The bending of bi-gels has been studied as a function of temperature, acetone concentration, and NaCl concentration. The bi-gels consist of acrylamide on one side, and the interpenetrating polymer networks of acrylamide and N-isopropylacrylamide on the other side. The maximum bending strain achieved by the bi-gel is about 0.85. The bending mechanism of the bi-gels reported here is due to the engineered structure heterogeneity, in contrast with previous homogeneous gel bending which is induced by external gradient fields. The kinetic behavior of the bi-gel is discussed. A theoretical model is used to estimate the collective diffusion coefficient D-c of the IPN side of the bi-gels in pure water and in salt solution. The results agree with those obtained by the light-scattering method.