Bidirectional\nEnzyme Inhibition and Activation for\nIn Situ Formation of Injectable Hydrogel Using a Bispecific Aptamer

In situ injectable hydrogels have been explored for biomedical\napplications, including regenerative medicine and drug delivery. However,\ncontrolling the kinetics of their gelation to facilitate easy injection\nremains a challenge. The purpose of this study was to demonstrate\nthe potential of using bispecific aptamers and complementary sequences\nas a bidirectional modulation system for controlling enzyme-mediated\nhydrogel formation kinetics. The results show that a bispecific thrombin-binding\naptamer effectively inhibits thrombin activity and significantly slowed\nfibrin hydrogel formation. Upon interaction with its complementary\nsequence, this inhibition could be reversed. As a result, the aptamer-bound\nthrombin was activated, leading to an acceleration of the fibrin formation\nkinetics. Thus, bispecific aptamers and complementary sequences can\neffectively function as dynamic control systems for enzyme-catalyzed\nin situ injectable hydrogel formation.