High-Performance Ink-Writable Polyurethane Elastomers Based on Crystalline PCL and Hindered Urea Bonds

Thermosetting elastomers possess good mechanical properties and aging resistance. However, chemically crosslinked polyurethanes are often difficult to print because they are fluid with poor mechanical performance in the prepolymer state and become infusible after crosslinking. Herein, we report a dynamically thermally enhanced solvent-free polyurethane ink for direct ink writing (DIW) 4D printing, which resolves the contradiction between rheological printability and post-molding mechanical strength. This is accomplished by incorporating crystalline poly(caprolactone) (PCL) and dynamic covalent bonds into the polyurethane matrix. Specifically, during the printing stage, the prepolymer utilizes the crystallinity of PCL to provide phase transition capability and high-fidelity shaping. Through a post-treatment strategy, the polymer topological network is remodeled after printing via the hydrolysis of hindered urea bonds, dynamically enhancing the mechanical properties. After thermal curing, the mechanical strength reaches 43.8 MPa with an elongation at break of 1038.1%, endowing the material with excellent mechanical performance. The resulting polyurethane elastomer exhibits shape memory properties recoverable near body temperature, allowing endogenous body heat to trigger shape changes for intelligent medical interventions. The solvent-free 4D-printed polyurethane vascular stents eliminate solvent leaching toxicity while exhibiting good biocompatibility and load-bearing capacity, demonstrating potential for biomedical applications.