Abstract
This study investigates how ion valency and coordination behavior modulate the formation, viscoelasticity, and recovery of hyaluronic acid (HA)/κ-carrageenan (κCG) hydrogels. Hydrogels were prepared by combining HA and κCG in the presence of monovalent (K+), divalent (Ca2＋), and trivalent (Al3＋) ions at concentrations of 15–60 mM. Microrheology, Fourier-transform infrared (FTIR) spectroscopy, and bulk oscillatory rheology were employed to correlate molecular interactions with mechanical behavior.
Frequency sweep measurements revealed that the moduli of the hyaluronic acid/κ-carrageenan (HA–κCG) blend increased by nearly two orders of magnitude relative to HA alone, confirming synergistic network reinforcement. Among ion-enriched systems, Ca2＋ produced the highest Gplateau′ (∼20 kPa) and lowest modulus loss between 25 °C and 37 °C (<10%), while Al3＋ induced intermediate moduli. Recovery tests demonstrated that Ca2＋-enriched hydrogels recovered ∼55% of their initial elasticity within 15 min, compared to ∼30% for K+ and ∼40% for Al3＋ systems. Microrheology confirmed corresponding trends in probe confinement, with subdiffusive exponents (α) ranging from 0.18 (K+) to 0.32 (Ca2＋).
FTIR analysis revealed that while K+ primarily stabilized κCG helices, Ca2＋ reinforced sulfate junction zones, and Al3＋ introduced additional HA–carboxylate coordination. Collectively, these results demonstrate that both ion charge and concentration govern the balance between elasticity and deformability in HA–κCG systems, defining whether true interpenetrating or semi-interpenetrating networks emerge. These insights establish design guidelines for improvement of mechanical performance in chemically unmodified HA-based hydrogels.
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•κ-carrageenan enhances structure in chemically unmodified hyaluronic acid hydrogels.•IPN formation in hyaluronic acid–κ-carrageenan gels is tunable via ion charge density.•Elasticity–recovery behavior shifts with ion charge and concentration