Development of ambient printable hydrogen-bonded crosslinked vitrimer hydrogel inks derived from low methyl apple pectin with reduced K+ concentration

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 Ca 2+ bridges to partially weaken the electrostatic repulsion, fabricating low-K + vitrimer gel inks. Using 67 mM K + and 0.9 mM Ca 2+ , 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 Ca 2+ not only reduces the K + concentration requirement but also increases the shaping temperature, broadening the gel ink's applications in the food industry.