Introduction of Hydrogen Bonds Improves the Shape Fidelity of Viscoelastic 3D Printed Scaffolds While Maintaining Their Low-Temperature Printability

In spite of the rapid adoption of three-dimensional (3D) printed scaffolds in biomedical applications, there is a paucity of low-modulus 3D printable biodegradable polymers available for fabrication of tissue-mimetic scaffolds. Extrusion-based direct-write 3D printing (EDP) enables printing and customization of low-modulus materials that match the modulus of the native tissue. However, the poor printability and low shape fidelity of such materials are significant limitations of soft materials. Herein, we demonstrate that these limitations can be overcome by the introduction of hydrogen bonds into 3D printable low-modulus polyester inks. We show that the hydrogen bonds serve as physical cross-links, which improve the printability and shape fidelity of 3D printed scaffolds without sacrificing the low modulus of the polyester. A 3D printable polyester ink comprising an unsaturated aliphatic side chain, a UV-curable coumarin pendant group, and a secondary amide group-containing side chain was designed. The long aliphatic side chains increase the flowability and allow 3D printing at room temperature. Coumarin groups function as cross-linking sites when irradiated with UV light, which help the scaffold maintain its shape after printing. The hydrogen bonds from the secondary amide groups impede the deformation of filament dimensions after extrusion and result in higher shape fidelity. Most significantly, introduction of hydrogen bonds does not compromise the softness of the polymer, which facilitates room-temperature printing and maintains the low-modulus nature of the polymer post printing.