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

Abstract 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.