On the finite bending of functionally graded light-sensitive hydrogels

Abstract

Considering vast applications of light-sensitive hydrogels in designing sensors and actuators, in this article, a semi-analytical solution is developed for predicting the mechanical behavior of light-responsive hydrogels. Having continuous stress and deformation fields, the swelling of a functionally graded (FG) hydrogel strip is investigated under finite bending. Bending of FG hydrogel stems from the variation of cross-link density distribution along the thickness in the form of an exponential function which causes the layer to have an inhomogeneous swelling ratio. Furthermore, the finite element method is utilized to validate the accuracy of the presented solution by comparing the stress and deformation fields inside the light-sensitive FG hydrogel layer. A constitutive model for the light-sensitive hydrogels is modified in this paper to avoid multiple unstable solutions to arrive at a unique solution in various light intensities. Considering various applications of FG hydrogels, some designing factors are studied including the bending curvature, semi-angle, neutral axes and aspect ratio. In contrast to the layered structures, the swelling induced finite bending of an FG hydrogel gives continuous deformation and stress fields distributions.