The Extracellular matrix (ECM) is a responsive material in tissue that not only houses cells but also directs their function. The ECM varies in composition across tissue types, and key properties of the ECM like elastic modulus, viscoelasticity, and the presence of biochemical cues have been shown to have an influence on cell behavior. Synthetic materials like poly(ethylene glycol) decouple material properties from biochemical cues and have played a critical role in understanding how cells respond to the mechanical stimuli. However, these materials are usually formed with immovable covalent cross-links that make it challenging to mimic the viscoelasticity of human tissue. My project focuses on the use of covalent adaptable thioester crosslinks as a means to build viscoelasticity into covalently crosslinked hydrogels. Through changes in pH, pKa, or stoichiometry, thioester exchange chemistry can be used to modulate viscoelasticity independent of elastic modulus. Combined with the photo-initiated thiolene polymerization, thioester exchange chemistry can be a powerful new tool to study how viscoelastic stimuli play a roll in directing cell behavior.