4D printing of bilayer tubular structure with dual‐stimuli responsive based on self‐rolling behavior

Self‐rolling allows the bilayer to transform into a 3D structure in response to specific external stimulation, such as heat, humidity, ions, etc. Herein, we report a 4D printing bilayer with a top sodium alginate layer and bottom polycaprolactone layer that could be rolled up to a tubular structure upon exposure to heat and Ca2+ solution stimulation. The discrepancy in the swelling and thermal‐responsiveness between alginate and polycaprolactone induced the self‐rolling under different stimuli. The self‐rolling behavior of the bilayer depends on the aspect ratio, thickness ratio of the bilayer film, the pattern, and external stimuli. Thus, a tailorable surface of the self‐rolled tube was obtained by tuning the bilayer parameter and the stimuli medium to meet varied demands. This controllable shape changing provides a strategy for the preparation of well‐defined tubular structures. Besides, the biocompatibility of bilayer film suggests the potential application in the field of biomedical device such as vascular stent.