Solvent-Non-Solvent Rapid Injection for the Preparation of Hierarchically Ordered Hydrogels

Non-solvent-induced phase separation is a non-equilibrium method used heavily in industry for fabricating separation membranes. The resulting microstructure forms when a homopolymer initially in a good solvent is immersed into a poor solvent, inducing polymer phase separation and forming a microporous membrane consisting of polymer-rich and non-solvent-rich regions. We recently showed that non-solvent-induced phase separation methods will produce hierarchically ordered physically crosslinked hydrogels when amphiphilic triblock copolymers are used instead of homopolymers. In our system, when triblock copolymers comprising of a hydrophobic-hydrophilic-hydrophobic chain sequence initially in a common solvent will rapidly self-assemble at the nano and microscale when injected into water. We have developed a universal and quantitative method for producing physically crosslinked hydrogels exhibiting tunable mechanical properties superior to typical physically crosslinked triblock copolymer hydrogels, and interesting structural color properties. At a fundamental level, the rapid injection process described here encompasses two self-assembly processes (microphase and macrophase separation), further increasing the tunable parameters for controlling material structure and property.