Controlling Nano- and Micro-Scale Ordering in Biomimetic Non-Equilibrium Hydrogels

Natural materials possess hierarchical ordering on a range of length scales, making these materials highly difficult to mimic. Triblock copolymers composed of hydrophobic end blocks and a hydrophilic midblock will self-assemble on contact with water, but the resulting hydrogel network only possesses nano-scale ordering and is very brittle when produced using processing methods that result in thermodynamic structures. Here, we propose a new, non-equilibrium method where the triblock copolymer is first dissolved in a water-miscible solvent favorable for both polymer blocks, then transferred to a mold and immersed in a water bath. The rapid diffusion of solvent results in hydrogels with porous microstructures, leading to remarkably soft and extensible hydrogels with both nano- and micro-scale structures. The presented work will highlight the impact of block copolymer molecular weight, relative block composition, solvent, and polymer solution concentration on the final structure of the hydrogels. Interestingly, we will demonstrate parameters that influence the porous microstructure without strongly affecting the nanostructure, allowing us to produce hydrogels with tunable properties and a hierarchical microstructure reminiscent of natural tissues.