Transformable mechanical metastructures with multi-dimensional programmability via spatiotemporal electrothermal stress relaxation

Programmable metastructures demonstrate exceptional potential in information processing and soft actuation through customizable mechanical behaviors. However, convenient programmability remains challenging due to heavy reliance on heterogeneous geometry-material design or specialized programming protocols. Herein, transformable mechanical metastructures (TMMs) are innovatively proposed, enabled by spatiotemporal electrothermal stress relaxation to achieve multi-dimensional programmability. This allows for transformable mechanical responses, spanning continuously tunable stress-strain curves, reversible “monostability-bistability” transitions, and automatic instantaneous deformation with controllable delays. The TMMs are fabricated via dual-material co-extrusion of continuous carbon fiber-reinforced polylactic acid (CCF-PLA). This combines PLA’s viscoelasticity, which regulates stress evolution via spatial deformation-determined initial stress and temporal relaxation duration, with CCFs’ Joule heating for precise electrothermal modulation. This synergy enables tailored internal stress dynamics, granting TMMs “one-structure-multi-change” programmability to customize mechanical responses without geometry/material/configuration modification. Scalable to large arrays, the strategy eliminates unit-cell heterogeneity requirements through localized electrothermal programming under global synchronized compression, unifying spatially customized performance control with uniform loading. The TMMs further integrate multifunctionality: rewritable/encryptable seven-segment displays with timed self-destruction, temporally switchable architectural patterns, and self-actuating launchers with programmable delays and high-energy instantaneous release. This work establishes a paradigm for programmable metastructures, bridging mechanical computing and adaptive soft actuators through spatiotemporal electrothermal relaxation control.