Exploring the mechanical, biological and degradation properties of PVA and PETG for engineering multi-material 4D printed actuators triggered by degradation

Shape-morphing actuators and devices, capable of transforming their geometries in a controlled way, are relevant for a wide set of industrial sectors and have become popular thanks to the geometrical freedom, multi-material processability and personalization options provided by additive manufacturing. In 4D printing, where 3D printed structures are triggered to change shape with time, a variety of stimuli can initiate the shape-morphing, with degradation being one of the less explored ones, despite its potential. To leverage the shape-morphing and industrial applicability of multi-material 4D printed polymeric actuators, the combination of structural polyethylene terephthalate glycol-modified (PETG) and degradable polyvinyl alcohol (PVA) is systematically investigated in this study. The mechanical, degradation and biological properties of these materials are assessed to demonstrate their applicability for developing shape-shifting actuators, including for use as medical devices. Furthermore, a conceptual actuator is designed, 4D printed, and evaluated to illustrate the engineering of PETG-PVA shape morphs triggered by degradation. • Underwater PVA erosion governs time-dependent triggering via degradation-induced loss of mechanical integrity. • The degradation rate followed exponential decay governed by the surface area-to-volume ratio. • PETG effectively stored and released elastic energy, enabling controlled actuation in aqueous environments. • The high cytocompatibility of PVA and PETG promotes their use in biomedical applications. • This triggering stimulus paves the way for sustainable and adaptive 4D printed matter.