Development of ambient printable hydrogen-bonded crosslinked vitrimer hydrogel inks derived from low methyl apple...

The K⁺-induced pectin-based vitrimer hydrogel ink, with dynamic exchange properties, offers an innovative solution for single-channel extrusion-based 3D food printing. However, forming hydrogen-bonded cross-linked vitrimer traditionally requires over 150 mM of K⁺ to overcome the electrostatic repulsion between enzyme-modified pectin (EMP) molecules, which raises health concerns due to the high K⁺ content. This study developed a novel strategy to introduce Ca²⁺ bridges to partially weaken the electrostatic repulsion, fabricating low-K⁺ vitrimer gel inks. Using 67 mM K⁺ and 0.9 mM Ca²⁺, a densely cross-linked gel (Ca-EMP-K 67 mM) was formed at 25 °C, exhibiting excellent mechanical performance (~140 g hardness). Meanwhile, the gel possessed excellent self-healing properties, with a relaxation time of 8.3 s at 80 °C, confirming its vitrimer status. Notably, the Ca-EMP-K 67 mM gel ink achieved a ~ 55 % reduction in K⁺ doses while enabling an increase in shaping temperature from 4 °C to 25 °C, compared to the traditional EMP-K 150 mM gel ink. These advancements enabled a low-K⁺ pectin ink for ambient 3D printing. The introduction of Ca²⁺ not only reduces the K⁺ concentration requirement but also increases the shaping temperature, broadening the gel ink's applications in the food industry.