PROJECT ABSTRACT Although hydrogel-based materials constitute a multibillion-dollar market, commercial applications for drug delivery and regenerative medicine are extremely limited. Hydrogels have garnered intense interest as extracellular matrix (ECM) mimics due to their tailorable permeability, mechanics, and degradability, yet their clinical use in this area largely depends on biological materials such as proteins. Although some success has been met with naturally-derived ECM, these naturally derived materials are often limited by long regulatory approval timelines due to the potential to react with other biologics. Synthetic materials are therefore attractive due to their known chemical compositions, but the challenge with their use lies in the lack of complexity as compared to biological systems, which translates to a lack of efficacy in the clinic. Hence, the goal of this proposal, and of our research lab, is to expand the toolbox for building complexity and functionality into synthetic hydrogel biomaterials by using dynamic chemistries and monomer sequence-based strategies. This strategy takes much inspiration from nature, as the structure and function of biological polymers arise from the precise placement of their amino acids or nucleotides. In addition, cells are able to remodel and reconfigure the natural ECM over time. Both of these characteristics have proven difficult to engineer into synthetic networks. Hence, our goals over the next five years are to 1) develop hydrogels with reversible crosslinks to quantitatively design reconfigurable matrices, 2) develop synthetic sequence-controlled linkers to control hydrogel properties (e.g., mechanics, degradation, activity) using polypeptoids, and 3) combine these approaches to develop self-assembled constructs for tissue engineering. We believe our goals will be useful for broad applications in regenerative medicine, therapeutic delivery, and preclinical models of tissue for drug development. In addition, we anticipate that the potential to alter current modes of thinking in hydrogel and biomaterial design is high, and that our work will shed insight to the biological processes underlying cell-matrix interactions. For these reasons, this work is well suited for the R35 Maximizing Investigators' Research Award for Early Stage Investigators.