Hydrogen bonded and ionically crosslinked high strength hydrogels exhibiting Ca²⁺-triggered shape memory properties and volume shrinkage for cell detachment

Abstract

A hydrogen bonded and calcium ion crosslinked hydrogel, termed PVDT-PAA, was synthesized by one-step photo-polymerization of 2-vinyl-4,6-diamino-1,3,5-triazine (VDT), acrylic acid (AA), and polyethylene glycol diacrylate (PEGDA, M_n = 4000). Combined physical crosslinking from inter-diaminotriazine and coordination of Ca²⁺ with carboxyls contributed to a significant enhancement in the mechanical properties of the PVDT-PAA hydrogels. Furthermore, reversible Ca²⁺ crosslinking imparted shape memory properties to the hydrogel allowing it to firmly memorize multiform shapes and return to its initial state in response to Ca²⁺. Interestingly, PVDT-PAA hydrogels with weaker H-bonding interactions demonstrated a sharp volume change phenomenon induced by Ca²⁺. This volume change could be utilized to trigger unharmful cell detachment from the hydrogel surface, which was thought to be due to Ca²⁺-induced marked variation in mechanotransduction between the cells and the substrate interface. This H-bonding and ionic crosslinking strategy opens up a new opportunity for designing and constructing multifunctional high strength hydrogels for biomedical applications.