Mechanotransducing hydrogels for switching enzyme reactions via modulation of multivalent interactions

Abstract

Mechanical forces, originating from both external sources and internal cellular activity, play a crucial role in various physiological processes such as tissue growth, wound healing, and tissue homeostasis. These functions are facilitated by mechanotransduction, the process through which mechanical forces are converted into biochemical signals. Cells can sense different types of stress, such as compression, tension, or shear, and respond by initiating signal transduction pathways that lead to cellular proliferation, migration, tissue repair, altered metabolism, and even the differentiation and maturation of stem cells. Inspired by the natural mechanotransduction process, significant attention has been directed toward mechano-responsive materials for their potential to modulate biomolecules. Enzyme reactions have emerged as a promising output of mechanotransduction, due to their biological significance, high catalytic activity, and substrate specificity. However, triggering enzyme reactions using mechanical stimuli remains a substantial challenge. In this thesis, a novel strategy for transducing mechanical stimuli into enzyme reactions using a hydrogel as a mechanotransducer is proposed. This represents the first mechano-responsive hydrogel system for switching enzyme reactions. The mechano-responsiveness of the hydrogel is achieved by modulating the multivalent interaction between enzymes and guanidinium (Gu+) ion-appended Gu-polymer. The Gu-polymer possesses Gu+ ions on a flexible backbone, which bind with an enzyme through adaptive multivalent salt bridges, effectively inhibiting the enzyme reaction. When physically stretched, the Gu-polymer becomes less effective for binding due to conformational restrictions, which partially liberates the enzyme to perform the reaction. To demonstrate this concept, two hydrogels, mechanochromic BGGu-gel and self-growing TB/FIBGu-gel, have been developed for the mechanotransduction of β-galactosidase and thrombin/fibrinogen enzyme reactions, respectively. Exploiting the universality and versatility of this hydrogel-based mechanotransducing platform, we extend this strategy toward developing hydrogels for mechanotransduction in biomineralization. Mechanically induced alkaline phosphatase reactions enable calcium phosphate (CaP) biomineralization within a mechanotransducing hydrogel (ALPGu-gel). Due to the tight interactions between Gu+ ions in the ALPGu-gel network and phosphate (PO43–) in the CaP, ALPGu-gel exhibits remarkable self-growing, self-healing, and shape memory properties. This innovative approach has the potential to significantly impact the fields of tissue engineering, regenerative medicine, and soft robotics.