Multi‐Responsive Jammed Micro‐Gels Ink: Toward Control over the Resolution and the Stability of 3D Printed Scaffolds

3D printing of hydrogels usually relies on a combination of fine-tuned material chemistry and polymer chain architecture to obtain an ink with adequate yield-stress flow, shear-thinning, and self-healing behavior. Recent approaches in hydrogel ink design include introduction of reversible covalent or supramolecular bonds or jamming of microparticles into a granular hydrogel. However, the dimensional stability of such systems is typically afforded by a post-printing covalent cross-linking step that impedes further on-demand degradation of the scaffolds. Here, a jammed micro-gels ink made of thermosensitive poly(N-isopropylacrylamide) micro-gels incorporating terpyridine ligand linkers are proposed as a 3D printable ink that is cured post-printing by iron (II) cations for long-term stabilization. The uncross-linked micro-gels ink exhibits the rheological characteristics of granular materials, meaning yield-stress, shear-thinning and fast recovery. Upon curing, iron (II)-bis-terpyridine coordination complexes between neighboring micro-gels are formed. The supramolecular bonds are sufficiently strong and long-lived to maintain scaffold integrity during manual handling or immersion in liquid medium for over two months. The thermosensitivity of the micro-gels endows the printed construct with reversible and cyclable temperature-induced resolution enhancement, while the supramolecular cross-linking provides an asset of disintegration on-demand. The proposed micro-gel scaffolds are biocompatible, revealing the potential for biomedical applications and 4D bioprinting.