Anti-freezing starch hydrogels with superior mechanical properties and water retention ability for 3D printing

As a novel material that can be used at subzero temperatures, anti-freezing hydrogels have been attracting extensive attention. Inspired by the freeze-tolerance phenomenon in seawater, which is achieved by mixing salts into water, an ionic compound (CaCl₂) was used to gelatinize starch to form anti-freezing hydrogels. Native potato starch (NPS) anti-freezing hydrogels were formed at -10 °C, -18 °C, -30 °C, and - 50 °C with 6-9 kPa tensile strength and 100-230% elongation at break. The compressive stress of anti-freezing hydrogels at different environmental temperatures increased from 18.586 kPa to 36.551 kPa with the glass transform temperature of starch hydrogels dropped to -50 °C. The anti-freezing hydrogels showed excellent water retention ability, which could maintain a water content of 55% after 7 days at ambient temperature. The prototyping of anti-freezing starch hydrogels broadens the applications of starch in food, adhesives, medical materials, and intelligent materials.