Dynamic Polymer Hydrogels through Reversible Thiol Conjugate Addition Crosslinks

This thesis describes the experimental development of new dynamic hydrogels based on reversible thiol conjugate additions. Redox-controlled hydrogels and self-healing injectable hydrogels have been achieved by introducing reversible thiol conjugate additions to crosslink polymers, leading to hydrogel formation. The overall objective in this thesis was to develop a new fuel-driven transient polymeric hydrogel formation system. Although this final aim was not entirely met, we developed several important concepts along the way, which are described in Chapters 2-5. Chapter 2 describes a new chemical reaction network for fuel-driven transient formation of covalent S-C bonds, based on redox-controlled conjugate addition and elimination. We found that the formation and breaking of covalent bonds in the reaction cycle can be realized in separate reactions, but side reactions hindered the operation in full cycle. If such problems would be solved, this CRN could have potential to be used to form fuel-driven polymer materials. Chapter 3 investigates the formation of a self-healing injectable hydrogel by introducing dynamic thiol-alkynone double addition crosslinks in a polymer network. Such dynamic hydrogels show self-healing and shear thinning properties, confirmed by rheological measurements, macroscopic self-healing, and injection tests. Good cytocompatibility of these hydrogels opens an opportunity for future biomedical applications such as tissue engineering and drug delivery. Chapter 4 describes a redox-controlled reversible thiol-alkynone double addition. First, we created a redox-responsive hydrogel by using such reversible addition for the formation of crosslinks in hydrogels. Second, based on this thiol-alkynone double addition, we developed a fuel-driven transient formation of thiol-alkynone double adduct on small molecules. Chapter 5 explores coupling and decoupling reactions of thiols to an azanorbornadiene bromo sulfone. A self-healing hydrogel can be formed by using azanorbornadiene bromo sulfone to couple two thiol groups together. Such hydrogels are also degradable, trigged by glutathione. Glutathione-triggered dye release experiments suggest this self-healing hydrogel is a potential carrier of drugs, cells or vaccines for biomedical applications.ChemE/Advanced Soft Matte