posted on 2024-03-02, 02:43authored byWenya Shu, C. Nadir Kaplan, Justin R. Barone
Thin
bilayers made of elastic sheets with different strain recoveries
can be used for dynamic shape morphing through ambient stimuli such
as temperature, mass diffusion, and light. As a fundamentally different
approach to designing temporal shape change, constituent polymer molecular
features (rather than external fields) are leveraged, specifically
the viscoelasticity of gelatin bilayers, to achieve dynamic three-dimensional
(3D) curls and helical twists with curvatures as high as 1.25 cm–1 when the strain difference between the layers is
0.45 cm/cm. After stretching and releasing, the acquired 3D shape
recovers its original flat shape on a time scale originating from
the polymer viscoelasticity. The recovery time is found to be dependent
on formulation and applied strain such that the recovery times at
an applied strain of 1 cm/cm are about 2 and 10 s when there is more
and less water plasticizer, respectively. The bilayer-time-dependent
curvature can be accurately predicted from hyperelastic and viscoelastic
functions using finite element analysis (FEA). FEA reveals the nonlinear
shape dynamics in space and time, in quantitative agreement with experiments.
The bilayers exploit intrinsic material properties in contrast with
state-of-the-art methods relying on external field variations, moving
one step closer to acquiring the autonomous shape-shifting capabilities
of biological systems for building engineered devices.