ABSTRACT Intestinal organoid models hold great promise as a tool to study intestinal development and disease, screen drug candidates, or even produce transplantable tissue in vitro. Current culture methods for growth of intestinal organoids rely almost exclusively on Matrigel, but Matrigel?s loosely-defined and variable composition makes clinical translation nearly impossible and obstructs fundamental investigations into the role of key matrix factors on organoid formation. While intestinal stem cells (ISCs) grown in Matrigel have a tremendous capacity for self- organization into functionally sophisticated intestinal organoid structures, the self-organization principles are also responsible for introducing variability and stochastic organoids that also differ from the native organ in multiple aspects. In the proposed research, we aim to develop tunable hydrogel matrices for ISC expansion, colony formation, and differentiation to form crypts. Unique to our materials is the ability to regulate the ISC microenvironment spatiotemporally using photochemical reactions, and we propose to use photoadaptable hydrogels to test hypotheses related to ISC mechanosensing and its effects on organoid growth (Aim 1); the role of local matrix stiffness on organoid shape, cell proliferation, and crypt formation (Aim 2); and the plasticity of crypt cells during their response to a stress or injury (Aim 3). We hypothesize that exogenous control of matrix properties can be used to support efficient ISC organoid growth, and subsequently mimic cell-mediated crypt formation and remodeling. The proposed material systems will allow us to not only study and direct the formation of the crypt-villus architectures that are physiologically relevant, but also test maintenance of these structures in response to dynamic changes in matrix properties corresponding to developmental processes, as well as crypt regeneration after injury. Specifically, we propose to: 1. Investigate the role of matrix mechanical properties and signaling on intestinal stem cells (ISCs) and their growth into spherical organoids. 2. Understand how spatial changes in hydrogel mechanics permit ISCs to undergo progenitor commitment and subsequent differentiation into functional cell types. and 3. Investigate the role of uniform and spatially variant cell-matrix interactions on the de-differentiation of lineage specific epithelial cells and crypt regeneration after injury.!!