Controllable spatiotemporal programming of shape memory polymer-elastomer bilayer composites for dynamic soft actuators

Stimuli-responsive bilayer composites integrating shape memory polymers (SMPs) with passive elastomers, offer a promising avenue for programmable shape morphing actuators. However, achieving spatiotemporal control over dynamic morphing behaviors, particularly time-dependent trajectory prediction and temporal sequence customization, remains challenging due to the intricate interplay of viscoelastic relaxation, material heterogeneity, and geometric design. Herein, we present a SMP-based bilayer composite (SMP-BC) system with dual-programmability in both deformation magnitude and temporal response. A multi-dimensional theoretical framework, across the spatial morphology and temporal response, is innovatively developed by incorporating viscoelastic behaviors (i.e., stress evolution and deformation recovery) into Timoshenko's bilayer beam theory. This enables accurate prediction of time-dependent arc angle and curvature radius during thermally activated bending. Parametric analysis reveals a critical material-geometry synergy: the maximum equilibrium bending angle is determined by both modulus ratio and thickness ratio, governed by the competition between shape recovery force and elastomer rigidity. Critically, spatiotemporal programmability is achieved by engineering stress relaxation kinetics during SMP programming. Adjusting relaxation duration from 1 s to 100 s modulates deformation magnitudes and bending rates (200° in 10 s vs. 120° in 60 s) via stress-dependent elastic strain release. This principle enables sequential morphing (e.g., flower blooming, “OK” gestures) and complex 3D deformations (e.g., saddle-shaped surfaces and programmable information patterns). Our work establishes a “material-structure-time” co-design paradigm for dynamic soft actuators, advancing spatiotemporal control in adaptive robotics.