Abstract
4D printing has been attracting widespread attention because its shape and performance can change under stimuli. The existing 4D printing technology is mostly limited to responsive to single stimulus, which means that the printing structure can only change under a pre-specified stimulus. Here we propose a 4D printing strategy with dual stimuli-responsive shape-shifting that responds to both temperature and water, by using a direct ink writing 3D printing method to deposit a polyurethane elastomer material with water-swelling characteristics on a heat-shrinkage shape memory polymer material to form a bilayer structure. Based on the systematic study of the adapted printing parameters of the polyurethane elastomer, the effect of programmable variables on the deformation shape was investigated. The diversified printing structure exhibits rich structural changes under one or both of the two stimuli of temperature and water. This research provides a universal multiple stimuli-responsive 4D printing method, which can effectively improve the intelligent responsiveness of 4D printing structures by combining multiple smart materials.
Highlights
Multi-Stimuli-Responsive 4D PrintingIn the research field of 4D printing, multiple stimuli-response is of great significance for broadening the practical application of the printed structure in different environments (Karis et al, 2017; Han et al, 2018)
We propose a 4D printing strategy based on the water-swellable polyurethane (PU) elastomer and the heatshrinkage shape memory polymer polyvinyl chloride (SMPVC)
After the PU is completely cured by absorbing moisture in the air, the PU/SMPVC bilayer structure was obtained by cutting along the outline of the printed sample for subsequent experiments
Summary
In the research field of 4D printing, multiple stimuli-response is of great significance for broadening the practical application of the printed structure in different environments (Karis et al, 2017; Han et al, 2018). By adding functional fillers to a certain type of smart material, the material has more responsiveness than the original one, which is one of the common strategies for achieving multi-response 4D printing. This draws on the existing multiresponse composite method (Hu et al, 2018; Li et al, 2018). This is not conducive to the use of a single printing structure in multiple environments Another pathway to achieve multiple stimuli-response 4D printing is to construct a bilayer structure by combining two materials with different response properties. Three shapes deformed by the same printing structure under different stimuli were used as three soft gripper to verify the gripping capabilities
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