4D Multi-Material Printing of Soft Actuators with Spatial and Temporal Control.

Soft actuators (SAs) are devices which can interact with delicate objects in a manner not achievable with traditional robotics. Whilst it is possible to design a soft actuator whose actuation is triggered via an external stimulus, the use of a single stimulus creates challenges in the spatial and temporal control of the actuation. One solution is to design soft actuators whose actuation requires the combination of stimuli (i.e., logic-gate type actuation) to initiate the actuation event. Herein, we present a 4D printed multi-material soft actuator design (MMSA) whose actuation is only initiated by a combination of triggers (i.e., pH and temperature). Using 3D printing, we designed a multi-layered soft actuator with a hydrophilic pH sensitive layer, and a hydrophobic magnetic and temperature responsive shape memory polymer layer. The hydrogel responds to environmental pH conditions by swelling or shrinking, whilst the shape memory polymer can resist the shape deformation of the hydrogel until triggered by temperature or light. The combination of these stimuli responsive layers allows for a high level of spatial and temporal control of the actuation. We demonstrate the utility of the 4D MMSA via a series of cargo capture and release experiments, validating its ability to demonstrate active spatiotemporal control. The MMSA concept provides a promising research direction to develop multifunctional soft devices with potential applications in biomedical engineering and environmental engineering. This article is protected by copyright. All rights reserved.