Light- and Enzyme-based Physicochemical Modifications of Hydrogel Biomaterials for Directing Cell-Matrix Interactions

Abstract

The extracellular matrix (ECM), the protein and sugar-rich mesh surrounding cells, plays a crucial part in tissue development and disease progression. While the ECM’s physical scaffolding role is well recognized, the physicochemical composition of these structural components, as well as any tethered growth factors and signaling molecules, also influences cellular behavior and fate. These revelations have further bolstered the “seed and soil” hypothesis of cancer metastasis—the thought that genetic instabilities of a malignant cell (the “seed”) are synergistic with the microenvironment (the “soil”) in driving metastasis. Conventional two-dimensional (2D) culture models fail to capture the innate three-dimensional (3D) nature of live tissues; alternatively, in vivo models, while extremely informative, are costly and it is often difficult to isolate and control specific variables in these models. Thus, 3D biomaterials with user-programmable properties have emerged as an attractive method to bridge this gap. This thesis focuses on designing and utilizing synthetic hydrogels to probe the role of ECM biochemical and mechanical cues on many cell types, with a special focus on colorectal cancer (CRC). To build and modulate these materials, we employbioorthogonal light and enzymatic reactions, with sortase—a bacterial transpeptidase—being a common player throughout. In the first project, we present a hydrogel system to systematically assess the role of ECM adhesion ligand presentation and mechanics on CRC cell line proliferation and signaling. While this construct is fully tunable, it is still a static environment; the ECM, however, is perpetually being remodeled during homeostatic and disease processes. Thus, in the second project, we introduce a novel interpenetrating network (IPN) system whose mechanical properties can be dynamically and reversibly modulated in the presence of cells prior to triggered material dissolution and cell recovery for downstream analysis. Highlighting the broad utility of this method, the system is used to assay how stiffness changes affect human mesenchymal stem cell morphology and Hippo signaling, as well as CRC mechanomemory on the transcriptomic and metabolic levels. Both platforms offer exciting opportunities for probing how regulation and dysregulation of these microenvironmental cues influence normal and pathological processes.