Programmed Buckling Of Hydrogel Plate To 3D Shape

Hydrogels have attracted much attention recently due to their excellent biocompatibility,admirable physical and chemical properties.In this thesis,we choose the light-cured hydrogels,whose crosslinking density and swelling ratio can be spatially controlled by using Digital Light Processing(DLP)technology.The non-homogeneous hydrogel films prepared by this method have diverse internal volume change ratios when swelling in°water and will induce strain mismatch in hydrogels.As the accumulated strain mismatch reaches a critical value,the buckling deformation occurs and the hydrogel plate will be transformed into three-dimensional(3D)structure.We investigated the dependence of the crosslinking density and swelling ratio on the light exposure time and established the finite element model for the buckling of hydrogel plate.Two kinds of axisymmetric circular disks with discontinuous and continuous spatial distribution of material properties are studied.The disk with discontinuous material properties buckles to a hat after absorbing water.The experimental results agree well with the finite element simulations.The shape of hat depends on the ratio of inner radius to the outer radius.The disk with continuous exponential distribution of material properties along the radius buckled to a flower after absorbing water.The wave number at the outer ridge depends on the coefficient that controls the swelling ratio.We also studied the Sydney Opera House using the finite element model and come up with an optimal design,which guides the experiments.The developed Opera House are in a good agreement with the prediction from finite element model.In addition,an theoretical model is established for the initial and postbuckling of a thin hydrogel strip with one edge clamped and the others free.The closed-form solutions for the critical buckling load and wavelength,and the evolution of the buckled shape are obtained,which agree well with finite element simulations.These results provide design guidelines for the buckling of 2D plate to 3D structure and could be very useful to enable the hydrogel as an effective shape changing materials.