Investigating the Effects of Mechanical Stimuli on Collective Cell Migration and Dynamics

Abstract

In recent years, the breadth and depth of mechanobiology has increased vastly as novel and more effective ways to probe and analyze complex cellular processes have become widespread and accessible. Within the subfield of tissue engineering, the ability to control the complicated behaviors of collective cell migration and expansion dynamics is critically important to producing and augmenting higher complexity tissue systems in processes such as cell differentiation, injury healing, and organ development. This thesis focuses on two domains of mechanical influence on tissue expansion dynamics: (a) the effects of mechanical substrate perturbations and (b) the interactive application of external strain. The former (a) is explored through methods of co-patterning ECM substrates in geometries that allow local differences in substrate mechanics to drive different responses within single epithelial microtissues. Strategically designed polydimethylsiloxane (PDMS) stencils with “trap-doors” cut with an inexpensive digital razor writer created sharp transitions between ECM substrates at spatial resolution of less than the diameter of an epithelial cell (~40um). This was then used to demonstrate co-patterned concentrations of the same substrate (type 1 collagen) as well as 2 different substrates (collagen and fibronectin) that were spanned by the same epithelial microtissue. Time-lapse and fluorescent microscopy along with expansion rate and particle image velocimetry (PIV) analysis provided evidence for the presence of local growth biases due to substrate mechanics. The latter domain of applied strain (b) is investigated through epithelial monolayers adhered to ECM that is adsorbed to PDMS, a biocompatible elastic material, that is dynamically and precisely stretched to induce an external strain field on the tissue. This larger project was divided into the biological aspects, which I independently explored, and the custom mechanical aspects, which were under the care of MAE undergraduate senior Diego Fierros. Our independent endeavors were combined at the final milestone of applying strain fields to cell monolayers. Initial tests show strong evidence that higher levels of strain (~50%) induce a tissue expansion bias for the component direction parallel to the applied strain field direction. While tests for externally applied strain as well as the previously mentioned trap-door ECM co-patterning assays were conducted at low N, interesting trends were observed; and most importantly, the methodological and procedural groundwork was laid for 2 experimental approaches to investigate the effects of mechanical stimuli on collective cell migration and dynamics.