Measurement of the stiffening parameter for stimuli-responsive hydrogels

A method of measuring the stiffening parameter \(\beta ^\circ \) for stimuli-responsive hydrogels using a simple tensile test is shown. 2-hydroxyethyl methacrylate (2-dimethylamino)ethyl methacrylate (HEMA–DMAEMA) stimuli-responsive hydrogels are examined using this method. HEMA–DMAEMA preconditioned in 3.0 pH, 7.0 pH, and 11.0 pH buffer solutions is studied experimentally. The stiffening parameter extracted at pH 7.0 is successfully used to predict the nonlinearity at pH 3.0 and 11.0. The measured stiffening parameter \(\beta ^\circ \) of the hydrogel is 0.870 ± 0.018, compared with 11.4 for ligament and 0.12–0.23 for brain.