Dynamic regulation properties of carrageenan hydrogels based on the Hofmeister effect.

κ-Carrageenan (KC) hydrogels are processed from a natural polysaccharide with abundant sources, simple preparation, and superior biocompatibility, which are widely used in the food industry and biomedical applications. Due to fixed water content and loose structure, KC hydrogels crosslinked by hydrogen bonding exhibit inflexible and inferior mechanical properties that considerably restrict their application potential. This study presents a comprehensive investigation of the Hofmeister effect for dynamically modulating KC hydrogels, combining multi-scale mechanistic analysis with versatile applications. The mechanical strength of KC hydrogels was reversibly tuned from 0 to 444 kPa and the hydrogel volume swelling ratio was varied from 0.7 to 1.3 times the original volume. Through a series of characterizations and molecular dynamics simulations, we elucidate the underlying mechanisms via three complementary perspectives: aggregation behavior of molecular chains, microstructural anisotropy, and molecular-level hydrogen bonding interactions. The Hofmeister effect confers dynamic shape tunability properties, regulable volume properties, and adjustable mechanical properties on KC hydrogel, positioning it as a potential shape-regulation material and also rendering it a suitable solution sieve and a probe to measure softness and hardness. The exploration of the Hofmeister effect on KC hydrogels establishes a generalizable framework for understanding Hofmeister effects in natural polymer hydrogels while significantly expanding their potential in intelligent materials.