Robust hydrogels have been developed by addition of imogolite, a perfect rigid polyelectrolyte with a nanotube shape, into polyacrylamide networks. It was revealed that the obtained gel exhibited the distinct isotropic-anisotropic structural transition in response to small tensile strain. The birefringence as large as about 7 x 10(-5) due to the anisotropic diffraction appeared/disappeared reversibly upon stretching and releasing the gels in-between of 3 and 0 mm/mm strain. (C) 2013 Elsevier Ltd. All rights reserved.