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

Abstract

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 lowmodulus 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 crosslinking 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.

3D Printing of Solvent-Free Supramolecular Polymers

“…Polymers with supramolecular interactions drastically improve their mechanical properties compared to non-modified analogs (Burattini et al, 2011). The fact was proven by Liu et al (2020) with hydrogen bonding polyesters (Figure 2C), where the materials display low printing quality due to their soft material properties, leading to spreading and flowing after the extrusion. The introduced hydrogen bonds now act as non-covalent crosslinker, improving the rheological properties for the material during printing (Liu et al, 2020).…”

“…The fact was proven by Liu et al (2020) with hydrogen bonding polyesters (Figure 2C), where the materials display low printing quality due to their soft material properties, leading to spreading and flowing after the extrusion. The introduced hydrogen bonds now act as non-covalent crosslinker, improving the rheological properties for the material during printing (Liu et al, 2020). Already small amounts of supramolecular polymers or end groups change the Young's modulus and tensile strength for polymethyl methacrylate (PMMA) polymers using FDM printing.…”

“…Supramolecular interactions change the flow properties compared to neat polymer materials improving the form stability after extrusion (C) . Reproduced with permission ( Liu et al, 2020 ). Copyright 2020, American Chemical Society.…”

“…The toolbox of supramolecular oligomers and polymers can address the limitations of 3D printing such as viscosity in the melt state, anisotropic mechanic properties, adhesion between layers, or advanced functionality post-printing. Supramolecular materials were developed for their strengthening, self-healing, stress-sensing, and shape-memory properties ( Colombani et al, 2005 ; Herbst et al, 2012 ; Herbst et al, 2013 ; Döhler et al, 2015 ; Jiang et al, 2017 ; Campanella et al, 2018 ; Jiang et al, 2020 ), and thus, the use of non-covalent bonds compared to their neat polymer counterparts improves their printing and material qualities to a high degree ( Liu et al, 2020 ).…”

Hierarchical ordering in light-triggered additive manufacturing

“…The [2+2] photodimerization of coumarines ( is max ≈ 340 ) one of the most prominent example of such systems. [73][74][75][76] Interestingly, the photo-induced dimerization of amino acids containing a photo-oxidizable group such as Trp, His, Tyr, Cys and Met has also been used for 3D-printing. [77][78][79][80][81][82][83][84] The photocrosslinking methods described above lead to the formation of 3D printed polymeric structures composed of, in most cases, an undefined internal structure due to the lack of control at the molecular level during the polymerization processes.…”