Form-finding describes the process of finding a stable equilibrium shape for a structure under a specific set of loading for a set of boundary conditions. Both physical (experimental) and numerical (computational) form-finding methods have been employed by structural engineers and architects for the design of shape-resistant structures: structures whose behavior depends mostly on their global spatial configuration and less on the properties of their individual components. The shape of dielectric elastomer minimum energy structures (DEMES) depends on the equilibrium between the pre-stressed elastomeric membrane and its inextensible frame. Therefore, DEMES can be modeled and analyzed using structural form-finding techniques. We applied dynamic relaxation (DR), a well-established explicit and efficient numerical form-finding and analysis method, to simulate DEMES equilibrium shapes and predict the elastic energy of DEMES. The DR-DEMES model shows generally good agreement with its physical implementation counterpart, as it captures the equilibrium shape and also the elastic energy in function of shape. However, we found that the numerical and the physical models differ in the pre-stress that is required to obtain a specific equilibrium shape. Therefore, in this study we introduce hyper-elasticity in the DR-DEMES model. With this refinement in physical parameters the DR-DEMES model approaches the pre-stress state of the physical DEMES implementation more closely, while it maintains the computational efficiency of the form-finding approach. We conclude that dynamic relaxation, with its low computational cost, is a powerful tool for the design of novel DEMES applications.

Hydrogel actuators were prepared by combining ionoprinting technique with reversible metal ion coordination chemistry found in mussel adhesive proteins. Hydrogels were formulated with biomimetic dopamine moiety, which contains a catechol side chain that is capable of forming mono-, bis-, and tris-complexes with ferric (Fe3+) ions with increasing pH. Catechol-Fe3+ complexation increased local crosslinking density, which induced hydrogel bending at the site of Fe3+ ionoprinting. The effect of pH on the dynamic response of hydrogel actuation was tracked by following the radius of curvature at the ionoprinting site. Both the rate of change and the maximum radius of curvature increased when the pH with increasing pH (2.5-9.5), indicating that pH can be used to modulate hydrogel actuation. Additionally, hydrogels containing Fe3+ demonstrated higher extent of deswelling when equilibrated at a basic pH. Similarly, dynamic mechanical analysis in the compression mode revealed that both the storage and loss modulus values for Fe3+-containing hydrogels increased with increasing pH. These results indicated that bis- and tris-complexes formed at an elevated pH level contributed to a faster rate of actuation and a more condensed network architecture. Hydrogel actuation and deswelling were also observed at pH of 3.5 although to a lesser degree, potentially due to a stronger affinity between network-bound catechol and Fe3+ ions as compared to complexes formed in a dilute solution.