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

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomedical Engineering

Background:

• Thermosetting elastomers offer desirable mechanical and aging properties but pose challenges for 3D printing due to their fluid prepolymer state and infusible crosslinked nature.
• Existing methods struggle to balance rheological printability with post-molding mechanical integrity in polyurethanes.
• Solvent-based printing methods raise concerns about toxicity and biocompatibility.

Purpose of the Study:

• To develop a dynamically thermally enhanced, solvent-free polyurethane ink for direct ink writing (DIW) 4D printing.
• To resolve the inherent contradiction between printability and mechanical strength in thermosetting elastomers.
• To create a material with tunable mechanical properties, shape memory capabilities, and biocompatibility for biomedical uses.

Main Methods:

• Incorporation of crystalline poly(caprolactone) (PCL) for phase transition and shaping during printing.
• Integration of dynamic covalent bonds (hindered urea bonds) for post-printing network remodeling.
• Utilizing a solvent-free formulation and DIW 4D printing technique.
• Post-treatment via hydrolysis of urea bonds followed by thermal curing.

Main Results:

• Achieved high-fidelity shaping during printing using PCL crystallinity.
• Dynamically enhanced mechanical properties post-printing via urea bond hydrolysis, reaching 43.8 MPa tensile strength and 1038.1% elongation at break.
• Demonstrated shape memory properties recoverable near body temperature, triggered by endogenous heat.
• Successfully fabricated solvent-free 4D-printed polyurethane vascular stents with good biocompatibility and load-bearing capacity.

Conclusions:

• The developed polyurethane ink enables DIW 4D printing of elastomers with excellent printability and superior mechanical performance.
• The dynamic covalent network and PCL crystallinity provide a versatile platform for advanced material design.
• The solvent-free, biocompatible material shows significant potential for intelligent medical interventions and biomedical applications, such as vascular stents.