Accurate in vitro recapitulation of complex biological phenomena such as tissue morphogenesis, tumorigenesis, and stem cell differentiation requires a truly 3D environment. Common physical hydrogel-based 3D cell encapsulation platforms such as matrigel and collagen require a shift in environmental conditions (e.g. temperature, pH) to initiate the sol-gel transition, which may be detrimental to cells.  By exploiting binding interactions between tandem repeats of the WW domain and its proline-rich ligand, we have designed a two-component physical hydrogel system that undergoes a sol-gel transition simply upon mixing. Furthermore, the addition of soluble proline-rich peptides results in competitive binding that causes rapid gel dissolution, thereby facilitating easy cell recovery under mild, non-enzymatic conditions.  Molecular engineering of the recognition domains is also being pursued to achieve independent control over mechanical and biochemical cues imparted to the cell.