A viscoelastic hydrogel based on a protein hetero-assembled with a polymer is provided. The protein cannot self-assemble with itself and the polymer cannot self-assemble with itself. The protein has a first association sequence (1stA) and a first spacer (1stSp). The polymer has a second association sequence (2ndA) and a second spacer (2ndSp). The first association sequence and the second association sequence are physically cross-linked to interact with each other with a 1:1 known and specific stoichiometry to form a three dimensional scaffold. The protein is represented by {1stA(1stSp)}x1stA, where x is ≧2, and the polymer is represented by {2ndA(2ndSp)}y2ndA, where y≧2.
