Water-Responsive hydroplastic 4D printing with programmable shape morphing and locking

This is the authors' abstract. We don't add key points for this paper.

• A DLP-based 4D printing strategy utilizing a hydroplastic photocurable resin enables water-induced shape morphing. • Non-uniform curing induces programmable self-bending upon water absorption and rigid shape locking upon drying. • Mechanical properties such as Young’s modulus vary reversibly between 0.57 MPa (Water absorption) and 9.96 MPa (Oven Drying). • The system demonstrates reconfigurable origami-based self-assembly and controlled deformation through patterned hydration. • Functional applications include conformal microfluidic systems on curved glass surfaces without adhesives. Hydroplastic materials undergo reversible mechanical changes upon water absorption, transitioning between soft and rigid states. Leveraging this characteristic promotes environmentally friendly shape-morphing technologies, recently attracting significant research interest. This study aims to develop a method for inducing non-uniform curing along the thickness of a hydroplastic photocurable resin by applying frontal photopolymerization (FPP) using a commercial projector, and for achieving shape-morphing behavior through water absorption. The 3D-printed structures deform according to a predefined design, soften upon water absorption, and harden upon drying while retaining a stable deformed shape. Materials that deform in response to water or humidity are typically ductile, making it difficult to maintain their deformed shape after stimulus removal. However, this study demonstrates that a single material can programmable self-assembly while retaining its deformed shape even after water removal. This hydroplastic shape-morphing structure can be used for fabricating microfluidic channels on glass surfaces, which are difficult to process.