Fabrication of hydrogen-bonded crosslinked hydrogel vitrimer with enhanced self-healing and printability via K+ induced low methyl apple pectin

Abstract

Low methyl pectin, conventionally extruded as sols and shaped through Ca2+ post-curing, face complexity and high production costs, limiting their application in 3D printing. We developed apple pectin (AP) vitrimer inks with shear-thinning behavior at elevated temperatures and self-supporting properties at low ones, via pectin methyl esterase (PME) modification and K+ induction, aiming to facilitate simpler extrusion 3D printing. PME-modified AP (PME-AP) exhibits a higher affinity for K+ compared to AP, attributed to an 8.76 % reduction in the degree of methyl esterification and a 9.72 % increase in the degree of blockiness. Consequently, 1 % PME-AP forms a robust hydrogel vitrimer characterized by a hardness of 121.33 g and a water holding capacity of 99.50 % at 150 mM K+, a 68 % reduction in K+ concentration requirement over AP gels. Through electrostatic shielding, K+ induces hydrogen-bonded crosslinked vitrimers with stress relaxation within 53 s at 80 °C and self-healing properties with minimal texture reduction (~2 g). These characteristics suggest that the hydrogen bond crosslinked vitrimer network can dynamically reorganize in response to temperature variations, making PME-AP gel ideal for 3D printing applications. This study establishes the groundwork for cost-efficient AP-based extrusion 3D printing.