Supramolecular Hydrogels with Properties Tunable by Calcium Ions: A Bio-Inspired Chemical System

Boc-L-DOPA(OBn)₂-OH is a simple synthetic molecule that promotes hydrogelation through electrostatic and π-π stacking interactions. Hydrogelation can occur in alkaline conditions by the use of triggers. Four hydrogels were prepared varying the base, NaOH or Na₂CO₃, and the trigger, GdL or CaCl₂. When the hydrogel formed in the presence of Na₂CO₃ and CaCl₂, the concomitant production of CaCO₃ crystals occurred, generating an organic/inorganic composite material. It was observed that the hydrogel once self-assembled preserved its status even if the trigger, the calcium ions, was removed. The viscoelastic behavior of the hydrogels was analyzed through rheological experiments, which showed a solid-like behavior of the hydrogels. The corresponding xerogels were analyzed mainly by scanning electron microscopy (SEM) and synchrotron X-ray diffraction analysis (XRD). They showed differences in structure, morphology, and fiber organization according to their source. This research presents a hydrogel system that can be applied as a soft biomaterial for tissue engineering, cosmetics, food, and environmental science. Moreover, it represents a model for biomineralization studies in which the hydrogel structure can act as an analogue of the insoluble matrix that confines the calcification site, provides Ca²⁺, and preserves its structure.