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

Abstract

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 Na 2 CO 3 , and the trigger, GdL or CaCl 2 . When the hydrogel formed in the presence of Na 2 CO 3 and CaCl 2 , the concomitant production of CaCO 3 crystals occurred, generating an organic/inorganic composite material. It was observed that the hydrogel once selfassembled 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 Ca 2+ , and preserves its structure.

Fluorine Effect in the Gelation Ability of Low Molecular Weight Gelators

“…We compared the gelation ability of Boc-D-F 2 -Phe-OH (Boc = tert -butoxycarbonyl) with that of dipeptides where it was coupled with L-Oxd or D-Oxd (Oxd = 4-methyl-5-carboxy-oxazolidin-2-one) and we found out that Boc-D-F 2 Phe-L-Oxd-OH has the best performance among them. We used the Oxd moiety because we could demonstrate that its introduction in a peptide sequence strongly enhances the tendency of the molecule to self-assemble to form supramolecular materials [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”

Controlled Hydrolysis of Odorants Schiff Bases in Low-Molecular-Weight Gels

“…To better control the hydrolysis rate of SB1 – SB4 and the fragrance release over time, which ideally should be completed within a few days, we inserted the four compounds inside two gelators derived from L-Dopa with different characteristics, as one is an ester (Boc-L-Dopa-(Bn) 2 -OMe, gelator ( A ) while the second displays an acidic moiety that should catalyze the SB hydrolysis (Boc-L-Dopa-(Bn) 2 -OH, gelator ( B ). We previously demonstrated that gelator B is very versatile, as it can form gels under several conditions in low concentrations [ 35 ].…”

“…These molecules can respond to a variety of triggers (light, pH, ions, solvents, enzymes, ultrasounds) that cause the gelation process to start [ 28 , 29 , 30 ]. LMW gels can also be functionalized depending on the final application, with the introduction of fillers (graphene, nanoparticles, catalysts) [ 31 , 32 , 33 , 34 ], crystals [ 35 , 36 ], drugs or active ingredients [ 37 , 38 , 39 ].…”

Short Peptide-Based Smart Thixotropic Hydrogels

“…In layman’s terms, thixotropy is a reversible, isothermal, time-dependent shear thinning behavior of gel systems distinguished by reversible transformation from gel-sol-gel structural transition [ 2 , 6 , 7 , 8 , 9 , 10 ]. Self-healing is another important rheological term recurrently connected to thixotropy and may be demarcated as the tendency of a gel system to eccentrically reorganize the bonding interactions after mechanical deformation [ 7 , 11 ]. The self-healing process can be visually established when separate pieces of gel connect to form an entity of hydrogel [ 4 , 5 , 12 , 13 ].…”

“…The most common classic procedure is the three intervals thixotropic test (3ITT), in which three zones were created in the whole cycle with “OFF–ON–OFF” modes [ 14 , 15 , 16 ]. In the first cycle (OFF state), a low strain is applied, i.e., within the linear viscoelastic region (LVR) [ 10 , 11 ] in which storage modulus (G′) is higher than loss modulus (G″) [ 11 , 13 ]. In the second cycle (ON state), a higher strain is applied, i.e., above the LVR region [ 10 , 11 , 17 ], and the change in dynamic mechanical moduli (G′ and G″) is monitored.…”