Abstract
We present a study on swelling-induced circumferential buckling of tubular shaped gels. Inhomogeneous stress develops as gel swells under mechanical constraints, which gives rise to spontaneous buckling instability without external force. Full control over the postbuckling pattern is experimentally demonstrated. A simple analytical model is developed using elastic energy to predict stability and post-buckling patterns upon swelling. Analysis reveals that height to diameter ratio is the most critical design parameter to determine buckling pattern, which agrees well with experimental and numerical results.