Researchers investigated the effect of various (bio)polymeric crosslinkers on the self-assembly process of this reaction-coupled hydrazide-aldehyde gelator into hydrogel materials as a model system. They selected duplex DNA, which acted as a stiff, negatively charged rigid rod below its persistence length ideal for the construction of (nano)materials,[38–40] and compared it against a soft, neutral poly(ethylene glycol) (PEG) polymer of comparable size. Aldehyde moieties were specifically incorporated at the terminal ends of the (bio)polymers to introduce them during the self-assembly of the reaction-coupled network composed another set of (bio)polymers. The researchers also examined the effect of these two crosslinkers on the gelation of the reaction-coupled monomers into hydrogels over several length scales and compared their resultant materials properties.@en

Low-molecular-weight hydrogels are attractive scaffolds for drug delivery applications because of their modular and facile preparation starting from inexpensive molecular components. The molecular design of the hydrogelator results in a commitment to a particular release strategy, where either noncovalent or covalent bonding of the drug molecule dictates its rate and mechanism. Herein, we demonstrate an alternative approach using a reaction-coupled gelator to tune drug release in a facile and user-defined manner by altering the reaction pathway of the low-molecular-weight gelator (LMWG) and drug components through an acylhydrazone-bond-forming reaction. We show that an off-the-shelf drug with a reactive handle, doxorubicin, can be covalently bound to the gelator through its ketone moiety when the addition of the aldehyde component is delayed from 0 to 24 h, or noncovalently bound with its addition at 0 h. We also examine the use of an l-histidine methyl ester catalyst to prepare the drug-loaded hydrogels under physiological conditions. Fitting of the drug release profiles with the Korsmeyer-Peppas model corroborates a switch in the mode of release consistent with the reaction pathway taken: increased covalent ligation drives a transition from a Fickian to a semi-Fickian mode in the second stage of release with a decreased rate. Sustained release of doxorubicin from the reaction-coupled hydrogel is further confirmed in an MTT toxicity assay with MCF-7 breast cancer cells. We demonstrate the modularity and ease of the reaction-coupled approach to prepare drug-loaded self-assembled hydrogels in situ with tunable mechanics and drug release profiles that may find eventual applications in macroscale drug delivery. @en