A two-component, molecular-recognition gelation strategy that enables cell encapsulation without the need for environmental triggers is provided. The two components, which in one example contain WW and polyproline-rich peptide domains that interact via hydrogen bonds, undergo a sol-gel phase transition upon simple mixing. Hence, physical gelation is induced by the mixing of two components at constant environmental conditions, analogous to the formation of chemically crosslinked epoxies by the mixing of two components. Variations in the molecular-level design of the two components are used to predictably tune the association energy and hydrogel viscoelasticity. These hetero-assembly physical hydrogels encapsulate neural progenitor cells at constant physiological conditions within 10 seconds to create uniform 3D cell suspensions that continue to proliferate, differentiate, and adopt well-spread morphologies.