Constrained swelling and instability of a temperature-sensitive hydrogel ring

We analyze the constrained swelling of a temperature-sensitive hydrogel ring, a key component of a previously developed adaptive liquid microlens. Hard constraints make the deformation and stress distribution within the gel nonuniform. The compressive stress may even cause the instability of the ring. We code a material model for poly(N-isopropylacrylamide) hydrogel and predict wrinkling instability at the inner periphery of the ring by using a commercial finite element method software. The presented model and the codes can be utilized to aid the design of soft devices based on temperature-sensitive hydrogels.