. The top layer is a PDMS chamber for cell loading and culture medium perfusion. It was found that the recirculatory flow patterns inside the devices facilitate cell trapping, while also serving to separate high velocity flow in the top chamber from the middle and the bottom layer thereby protecting the cells from shear stress. MDA-MB-231 cells were used in this study. It was found that they can undergo cell cycling normally in the microhole devices, and migrate along an SDF-1α solution gradient produced inside the device, towards high SDF-1α concentration. To explore whether the cells were sensitive to SDF-1α on the surface to which they adhered (as opposed to solution gradients), the microhole devices were modified to have SDF-1α immobilised on selected interior surfaces. Despite each stage of the immobilisation process being verified using the appropriate fluorescence assays, relatively low levels of SDF-1α were detected in the completed devices. This may be due to fabrication processes that might deteriorate the immobilised SDF-1α functionality. It was found that unlike the situation when SDF-1α is in solution form, the MDA-MB-231 cells showed no migratory preference toward the immobilised SDF-1α. Taken together, the microhole devices developed in this thesis provide suitable environments for study cell migration toward stimuli under perfusion conditions. The geometry and the flow characteristics inside the array facilitate cell trapping and serve to protect cells from shear stress caused by high fluid flow. Further applications of the multilayer microhole devices can be found through modifying the different layers to accommodate different geometries for different cell types as well as more complex stimulation conditions, or in other application areas associated with droplet microfluidics and synthetic biology